U.S. Department of Energy

Office of FreedomCAR and Vehicle Technologies

1000 Independence Avenue S.W.

Washington, DC 20585-0121

FY 2002

Progress Report for Automotive Propulsion

Materials Program

Energy Efficiency and Renewable Energy

Office of FreedomCAR and Vehicle Technologies

Steven Chalk Program Manager

December 2002

iii

CONTENTS

INTRODUCTION ...................................................................................................................................... 1

2. POWER ELECTRONICS .................................................................................................................. 9

A. Low-Cost, High-Energy-Product Permanent Magnets.................................................................... 9

B. Development of Improved Powder for Bonded Permanent Magnets.............................................. 15

C. Carbon Foam for Electronics Cooling............................................................................................. 21

D. dc Bus Capacitors for Hybrid Vehicle Power Electronics............................................................... 27

E. Mechanical Reliability of Electronic Ceramics and Electronic Ceramic Devices .......................... 33

3. FUEL CELLS....................................................................................................................................... 39

A. Carbon Composite Bipolar Plates.................................................................................................... 39

B. Cost-Effective Surface Modification for Metallic Bipolar Plates ................................................... 43

C. Low-Friction Coatings and Materials for Fuel Cell Air Compressors ............................................ 49

D. Microstructural Characterization of PEM Fuel Cells ...................................................................... 55

E. Nano-Particulate Porous Oxide Electrolyte Membranes as Proton

Exchange Membranes ..................................................................................................................... 61

F. Bacterial Cellulose Membranes....................................................................................................... 67

G. Carbon Foam for Radiators for Fuel Cells ...................................................................................... 71

4. ADVANCED COMBUSTION ............................................................................................................ 79

A. Materials Improvements and Durability Testing of a Third-Generation MicrowaveRegenerated Diesel Particulate Filter .............................................................................................. 79

B. Rapid Surface Modifications of Aluminum Automotive Components for Weight Reduction ....... 85

C. Material Support for Nonthermal Plasma Diesel Engine Exhaust Emission Control ..................... 91

D. Fabrication of Small Fuel-Injector Orifices..................................................................................... 95

E. Technology for Producing Small Holes in Advanced Materials ..................................................... 99

F. Electrochemical NOx Sensor for Monitoring Diesel Emissions...................................................... 103

APPENDIX A: ACRONYMS AND ABBREVIATIONS....................................................................... 107

1 

1. INTRODUCTION 

Automotive Propulsion Materials R&D: 

Enabling Technologies to Meet Technology Program Goals 

On behalf of the Department of Energy’s (DOE’s) 

Office of FreedomCAR and Vehicle Technologies 

(FCVT), I am pleased to introduce the FY 2002 

Annual Progress Report for the Automotive 

Propulsion Materials Research and Development 

Program. I am also pleased to introduce you to 

Rogelio Sullivan, who is taking over management of 

this important program starting in FY 2003. For the 

last ten years, Rogelio has worked at DOE on a 

variety of automotive engineering projects, including 

the development of electronics/electric drive systems 

and lightweight materials. Rogelio is currently the 

Team Leader for the Automotive Lightweight 

Materials group in the FCVT Office. It is noteworthy that the materials projects that support the goals of the 

Fuel Cell Program will be moving with me in FY 2003 to the Hydrogen, Fuel Cells, and Infrastructure 

Technologies Program. Together with DOE national laboratories and in partnership with private industry and 

universities across the United States, the program will continue to engage in high-risk research and 

development (R&D) that provides enabling materials technology for fuel-efficient and environmentally 

friendly light-duty vehicles. 

This introduction summarizes the objectives and progress of the program in FY 2002 and highlights the 

technical barriers remaining and the future direction of the program. The FY 2002 annual progress reports on 

Combustion and Emission Control for Advanced CIDI Engines and Hydrogen, Fuel Cells, and Infrastructure 

Technologies provide additional information on FCVT’s R&D activities that support the development of 

propulsion materials technology. 

In May of 2001, the President’s National Energy Policy 

Development Group published the National Energy Policy (NEP). 

This comprehensive energy policy specifically addresses the 

development of energy-efficient vehicle technologies, including 

hybrid systems, advanced emission control technologies, fuel cells, 

and hydrogen-based systems. The NEP is a strong indicator of the 

continuing federal support for advanced automotive technologies 

and the materials work that supports them. 

The Automotive Propulsion Materials R&D Program has supported 

the FreedomCAR Program since its inception. FreedomCAR is not 

an automobile or prototype but rather a new approach to powering 

the vehicles of the future. In research areas where industry views 

the risks as too high and uncertain, the FreedomCAR Program 

conducts long-term research, development, and demonstration 

activities for cars, light trucks, and heavy vehicles to reduce oil 

consumption and emissions. 

Nancy L. Garland 

Technology Development 

Manager

Rogelio Sullivan 

Technology Development 

Manager

Report of the National Energy 

Policy Development Group 
2 

The Automotive Propulsion Materials Program is a partner with the programs for Vehicle Power Electronics 

and Electric Machines, Combustion and Emissions Control for Advanced CIDI Engines, and Fuel Cells for 

Transportation. Projects within the Automotive Propulsion Materials Program address materials concerns that 

directly impact the critical technical barriers in each of these programs—barriers such as thermal 

management, emissions reduction, and reduced manufacturing costs. The program engages only the barriers 

that involve basic, high-risk materials issues. 

Enabling Technologies 

The Automotive Propulsion Materials Program 

focuses on enabling materials technologies that are 

critical in removing barriers to the power 

electronics, fuel cell, and compression-ignition, 

direct-injection (CIDI) engine combustion and 

emissions control research programs. 

Thermal management is a cross-cutting materials 

issue that affects both the power electronics and 

fuel cell programs. The components necessary for 

high-fuel-economy, low-emission hybrid vehicles 

require that power electronics be smaller and 

lighter and operate at higher temperatures. These 

requirements are being addressed by developing 

electronic materials (i.e., low-cost dc bus 

capacitors) that operate at higher temperatures and 

by improving the capability to dissipate heat generated in electronic devices. Fuel cell systems also require 

improved heat dissipation because the lower operating temperature of the fuel cell system (80°C) provides a 

smaller temperature differential between the fuel cell system and ambient conditions. The Propulsion 

Materials Program has been addressing both heat dissipation issues through the development of advanced 

carbon foam technology. 

The Program has supported the development of two innovative membrane materials for polymer electrolyte 

membrane (PEM) fuel cells: high-surface-area microporous inorganic oxide (TiO2 and Al2O3) and metallized 

bacterial cellulose. Both types of membranes promise to be capable of operating at temperatures above 

100°C, to improve waste heat dissipation, to involve minimal water management problems and less CO 

poisoning, and to reduce the cost of the fuel cell system by minimizing the quantity of expensive platinum 

required. 

CIDI engine and aftertreatment system development will greatly benefit from the Program’s efforts to 

develop improved particulate filters for diesel engines. Current CIDI engine technology must strike a difficult 

balance between engine efficiency and tailpipe emissions. The Propulsion Materials Program initiated two 

projects in FY 2002 to develop technology to produce very small (~50 microns) orifices for fuel injectors 

used in high-pressure common rail systems. The smaller orifices would enable better control of fuel 

vaporization and would increase efficiency and reduce emissions. The Program is working to reduce emissions through the development of advanced particulate filters and is collaborating with Pacific Northwest 

National Laboratory in the development of a nonthermal plasma aftertreatment device to reduce NOx

emissions from diesel engines. 

Collaboration and Cooperation 

As with other programs under FreedomCAR, collaboration and cooperation across organizations is a critical 

part of the Automotive Propulsion Materials Program. Across the materials projects, scientists at the national 

Fuel

Cells

CIDI Power

Electronics

Propulsion

Materials

The Propulsion Materials Program 

focuses on three applications. 
3 

laboratories are collaborating with 

manufacturers to identify and refine 

the characteristics necessary for 

meeting performance requirements. 

Researchers at Lawrence Livermore 

National Laboratory are working 

with Ford to develop low-cost, 

rapid-response NOx sensors that can 

be utilized in feedback control loops 

to minimize NOx emissions from 

diesel engines. Component 

manufacturers and scientists from 

the national laboratories and from 

contractors are also working 

together to identify the 

technological barriers to manufacturing optimal materials to meet 

component requirements. 

There is also cooperation among 

national laboratories to take 

advantage of the expertise of each 

facility. Oak Ridge and Argonne National Laboratories (ORNL and ANL), for example, are collaborating in 

the development of higher-strength NdFeB permanent magnets that will enable significant reductions in the 

size, weight, and cost of electric motors used in hybrid vehicles. In another project, Sandia National 

Laboratories (SNL) is fabricating smaller, higher-temperature dc bus capacitors; and ORNL is developing 

techniques to characterize the ~5-micron-thick polymer films developed by SNL and correlate their 

mechanical properties with their dielectric behavior. 

In addition to national laboratory and large industry participation, the FY 2002 Automotive Propulsion 

Materials Program included important R&D conducted by a small business. Industrial Ceramic Solutions, 

LLC (ICS), located in Oak Ridge, Tennessee, is developing a ceramic filter to reduce particulate emissions 

from diesel engines. As in the collaborative efforts of national laboratories with industry, researchers at ICS 

are working closely with representatives from DaimlerChrysler, Ford, General Motors, and ORNL to develop 

a filter that will meet the emissions targets of the program. 

Accomplishments 

FY 2002 featured notable accomplishments in all three materials program areas. The remainder of the report 

provides summaries of all of the Automotive Propulsion Materials projects; this section highlights some 

major accomplishments during FY 2002. Materials R&D in support of power electronics, for example, 

resulted in the development of improved heat sinks capable of dissipating the heat generated by high-power 

devices. Fuel-cell-related materials projects demonstrated metallic bipolar plates that are low in cost, weigh 

about half as much as graphite materials, and have significantly better electrical properties. Finally, materials 

research supporting combustion engine and aftertreatment technologies led to the demonstration of 

microwave-regenerated exhaust particulate filters in diesel-powered vehicles. 

Power Electronics 

High-power electronic components like power modules and inverters being developed for hybrid electric 

vehicles generate significantly more heat than conventional devices. Heat generated by these devices must be 

effectively dissipated to prevent overheating and failure of the devices. In the past, air-cooled aluminum or 

Laboratory/Contractor-Industry Collaboration

Laboratory Industrial Partner 

Argonne 

National 

Laboratory 

 Ability Engineering Technology, Inc. 

 Atlas Cylinders, Inc. 

 Bronson and Bratton, Inc. 

 Cryomagentics, Inc. 

 CRUMAX 

 Daimler-Chrysler Corporation 

 Ford Motor Company 

 Lucas-Varity 

 Purdue University 

 UGIMAG, Inc. 

Oak Ridge 

National 

Laboratory 

 AVX 

 Bronson and Bratton, Inc. 

 Caterpillar 

 Conoco Corporation 

 Cryomagnetics, Inc. 

 CRUMAX 

 Daimler-Chrysler Corporation 

 Dow Chemical Company 

 Ford Motor Company 

 General Motors 

 Industrial Ceramic Solutions 

 Motorola 

 Murata 

 Peterbilt 

 Poco Graphite 

 Plug Power, LLC 

 UGIMAG, Inc. 

 SatCon 

 University of Tennessee 

 University of Wisconsin 

Sandia National 

Laboratory 

 AVX 

 Daimler-Chrysler Corporation 

 Ford Motor Company 

 General Motors 

 Degussa 

 Ferro 

 Kemet 

 Materials Research Associates 

 Murata 

 Pennsylvania State University 

 TAM 

 Tokay 

 TPC Ligne Puissance 

 TPL, Inc. 

 TRS Ceramics 
4 

copper heat sinks could easily handle the heat load (<25 W/cm2

). The higher power requirements of today’s 

devices generate significantly more heat and will require more sophisticated heat sinks. 

Current computer chips are packaged printed-side-up in a ceramic package with over-the-top wire bonds. 

Unfortunately, this design is not suited for significant heat dissipation through the top of the package to a 

standard heat sink because there is an insulating air gap between the silicon chip and the ceramic package. A 

new concept being developed is the flip-chip design in which the silicon chip is inverted, with the back of the 

printed chip oriented toward the top of the package. In this design, a heat spreader can be joined directly to 

the chip with no air gap to impede the heat flow. The National Security Agency (NSA) has been working for 

a number of years to develop an evaporatively-cooled heat sink that immerses the heat spreader in a cooling 

fluid such as fluorocarbon. In this process, the latent heat of vaporization removes significantly more heat 

than is transferred to the fins of a conventional heat sink. The limitations of this design are the surface area 

and thermal conductivity of the heat spreader attached to the back of the chip. The heat spreader developed by 

the NSA is polycrystalline diamond wafers with a thermal conductivity of ~1600 W/m•K. The maximum 

power density achieved without overheating the system was 28 W/cm2

. 

A collaborative effort between the NSA and ORNL has effectively used 

high-conductivity carbon foam to dramatically increase the cooling 

capacity of the system. The lightweight carbon foam has a ligament 

thermal conductivity comparable to that of diamond wafers but has a 

surface area that is more than 2 orders of magnitude greater. When the 

diamond spreader was replaced by graphite foam, a power density of 

greater than 110 W/cm2

 was attained without overheating the system (see 

schematic). The same technology has been used to develop a low-cost 

passive heat sink for power modules and inverters. 

Fuel Cells R&D 

PEM fuel cells are of great current interest for automotive applications 

because they are highly efficient and environmentally friendly, producing 

near-zero emissions. Cost remains a key barrier to their widespread use. One of the most expensive 

components in PEM fuel cells is the bipolar plate that serves to electrically connect individual cells in a stack 

and to separate and distribute reactant and product streams. Thin metallic bipolar plates offer the potential for 

significantly lower cost than benchmark machined graphite bipolar plates, and better power density 

performance than developmental polymer/carbon fiber and graphite composite bipolar plates currently under 

consideration. However, inadequate corrosion resistance can lead to high electrical resistance caused by the 

formation of resistive surface oxides and/or can contaminate the PEM with metal ions, both of which degrade 

performance. 

To solve this problem, ORNL is developing a new family 

of Ni-Cr base alloys specifically designed to form a 

protective and electrically conductive Cr-nitride surface 

layer upon thermal nitridation. Thermal nitridation is an 

inexpensive, well-established industrial technique and is 

viable for covering complex geometries such as bipolar 

plate flow field features (see the figure). Further, the 

alloy can be formed into final shape by inexpensive 

metal forming techniques, such as stamping, prior to the 

nitridation treatment. 

The nitrided Ni-Cr base alloys exhibited minimal corrosion (current densities of less than 1 × 10-6 A/cm2

) in 

an 80°C, pH 3 sulfuric acid environment designed to simulate PEM fuel cell operating conditions. Over 

Ni-Cr Alloy Nitrided

Ni-Cr Alloy - - Ni Cr Alloy Nitrided

Ni Cr Alloy

Nitrate coverage of flow field grooves. 
5 

1800 h of exposure have also been accumulated in the Los Alamos National Laboratory Bipolar Plate 

Corrosion Test Cell Facility with electrical resistance increases of only 0.5 mV/1000 h at the anode and 

2mV/1000 h at the cathode (for comparison, 316 stainless steel exhibits resistance increases of 16 and 

21 mV/1000 h, respectively). A provisional patent disclosure on this family of alloys has been filed and 

coupons have been delivered to several fuel cell manufacturers for evaluation. Delivery of 50-cm2

 active-area 

plates to Los Alamos National Laboratory for in-cell testing is planned for Fall 2002. 

Advanced Combustion Engine and Emissions R&D 

A major FreedomCAR goal is to develop a vehicle with outstanding 

fuel economy that meets stringent emissions standards. Balancing 

high fuel economy with low emissions is a challenge being 

addressed through materials activities in support of the R&D 

program for Combustion and Emission Control for Advanced CIDI 

Engines. Specifically, work conducted at ICS has led to the 

development and demonstration of an advanced exhaust filter 

system capable of capturing more than 95% of the carbon 

particulates from diesel engine exhaust. ICS has developed a new, 

patented technology known as the “microwave-cleaned particulate 

filter system” that can remove and destroy fine particulate pollution 

from diesel exhaust streams. The system features a ceramic-fiber 

filter that can be automatically cleaned through the use of 

microwave power. 

During FY 2002, ICS developed a pleated filter that exhibits only 

1/20 the backpressure of the wall-flow filters that were used in the 

past. ICS developed a technology that uses a ceramic binder, rather 

than a thermosetting resin, to pleat the fibrous filter paper. 

Evaluated on a 1.7-L Mercedes diesel engine at ORNL, the filter 

demonstrated a 96 to 98% particulate removal efficiency with a low 

backpressure. The microwave filter was installed on a Ford F-250 

7.3-L diesel pickup, with full exhaust backpressure and temperature 

data acquisition. Road testing proved that the filter could survive the 

full loading of 1000 ft3

 per minute of exhaust flow without mechanical failure. A fully automated microwave 

filter system with the flat, pleated filters is being installed on the Ford truck for a 7000-mile controlled test 

track evaluation, with periodic Federal Test Protocol cycle emission testing. Data from these on-road tests 

will be used to improve the performance of the microwave-regenerated particulate filter, verify system 

durability, and precisely quantify the fuel penalty resulting from filter operation. 

Positive results from these tests should lead to product development partnerships with exhaust system 

suppliers, engine builders, or vehicle manufacturers. These strategic partnerships can move this technology to 

integration into a total commercial diesel exhaust emissions control system for pick-up trucks, sport utility 

vehicles, and large trucks. 

Scale-Up/Commercialization 

Durability-enhancing coatings for automotive applications―such as engine block cylinder liners, compressor 

housings, and fuel pumps—have been developed at ORNL using innovative rapid, high-density infrared (IR) 

surface modification processes. A collaborative effort with researchers at Ford has developed an improved 

joining and resin curing process that uses this process. The Lincoln LS has a welded seam in the middle of the 

C-pillar (behind the rear door). The finishing process for the seam included labor-intensive welding, thermal 

spraying, and multi-step sanding and painting processes. The process is operator-dependent and susceptible to 

quality concerns and throughput issues. 

On-road controlled test-track 

vehicle. 

Flat, pleated microwave 

regenerated particulate filter. 
6 

A one-component epoxy material was chosen to replace the thermalsprayed silicon bronze that Ford had been using. The epoxy is conductive 

to the electrostatic coat, is fully paintable and sandable, and has low 

porosity. The IR line heater developed at ORNL was found to be an 

efficient, robust in-line heating source to cure the epoxy coating. The 

heater can go from cold to full power in less than a second, converts 

electrical power into radiant energy at 90% efficiency, and targets the 

energy to only the area that needs curing. Full commercial-scale process 

trials proved that the IR heater cured the epoxy in only 20 seconds, from 

a distance of 6 inches and in a 10-inch-wide sweep, to achieve a 92% 

cure that was suitable for grinding and finishing. The process was so 

successful that Ford adopted the IR lamp technology in one of its plants. 

The benefits of using the epoxy filler and IR curing include (1) a cost 

savings of $28 per vehicle, (2) a 2-minute reduction in cycle time, (3) less 

porosity in the coating, (4) reduced energy consumption, and (5) safer, 

more environmentally friendly processing. 

High-Performance Bipolar Plate 

Through licensing of a key material and manufacturing method invented 

at ORNL, Porvair Fuel Cell Technology (PFCT) is scaling up a process to 

manufacture large quantities of composite bipolar plates. The 3-year 

program will result in a process capable of manufacturing 300 plates per 

hour. The ORNL technology uses a low-cost, water-based carbon fiber 

slurry-molding process to produce a porous carbon-fiber preform. The 

molded carbon-fiber component has impressed flow-field channels for 

diffusing fuel or air to the electrolyte surface. The bipolar plate is made 

hermetic through chemical vapor infiltration with carbon. The carbon 

deposit provides exceptional strength and enhanced conductivity to the 

bipolar plate material. The high strength of the material enables it to be 

formed into bipolar plates that are thinner than those made through 

competitive technologies, and the high conductivity increases fuel cell performance. 

The benefits of the manufacturing technology 

include 

• Suitability for mass production 

• Low cost 

• High material strength 

• High bulk conductivity 

• Non-corrosiveness of carbon 

• Potential for very thin plates 

• Excellent sealing performance 

PFCT is actively supplying test plates to major fuel 

cell manufacturers. Fuel cell testing has confirmed 

that the product achieves excellent performance in 

a stack, and aggressive production activities are 

under way to supply prototype materials for 

commercial and transportation applications. Price 

Epoxy being cured with IR 

heating on the Lincoln LS 

prototype

Lincoln LS joint before (top) 

and after IR cure and 

finishing. 

Prototype thermal processing equipment for 

bipolar plates 
7 

estimates have been provided to one customer for interim-production quantities in CY 2003 to support 

introductory product requirements for bipolar plates in the short term. Plans are to accelerate the development 

of the proposed high-volume production line to mid-year 2003 to stay ahead of anticipated product demand. 

Future Direction 

The Automotive Propulsion Materials Program will continue to work closely with FreedomCAR partners and 

industry to understand propulsion materials–related requirements. Building upon the recent advances in 

materials technologies, many of this year’s projects will be moved out of the laboratory and over to industry 

for testing. Strategic partnerships will be established in 2003 with exhaust system, engine, or vehicle 

manufacturers to move the microwave particulate filter system from vehicle testing toward 

commercialization. The scale-up and commercialization of carbon foam at POCO Graphite for thermal 

management applications will continue, with the focus on cost reduction. Other projects will continue to 

refine manufacturing requirements and necessary characteristics to meet the challenges of the FreedomCAR 

program. 

A promising new activity in the Automotive Propulsion Materials Program for FY 2002 was the collaboration 

between Ford Motor Company and ORNL to develop a resin curing process that was commercialized on the 

Lincoln LS vehicle. This cost-effective process will be extended in FY 2003 to other applications at Ford as 

well as at other companies. 

As advanced automotive technology developments uncover new challenges, the Automotive Propulsion 

Materials Program will continue to provide breakthrough technology solutions through collaboration with 

industry, FreedomCAR partners, national laboratories, and small businesses. 

Project Abstracts 

The remainder of this report communicates the progress achieved during FY 2002 under the Automotive 

Propulsion Materials Program. It consists of 18 abstracts of national laboratory projects—five that address 

power electronics, six that address combustion and emission technologies, and seven that address fuel cells. 

The abstracts provide an overview of the critical work being conducted to improve these systems, reduce 

overall cost, and maintain component performance. In addition, these abstracts provide insight into the 

challenges and opportunities associated with advanced materials for high-efficiency automobiles. 

Nancy L. Garland 

Technology Development Manager 

Office of FreedomCAR and Vehicle Technologies 

Energy Efficiency and Renewable Energy 

Propulsion Materials FY 2002 Progress Report

9

2. POWER ELECTRONICS

A. Low-Cost, High-Energy-Product Permanent Magnets

Y. S. Cha and John R. Hull

Energy Technology Division, Bldg. 335

Argonne National Laboratory, Argonne, IL 60439

(630) 252-5899; fax: (630) 252-5568; e-mail: yscha@anl.gov

Andrew E. Payzant

Oak Ridge National Laboratory

P.O. Box 2008, MS 6064

Oak Ridge, TN 37831-6069

(865) 574-6538; fax: (865) 574-3940; e-mail: payzanta@ornl.gov

DOE Technology Development Manager: Nancy Garland

(202) 586-5673; fax: (202) 586-9811; e-mail: nancy.garland@ee.doe.gov

ORNL Technical Advisor: David Stinton

(865) 574-4556; fax: (865) 241-0411; e-mail: stintondp@ornl.gov

Contractor: Argonne National Laboratory, Argonne, Illinois

Prime Contract No.: W-31-109-Eng-38

Objectives

• Develop a low-cost process to fabricate an anisotropic NdFeB permanent magnet (PM) with an increase in

energy product of up to 25%, which is a measure of the torque that a motor can produce for a given magnet

mass. The higher-performance magnets will replace ones made by traditional powder metallurgy processing

and enable significant size and weight reductions in traction motors for hybrid vehicles.

• Use high fields of superconducting solenoids to improve magnetic grain alignment while pressing compacts

for sintering, thus producing higher-performance magnets.

Approach

• Develop a batch-mode press that enables alignment of the magnetic domains of NdFeB powders in the

higher-strength magnetic fields created by a superconducting solenoid.

• Characterize, compare, and correlate engineering and microscopic magnetic properties of magnets processed

under varying conditions, including some in current production.

• Use a reciprocating feed to automate the insertion of loose and compacted magnet powder into, and its

removal from, the steady magnetic field of a superconducting solenoid.
FY 2002 Progress Report Propulsion Materials

10

Accomplishments

• Achieved energy products that were within 10% of the theoretical maximum by optimizing batch-mode

alignment/pressing of cylindrical axial-die-pressed PMs in a 9-Tesla (T) superconducting solenoid. The

magnetic properties are comparable to those of the more expensive magnets made by the transverse-die

pressing technique.

• Achieved energy product improvements of 15% for thin near-final-shape magnets, production of which is the

current cost-saving thrust in the PM industry. Additional PMs made with relatively small length-to-diameter

ratios (L/D <0.5) support the previous findings.

• Proved the crucial step in making automation feasible. For the first time, powder-filled dies were inserted

into and pressed compacts were removed from an active (always on) superconducting solenoid. Most

important, these magnets were the best made.

• Carried out electromagnetic code study of grain alignment in powder compacts. The results show that the

distortion of the alignment field (caused by the self-field of the compact) is proportional to the density of the

compact and inversely proportional to the magnitude of the alignment field. There is a maximum distortion of

the alignment field at a certain L/D ratio. These results will help us provide scale-up design rules to industry.

• Characterized the microscopic texture (alignment) of PMs made in the Argonne National Laboratory axialdie press facility and correlated the alignment with macroscopic magnetic properties.

Future Direction

• Demonstrate the feasibility of competitive factory operation by fabricating and operating a reciprocating

press in continuous-mode operation.

• Continue the electromagnetic code study to better understand the grain alignment process.

• Provide design rules for the fabrication of PMs, including knowledge related to scale-up to larger magnets at

commercial rates of production.

• Continue to collaborate with Oak Ridge National Laboratory (ORNL) on microstructure characterization of

the finished PM samples and with Ames Laboratory on processing the NdFeB powder for bonded PMs.

Introduction

Industry considers an improvement of 2–3% in

the magnetic properties of today’s PMs as

significant. The properties of current PMs can be

brought to within 5–25% of their theoretical

maximums. The strength of the magnet greatly

depends on the method by which the compact is

aligned magnetically and pressed. Large blocks can

be made by cold-isostatic pressing that are within

5% of their theoretical maximum, but then the

blocks must be sliced, diced, and ground to final

shape. Machining operations add significantly to the

cost of magnets. Magnets that are axial-die pressed

and sintered to near-final shape have magnetic

properties farthest from their theoretical maximums,

but they are the least expensive to make. The current

industry goal is to make better near-final-shape

magnets by axial-die pressing. The major objectives

of this project are to improve the magnetic

properties (mainly the energy product) of the

sintered PMs and to develop low-cost methods of

production for high energy-product, near-final-shape

PMs.

Approach

Our approach is to align the NdFeB powder in a

superconducting magnet, which can generate

magnetic fields much higher than those generated by

an electromagnet commonly used in industry. The

alignment of the powder in higher magnetic fields is

expected to improve the properties of the PMs. To

develop a low-cost production method for highenergy-product PMs, we plan to design, fabricate,

and demonstrate the reciprocating axial-die press

system for automation.

Previously, a 9-T superconducting solenoid,

which can produce alignment fields that

significantly exceed those of the 2-T electromagnets
Propulsion Materials FY 2002 Progress Report

11

in common industrial use, was completed in the

fourth quarter of 2000. Production-grade magnet

powder was obtained from Magnequench UG. The

3- to 5-micron, single-crystal grains of powder were

aligned in the same direction and compacted at

Argonne. Then anisotropic compacts, with their

grains mechanically locked in place, were returned

to Magnequench UG for sintering, annealing,

machining, and measurement of engineering

magnetic properties. Finally, selected PMs were sent

to ORNL for measurement of microscopic properties

and texture (the alignment of the crystals’ easy

magnetic axes). The better the alignment, the greater

is the energy product.

Results

Previously, we have demonstrated that

significant improvement (10–15%) of energy

product can be achieved by using higher alignment

fields (>2 T). These results were based on a limited

number of PM samples.1

 In FY 2002, we continued

the previous study with an emphasis on a smaller

L/D ratio where improvement in energy product is

expected to be greater. The most effective use of the

high alignment fields that can be provided by

superconducting solenoids is in making near-finalshape magnets. Their finite and usually short length

in the direction of magnetization makes alignment of

the powder grains especially difficult. When

subjected to a uniform alignment field, the powder

in the die cavity develops a highly nonuniform selffield. Because grains align along the total field lines,

unidirectional alignment can be achieved only by

increasing the strength of the applied alignment field

until the effects of the self-field become negligible.

Because the self-field distortion becomes greater for

shorter magnets, there will always exist short

magnets that the 2-T electromagnets of industry

cannot adequately align.

Clearly, the higher fields produced by a

superconducting solenoid can provide the necessary

alignment. A total of 69 compacts were fabricated

with L/D ratios ranging from 0.27 to 0.52. These

powder compacts were processed in alignment fields

ranging from 1 to 8 T. The results are shown in

Figure 1, where the remnant magnetization Br

Figure 1. Remnant flux density Br(T) of different Lc/Dc

compacts pressed in increasing alignment

fields H(T).

(the energy product is proportional to the square of

the remnant magnetization) is plotted against the

alignment field H. It can be observed that in general,

the remnant magnetization increases with the

alignment field. The improvement in Br is the

greatest for the smallest L/D ratio (0.27). These

results confirm the trends of improvement in Br of

the previous study.

An attempt was made to fabricate PMs with

even smaller L/D ratio (<0.25) where cost savings

may be even greater because distortion of the

alignment field due to the self-field of the powder is

expected to be greater. A 1.125-in. die (the die used

in the previous study was 5/8 in.) was designed,

fabricated, and used to make PMs with an L/D ratio

of less than 0.25. The attempt was not successful

because the samples cracked during ejection from

the die. Unlike the system used by the industrial

manufacturer, the present die and press set is not

designed so that it can eject the sample under

pressure, which could have prevented it from

cracking. We plan to investigate methods for

alleviating this problem.

To understand the effect of the self-field of the

magnet powder on the distortion of the alignment

field, we carried out an electromagnetic study of

grain alignment in powder compacts using the

computer code Opera developed by Vector Field,

Inc. The results of this study will be helpful in

scaling up design rules to industry. Figures 2 to 4
12

Figure 2. Field lines (one-quarter) for compact partially

pressed to mechanical lockup, with no

alignment field, H ~ 0. Parameters:

ρl = 3.5 g/m3

, L/D = 0.643, B0 = 0.65 T.

Figure 3. Field lines (one-quarter) for compact partially

pressed to mechanical lockup. Alignment field

H = 1 T. Parameters: ρl = 3.5 g/m3

,

L/D = 0.643, B0 = 0.65 T.

show the calculated field lines of one-quarter of a

PM in increasing alignment fields of 0, 1, and 8 T,

respectively. These calculations were carried out

using the same powder density (3.5 g/m3

) and the

same L/D ratio (0.643). The field lines will all be

parallel to the z-axis if there is no distortion. It is

clear that distortion of the alignment field is the

largest when the alignment field is zero (Figure 2).

The distortion decreases with increasing alignment

field. At an alignment field of 8 T, the distortion

becomes very small (Figure 4). The distortion

Figure 4. Field lines (one-quarter) for compact partially

pressed to mechanical lockup. Alignment field

H = 8 T. Parameters: ρl = 3.5 g/m3,

L/D = 0.643, B0 = 0.65 T.

appears to be largest on the faces of the PM, and it

increases with the radial position.

Figure 5 shows the inclination of the field line

along the magnet upper face (z = 10.2 mm) as a

function of the radial position and the alignment

field. It shows that the inclination (distortion)

increases with radial position and decreases with

alignment field. If Br and Bz are defined as the radial

and the axial components of the magnetic flux

density B, respectively, then the volume average of

the ratio Br/Bz is a good measure of the overall

distortion of the field lines. We have found that the

following equation describes the overall distortion of

the field lines very well for all the cases calculated

by the computer code Opera.

(Br/Bz)vol (%) = 10.5 B0 / (H + 0.4430) ,

where B0 is the residual field of the powder compact

(B0 is proportional to the density of the powder) and

H is the alignment field. This equation clearly shows

that the overall distortion of the alignment field is

proportional to the density of the powder compact

and inversely proportional to the alignment field.

Our calculations also show that the overall distortion

of the field lines peaks at an L/D between 0.6 and

0.7. However, this conclusion depends on the

assumption made in the analysis. The main

assumption was that the powder is a perfectly hard

material, which resulted in providing a lower bound

on the distortion of the field lines. We plan to
Propulsion Materials FY 2002 Progress Report

13

Figure 5. Field-line inclination along face (z = 10.2 mm)

of compact partially pressed to mechanical

lockup and subject to different alignment

0 ≤ H(T) ≤ 8 T. Parameters: ρl = 3.5 g/m3

,

L/D = 0.643, B0 = 0.65 T.

continue the electromagnetic code analysis by

assuming that the powder is a soft magnetic

material. All the information obtained from the

analysis will help to make better PMs and provide

guidance on scaling up to industrial production.

At ORNL, crystallite size, texture (or preferred

orientation), and composition of the PM materials

pressed at Argonne are being characterized using

X-ray diffraction measurements (or neutron

diffraction, if required). All these features impact the

macroscopic magnetic properties. A goal of this part

of the project is to characterize, compare, and

correlate engineering and microscopic magnetic

properties of magnets aligned in the superconducting

solenoid. A select group of the magnets, whose

energy products are included in Figure 1, were

shipped to ORNL for characterization. The

condensed (105) pole figure data for these samples

is given in Figure 6. The poorest alignment is

observed for sample #200 (L/D = 0.27, H = 1 T).

Consistent with the previous discussion, the best

alignments were observed for the highest (8-T)

fields, irrespective of the L/D ratio, indicating that

these fields overcome the L/D geometric effects; but

at lower fields the L/D ratio becomes more

significant.

Finally, in FY 2002, we began to collaborate

with Ames Laboratory on processing the NdFeB

Figure 6. Condensed (105) pole figure data for ANL

samples.

powder for bonded PMs in our 9-T superconducting

magnet. A number of powder samples were

processed and shipped back to Ames Laboratory for

further examination and characterization.

Conclusions

A total of 69 PM samples were fabricated for

relatively small L/Ds (≤0.52) under alignment fields

between 1 and 8 T. Results from measurements

show that the relative improvement in remnant

magnetization or energy product is of the same order

of magnitude as in the previous study on a limited

number of samples.1

 The improvement in energy

product is of the order of 10–15%, with greater

improvement in shorter samples (smaller L/D).

Industry considers an improvement of 4–6% in the

energy product of current PMs as significant. The

present and previous results demonstrate

convincingly that alignment of PM powder in higher

magnetic fields, such as the 9-T superconducting

solenoid used in these studies, can indeed improve

the properties of the PM.

To better understand the alignment process, we

carried out an electromagnetic analysis using the

computer code Opera. The alignment field is

distorted by the self-field of the powder compact,

and the distortion varies with several parameters,
14

such as the L/D ratio, the powder density, and the

magnitude of the alignment field. Our results show

that overall distortion of the alignment field in the

powder compact is proportional to the density of the

powder compact and inversely proportional to the

magnitude of the alignment field. We also found that

there is a maximum in the overall distortion when it

is plotted against the L/D ratio. The information

obtained from the electromagnetic analysis will help

to make better PMs and provide guidance on scaling

up to industrial production.

Finally, a selected number of samples were sent

to ORNL for microstructure characterization so that

engineering and microscopic magnetic properties of

the processed PMs can be correlated. We also

collaborated with Ames Laboratory (see next report)

and processed a number of NdFeB powder samples

for bonded magnets in the 9-T superconducting

magnet facility at Argonne National Laboratory.

References

1. 2001 Annual Progress Report, Automotive

Propulsion Materials, U. S. Department of Energy,

Office of Energy Efficiency and Renewable Energy,

Office of Transportation Technologies,

Washington, D.C.

FY 2002 Publications/Presentations

T. M. Mulcahy, J. R. Hull, E. Rozendaal, and

J. H. Wise, “NdFeB Magnets Aligned in a 9-Tesla

Superconducting Solenoid,” presented at the 17th

International Workshop on Rare Earth Magnets

and their Applications, Newark, Delaware,

August 18–22, 2002.

T. M. Mulcahy and J. R. Hull, “A

Superconducting Solenoid and Press for Permanent

Magnet Fabrication,” presented at the 2002 Applied

Superconductivity Conference, Houston, Texas,

August 4–9, 2002.
Propulsion Materials FY 2002 Progress Report

15

B. Development of Improved Powder for Bonded Permanent Magnets

Iver E. Anderson, R. William McCallum, and Matthew J. Kramer

Metallurgy and Ceramics Program

Ames Laboratory, Iowa State University

Ames, IA 50011

(515) 294-9791; fax: (515) 294-8727; e-mail: andersoni@ameslab.gov

DOE Technology Development Manager: David Hamilton

(202) 586-2314; fax: (202) 586-1600; e-mail: david.hamilton@ee.doe.gov

Contractor: Ames Laboratory, Iowa State University, Ames, Iowa

Prime Contract No.: W-7405-Eng-82

Objectives

• Increase the maximum operating temperature of electric drive motors from 150 to 200EC while maintaining

sufficient operating characteristics.

• Reduce the cost of permanent magnet (PM) material in electric drive motors through the use of bonded magnets

and injection molding technologies for high-volume net-shape manufacturing.

Approach

• Develop innovative PM alloy design and processing technology for production of improved PM alloy powders

for bonded magnets with a tolerance for high temperatures.

• Investigate alloy design improvements through melt-spinning methods, with the specific goal of developing an

improved spherical magnet alloy powder through gas atomization processing.

• Develop an enhanced gas atomization process, along with a gas-phase powder surface reaction capability, for

production and environmental protection of powder for bonded magnets.

• Explore the effect of a novel crystallization/alignment procedure at high magnetic field in collaboration with

Argonne National Laboratory (ANL).

• Conduct experimental magnet molding trials on as-atomized and annealed magnet powders to characterize

bonded magnet properties in collaboration with Oak Ridge National Laboratory (ORNL).

Accomplishments

• Demonstrated and quantified quench compatibility between melt spinning and gas atomization in ribbon and

powder samples of experimental PM alloys for bonded magnets.

• Demonstrated improved high-temperature magnetic stability in preliminary work on a design approach that uses

an alternative magnet alloy.

• Produced an increased yield of amorphous magnet alloy powders, suitable for controlled annealing to enhance

bonded magnet properties, using modified high-pressure helium atomization processing.

• Demonstrated a fluidized bed fluorination process concept for magnet alloy powders, resulting in improved

resistance to air oxidation of coated powder in initial testing.
FY 2002 Progress Report Propulsion Materials

16

Future Direction

• Proceed with the development path for a new family of PM alloys to boost coercivity at elevated temperatures,

adjusting alloy constituents to balance gains in ambient-temperature magnetic strength and high-temperature

magnetic stability. Perform test of required quenchability for gas atomization.

• Continue parallel alloy development path with highly quenchable alloys (Nd2Fe14B-based) that exhibit high

magnetic strength at ambient temperature and that may gain high-temperature magnetic stability from extrinsic

effects.

• Develop a gas-phase reaction coating process for atomized PM alloy powder beyond the initial concept to

protect PM powders during the injection molding process and bonded magnet use.

• Characterize the magnetic properties of bonded magnets as a function of process variables, especially

modifications of crystallization conditions and temperature (up to 200EC), in collaboration with ORNL and an

industrial partner.

Introduction

To meet the cost and performance objectives of

advanced electric drive motors for automotive

applications, it is essential to improve the alloy

design and processing of PM powders. To enable the

widespread introduction of electric drive

automobiles, two primary objectives to be pursued

for PM materials are (1) to increase the useful

operating temperature for magnets to 200EC and

(2) to reduce the active magnet material cost to

about 25% of its current level. Currently, magnet

material can operate in temperatures ranging from

120 to 150EC, and the finished cost of sintered

magnetic material is approximately $90/kg. As an

alternative PM material form, polymer-bonded

particulate magnets offer the benefit of greatly

simplified manufacturing, but at a more moderate

level of stored magnetic energy that is still

compatible with innovative PM motor designs.

However, to exploit the potential of bonded PM

materials for such motors, it is necessary to develop

a particulate magnet material with high-temperature

properties that can be loaded to a high volume

fraction in an advanced polymer binder. Improving

materials and processing to allow for increased

operating temperature and mass production of netshape bonded magnets by gas atomization and

injection molding will be a significant advance

toward high-volume production of advanced electric

drive motors at reduced cost.

Approach

Innovative PM alloy design and processing

technology will be developed for production of

improved PM alloy powders for bonded PM

magnets with a tolerance for high temperatures.

Melt-spinning will be used to select alloy

modifications that boost coercivity at elevated

temperatures (up to 200EC) and improve alloy

quenchability for optimum yield from a gas

atomization process. This effort builds on an alloy

concept that was patented by Ames Laboratory. A

modified high-pressure gas atomization process will

be developed for the improved PM alloys to enhance

the yield of spherical, rapidly solidified powder.

This work furthers another Ames Laboratory

patented technology. A gas-phase reaction coating

process will be developed to enable enhanced

environmental protection of fine atomized powder

without degrading magnetic properties or molding

rheology, building on recent studies of fluidized bed

fluorination of similar rare earth alloy powders. A

model polymer will be selected and used to test

injection molding properties for high-temperature

bonded magnets. The effects of a conceptual

crystallization/alignment procedure conducted at a

high magnetic field [8 Tesla (T)] will be investigated

in collaboration with ANL. The magnetic properties

of bonded powder samples will be determined as a

function of loading fraction, powder size, annealing

schedule, coating treatment, and temperature, up to a

maximum of 200EC. Some of the bonded magnets

also will be provided to ORNL for additional

characterization. To improve the potential for

successful technology transfer, industrial

interactions have been emphasized at Ames

Laboratory. These include work with Magnequench

International (Raleigh-Durham, North Carolina) on

alloy design and rapid solidification processing
Propulsion Materials FY 2002 Progress Report

17

through a DOE cooperative research and

development agreement on advanced sensors and

control of the melt-spinning process.

Results

Innovative PM alloy design and processing

technology is being developed for production of

improved PM alloy powders for bonded PM

magnets with tolerance for high temperatures. Meltspinning methods generated ribbon samples that can

be crushed into particulate (see Figure 1) and that

permit rapid alloy design modifications. Modified

high-pressure gas atomization allowed production of

enhanced yields of spherical, rapidly solidified

powder (see Figure 1) of the improved PM alloys for

magnetic characterization, for development of a

Figure 1. A micrograph from a scanning electron

microscope shows fragmented flake powder

from melt spun ribbon (top), compared with

spherical powder from the high-pressure gas

atomization process (bottom).

protective coating process, and for development of

bonded magnet processing methods. Modified highpressure helium atomization processing produced an

increased yield of amorphous magnet alloy powders,

suitable for controlled annealing to enhance bonded

magnet properties.

Quench compatibility between melt spinning

and gas atomization has been demonstrated and

quantified in ribbon and powder samples of

experimental PM alloys for bonded magnets.

Figure 2 shows magnetic hysteresis loops for melt

spun ribbon samples and gas atomized powder of the

same magnet alloy powder in both the as-solidified

and annealed condition. The magnetic

characterization results for the ribbon sample with a

wheel speed of 16m/s seem compatible with the

results for powder of a diameter of <25μm in this

example.

A gas-phase reaction coating process, fluidized

bed fluorination, is being developed to enable

enhanced environmental protection of fine atomized

powder without degrading magnetic properties or

molding rheology. The effectiveness of this process

can be indicated by the Auger electron spectroscopy

results shown in Figure 3. The depth of penetration

Figure 2. Comparison of magnetic hysteresis

measurements for melt spun ribbon (top) and

for gas atomized powder (bottom) of the same

magnet alloy.
FY 2002 Progress Report Propulsion Materials

18

Figure 3. Scanning auger electron spectroscopy depth

profile showing the presence of a 15-nm

fluorine-containing layer on the surface of

treated powders.

of fluorine appears to be about 15 nm, suggesting

the formation of NdF3 on the surface of this powder

particle.

Improved high-temperature magnetic stability

has been shown in preliminary work on an

alternative magnet alloy design approach with

significant patent potential. The alloy design appears

to stabilize coercivity and remnance at elevated

temperatures (tested at up to 127EC) in the data that

are presented in Table 1, compared with the best

data for commercial powder products available from

Magnequench International.

Some experimental magnet material annealing

trials were performed at ANL to investigate the

effect of a high-energy alignment procedure.

Crystallization annealing experiments under high

(8 T) magnetic field were performed at ANL to

investigate the potential for alignment of new

magnetic grains from an amorphous parent phase in

melt spun ribbon samples of a Nd2Fe14B-Ti-C

magnet alloy. Polyphenyl sulfide has been selected

as the model polymer for testing injection-molding

properties for high-temperature bonded magnets in

collaboration with industrial partners. Industrial

interactions have been initiated with both Arnold

Engineering and Magnequench International to

develop relevant comparisons of bonded magnet

samples.

Conclusions

New alloy design work with a melt-spinning

approach can use a quench rate based on wheel

speeds of about 16 m/s to produce the magnetic

properties of as-atomized (Ar) powders with a

diameter of <25 μm (approximately). A novel alloy

design approach for high-temperature magnetic

stability has the potential for enhanced ambienttemperature energy product with a further reduction

of temperature coefficient, better for traction motor

applications than the current commercial powders.

Melt-spun ribbons of Nd2Fe14B-Ti-C magnet alloy in

a partially crystallized state appear to have

insufficient anisotropy in paramagnetic

susceptibility to affect crystal growth alignment

during annealing in a dc magnetic field at

temperatures of as low as 650 ̊C. Helium

atomization processing may be adopted as a

standard practice to maximize the yield of

amorphous and microcrystalline magnet alloy

powders as precursors of high-performance bonded

magnets. Fluidized bed fluorination appears

promising for developing improved oxidation and

corrosion resistant coatings on magnet alloy

powders based on Nd2Fe14B.

Bibliography

R. W. McCallum, K. W. Dennis, B. K.

Lograsso, and I. E. Anderson, “Method of Making

Bonded or Sintered Permanent Magnets,” U.S.

Patent 5,240,513, August 31, 1993.

Table 1. Magnetic properties and temperature coefficient of “high-performance” magnetic

materials

MQP-S-9-8 MQP-O MQ1-8-13 X5-132B

Br(kG) 6.8–7.2 7.9–8.2 6.0–6.4 6.1

(BH)max(MGOe) 8.5–10.0 12.6–14.0 7.7 8.1

Intrinsic coercivity Hci(kOe) 8.0–9.5 11–14 11 15

Coercive force Hc (kOe) 4.8–5.3 6.2–7.0 5.2 5.5

Temperature coefficient for Br −0.11 %/C°

(to 100°C)

−0.13 %/C°

(to 100°C)

−0.07 %/C°

(to 130°C)

Temperature coefficient of Hci −0.4 %/C°

(to 100°C)

−0.37 %/C°

(to 100°C)

−0.33 %/C°

(to 130°C)
Propulsion Materials FY 2002 Progress Report

19

I. E. Anderson, B. K. Lograsso, and R. L.

Terpstra, “Environmentally Stable Reactive Alloy

Powders and Method of Making Same,” U.S. Patent

5,372,629, December 13, 1994.

R. W. McCallum, K. W. Dennis, B. K.

Lograsso, and I. E. Anderson, “Method of Making

Bonded or Sintered Permanent Magnets

(continuation),” U.S. Patent 5,470,401,

November 28, 1995.

I. E. Anderson and R. L. Terpstra, “Apparatus

for Making Environmentally Stable Reactive Alloy

Powders,” U.S. Patent 5,589,199, December 31,

1996.

I. E. Anderson, B. K. Lograsso, and R. L.

Terpstra, “Environmentally Stable Reactive Alloy

Powders and Method of Making Same,” U.S. Patent

5,811,187, September 22, 1998.

R. W. McCallum and D. J. Branagan,

“Carbide/Nitride Grain Refined Rare Earth-IronBoron Permanent Magnet and Method of Making,”

U.S. Patent 5,803,992, September 8, 1998.

R. W. McCallum and D. J. Branagan,

“Carbide/Nitride Grain Refined Rare Earth-IronBoron Permanent Magnet and Method of Making,”

U.S. Patent 5,486,240, January 23, 1996.

D. J. Branagan and R. W. McCallum, “The

Effects of Ti, C, and TiC on the Crystallization of

Amorphous Nd2Fe14B,” J. Alloys and Compds., 245

(1996).

D. J. Branagan, T. A. Hyde, C. H. Sellers, and

R. W. McCallum, “Developing Rare Earth

Permanent Magnet Alloys for Gas Atomization,”

J. Phys. D: Appl. Phys., 29, p. 2376 (1996).

M. J. Kramer, C. P. Li, K. W. Dennis, R. W.

McCallum, C. H. Sellers, D. J. Branagan, L. H.

Lewis, and J. Y. Wang, “Effect of TiC Additions to

the Microstructure and Magnetic Properties of

Nd9.5Fe84.5B6 Melt-spun Ribbons,” J. Appl. Phys.,

83(11), pt. 2, p. 6631 (1998).

D. J. Branagan and R. W. McCallum, “Changes

in Glass Formation and Glass Forming Ability of

Nd2Fe14B by the Addition of TiC,” J. Alloys and

Compds., 244 (1–2), p. 40 (1996).

Publications/Presentations

Iver E. Anderson, Youwen Xu, Kevin Dennis,

R. William McCallum, and Matthew J. Kramer,

“Permanent Magnet Alloy Development for Gas

Atomization Processing,” 2002 International

Conference on Powder Metallurgy and Particulate

Materials, Orlando, Fla., June 16–21, 2002.

Propulsion Materials FY 2002 Progress Report

21

C. Carbon Foam for Electronics Cooling

J. W. Klett, April McMillan, and Nidia Gallego

Carbon and Insulation Materials Technology Group

Oak Ridge National Laboratory

P.O. Box 2008, MS 6087, Bldg. 4508

Oak Ridge, TN 37831-6087

(865) 574-5220; fax: (865) 576-8424; e-mail: klettjw@ornl.gov

DOE Technology Development Manager: Nancy Garland

(202) 586-5673; fax: (202) 586-9811; e-mail: nancy.garland@ee.doe.gov

ORNL Technical Advisor: David Stinton

(865) 574-4556; fax: (865) 574-6918; e-mail: stintondp@ornl.gov

Contractor: Oak Ridge National Laboratory, Oak Ridge, Tennessee

Prime Contract No.: DE-AC05-00OR22725

Objective

• Coordinate with automotive partners to develop a carbon foam heat exchanger and heat sink designs to dissipate

30 W/cm2

 using current cooling fluids, achieving a targeted heat flux/weight ratio of >30% over current

standards.

Approach

• Study fundamental mechanisms of heat transfer utilizing the carbon foam and engineering solutions to reduce

pressure drop.

• Compare results with existing data on heat sinks and current heat exchanger designs.

• Collaborate with original equipment manufacturers (OEMs) on designs and explore options together.

Accomplishments

• Demonstrated heat transfer capabilities of 22 W/cm2 with a reduction in pressure drop of more than an order of

magnitude compared with previous tests, yielding a heat sink with pressure drops equivalent to those of metal

foams but with higher heat transfer.

• Began environmental testing according to SAE J1211, “Recommended Environment Practices for Electronic

Equipment.”

Future Direction

• Continue collaboration with industrial suppliers and OEMs for enhanced design studies.

• Conduct processing studies to increase understanding of the effects of processing conditions on foam

microstructure and thermal and mechanical properties (strength, durability, and toughness).

• Develop relationships with industrial partners to get several more licensees for the fabrication of the foam,

thereby improving competition and reducing costs.

• Continue development of the foam extrusion process.
FY 2002 Progress Report Propulsion Materials

22

Introduction

Approximately two-thirds of the world’s energy

consumption is wasted as heat (e.g., incandescent

light bulbs, internal combustion engines, air

conditioning, power plants). This situation is likely

to get worse as the power levels of computer

processors and other electronic devices increase.

Computer chips with power levels of up to 1000 W

may be commonplace in less than 5 years;

unfortunately, the means to cool these chips are not

available at an affordable price. High-efficiency heat

exchangers are being incorporated into computers

and electronics to recover some of the heat lost and

increase efficiencies. The primary function of the

heat exchanger in these applications is to reduce the

temperature of the electronics, improving both life

and reliability. The second task of the heat

exchanger is to recover the energy for use in other

applications, thereby reducing the total energy

consumed. Unfortunately, most heat exchangers

dissipate captured heat from the electronics as lowquality heat (a very low temperature compared with

the ambient). Subsequently, this recovered heat is

simply dumped to the ambient environment and

wasted.

A unique graphite foam developed at the Oak

Ridge National Laboratory (ORNL) and licensed to

Poco Graphite, Inc., promises to allow for novel,

more-efficient heat exchanger designs that can

possibly dump high-quality heat, allowing recovery

of energy for other applications. This unique

graphite foam (Figure 1) has density values of

between 0.2 and 0.6 g/cm3

 and a bulk thermal

conductivity of between 40 and 187 W/m·K. The

ligaments of the foam exhibit a thermal conductivity

higher than that of artificial diamond. The high

conductivity, combined with a very accessible

surface area (>4 m2

/g), results in overall heat

transfer coefficients for foam-based heat exchangers

that are up to two orders of magnitude greater than

those of conventional heat exchangers. As a result,

foam-based heat exchangers could be dramatically

smaller and lighter than conventional designs.

Power Electronics Cooling

In previous research, it was shown that graphite

foam performed substantially better in transferring

heat in a smaller package than the existing heat

transfer mediums (Figure 2). However, the biggest

concern is the overall large pressure drop through

the

Figure 1. Graphite foam material developed at ORNL.

foam. A large pressure drop requires large amounts

of pumping power and thus increases the parasitic

losses. Therefore, research was focused on

engineering a design using the foam in which the

heat transfer remains high, but the pressure drop is

reduced. Several designs were considered, i.e.,

horizontal blind holes, vertical blind holes, and

corrugation.

To characterize the behavior of a simulated heat

sink, a test chamber was built that allowed

measurements of the power dissipation capacity. As

shown in Figure 3, the foam was mounted to an

aluminum plate (usually by brazing) and placed in a

cavity where the cooling fluid flows. The system

was designed with no gap around the foam, forcing

the fluid to pass through the pores of the foam. The

system was sealed with O-rings, and pressure taps

were inserted into the chamber to measure the

pressure drop of the foam heat sink. A simulated

power inverter, capable of generating up to 800 W

(32 W/cm2

), was mounted to the aluminum plate. As

the cooling fluid passed through the system, the

temperatures of the heater and inlet and outlet fluid

were measured. The overall heat transfer coefficient

(Uo) was calculated from Eq. (1) where ∆TLM is the

log mean temperature difference between the heater

and the cooling fluid, A is the area (foot print) of
Propulsion Materials FY 2002 Progress Report

23

foam attached to the aluminum plate, and q is the heat dissipated to the cooling fluid. This test rig was

Figure 2. Simulated power electronic temperature vs power density for various heat sinks.

Figure 3. Schematic of test rig to evaluate heat sink

geometries.

used to measure heat transfer coefficients with

different base plates, foam geometries, and other

heat sink devices, such as aluminum foam.

Uo = q / (A· ∆TLM) (1)

Figure 4 illustrates the design concept of

corrugation to reduce pressure drop. In the solid

block, the fluid has to pass through a given length of

foam with tiny pores. However, in the corrugated

foam, the overall length of the heat sink is the same,

but the flow length is reduced dramatically. Since

the pressure drop is linearly related to the flow

length, the overall pressure drop can be reduced by

more

than an order of magnitude if the flow length is

reduced by a similar amount. Figure 5 illustrates the

effects of corrugating a solid graphite foam heat

sink. As can be seen, the heat transfer was still

dramatically greater than that of the aluminum foam,

but the pressure drop was reduced to 7% of that of

the original solid graphite foam heat sink.

Obviously, this design needs to be optimized, but it

was demonstrated that the pumping power required

for the foam can be dramatically reduced.

Environmental Testing

Another focus of this year’s effort has been the

testing of the foams in different environmental

conditions. As was recommended by the Electrical

and Electronic Tech Team, testing is being

conducted using SAE J1211, “Recommended

Environment Practices for Electronic Equipment.” A

test plan was developed and testing has begun.

Testing includes thermal cycling, humidity, salt

spray, immersion and splash, dust bombardment,

and vibration. The test plan requires the use of five

different forms of the graphite foam in each test

(control, nickel plated, chromium plated, brazed to

copper and brazed to aluminum). Each sample will

be evaluated both physically and thermally prior to

testing and post-testing. Then compression testing

∆P=0.02 psi/in.

∆P=2.4 psi/in.
FY 2002 Progress Report Propulsion Materials

24

will be conducted to determine effects on

mechanical properties of the foams.

Solid Corrugated

Figure 4. Schematic illustrating the effects of corrugation on the resulting pressure drop.

0.0

20.0

40.0

60.0

80.0

100.0

120.0

140.0

160.0

180.0

0 5 10 15 20 25

Power Density [W/cm2

]

Electronic Temperature [C]

no cooling

Aluminum Foam

Copper Foam

Graphite Foam

Corrugated Graphite Foam

Aluminum Foam:

∆P=0.03 psi/in.

Copper Foam:

∆P=0.02 psi/in.

Corrugated Graphite Foam:

∆P=0.03 psi/in.

Graphite Foam:

∆P=2.4 psi/in.

Figure 5. Heat transfer properties of corrugated graphite foam with other foam heat sinks.

Conclusions

It has been shown that the graphite foam heat

sinks can be engineered to reduce the overall

pumping power needed while maintaining high heat

transfer coefficients. Through modification of the

slot thickness, web thickness, and flow length,

corrugated graphite foams can be almost as effective

as a solid block of graphite foam in removing heat,

but maintain a low pressure drop. In fact, it was

shown that the corrugation yielded a pressure drop

with water to a level similar to that exhibited by

copper and aluminum foams. This research further
Propulsion Materials FY 2002 Progress Report

25

demonstrates the tailorability of the graphite foam

into an excellent heat sink for power electronics.

Environmental durability testing has begun

according to SAE J1211, and results are expected

sequentially over the next year.

References

“Recommended Environment Practices for

Electronic Equipment,” SAE J1211, Society of

Automotive Engineers, 1978.

FY 2002 Publications

J. Klett, A. D. McMillan, and Dave Stinton,

“Modeling Geometric Effects on Heat Transfer with

Graphite Foam,” 26th Annual Conference on

Ceramic, Metal, and Carbon Composites, Materials,

and Structures, Cocoa Beach, Florida, January 2002.

J. Klett, A. D. McMillan, Lynn B. Klett, “The

Effect of Thermal Cycling on Prototype Graphite

Foam Heat Exchangers,” 26th Annual Conference

on Ceramic, Metal, and Carbon Composites,

Materials, and Structures,” Cocoa Beach, Florida,

January 2002.

Patents Issued

J. W. Klett, “Process for Making Carbon Foam,”

U.S. Patent Number 6,033,506, March 7, 2000.

J. W. Klett and T. D. Burchell, “Pitch-Based

Carbon Foam Heat Sink with Phase Change

Material,” U.S. Patent Number 6,037,032,

March 14, 2000.

J. W. Klett, “Pitch-Based Carbon Foam and

Composites,” U.S. Patent Number 6, 261,485,

July 17, 2001.

J. W. Klett, “Pitch-Based Foam with

Particulate,” U.S. Patent Number 6,287,375,

September 11, 2001.

J. W. Klett, “Method for Extruding Pitch-based

Carbon Foam,” U.S. Patent Number 6,344,159,

February 5, 2002.

J. W. Klett, “Pitch Based Carbon Foam and

Composites,” U.S. Patent Number 6,387,343,

May 14, 2002.

J. W. Klett, “Method of Casting Pitch-Based

Carbon Foam,” U.S. Patent Number 6,398,994,

June 4, 2002.

J. W. Klett and T. D. Burchell, “Pitch-based

Carbon Foam Heat Sink with Phase Change

Material,” U.S. Patent Number 6,399,149,

June 4, 2002.

Propulsion Materials FY 2002 Progress Report 

27 

D. dc Bus Capacitors for Hybrid Vehicle Power Electronics 

B. A. Tuttle, G. Jamison, D. Wheeler, J. S. Wheeler, and D. Dimos 

Sandia National Laboratories 

P.O. Box 5800, MS 1411 

Albuquerque, NM 87185-1405 

(505) 845-8026; fax: (505) 844-2974; e-mail: batuttle@sandia.gov 

DOE Technology Development Managers: David Hamilton 

(202) 586-2314; fax: (202) 586-1600; e-mail: david.hamilton@ee.doe.gov 

Rogelio Sullivan 

(202) 586-8042; fax: (202) 586-1600; e-mail: rogelio.sullivan@ee.doe.gov 

Contractor: Sandia National Laboratory, Albuquerque, New Mexico 

Prime Contract No.: 04-94AL85000 

Objectives 

• Develop a replacement technology for the currently used aluminum electrolytic dc bus capacitors for hybrid 

electric vehicles. 

• Develop a high-temperature polymer dielectric film technology that has dielectric properties technically 

superior to those of aluminum electrolytic dc bus capacitors and is of comparable or smaller size. 

• Scale up cost-competitive polymer film dielectric technology: (1) develop a continuous process for dielectric 

sheet fabrication and (2) fabricate prototype capacitors. 

Approach 

• Work with automobile design and component engineers, dielectric powder and polymer film suppliers, and 

capacitor manufacturers to determine state-of-the-art capabilities and to define market-enabling technical goals. 

• Develop a project plan with automobile manufacturers and large and small capacitor companies to fabricate 

polymer dielectric sheets suitable for the manufacture of capacitors for hybrid electric vehicles. 

• Synthesize unique conjugated polyaromatic chemical solution precursors that result in dielectric films with low 

dissipation factors (DFs) and excellent high-temperature dielectric properties. 

• Develop polymer film processes and technologies that will lower costs to permit competitive high-volume 

capacitor manufacturing. 

• Interact with Oak Ridge National Laboratory (ORNL) with regard to mechanical characterization of films. 

Accomplishments 

• Invented chemical synthesis procedures that resulted in polymer films with four times the energy density of 

commercial polyphenylene sulfide at 110EC. Scaled-up hydroxylated polystyrene or polyvinyl phenol (PVP) 

films exhibited dielectric constants of 4.7 and DFs of 0.009 at up to 110EC, meeting technical requirements for 

commercialization. 

• Collaborated with TPL, Inc., to develop a continuous process for Sandia National Laboratories’ (SNL’s) 

dielectric film fabrication and fabricated 25-cm-wide and 20-m-long rolls of dielectric film that had breakdown 

strengths of greater than 4 MV/cm from −40E to 110EC. 

• Collaborated with Brady Corporation, a high-volume capacitor manufacturer, to co-develop fabrication 

procedures for 25-cm-wide, 90-m lengths of SNL dielectric film on a pilot production prototype coater. 
FY 2001 Progress Report Propulsion Materials 

28 

• Collaborated with Steiner Corporation to develop a high-volume electrode process for our dielectric films. 

Developments are still needed to provide adequate release from the underlying carrier. 

• Collaborated with ORNL to characterize mechanical properties of PVP films. 

Future Direction 

• Perform extensive electric field and temperature characterization to determine that the SNL polyfilm dielectrics 

fabricated using high-volume processes will meet FreedomCAR requirements for breakdown field and DF for 

temperatures from −40E to 110EC. 

• Perform extensive electric field and temperature characterization on 1-μF to 10-μF wound capacitors to 

determine if they will meet General Motors (GM) requirements. Supply capacitors to GM for testing in 

inverter-type environments. 

• Interface with Brady Corporation and TPL to fabricate large rolls of slit dielectric polymer sheet (10-kg lots) on 

a production caster that are suitable for fabrication of multilayer capacitors (20 to 200 μF). 

• Along with GM, evaluate large-value (20-μF to 200-μF) capacitors fabricated by vendor(s) in simulated electric 

hybrid vehicle environments. 

Results 

Strategy and Interactions 

SNL has actively interacted with a number of 

representatives from the automobile industry to 

obtain their perspective on what is needed for hybrid 

electric vehicles. In FY 2002, SNL has continued its 

emphasis on the development of polymer film 

dielectrics for two reasons. First, GM has been 

adamant about soft-breakdown dielectric film 

technology—a phenomenon that bulk ceramic 

capacitors do not exhibit. Second, emphasis on 

polymer dielectrics provides greater balance of the 

DOE effort between polyfilm and ceramic 

technologies, as requested by the Electrical and 

Electronics (E/E) Tech Team. SNL has developed a 

close working relationship with development 

personnel in the Advanced Technology Vehicles 

Division of GM. SNL has modified project plans for 

the development of polymer film dielectrics for 

hybrid vehicle applications according to E/E Tech 

Team recommendations. 

These interactions led us to the conclusion that 

the most viable replacement technology for 

electrolytic dc bus capacitors by 2004 was 

multilayer polymer film capacitors. Reducing the 

size of the polymer capacitors was most often cited 

by automobile design engineers and capacitor 

manufacturers as a needed technology-enabling 

breakthrough. In addition, it is necessary to improve 

high-temperature (110EC) performance while 

keeping the technology cost-competitive. For 

polymer film dielectrics, a commercialization goal 

of a dielectric constant of 6 and a DF of less than 

0.01 was initially agreed to by AVX/TPC and GM. 

However, based on the GM 2004 criterion for 

capacitance density of 2.0 μF/cm3

, the team agreed 

that if a polyfilm of K = 4.5 could be developed that 

could meet the temperature requirements, it would 

be suitable for scale-up activities. 

The initial scale-up strategy consisted of the 

following steps: (1) develop a polymer film 

technology that meets requirements, (2) synthesize 

10-kg to 20-kg batches, (3) develop a continuous 

process for 3-μm-thick polymer films, and 

(4) fabricate them into prototype capacitors. This 

approach had to be modified because the synthesis 

and the development of a continuous process had to 

be broken down into multiple steps to be 

accomplished. While an initial polymer film 

technology, hydroxylated polyphenylene (PP+OH), 

was developed that met all criteria and was 

exceedingly low-loss, its cost was prohibitive. 

Although SNL was successful in developing three 

new processes that reduced the cost of the PP+OH 

technology by a factor of ten, costs were still not 

satisfactory for FreedomCAR applications. Thus a 

second polymer film technology, PVP, was 

developed that exhibited more loss than PP+OH but 

is 10 to 100 times more cost-efficient. This new 

technology has four times the energy-densityhandling capability at 110EC of the commercial 

standard of polyphenylene sulfide. 
Propulsion Materials FY 2002 Progress Report 

29 

Inverter designs and operating conditions for dc 

bus capacitors vary from manufacturer to 

manufacturer. GM has presented 2- to 5-year and 

10-year goals for dc bus capacitors that other auto 

manufacturers feel are satisfactory milestones for the 

program. Specific goals for 2004 commercialization 

include (1) –40E to 110EC operation, (2) greater 

than 2 μF/cm3

 capacitance density, and (3) 575-V dc 

with 600-V peak for 50-ms operation. In addition, 

GM has requested fail-safe operation; Ford and 

DaimlerChrysler have not voiced as strong an 

opinion regarding the fail-safe criterion. The failsafe criterion is analogous to soft breakdown of the 

dielectric, rather than catastrophic electrical 

discharge and mechanical failure that can be 

observed in bulk ceramic dielectrics. Soft 

breakdown occurs as a result of the vaporization of 

the thinner electrode layers of the polymer dielectric 

near electrical breakdown sites. 

Based on these criteria, an individual dielectric 

layer thickness of approximately 3 μm for polyfilm 

capacitors is projected. These thickness values are 

based on operating field strengths of 2 MV/cm for 

the newly developed polyfilm capacitors. Based on 

these assumptions and on measurement of presently 

available commercial capacitors, size comparisons 

and capacitance densities of 500-μF dc bus 

capacitors for different technologies were obtained 

(Figure 1). Soft-breakdown behavior and lower cost 

are assets for polymer film capacitors. The projected 

polymer film capacitor volume is calculated 

assuming that 40% of the capacitor space is nonactive and 200-nm-thick electrodes are used. Note 

that the volumetric capacitance efficiency for a 

K = 4.5 polyfilm capacitor of 2.4 μF/cm3

 exceeds 

the 2004 commercialization goal of 2 μF/cm3

. 

Polymer Film Dielectric Development 

SNL polymer film dielectric development has 

been based on the request from manufacturers that 

the new polyfilm dielectrics have voltage and 

temperature stability that is equivalent to that of 

present polyphenylene sulfide (PPS) technology. 

Thus a structural family of polymer dielectrics has 

been designed and synthesized to meet two of the 

most stringent requirements: (1) low dielectric loss 

and (2) extremely good temperature stability. 

Figure 2 shows a schematic diagram of Sandia’s 

conjugated, polyaromatic-based structure and 

indicates the large number of molecular 

modifications to this structure that are possible. Our 

present effort emphasizes molecular engineering of 

higher-polarizability structures that will enhance 

dielectric constants yet retain acceptable dielectric 

loss characteristics. A patent disclosure has been 

initiated covering the design and synthesis 

techniques for this polymeric family.1

 Three initial 

molecular modifications to the base structure were 

made: (1) propyl bridge substitution, (2) sulfur 

bridge substitution, and (3) replacement of R-side 

groups with high-electronegativity fluorine ions to 

enhance polarizability. 

For FY 2002, we have concentrated our efforts 

on the PVP film structural family. Synthesis routes 

for PVP films were designed and implemented 

because the cost of this technology was 1 to 2 orders 

of magnitude less than that of the PP+OH 

technology previously developed by SNL. Because 

of the chemical structure of the PVPs, it was 

postulated that these films would not have loss 

characteristics as good as those of the hydroxylated 

polyphenylene films. Although the PVP loss met 

specifications (DF <0.01) at 25EC, unacceptable loss 

 Al electrolytic 

 400 cm3 

 1.3 μF/cm3

PPS polyfilm 

933 cm3

K = 3,310 cm3

1.6 μF/cm3

Projected SNL poly 

K = 6, 155 cm3 

3.2 μF/cm3

Projected SNL ceramic 

84 cm3 

6 μF/cm3

Figure 1. Size diagram of 500-μF dc bus capacitors of different technologies. 
FY 2001 Progress Report Propulsion Materials 

30 

Y

Ar

Ar Ar

Ar

Ar Ar

R1 R2

R3 R4

X

n

Figure 2. Schematic diagram of SNL conjugated 

polyaromatic film base structure. 

(DF = 0.065) was measured at 110EC. A study was 

initiated to incorporate crosslinker chemistry into 

our PVP polymers to reduce the flexibility of the 

polymer chains and thus decrease dielectric loss. 

Development and incorporation of a VEctomer 

crosslinker chemistry reduced the loss to 0.01 at 

110EC as shown in Figure 3. As expected, the 

dielectric constant also decreased. However, the 

dielectric constant of 4.7 is acceptable for hybrid 

vehicle applications and scale-up activities. 

Figure 3. Dielectric constant and dissipation factor of 

SNL hydroxylated polystyrene film with 

VEctomer cross-linker. 

Figure 4 is a pictorial chronology of our PVP 

film scale-up activities in FY 2002. Our technology 

evolved from 5 × 5-in. single-cast dielectric sheets 

[Figure 4(a)] to continuous slot-die-cast rolls of 

dielectric sheets of approximate 5 to 20 meter length 

in December 2001 [Figure 4(b)]. We worked with 

TPL of Albuquerque to fabricate these rolls. 

Development of technology that was more amenable 

to high-volume production required interaction with 

Brady Corporation of Milwaukee. We were able to 

cast 150-m lengths of 25-cm-wide polymer film 

using the Brady prototype caster in March of 2002 

on 5-cm-diam. mandrills. A high-volume electrode 

deposition process is another process that is essential 

to manufacturing large-value capacitors. Steiner 

Corporation deposited aluminum electrodes on SNL 

films using a proprietary high-volume 

manufacturing process. The slit and Steiner 

electroded film roll are shown in Figure 4(c). A 

wound polymer capacitor with the metallized film 

roll is shown in Figure 4(d). Our dielectric film 

thickness is presently 4 to 5 μm. 

A prototype PVP capacitor was fabricated using 

metallized paper electrodes. The metallized paper 

electrodes permitted electrical characterization of the 

dielectric without having to develop a sophisticated 

high-volume metallization technology. The 

dielectric for this capacitor was fabricated using a 

Brady Corporation prototype coater. The prototype 

coater at Brady Corporation is shown in Figure 5 

during the coating of SNL PVP film on a Mitsubishi 

smooth Mylar carrier using a reverse Gravure roller 

configuration. Casting rates were ~1 m/min, and 

roughly 31 wt % SNL polymer was used in the 

coating solution. The dielectric film and metallized 

paper rolls were wound into 0.8 μF capacitors at 

SNL using a custom dielectric film winder. 

Termination electrode procedures were performed at 

TPL. Both capacitance and DF as a function of 

temperature are shown in Figure 6. The capacitance 

varies by ± 7% from −40o

C to 55EC. DFs were 

below 0.01 for a temperature range that exceeded 

100EC. The DF of 0.007 at 110EC was particularly 

encouraging. These film properties were considered 

to be acceptable for continuation of scale-up 

activities with this technology. 

Summary

Critical economic and technical issues for 

improvements of dc bus capacitors for hybrid 

electric vehicles were determined through discussion 

and visitation with automobile design engineers, 

chemical synthesis companies, and capacitor 

manufacturers. PVP film dielectric development has 

been emphasized in FY 2002, and we have 

developed a multi-step project plan for large-scale 

commercialization of polymer film dc bus 

capacitors. In FY 2002, we developed, in 

conjunction with TPL, a continuous process for 

fabricating 5- and 20-m-long rolls of SNL PVP 

sheets. For high-volume production, Brady 

Corporation in Milwaukee was contacted. Near 

high-volume continuous casting techniques were 

Temperature (oC) 

0

1

2

3

4

5

6

0

0.01

0.02

0.03

0.04

0.05

20 40 60 80 100 120

Dielectric Constant

Dissipation Factor

PVOH - vectomer

250 o

C / 2min

9.5 μm Sheet

Dielectric Constant 

Dissipation Factor
Propulsion Materials FY 2002 Progress Report 

31 

(a) 5 × 5 in. sheets 9-01 (b) 20-ft rolls TPL slot-die caster 12-01 

(c) Wound metallized SNL film 3-02 (d) Wound capacitor 4-02 

Figure 4. Pictorial chronology of FY 20O2 SNL polymer film scale-up activities. 

Figure 5. Brady pilot production coater with SNL film. 

developed for SNL films on three separate trips to 

Brady Corporation using Brady’s prototype caster. 

We also interfaced with Steiner Corporation for 

high-volume aluminum electrode deposition. After 

the initial metallization, the film did not release 

satisfactorily from the underlying smooth Mylar 

carrier. This problem was attributed to additional 

curing that occurred during the metallization 

process. Solving this issue appears to be the final 

Figure 6. Capacitance and dissipation factor of SNL 

dielectric—metallized paper capacitor vs 

temperature. 

hurdle before SNL films can be fabricated on the 

high-volume Brady production caster. Initial SNL 

polymer film wound capacitors of 1 μF capacitance 

were fabricated using metallized paper electrodes. 

These capacitors met the extended temperature 

requirements for hybrid electric and fuel cell 

vehicles. Future work includes further interfacing 

with Steiner Corporation to obtain high-quality SNL Capacitance (μF)Dissipation Factor

0

0.2

0.4

0.6

0.8

1

0

0.05

0.1

0.15

0.2

-40 -20 0 20 40 60 80 100

Capacitance

Dissipation Factor

SNL Brady1 Wound Capacitor

Metallized Paper

f = 1 kHz

2o

C per minute cooling

Temperature (oC) 
FY 2001 Progress Report Propulsion Materials 

32 

polymer film dielectric using high-volume 

aluminum deposition procedures. Capacitors in the 

range of 1 to 4 μF range will be fabricated for hightemperature characterization by SNL. Further, GM 

will determine their suitability in inverter 

environments. In addition, we are supplying—on a 

continuous basis—dielectric films to Matt Ferber of 

ORNL from our scale-up activities. An 

understanding of mechanical property–process 

relationships is critical to developing film 

technology that exhibits adequate release from the 

underlying carrier and can thus be used for highvolume manufacturing. When these technical issues 

are solved, we will use the production scale coater at 

Brady Corporation to fabricate roughly 3500-m by 

3.1-m rolls of polymer film. These film rolls will be 

used to fabricate a series of 200-μF capacitors for 

evaluation by SNL, ORNL, GM, Ford, and 

DaimlerChrysler. 

Technical Disclosures

1. D. Wheeler and G. Jamison, “Novel Polymer 

Film Synthesis Routes of Voltage and Temperature 

Stable Dielectrics,” October 5, 1999. 

Presentations

B. A. Tuttle, D. Wheeler, G. Jamison, and 

D. Dimos, “dc Bus Capacitors for PNGV Power 

Electronics,” pp. 27–32 in Automotive Propulsion 

Materials 2001 Annual Progress Report, October 

2001. 

B. A. Tuttle, P. G. Clem, D. Wheeler, 

G. Jamison, P. Yang, W. R. Olson, and J. S. 

Wheeler, “dc Bus Capacitors for Hybrid Electric 

Vehicle Power Electronics,” 26th Annual 

International Conference on Advanced Ceramics 

and Composites, Cocoa Beach, Florida, January 14, 

2002 (invited presentation).
Propulsion Materials FY 2002 Progress Report

33

E. Mechanical Reliability of Electronic Ceramics and Electronic Ceramic

Devices

M. K. Ferber, L. Riester, C-H Hsueh, and M. Lance

Mechanical Characterization and Analysis Group

Oak Ridge National Laboratory

P.O. Box 2008, MS 6068, Bldg. 4515

Oak Ridge, TN 37830-6069

(865) 576-0818; fax: (865) 574-6098; e-mail: ferbermk@ornl.gov

DOE Technology Development Manager: Nancy Garland

(202) 586-5673; fax: (202) 586-9811; e-mail: nancy.garland@ee.doe.gov

ORNL Technical Advisor: David Stinton

(865) 574-4556; fax: (865) 241-0411; e-mail: stintondp@ornl.gov

Contractor: Oak Ridge National Laboratory, Oak Ridge, Tennessee

Prime Contract No.: DE-AC05-00OR22725

Objectives

• Predict and assess the mechanical reliability of electronic devices with emphasis on those used for automotive

power electronics (e.g., capacitors).

• Correlate the mechanical characterization of polymer film capacitors developed by Sandia National

Laboratories (SNL) to the dielectric behavior.

Approach

• Develop techniques to characterize polymer films developed by SNL and correlate mechanical behavior with

dielectric behavior.

• Correlate mechanical performance of films as a function of processing.

Accomplishments

• Characterized three series of SNL polymer film samples using a mechanical properties microprobe.

• Developed low-cost grips for evaluating the room-temperature tensile stress-strain behavior of polymer films.

Future Direction

• Develop hardware and test procedures for characterizing polymer films as a function of temperature.

• Use the mechanical properties microprobe to track changes in polymer structure resulting from processing

variations, as well as in-service use.

Introduction

A major focus of the power electronics effort in

the Automotive Propulsion Materials Program is to

develop a capacitor technology that will replace

current electrolytic dc bus capacitors for power

electronics modules in hybrid electric vehicles. The

ultimate objective is to make the power modules

more compact while maintaining the tight voltage

and temperature requirements. Because of the

interest in polymer film capacitors, a collaboration

with SNL was initiated to evaluate SNL’s materials.

Synthetic chemists at SNL are currently fabricating a
FY 2002 Progress Report Propulsion Materials

34

number of different temperature-stable polymers for

the power electronics program. The 2004 goal is to

have a polymer film dielectric that can operate

continuously at 110EC. Although these films are

expected to be similar to polyphenylene sulfide in

terms of properties, they are truly unique films that

have not been used before by the capacitor industry.

Therefore, the goal of this project is to mechanically

characterize these films to (1) generate baseline data

for comparison with other commercial films,

(2) identify any changes in performance arising from

process variations, and (3) evaluate the mechanical

behavior of films once they are incorporated into

multiplayer capacitors. The importance of

mechanical characterization of these dielectric films

is illustrated in Figure 1, which shows the strong

correlation between loss factor and the elastic

modulus.

Figure 1. Correlation of mechanical and dielectric

performance for a commercial polymer film.

Results

Given the limited thickness of these films

(<10 μm), specialized techniques are required to

assess the mechanical behavior. One approach is to

use a mechanical properties microprobe (MPM) to

interrogate the material on the nanometer scale

(Figure 2). The MPM is an automated instrument

that consists of four primary components: an

indenter (Berkovich indenter) whose vertical

displacement (nanometer resolution) and applied

load (microgram resolution) are controllable; an

optical microscope (OM) with several objective

lenses; a precision X and Y stage that translates the

metallographically prepared specimen between the

OM and the indenter; and a computer that controls

Figure 2. Schematic representation of the mechanical

properties microprobe.

the OM’s lens turret (50–1500× magnification),

stage movement, and indenter load and

displacement. The computer also collects data on the

indenter’s displacement and load and is interfaced

with a TV monitor and camera that show the

microscope’s field of view and allow inspection of

each indent. The MPM (not including the computer)

is housed inside an insulated cabinet that minimizes

its susceptibility to laboratory room temperature

fluctuations and vibrations (which are problematic

when controlling displacement at the nanometer

level). The computer is outside the insulated cabinet

to further minimize the introduction of thermal

instabilities and remotely operates the MPM.

The load/displacement history generated during

indentation can be interpreted with the aid of an

appropriate model to calculate elastic modulus (E)

and hardness (H) of the material (Figure 3).

Specifically, the hardness is calculated by dividing

the peak load by the residual indent area, while the

elastic modulus is determined from the slope of the

unloading curve.

In the present study, the MPM was initially used

to examine a number of films (Table 1) provided by

SNL. Six of the initial films were deposited on

100-nm aluminum/400-nm SiO2/Si wafers. The

SiO2, which is applied by chemical vapor deposition

and then thermally annealed, was put on by a

commercial manufacturer to passivate the silicon.

The second series of films evaluated with the MPM

were deposited on a Mylar sheet using the

continuous deposition procedures developed under

the SNL project. These films were removed from the

Mylar before testing.
Propulsion Materials FY 2002 Progress Report

35

Figure 3. Typical load-displacement curve generated

during loading and unloading with the

mechanical properties microprobe.

Values of H and E were first measured as a

function of residual depth of penetration (yp), as

shown for the first set of films in Figure 4. Note that

at some critical value of yp, H and E increase with

increasing yp. This effect occurs because of the

influence of the substrate, which in the case of

silicon is both harder and stiffer than the film. The

critical value of yp depends upon the film thickness.

Because of this effect, the film properties must be

determined from indents that are below the critical

depth. A good rule of thumb is that the depth must

be less than 1/10th of the film thickness.

In the present study, the indentation data

generated at 20 nm and below were used to calculate

the substrate-independent values of H and E.

Figure 5 illustrates the effect of film thickness upon

E and H for the first set of films. There is a tendency

for the H and E to increase slightly as the film

thickness decreases.

One limitation of the MPM is that data are

typically generated at room temperature only. To

evaluate temperature effects in the present study,

free-standing films were also mechanically

evaluated using a tensile stress-strain test. Initially,

commercial grips were used to mechanically load

polymer films to ultimate failure. The films were in

the shape of rectangular strips 25.4 mm long and

0.0095 mm thick. The stress-strain data are shown in

Figure 6. Results for a commercially available film

are provided for comparison. The polyvinyl phenol

films provided by SNL exhibited limited ductility, as

reflected by the low values of failure strain.

Subsequent differential scanning calorimetry

measurements suggested that the glass transition

temperature (temperature below which the

amorphous component of the polymer becomes

brittle) was in the range 40–45EC. This would

explain the limited strain-to-failure values measured

in the room-temperature stress-strain testing.

A number of low-cost approaches for gripping

the films for stress-strain testing were also

investigated. The first approach, similar to that used

to test small fibers, involved first gluing the film into

a special cardboard holder. This holder was then

mounted in the test frame using conventional pin

grips. The most successful method required the use

of precision stages to mechanically load the film

(Figure 7).

Table 1. Summary of polymer films evaluated with the mechanical properties microprobe

No. Base designation Substrate Thickness (μm) Comments

1 PVP5 Si 0.394

2 PVP5-2X Si 2.849

3 PVP5-2X Si 2.006

4 PVP5 Si 0.499

5 PVP5 Si 0.583

6 PVP5 Si 0.498

7 PVP Mylar 12.000 Smooth roller

8 PVP Mylar 2.500 Gravure Roller 900 RPM boost motor

9 PVP Mylar 5.000 Gravure Roller 250 RPM

10 PVP Mylar 7.500 Gravure Roller 0 RPM, boost off

PVP = polyvinyl phenol, or hydroxylated polystyrene.
FY 2002 Progress Report Propulsion Materials

36

(a) (b)

Figure 4. Effect of penetration depth upon hardness (a) and elastic modulus (b).

(a) (b)

Figure 5. Effect of film thickness upon hardness (a) and elastic modulus (b).

Figure 6. Preliminary tensile stress-strain data obtained

using commercially available grips. Figure 7. Arrangement of precision stages used to

grip films.
Propulsion Materials FY 2002 Progress Report

37

Conclusions

The MPM was used to evaluate the hardness and

elastic modulus of the polymer films. In the initial

testing of the films deposited on the silicon

substrates, these properties were found to depend

slightly upon film thickness. The subsequent

evaluation of the films prepared using the

continuous deposition procedures showed that the

film properties were relatively independent of the

roller characteristics. The first room-temperature

tensile stress-strain measurements of a polymer film

were conducted. The addition of a temperature

chamber will allow us to conduct measurements

throughout the temperature range of interest. The

resulting structural information will be correlated

with dielectric properties measured at SNL.

Publications

C-H Hsueh and M. K. Ferber, “Effective

Coefficient of Thermal Expansion and Residual

Stress in Multilayer Capacitors,” accepted for

publication in Journal of Composites, Part A.

Propulsion Materials FY 2002 Progress Report 

39 

3. FUEL CELLS 

A. Carbon Composite Bipolar Plates 

T. M. Besmann, J. W. Klett, and J. J. Henry, Jr. 

Surface Processing and Mechanics Group and Carbon and Insulating Materials Group 

Oak Ridge National Laboratory 

P.O. Box 2008, MS 6063, Bldg. 4515 

Oak Ridge, TN 37831-6063 

(865) 574-6852; fax: (865) 574-6198; e-mail: besmanntm@ornl.gov 

DOE Technology Development Manager: JoAnn Milliken 

(202) 586-2480; fax: (202) 586-9811; e-mail: joann.milliken@ee.doe.gov 

ORNL Technical Advisor: David Stinton 

(865) 574-4556; fax: (865) 241-0411; e-mail: stintondp@ornl.gov 

Contractor: Oak Ridge National Laboratory, Oak Ridge, Tennessee 

Prime Contract No.: DE-AC05-00OR22725 

Objectives 

• Develop a slurry-molded carbon fiber material with a carbon chemical-vapor-infiltrated sealed surface as a bipolar 

plate. 

• Collaborate with potential manufacturers with regard to testing and manufacturing of such components. 

Approach 

• Fabricate fibrous component preforms for the bipolar plate by slurry-molding techniques using carbon fibers of 

appropriate lengths. 

• Fabricate hermetic plates using a final seal with chemical-vapor-infiltrated carbon. 

• Develop commercial-scale components for evaluation. 

Accomplishments 

• Developed a carbon composite material with graphite particulate filler to control pore size and speed surface 

sealing. 

• Further characterized and measured the mechanical properties of the carbon composite plate material. 

• Significantly improved wetting of the bipolar plate surface. 

• Determined the surface roughness of finished bipolar plate components. 

• Supported scale-up efforts at licensee Porvair Fuel Cell Technology. 

Future Direction 

• Develop bipolar plate material/configuration to meet various users’ unique requirements. 

• Improve wetting properties of carbon surfaces. 
FY 2002 Progress Report Propulsion Materials 

40 

• Decrease component thickness. 

• Transfer technology and aid Porvair with scale-up. 

Introduction

In FY 2002, the carbon composite bipolar plate 

effort at Oak Ridge National Laboratory has 

achieved several programmatic goals in measuring 

plate properties and improving wetting. It is 

necessary to have accurate mechanical properties 

information for the bipolar plates to ensure they will 

survive handling, assembly, and service. These 

measurements need to go beyond simple tensile or 

flexure strength, since the relatively thin plates will 

be subjected to tension-torsion in assembly and 

potential high-rate stresses during handling and 

service. Thus, it is particularly important to 

understand torsion behavior and fracture toughness. 

Measurements of these properties, along with 

methodologies to demonstrate material uniformity 

through thermal imaging, have been developed. 

Approach

Fibrous component preforms for the bipolar 

plate are prepared by slurry molding using 100-μm 

carbon fibers (e.g., Fortafil) in water containing 

phenolic resin, followed by curing. Molds are used 

to impress channels and other features into the 

preform, and the surface of the preform is sealed 

using a chemical vapor infiltration (CVI) technique 

in which sufficient carbon is deposited on the nearsurface fibers to make the surface hermetic. In the 

current work, differing amounts of carbon flake 

filler were used and the effects on properties 

determined. Infrared imaging was performed to 

identify defects and inhomogeneities by heating one 

side of the samples and imaging the opposite side. 

Because shear stress is a good measure of torsion 

behavior, the Iosipescu method was used to measure 

shear properties. The efforts to improve wetting of 

the carbon surface consisted of a simple heat 

treatment of the components to 1000°C in air. 

Results

Slurry-molded preforms 2.5 mm in thickness 

were produced and cut into 10-cm squares. 

Illustrative results of the thermal imaging are seen in 

Figure 1. The relative uniformity indicates little 

density difference within the plates and between 

plates. There is some indication of delamination 

along the edges, although it is likely due to cutting 

of a larger plate into the 10-cm samples. 

The Iosipescu torsion measurements are given in 

Table 1, and a sample stress-displacement curve is 

shown in Figure 2. These values are indicative of a 

relatively torsion-resistant material, particularly 

given the low density of the carbon composite. The 

stress-displacement curves indicate little 

delamination or other failures until ultimate failure. 

Filler content appears not to affect shear stress. 

The dramatic improvement in wetting of the 

carbon composite surface is seen in Figure 3. 

Whereas prior to oxidative treatment, water 

appeared to have a small wetting angle on the 

surface of the carbon composite, after treatment, 

water readily spread on the surface with an apparent 

large wetting angle. 

Conclusions

During this period, the mechanical properties of 

the carbon composite bipolar plate material were 

assessed, including measurements of uniformity and 

defect distribution by infrared imaging. The results 

indicate good material uniformity and substantial 

resistance to torsional stresses. Significant 

improvement in the wetting of the material was 

demonstrated after a simple oxidation treatment. 

FY 2002 Publications/Presentations

T. M. Besmann, J. W. Klett, J. J. Henry, Jr., and 

T. D. Burchell, “Carbon Composite Bipolar Plates 

for PEMFC,” 26th Annual International Conference 

on Advanced Ceramics and Composites, January 

13–18, Cocoa Beach, Fla. 

T. M. Besmann, J. W. Klett, J. J. Henry, Jr., and 

E. Lara-Curzio, “Carbon/Carbon Composite Bipolar 

Plate for PEM Fuel Cells,” National Meeting of the 

American Institute of Chemical Engineers, 

March 10–14, New Orleans. 
Propulsion Materials FY 2002 Progress Report 

41 

 

Figure 1. Infrared images of carbon composite bipolar plate material samples. 

Table 1. Measurements of shear stress by the 

Iosipescu method for carbon 

composite samples with differing 

amounts of carbon flake filler 

Sample (% filler) Strength measure 

PMP10R (0%) 25.9 ± 9.9 MPa 

PMP10T (0%) 19.3 MPa (1 test) 

PMP09K (15%) 24.4 ± 11.8 MPa 

PMP11E (30%) 43.3 ± 2.7 MPa 

PMP11G (30%) 17.1 ± 1.1 MPa 

PMP11H (30%) 18.7 ± 4.7 MPa 

Figure 2. Typical stress-displacement curve for the 

Iosipescu torsion measurement of the carbon 

composite bipolar plate material. 

0

5

10

15

20

0 0.02 0.04 0.06 0.08 0.1

Shear Stress (MPa)

Displacement (mm)
FY 2002 Progress Report Propulsion Materials 

42 

Before oxidation

After oxidation

Figure 3. Water illustrates a much larger wetting 

angle on the carbon composite after 

oxidative treatment. 
Propulsion Materials FY 2002 Progress Report 

43 

B. Cost-Effective Surface Modification for Metallic Bipolar Plates 

M. P. Brady 

Oak Ridge National Laboratory 

P.O. Box 2008, MS 6115 

Oak Ridge, TN 37831-6115 

(865) 574-5153; fax: (865) 241-0215; e-mail: bradymp@ornl.gov 

DOE Technology Development Managers: Nancy Garland 

(202) 586-5673; fax: (202) 586-9811; e-mail: nancy.garland@ee.doe.gov 

JoAnn Milliken 

(202) 586-2480; fax (202) 586-9811; e-mail: joann.milliken@ee.doe.gov 

ORNL Technical Advisor: David Stinton 

(865) 574-4556; fax: (865) 241-0411; e-mail: stintondp@ornl.gov 

Contractor: Oak Ridge National Laboratory, Oak Ridge, Tennessee 

Prime Contract No.: DE-AC05-00OR22725 

Objective 

• Develop a low-cost metallic bipolar plate alloy that will form an electrically conductive and corrosion-resistant 

nitride surface layer during thermal nitriding to enable its use in a polymer electrolyte membrane (PEM) fuel 

cell environment. 

Approach 

• Conduct a study of the nitridation behavior of a series of model Ni-X and Fe-X base alloys (X = nitride-forming 

elements such as Cr, Nb, Ti, and V) that could meet DOE bipolar plate cost goals. 

• Identify the most promising combination of X additions, ternary and higher-order alloying addition(s), and 

nitridation reaction conditions that result in the formation of an adherent, dense nitride surface layer. 

• Evaluate corrosion behavior in 80EC sulfuric acid solutions to simulate PEM fuel cell environments (in 

collaboration with K. Weisbrod and C. Zawodzinski of Los Alamos National Laboratory and I. Paulauskas and 

R. A. Buchanan of the University of Tennessee). 

• Characterize nitride layer microstructure and composition by X-ray diffraction, electron probe microanalysis, 

scanning electron microscopy, and transmission electron microscopy. Use this information in a feedback loop 

to modify alloy chemistry and nitridation processing conditions to optimize the protectiveness of the nitride 

surface layer. 

• Measure electrical conductivity of select nitrided alloys by dc four-point probe. 

• Down-select a model Ni-Fe-X alloy for in-cell performance evaluation and begin modification and optimization 

of alloy composition/nitridation conditions for commercial scale up, and/or identify nitridation conditions 

suitable for commercially available alloys (if feasible). 

Accomplishments 

• Tested a model nitrided Ni-50Cr wt % alloy and found it exhibited no discernible degradation after 1 week of 

immersion in pH 2 sulfuric acid at 80°C, and a corrosion current density of less than 1 × 10–6 A/cm2

 up to 

~0.9 V vs standard hydrogen electrode (SHE) in pH 3 sulfuric acid at 80EC. This level of corrosion resistance 

is in the range of the goal for metal bipolar plates and warrants scale-up to in-cell testing and evaluation. 

Further, the Cr-nitride layers formed on the Ni-50Cr alloy grow in a very robust manner so that features such as 
FY 2002 Progress Report Propulsion Materials 

44 

stamped flow fields will always be completely covered. Preliminary measurement of electrical properties of a 

nitrided coupon indicated an electrical conductivity in the 104 Ω–1 cm–1 range, which is two orders of 

magnitude greater than the DOE target. 

• Delivered coupons of nitrided Ni-50Cr to Los Alamos National Laboratory for further corrosion testing and 

evaluation. Preliminary feedback from ongoing exposure in the corrosion test cell indicates stable electrical 

resistance (collaboration with K. Weisbrod). 

• Submitted a U.S. provisional patent disclosure in April 2002 for nitrided Ni-Cr and related base alloys. 

Future Direction 

• Pursue in-cell testing of nitrided Ni-50Cr to determine if the promising corrosion resistance translates to in-cell 

performance. 

• Optimize nitridation conditions and reduce the level of chromium to below 40–42 wt % in order to improve the 

cold formability of the alloy and reduce processing and raw material costs (based on input from commercial 

alloy producers). 

• Investigate the nitriding characteristics of existing commercial high-Cr, Ni- and Fe-based alloys to determine if 

a similar corrosion-resistant Cr-nitride layer can be formed in order to facilitate scale-up and transfer of this 

technology. 

• Establish partnerships with alloy producers and fuel cell manufacturers. 

Introduction

The bipolar plate is one of the most expensive 

components in PEM fuel cells. Thin metallic bipolar 

plates offer the potential for significantly lower cost 

than the machined graphite bipolar plates currently 

used, as well as reduced weight/volume and better 

performance than developmental carbon fiber and 

graphite bipolar plates currently under consideration. 

However, inadequate corrosion resistance can lead 

to high electrical resistance and/or contaminate the 

proton exchange membrane. Metal nitrides (e.g., 

TiN or Cr2N) offer electrical conductivities that are 

up to an order of magnitude greater than that of 

graphite and are highly corrosion-resistant. 

Unfortunately, most conventional coating methods 

(for metal nitrides) are too expensive for PEM fuel 

cell stack commercialization or tend to leave pinhole 

defects, which result in accelerated local corrosion 

and unacceptable performance. 

Approach

The goal of this effort is to develop a bipolar 

plate alloy that will form an electrically conductive 

and corrosion-resistant nitride surface layer during 

thermal (gas) nitriding. There are three advantages 

to this approach. First, with the nitriding performed 

at elevated temperatures, pinhole defects are not 

expected because thermodynamic and kinetic factors 

favor complete conversion of the metal surface to 

nitride. Rather, the key issues are nitride layer 

cracking, adherence, and morphology (discrete 

internal precipitates vs continuous external scales), 

which can potentially be controlled through proper 

selection of alloy composition and nitridation 

conditions. Second, thermal nitridation is an 

inexpensive, well-established industrial technique. 

Third, the alloy can be formed into final shape by 

inexpensive metal-forming techniques such as 

stamping prior to thermal nitridation. 

Results

A series of model Ni-base alloys with additions 

of (5–15)Ti, (5–10)Nb, (10–15)V, (5–10)Nb + 

(5–15)V and (35–50)Cr wt %, to form external Ti-, 

Nb-, V-, Nb+V-, or Cr-based nitride layers, were 

studied (Table 1). Ni was selected as the initial alloy 

base because it is relatively inexpensive ($2–4/lb) 

and ductile, does not form a stable nitride during 

thermal nitridation, and exhibits a relatively low 

permeability to nitrogen, which favors external 

nitride layer formation. 

Table 1. Summary of nitriding conditions 
Propulsion Materials FY 2002 Progress Report 

45 

Nitridation conditions 

(high-purity nitrogen) Alloy base 

(wt %) Temperature Time (h) 

Nitrogen uptake 

(mg/cm2

) 

Ni-(5–15)Ti 1000–1100EC 8–48 0.1–1 

Ni-(5–10)Nb 900–1100EC 1–48 0.1–2 

Ni-(10–15)V 1100EC 24–48 0.5–1 

Ni-(5–10)Nb-(5–15)V 1100EC 24–48 0.5–1 

Ni-(35–50)Cr 1100EC 1 1.5–2 

Corrosion behavior was screened by a 1-week 

immersion in pH 2 sulfuric acid at 80EC to optimize 

alloy composition and nitridation conditions. Anodic 

polarization testing was then conducted on the most 

promising nitrided alloys in aerated pH 3 sulfuric 

acid at 80EC to quantify corrosion resistance. A 

corrosion current density of less than 1 × 10–6 A/cm2

up to a range of approximately 0.9 V vs SHE was 

considered indicative of sufficiently promising 

behavior to warrant further development and future 

in-cell stack testing. 

Nitrided Ni-(5–10)Ti base alloys (to form an 

external TiN base layer) exhibited relatively low 

corrosion currents (Figure 1). However, regions of 

Figure 1. Anodic polarization data in aerated pH 3 

sulfuric acid at 80EC (scan rate of 0.1mV/s) vs 

standard hydrogen electrode. 

through-thickness local attack of the TiN surface 

layer were evident in most of the coupons. Nitrided 

Ni-(5–10)Nb + (5–15)V wt % base alloys formed 

external Ni-Nb-V-N and Nb-V-N scales, which 

resulted in good corrosion resistance in the 1-week 

immersion screening in pH 2 sulfuric acid at 80EC 

(weight loss < –0.05 mg/cm2

) but exhibited high 

corrosion currents in the anodic polarization testing 

(10–5 to 10–4 A/cm2

 range at 0.9V vs SHE). The Ni-

(10–15)V wt % alloys formed external V-N layers 

after the nitridation treatment, but they exhibited 

relatively high weight losses in the sulfuric acid 

immersion screenings (3–5 mg/cm2

 loss after 

1 week). External Nb-N layers could not be formed 

on Ni-(5–10)Nb wt % alloys under the nitridation 

conditions used in the present work (Table 1). 

Of the nitrided alloys examined, Ni-50Cr wt % 

exhibited the most corrosion resistance and met the 

target corrosion current of less than 1 × 10–6 A/cm2

up to ~0.9V vs SHE in pH 3 sulfuric acid at 80EC 

(Figure 2 and Table 1). The post-nitridation 

microstructure of all the Ni-Cr alloys examined 

(35Cr, 45Cr, 50Cr wt %), nitrided for 1–2 h at 

Figure 2. Scanning electron microscopy cross-section of 

Ni-50Cr wt % nitrided for 2 h at 1100EC in 

N2. Point 1: external Cr2N scale: 69Cr-30N1Ni atomic percent (at %). Point 2: Crdepleted Ni(Cr) metal (light): 68Ni-32Cr at % 

(71Ni-29Cr wt %). Point 3: subscale ternary 

Ni-Cr-N phase (dark): 52Cr-14N-34Ni at %. 

Compositions were determined by electron 

probe microanalysis using pure element 

standards for Ni-Cr, and a Cr2N standard for 

nitrogen. 

1100EC in nitrogen, consisted of external Cr2N 

overlying a mixed zone of Cr-depleted Ni(Cr) and a 

ternary Ni-Cr-N subscale nitride (Figure 2). 

Ti Metal

Ni-50Cr

Metal

Nitrided

Ni-50Cr

Nitrided

Ni-5Ti

Nitrided

Tribocor

Corrosion Current (A/cm2)

Potential (V vs SHE)

10-8 10-7 10-6 10-5

0

0.2

0.4

0.6

0.8

1.0

Goal Corrosion

Current Density

8 μm

Cr2N 1

2

3

8 μm

Cr2N 1

2

3
FY 2002 Progress Report Propulsion Materials 

46 

(Occasional examples of internal Cr2N were also 

observed in the lower Cr alloys). The degree of 

continuity, and hence protectiveness, of the external 

Cr2N improved with increasing alloy chromium 

content, with a dense, nearly continuous/continuous 

layer formed on Ni-50Cr. Optical analysis after 

testing revealed no evidence of significant corrosion 

or breaching of the nitride layer formed on the Ni50Cr. Uncoated Ni-50Cr metal also exhibited 

relatively low corrosion currents (Figure 1) but 

showed evidence of pitting after the test exposure. 

The nitridation of the Ni-50Cr alloys was very 

robust with no evidence of inadequate coverage at 

sharp corners or edges. Figure 3 shows a coupon of 

Ni-50Cr that was hand-stamped with the letters 

“ORNL,” nitrided, and then immersed in pH 2 

sulfuric acid at 80°C for 1 week; there was no attack 

evident in the stamped regions. These results suggest 

that the present approach is amenable to coverage 

and protection of stamped flow field features in a 

bipolar plate. Bulk electrical conductivities were in 

the range of 1–2 × 104 Ω–1 cm–1 after nitriding, 

which surpasses the DOE electrical conductivity 

target by two orders of magnitude. 

Figure 3. Macrograph of stamped and nitrided Ni-50Cr 

coupon after 1 week of exposure in pH 2 

sulfuric acid at 80EC (coupon dimensions 

1 × 1⁄2 in.). 

Conclusions/Future Work

These results indicate that nitrided Ni-Cr base 

alloys show potential for use as bipolar plates in 

PEM fuel cells. Future work will focus on in-cell 

testing of nitrided Ni-50Cr to determine if the 

promising corrosion resistance demonstrated in the 

anodic polarization testing translates to good in-cell 

performance. From a cost and alloy processing 

perspective, lower levels of chromium are needed, 

≤ ~40–42 wt % range (G. Smith and M. Harper, 

private communication with Special Metals Corp., 

2002), particularly in terms of the rate of work 

hardening during cold rolling to allow the 

economical production of alloy sheet. The critical 

level of chromium needed to form an external nitride 

layer on binary Ni-Cr alloys is in the range of 30–40 

wt % chromium,1

 so a reduction to less than 50 wt % 

chromium appears feasible with proper adjustment 

of nitridation conditions (e.g., temperature, N2 vs 

NH3 environments, initial surface condition) to form 

a sufficiently continuous and dense Cr2N (or 

possibly CrN) layer. Reduction in chromium level 

may also be achievable through ternary alloying 

additions that form nitrides of intermediate 

thermodynamic stability between those of chromium 

and nitrogen [i.e., secondary gettering (e.g., ref. 2)]. 

For example, the level of aluminum needed to form 

an external alumina layer on Cu-Al alloys can be 

significantly reduced by additions of zinc (e.g., ref. 

2). It may also be possible to form similar corrosionresistant nitride layers on Fe-Cr or Ni(Fe)-Cr base 

alloys, which would also further reduce alloy cost. 

The nitriding characteristics of existing commercial 

Ni-Fe-Cr alloys will also be investigated. Emphasis 

in the next year will also be placed on establishing 

collaborations with commercial alloy producers and 

fuel cell manufacturers to facilitate technological 

assessment (particularly in-cell testing) and scale-up 

of this approach. 

References

1. R. P. Rubly and D. L Douglass, Oxid. Met., 

35, p. 259 (1991). 

2. M. P. Brady, B. Gleeson, I. G. Wright, JOM, 

52(1), p. 16 (2000). 

Publications

“Assessment of Thermal Nitridation to Protect 

Metal Bipolar Plates in PEM Fuel Cells,” M. P. 

Brady, K. Weisbrod, C. Zawodzinski, I. Paulauskas, 

R. A. Buchanan, and L. R. Walker, submitted to 

Electrochemical and Solid State Letters. 

Stamped by hand
Propulsion Materials FY 2002 Progress Report 

47 

Patents

M. P. Brady, J. H. Schneibel, B. A. Pint, and 

P. J. Maziasz, “Metallic Bipolar Plate Alloys 

Amenable to Inexpensive Surface Modification for 

Corrosion Resistance and Electrical Conductivity,” 

U.S. Provisional Patent Disclosure, April 2002.

Propulsion Materials FY 2002 Progress Report 

49 

C. Low-Friction Coatings and Materials for Fuel Cell Air Compressors 

George R. Fenske, Oyelayo Ajayi, John Woodford, and Ali Erdemir 

Argonne National Laboratory 

ET-212, 9700 S. Cass Ave. 

Argonne, Illinois 60439 

(630) 252-5190; fax: 630-252-4798; e-mail: gfenske@anl.gov 

DOE Technology Development Manager: Nancy L. Garland 

(202) 586-5673; fax: (202) 586-9811; e-mail: nancy.garland@ee.doe.gov 

ORNL Technical Advisor: David Stinton 

(865) 574-4556; fax: (865) 241-0411; e-mail: stintondp@ornl.gov 

Contractor: Argonne National Laboratory, Argonne, Illinois 

Prime Contract No.: W-31-109-Eng-38 

Objectives 

• Develop and evaluate the friction and wear performance of low-friction coatings and materials for fuel cell air 

compressor/expander systems. Specific goals are 

― 50–75% reduction in friction coefficient 

― An order of magnitude reduction in wear 

• Transfer the developed technology to DOE’s industrial partners. 

Approach 

• Identify critical compressor components requiring low friction. 

• Apply and evaluate Argonne National Laboratory’s (ANL’s) near-frictionless carbon (NFC) coatings to the 

components when appropriate. 

• Develop and evaluate polymer composite materials containing boric acid solid lubricant. 

• Develop a tribological mechanism–based material selection methodology for various compressor/expander 

components. 

Accomplishments 

• Identified the radial air bearings and thrust bearings of Meruit’s turbocompressor as components that require 

both low friction and low wear rate for satisfactory performance. 

• Conducted thrust washer wear tests that showed that ANL’s NFC coating reduced friction by about four times 

and wear rate by two orders of magnitude. Both exceeded the project goals. 

• Increased the scuffing resistance of a steel surface about 10 times using NFC coatings. 

• Began durability testing of NFC-coated air bearing hardware components. 

• Completed initial friction and wear testing of nylon-12 polymer with B2O3 addition. Significant reduction in 

wear was observed with the addition of B2O3, especially under high relative humidity. 

• Achieved a 50% reduction in friction for application in a Vairex-variable displacement compressor/expander 

using Hitco C/C composite and anodized aluminum contact pairs. 
FY 2002 Progress Report Propulsion Materials 

50 

• Designed and constructed a new high-speed friction and wear test rig for evaluation of materials for 

Mechanology’s toroidial intersecting vane machine (TIVM). 

• Evaluated the high-speed frictional performance of several candidate materials and coatings for TIVM vanes. 

Future Direction 

• Evaluate the effect of humidity on the durability of NFC-coated air bearing components. 

• Conduct detailed tribological performance evaluation of TIVM select candidate materials based on high-speed 

frictional behavior. 

• Optimize an NFC coating for TIVM vane application. 

• Coat TIVM components with optimized NFC for rig testing at Mechanology. 

• Continue development of collaborative efforts with DOE fuel cell contractors addressing reliability, durability, 

and parasitic energy losses in air management systems. 

Introduction

A critical need in fuel cell systems for vehicles 

is an efficient, compact, and cost-effective air 

management system to pressurize the fuel cell 

systems to about 3 atmospheres. Pressurization of 

fuel cells will result in higher power density and 

lower cost. Several compressor/expander systems 

are currently being developed for DOE. The 

efficiency, reliability, and durability of compressors 

depend on effective lubrication or friction and wear 

reduction in critical components such as bearings 

and seals. Conventional oil or grease lubrication of 

compressor components is not desirable because 

such lubricants can contaminate and poison the fuel 

cell stack. The objective of this project is to develop 

and evaluate low-friction coatings and/or materials 

for critical components of air compressor/expanders 

being developed by various contractors for DOE 

vehicle fuel cell systems. The work this year focused 

on Meruit’s turbocompressor air bearings and 

Mechanology’s TIVM. 

Approach

For various air compressor/expanders being 

developed, we will identify the key critical 

components that require a low friction coefficient 

and wear resistance. Over the years, the tribology 

group at ANL has developed low-friction and lowwear coatings and materials. Most notable is the 

discovery of an amorphous carbon coating with 

extremely low friction coefficients (<0.001 in dry 

nitrogen) and very low wear. Where appropriate, the 

NFC coating will be applied to the critical 

component(s). In other cases, alternative lowfriction polymeric materials and other low-friction 

coatings will be evaluated. 

Results

Meruit Air Bearing 

As reported in 2001, we started durability 

testing of NFC-coated, air-bearing hardware 

components (Figure 1). The durability test consists 

of start-and-stop cycling of the air bearing. Under 

full-speed operation, there is no contact in either the 

journal or the thrust bearings. Contact and sliding 

between surfaces occur only during start-and-stop 

periods when damage can occur; hence, they 

determine the durability of the bearing. Dimples of 

known dimensions were inserted into contact areas 

of the coated bearing shaft (Figure 1). A wear 

measurement is taken after some predetermined 

number of start/stop cycles by measuring changes in 

the dimple dimension. In the first test, wear 

measurements were taken after 250, 1000, 2000, and 

4000 cycles. Initial results from this test were 

presented in the 2001 progress report. Unfortunately, 

the bearing in this test failed shortly after 4000 

cycles because of debris contamination. 

After a slight design modification to the airbearing shaft, a second durability test of an NFCcoated bearing was conducted. Plots of linear wear 

on both side 1 and side 2 of the air-bearing shaft are 
Propulsion Materials FY 2002 Progress Report 

51 

Figure 1. Schematic diagram of dimples on NFC-coated air-bearing shaft for wear 

measurement after testing. 

shown in Figures 2a and 2b. The original coating 

thickness was about 2.5 μm. There was considerably 

more wear on side 2 than on side 1, especially after 

8000 start/stop cycles. This difference is due to an 

apparent imbalance in the air bearing. The bearing 

finally failed after about 11,000 start/stop cycles, 

again because of debris contamination. However, at 

the point of failure, the coating was not worn 

through in any of the dimples. The coating wear 

mechanism consists of abrasive polishing, as shown 

in Figure 3. 

Mechanology TIVM 

The primary sources of friction in the TIVM are 

the vane sliding interface, the housing compressor 

seal, and expander bearings. Design analysis shows 

that an overall system friction coefficient of <0.3 is 

required to meet the DOE program target for 

efficiency. The most critical of these three sources is 

the vane sliding interface because of its high sliding 

speed of 60–75 m/s. The selection of an appropriate 

vane material is critical for successful operation of 

the TIVM compressor/expander. Frictional behavior 

as a function of sliding speed was evaluated for 

several material and coating combinations 

(including NFC). Some material combinations with 

adequate friction behavior at high sliding speeds 

were identified. 

When a 440EC stainless steel ball slid against an 

NFC-coated steel disc, the friction coefficient was 

about 0.2 at the start of the test, but it increased 

slightly as the test progressed (Figure 4). There was 

a frictional spike at the end of the test as a result of 

trapping of iron oxide debris generated on the 

uncoated steel ball surface. When both the steel ball 

and the disc surfaces were coated with NFC, the 

friction coefficient was low (0.23) and symmetrical 

with the sliding speed profile (Figure 5). The friction 

coefficient showed a very small increase with 

increasing sliding speed. Furthermore, compared 

with many other material combinations evaluated, 

the frictional signal from tests with both surfaces 

coated was relatively smooth. This result may have 

an implication for quiet running of the TIVM 

machine. 

Other promising combinations include 440EC 

steel sliding against PEEK polymeric material 

(Figure 6). For this combination, the friction 

coefficient appears to be independent of sliding 

speed, as the friction coefficient remained nearly 

constant at about 0.25 for the entire speed range 

tested. In another combination of 440EC stainless 

steel and Armoloy- (thin, dense chrome-) coated 

bronze, the friction coefficient in the high speed 

range (> 60m/s) was about 0.3. However, for this 

contact pair, the friction at lower speeds was higher. 

The frictional behavior is also symmetrical with the 

speed profile (Figure 7). 

Publications

O. O. Ajayi, J. Woodford, A. Erdemir, and G. R. 

Fenske, “Performance of Amorphous Carbon 

Coating in Turbocompressor Air Bearing,” Society 

of Automotive Engineers (SAE) Paper 2002-01-

1922, SAE Future Car Congress, Arlington, Va., 

June 3–5, 2002.
FY 2002 Progress Report Propulsion Materials 

52 

Figure 2. Linear wear (micron) at various dimples on (a) side 1 and (b) side 2 of air-bearing shaft. 

(a) (b) 

Figure 3. Optical micrograph of dimple 9 on side 1 after (a) 250 cycles and (b) 4000 cycles. 

Figure 4. Variation of friction with sliding speed for 

uncoated steel ball sliding on NFC-coated 

disc. 

Figure 5. Variation of friction coefficient with sliding 

velocity for NFC-coated ball sliding on NFCcoated disc. 
Propulsion Materials FY 2002 Progress Report 

53 

Figure 6. Variation of friction coefficient with sliding 

velocity for steel-on-PEEK contact pair. 

Figure 7. Variation of friction coefficient with sliding 

speed for steel ball sliding on Armoloy 

(TDC) coated bronze disc. 

Propulsion Materials FY 2002 Progress Report 

55 

D. Microstructural Characterization of PEM Fuel Cells 

D. A. Blom and L. F. Allard 

Microscopy, Microanalysis, and Microstructures Group 

Oak Ridge National Laboratory 

P.O. Box 2008, MS 6064, Bldg. 4515 

Oak Ridge, TN 37831-6064 

(865) 241-3898; fax: (865) 576-5413; e-mail: blomda@ornl.gov 

DOE Technology Development Manager: Nancy Garland 

(202) 586-5673; fax: (202) 586-9811; e-mail: nancy.garland@ee.doe.gov

ORNL Technical Advisor: David Stinton 

(865) 574-4556; fax: (865) 241-0411; e-mail: stintondp@ornl.gov 

Contractor: Oak Ridge National Laboratory, Oak Ridge, Tennessee 

Prime Contract No.: DE-AC05-00OR22725 

Objectives 

• Use transmission electron microscopy (TEM) characterization techniques to optimize the distribution of 

precious metal catalyst for increased efficiency and reduced catalyst loading. 

• Characterize/quantify microstructural changes and their relation to performance loss in polymer electrolyte 

membrane (PEM) membrane electrode assemblies (MEAs) upon use in a fuel cell system to understand issues 

relating to durability and lifetime

Approach 

• Characterize the microstructure and chemical composition of PEM MEAs before and after use to correlate 

performance to the microstructure at nanometer and greater levels. 

• Prepare samples that are thin over large areas for TEM observation to facilitate the ability to understand the 

entire MEA as a unit. 

• Maintain the relationships among the constituents of the MEA in TEM samples in order to achieve insight into 

the operation of the real system. 

Accomplishments 

• Established a new state-of-the-art cryo-ultramicrotomy facility at Oak Ridge National Laboratory (ORNL). 

• Prepared successful sections of MEA tested to failure. 

• Characterized microstructure of failed MEA (aged 1200 h). 

• Quantified change in platinum catalyst size distribution upon aging (fresh vs short time vs failed). 

Future Direction 

• Improve room-temperature sectioning technique to allow for the routine preparation of thin MEA crosssections. 

• Develop cryo-ultramicrotomy technique for preparation of ultrathin (<100-nm) samples to achieve improved 

analytical results. 
FY 2002 Progress Report Propulsion Materials 

56 

• Continue collaborative research with Los Alamos National Laboratory on the microstructural changes that occur 

during the MEA preparation process. 

Introduction

Polymer electrolyte membrane fuel cells hold 

great promise for use as an environmentally friendly 

power source for automobiles. One of the key 

challenges in making PEMs commercially viable is 

to reduce the cost by reducing the amount of 

precious metal catalyst necessary to provide highpower-density operation at low temperatures. 

For efficient catalysis to occur, gas molecules 

must be able to easily interact with the surface of the 

catalyst particles. A pathway for diffusion of protons 

must exist in close proximity to the active sites on 

the catalyst, and an electrically conductive pathway 

from the catalyst to the electrodes is required for 

electron transport. Finally, water (the by-product of 

the fuel cell reaction) has to be transported away 

from the catalyst for continuing reaction to occur. 

These requirements show the complexity of building 

an efficient PEM fuel cell and clearly indicate the 

opportunity for atomic-scale microstructural and 

chemical characterization to provide feedback on the 

geometry and distribution of the various components 

for optimum performance. 

Approach

Cross-sections of PEM MEAs were prepared for 

TEM using an ultramicrotome. Small sections from 

the MEAs, approximately 3 × 8 mm, were selected 

for sample preparation. The samples were placed 

into silicone embedding molds, and an Araldite 

epoxy resin was added to the molds to embed the 

sample. The resin was polymerized at least 16 h at 

60°C to produce a solid epoxy piece with the MEA 

sample embedded. Initial trimming of the epoxyembedded sample was performed with a Leica EM 

Trim tungsten carbide trimming tool. A tungsten 

carbide tip was used to rapidly remove excess epoxy 

from around the MEA sample and produce a small 

flat area suitable for ultramicrotomy. The nature of 

the MEAs dictated a narrow (0.25–0.5 mm), long 

(1–2 mm) area for ultramicrotomy. The epoxyembedded MEA was then secured into the cutting 

arm of a Leica Ultracut UCT Ultramicrotome. The 

ultramicrotome is designed to allow for the slicing 

of thin sections of epoxy-embedded samples for 

TEM characterization. A 45° diamond knife was 

used to slice several sections of various thicknesses 

from each sample. The goal is always to produce the 

thinnest possible slice for TEM examination. Slice 

thicknesses were typically 300 nm or less. The thin 

slices were floated off the diamond knife edge onto 

distilled water and then collected onto copper mesh 

grids. 

Results

During FY 2002, a new ultramicrotomy facility 

for room-temperature sectioning of materials was 

established at ORNL. Figure 1 shows the Leica 

Figure 1. Leica UCT ultramicrotome and controller. 

ultramicrotome and its control interface. The 

ultramicrotome is a computer-controlled, motorized 

device for reproducibly moving the sample past a 

fixed knife and advancing the sample in a controlled 

manner to produce thin sections of material. The 

cutting arm moves up and down to produce the thin 

sections. The stereomicroscope is used to position 

the knife appropriately relative to the sample and 

observe the sectioning action at moderate 

magnification. Figure 2 is a close-up of a diamond 
Propulsion Materials FY 2002 Progress Report 

57 

Figure 2. Close-up of cutting arm, sample, and 

diamond knife. 

knife with water trough and the epoxy-embedded 

sample in the cutting arm. 

MEA cross-sections have been successfully 

prepared for TEM examination using this 

equipment. The sections are typically 200–300 nm 

in thickness, which is thicker than desired for best 

resolution and analytical characterization. 

Additional work is needed to improve our ability to 

routinely produce sections that are less than 200 nm 

thick. 

W. L. Gore and Associates aged a third-party 

MEA for 1200 h at an accelerated rate in order to 

cause failure of the MEA. Samples from this MEA 

were prepared for TEM characterization via roomtemperature ultramicrotomy. Figure 3 shows the 

interface between the membrane and the anode for 

this aged MEA. The image was collected on a 

Hitachi HF-2000 cold field emission gun 200-kV 

transmission electron microscope. The small, dark 

features are the platinum catalyst particles or 

agglomerates of the catalyst, while the featureless 

area at the bottom of the figure is the PEM. A highangle annular dark field, or Z-contrast, image of the 

same sample is seen in Figure 4. In this case, the 

platinum particles appear as bright features against 

the background of the anode. 

At least ten images were taken from both the 

anode and cathode and analyzed to determine the 

size distribution of the platinum catalysts. Figure 5 

is the histogram of platinum catalyst size for an 

unaged MEA that had previously been analyzed. 

The most common particle size was less than 1 nm, 

with a median size of 1.78 nm. There was no 

difference in 

Figure 3. Bright field TEM image of membrane/anode 

interface in MEA subjected to accelerated 

aging for 1200 h. Platinum catalyst particles 

are the small, dark features. 

Figure 4. Z-contrast scanning TEM image of aged MEA. 

The platinum catalyst is bright relative to the 

electrode. 

the distributions between the anode and cathode of 

the fresh MEA. Figure 6 shows the catalyst size 

distribution for the anode of the MEA aged for 

1200 h (shown in Figures 3 and 4). The most 

common size was between 2 and 3 nm, and the 

median size was 4.49 nm. Figure 7 is the size 

distribution of the catalyst particles in the cathode of 
FY 2002 Progress Report Propulsion Materials 

58 

the same MEA. The most common size was between 

1 and 2 nm, and the median size was 3.66 nm. 

Figure 5. Platinum catalyst size histogram for the fresh 

MEA. Median particle size is 1.8 nm, and most 

common size is 0-1 nm. 

Figure 6. Platinum catalyst size histogram for the anode 

of the aged MEA. Median particle size is 

4.49 nm, and most common size is 2-3 nm 

Table 1 summarizes the particle sizing data, 

including some data from another MEA that was 

aged for a shorter period of time and showed no 

discernible loss of performance. 

Conclusions

New ultramicrotomy equipment was established at 

ORNL. Room-temperature ultrathin sectioning of 

PEM MEAs was successfully demonstrated. A PEM 

MEA that had been subjected to an accelerated 

aging schedule was successfully prepared for TEM 

characterization. After the accelerated aging, 

significant changes in the size distribution of 

Figure 7. Platinum catalyst size histogram for the 

cathode of the aged MEA. Median particle size 

is 3.66 nm, and most common size is 

1–2 nm 

Table 1. Summary of platinum particle size 

distributions for fresh, 325-h-aged MEA and 

1200-h-aged MEA 

Mean 

(nm) 

Median 

(nm) 

No. of 

particles (N) 

Fresh MEA 2.93 1.78 675 

After 325 h 4.32 3.16 994 

1200 h cathode 4.99 3.66 2547 

1200 h anode 6.11 4.49 2151 

platinum catalyst particles were observed. Even the 

moderate temperatures of PEM operation (80°C), 

when coupled with electrochemical driving forces, 

were sufficient to produce coarsening of the 

platinum catalyst. The anode catalyst coarsened 

more than the cathode catalyst. The changes 

observed are not sufficient to explain the complete 

failure of the MEA. Degradation of the PEM itself 

and the development of pinholes across the PEM 

may account for the complete failure of the MEA. In 

previous PEM MEAs, a chemically distinct layer 

was found to form at the interface between the 

electrodes and the membrane. No such layer was 

observed in the MEA subjected to an accelerated 

aging process. Review of the accelerated aging 

protocol may be warranted to ensure that the 

degradation processes remain the same in both the 

accelerated test and typical usage conditions. 
Propulsion Materials FY 2002 Progress Report 

59 

Publications

D. A. Blom and L. F. Allard, “Microstructural 

Characterization of Proton Exchange Membrane 

Fuel Cells,” DOE 2002 Review, OTT Fuel Cells 

Program, National Renewal Energy Laboratory, 

May 9–10, 2002. 

Propulsion Materials FY 2002 Progress Report 

61 

E. Nano-Particulate Porous Oxide Electrolyte Membranes as Proton 

Exchange Membranes 

M. Isabel Tejedor, Marc A. Anderson, and Walt Zeltner 

Environmental Chemistry and Technology Program 

University of Wisconsin 

Room 109, 660 North Park Street 

Madison, WI 53706 

(608) 262-2674; fax: (608) 262-0454; e-mail: nanopor@facstaff.wisc.edu 

Mark A. Janney and James O. Kiggans 

Metals and Ceramics Division 

Oak Ridge National Laboratory 

P.O. Box 2008, MS 6087 

Oak Ridge, TN 37831-6087 

(865) 574-8863; fax: (865) 574-8271; e-mail: kiggansjo@ornl.gov 

DOE Technology Development Managers: Nancy Garland 

(202) 586-5673; fax: (202) 586-9811; e-mail: nancy.garland@ee.doe.gov

JoAnn Milliken

(202) 586-2480; fax: (202) 586-9811; e-mail: joann.milliken@ee.doe.gov 

Contractor: University of Wisconsin—Madison 

Prime Contract No.: DE-FC02-99EE50583 

Objectives 

• Develop microporous inorganic oxide-based membranes of TiO2 with high proton conductivity that can operate 

at above 100EC with minimal water management problems. 

• Develop processes to fabricate porous nickel or graphite paper electrodes that support the membrane. 

• Demonstrate fuel cell behavior in porous oxide electrolyte membrane- (POEM-) based membrane electrode 

assemblies (MEAs). 

Approach 

• Phase 1: (a) Determine conditions under which nano-particle sols of candidate oxides yield microporous gels; 

(b) measure proton conductivities of these gels as a function of temperature and relative humidity; 

(c) chemically adsorb anionic or cationic functional groups onto oxide particles contained in xerogels or 

membranes in order to enhance proton conductivity. 

• Phase 2: (a) Develop methods for depositing platinum on asymmetric mesoporous electrodes; (b) deposit crackfree films of POEMs on mesoporous electrodes; (c) characterize permeabilities of H2 and O2 through the 

resulting supported membranes under desired conditions of relative humidity and temperature; (d) fabricate and 

test an entire inorganic MEA containing a POEM deposited on mesoporous electrodes. 

Accomplishments 

• Demonstrated proton conductivity in POEMs at temperatures of up to 130EC at a relative humidity of 81%. 

• Better defined the effects of pore size and pH on proton conductivity in POEMs. 
FY 2002 Progress Report Propulsion Materials 

62 

• Fabricated a first-generation test apparatus to measure the performance of our POEMS and MEAs containing 

POEMs in a functional fuel cell configuration. 

• Collected initial data concerning open circuit potential and current-voltage relationships for an oxide-based 

anode/POEM configuration (i.e., 2/3 of an MEA) (platinum loading in anode = 0.003 mg/cm2

). 

Future Direction 

• Develop a better understanding of the relationships and interactions among the various layers in the MEA 

(particularly the cathode layer) and how they control the performance of the overall fuel cell system. 

• Characterize and subsequently optimize the performance of fuel cells that contain POEMs.

• Develop testing techniques for measuring proton conductivity at temperatures approaching 150EC at ≥40% 

relative humidity. 

• Investigate the nickel substrate as the support for the cathode instead of the anode in an inorganic MEA. 

• Further develop graphite fiber paper supports as a potential substitute for nickel substrates. 

Introduction

Nano-particulate POEMs are being developed as 

a radical alternative to polymeric proton exchange 

membranes for fuel cells. These new membranes can 

operate at temperatures over 100EC, retain water at 

these elevated temperatures, and provide proton 

conductivities of the same order of magnitude as the 

Nafion membranes presently employed. In addition, 

inorganic MEAs that incorporate POEMs should 

reduce the cost of fuel cells because they 

substantially reduce the amount of platinum catalyst 

required to operate the fuel cell and they minimize 

CO poisoning of the platinum by operating at 

elevated temperatures. 

One constraint in using POEMs is that they must 

be supported on a structural substrate because the 

membranes are thin (≤500 nm), porous (~40 vol % 

void space), and brittle (an inherent property of 

ceramic membranes). The porous substrate provides 

both electrical conductivity and gas distribution. 

Because the POEM itself is composed of 5–10 nm 

particles, an intermediary sandwich layer (particle 

diameter 50–500 nm) is required to provide 

geometric compatibility. 

Approach

The objective of this effort is to develop MEAs 

for H2 fuel cells based on POEMs. These 

membranes are made of nano-particle oxides such as 

TiO2, SiO2, ZrO2, or Al2O3 that are hydrophilic and 

offer higher-temperature stability and operation than 

polymeric proton exchange membranes. These 

membranes are supported on tape-cast porous nickel. 

The POEM MEA is a complex materials system, 

not just a collection of individual components. This 

oxide-based MEA [anode/membrane electrolyte 

(separator)/cathode] is a composite material that 

simultaneously performs a variety of operations. 

One cannot consider any particular aspect of this 

materials system in isolation; all functions must 

operate in concert with one another. The anode must 

conduct electrons and at the same time convert 

hydrogen gas to protons at one interface with the 

POEM. The POEM itself must conduct protons—

but not electrons, which would cause a short—while 

also preventing crossover of hydrogen and oxygen 

across the POEM. Finally, the cathode must convert 

gaseous oxygen to O−2

 ions that then combine, at the 

other interface with the POEM, with protons that 

have migrated through the POEM. This cathode 

reaction is a four-electron-transfer reaction that is 

quite difficult to perform efficiently. More will be 

said about the cathode layer and about reasons for 

improving its performance later in this report. 

Results and Discussion

Membrane Development—pH Effects 

Proton conductivity in fluid-filled, hydrophilic, 

mesoporous, inorganic membranes such as these 

POEMs derives from the movement of H+

 ions 

(1) by hopping along surface sites from particle to 

particle, (2) by migrating through the electrical 

double layer in the pores near the surface of the 
Propulsion Materials FY 2002 Progress Report 

63 

particles, or (3) by migrating through the bulk pore 

fluid. As shown in Figure 1, proton transport and the 

Figure 1. Dependence of proton conductivity on pH at 

40EC. 

resulting conductivity drastically change with the pH 

at which the membrane is equilibrated. Note that 

Nafion-type membranes are often soaked in strong 

acids to protonate their acid groups. In this regard, 

our membranes are similar, although full protonation 

of the surfaces of these inorganic membranes may 

be reached at higher pH values than are required for 

Nafion. 

Proton transport behavior also greatly depends 

upon the nature of the oxide, as shown in Figure 2. 

Note that at lower relative humidities, TiO2/ZrO2

and Al2O3 membranes have conductivities that are 

Figure 2. Proton conductivity for various oxides as a 

function of relative humidity at 80EC. 

two to three orders of magnitude higher than those 

of SiO2, even though the silica membranes are more 

acidic. The reason for this behavior is that these 

membranes were pre-equilibrated at pH 1.5. This pH 

is very close to the isoelectric pH (i.e., the pH at 

which the surface of the oxide is electrically neutral) 

of SiO2, which is ≈ 2–3, but 4 to 7 pH units more 

acidic than the isoelectric pH values of TiO2/ZrO2

and Al2O3, respectively. As a result, the SiO2

membranes are not highly protonated at pH 1.5, 

whereas the other two membranes have almost 

achieved maximum charging and therefore 

maximum proton conductivity. 

Membrane Development—Pore Size 

Dependence 

The conductivity of a particular membrane 

depends on the conditioning of the surfaces within 

the pores, as well as the relative humidity. These two 

factors interact to determine how much water resides 

inside the pores. In the as-fired condition, the pore 

surfaces are poorly protonated. Conditioning the 

membrane material by exposing the membrane to an 

aqueous solution tends to increase the degree of 

protonation, depending on the pH of the solution, as 

noted earlier. However, as can be seen in Figure 3, 

proton conductivity for TiO2 at 40EC also depends 

upon pore size, increasing one order of magnitude at 

low relative humidity values as pore diameter 

decreases from 35 to 25 Å. We can reduce the pore 

size in this membrane even further to about 15 Å, 

which may further enhance its proton conductivity. 

Figure 3. Dependence of proton conductivity on relative 

humidity for TiO2 membranes of various pore 

sizes. 

Initial Evaluation of an Inorganic MEA 

Because these POEMs are not self-standing 

materials like organic polymer membranes such as 

Nafion, we cannot fabricate an MEA unless we cast 
FY 2002 Progress Report Propulsion Materials 

64 

our membranes on a rigid but porous support. 

Furthermore, the support must be electrically 

conducting and must already be coated with a 

porous catalyst layer before we cast the membrane. 

The resulting composite MEA will be activated by 

imbibing an acid solution into the MEA before it is 

used. 

Enable Fuel Cell Corp. (Middleton, Wis.) 

fabricated a passive test chamber to evaluate the 

performance of our materials. For these initial roomtemperature tests, we fabricated 2/3 of an inorganic 

MEA (i.e., porous nickel support/nano-particle TiO2

membrane loaded with platinum catalyst to serve as 

one electrode/TiO2 POEM). We used a carbon fabric 

loaded with platinum as the second electrode. We 

ran the inorganic MEA as either an anode or a 

cathode depending on the polarity of the test circuit. 

When hydrogen contacted the inorganic MEA (i.e., 

our MEA was operated as a working anode), we 

achieved open-circuit voltages between 0.74 and 

1.02 V. When our inorganic MEA was operated as a 

cathode, we obtained slightly lower voltages 

(0.76–0.88 V). More will be said about this later. 

Unfortunately, it was difficult to seal the cell to 

prevent hydrogen leaks. In addition, it was difficult 

to test individual layers of our MEA system because 

the carbon fabric glued itself to the inorganic MEA 

and could not be detached without delaminating the 

MEA. To resolve these issues, we built a new test 

cell, as shown in Figure 4. As shown, our MEA was 

now sealed in a metal O ring using ceramic cement. 

This cell proved to be easily sealed without 

hydrogen leaks; furthermore, it could be readily 

disassembled. However, we still need to improve the 

ohmic contacts to the anode and cathode layers. We 

used copper wool to provide contacts in this 

apparatus. However, copper wool easily oxidizes in 

contact with acids and does not provide a uniform 

contact with the electrodes. 

Test Performance 

Shown in Figure 5 are initial current-voltage 

curves for the 2/3 of an inorganic MEA system 

described versus a similar Nafion-based system in 

tests at room temperature. As can be seen, the 

Figure 4. Teflon test cell and our membrane electrode 

assembly system. 

Figure 5. Current-voltage curves for our membrane 

electrode assembly versus a Nafion system. 

Nafion system performs somewhat better than our 

initial prototype when the inorganic MEA operates 

as an anode. When we invert the contacts so that the 

inorganic MEA operates as a cathode, the inorganic 

MEA system performs much worse. A positive 

aspect of this performance is that the platinum 

content of the inorganic MEA is 0.003 mg/cm2

. 

Cathodes and the Total MEA 

Shown in Figure 6 is a diagram of a nickel 

support and a platinum-loaded nano-particulate 

oxide acting as a porous cathode. Organic-based fuel 

cell cathodes often add some Nafion to this layer to 

improve its proton conductivity, but at the cost of 

decreasing its electrical conductivity. However, we 

have the reverse problem—we have excellent proton 

conductivity in our inorganic cathode, but our 

oxides are electrical insulators. We need to boost the 

electrical conductivity of our 
Propulsion Materials FY 2002 Progress Report 

65 

Figure 6. Diagram of an inorganic fuel cell cathode. 

cathode in order to fabricate a total inorganic MEA. 

This is a major objective of our future work. 

Conclusions

We have successfully fabricated and tested 2/3 

of an inorganic MEA consisting of a porous nickel 

support, a nano-particle TiO2 membrane containing 

platinum catalyst that served as an effective anode, 

and a nano-porous TiO2 POEM. A novel test cell 

was built to facilitate testing, but additional 

modifications are needed. Although the performance 

of this prototype inorganic MEA was not as good as 

that of a corresponding Nafion-based system at room 

temperature, the inorganic MEA required only a 

small amount of platinum to function. In order to 

prepare this inorganic MEA, a novel method had to 

be developed for applying a ceramic sandwich layer 

to the porous, electrically conducting nickel 

substrate. This method should be useful in other 

membrane applications. 

Efforts will continue to fabricate a full inorganic 

MEA and to test these systems at high temperatures. 

It appears that a functional inorganic MEA will 

require a cathode with higher electrical conductivity 

than was available in our initial tests. In addition, we 

are attempting to develop a graphite fiber-based 

substrate having the requisite chemical compatibility 

with the proton exchange membrane environment. 

As part of this development, POEM fuel cell 

assembly using standard, multilayer manufacturing 

technologies will be investigated. 

Publications/Presentations

Results were presented at the national meeting 

of the American Institute of Chemical Engineers in 

New Orleans in March 2002. 

Propulsion Materials FY 2002 Progress Report 

67 

F. Bacterial Cellulose Membranes 

Hugh O’Neill, Barbara R. Evans, and Jonathan Woodward 

Chemical Sciences Division 

Oak Ridge National Laboratory 

P.O. Box 2008 

Oak Ridge, TN 37831-6194 

(865) 574 5004; fax: (865) 574 1275; e-mail: oneillhm@ornl.gov 

DOE Technology Development Manager: JoAnn Milliken 

(202) 586-2480; fax: (202) 566-9811; e-mail: joann.milliken@ee.doe.gov 

ORNL Technical Advisor: David Stinton 

(865) 574-4556; fax: (865) 241-0411; e-mail: stintondp@ornl.gov 

Contractor: Oak Ridge National Laboratory, Oak Ridge, Tennessee 

Prime Contract No.: DE-AC05-00OR22725 

Objectives 

• Synthesize a proton-conductive membrane for a polymer electrolyte membrane (PEM) fuel cell. 

• Synthesize a membrane that is stable at temperatures >120EC. 

• Synthesize a membrane that maintains the conditions conducive to proton conductance from the anode to the 

cathode through the polymeric medium while operating at high temperatures. 

Approach 

• Modify bacterial cellulose so as to preserve its properties that have been identified as useful for PEM fuel cell 

development, including thermal stability and low hydrogen crossover. 

• Modify bacterial cellulose membranes with acid groups to produce a proton-conductive membrane without 

compromising the structure of the cellulose membrane. 

Accomplishments 

• Investigated different strategies to confer ion-exchange properties on bacterial cellulose. 

• Synthesized a cellulose membrane activated with phosphate groups. 

• Evaluated the properties of the cellulose phosphate membrane. 

Future Direction 

• Complete the characterization of phosphate membranes. 

• Revisit and evaluate other strategies for chemical modification of cellulose. 

• Test performance of ion-exchange membranes in a membrane electrode assembly. 

• Modify cellulose in vivo by using activated glucose monomers. 
FY 2002 Progress Report Propulsion Materials 

68 

Introduction

Bacterial cellulose is produced by 

Gluconoacetobacter sp. bacteria during growth on 

carbohydrate sources. Nascent cellulose strands, 

synthesized by the bacteria, are secreted and form 

layers at the air-liquid interface (Figure 1A, 1B). 

This network of cellulose fibrils resembles a sponge 

and is called a “pellicule.” After cleaning to remove 

cellular debris, the pellicule typically contains more 

than 99% H2O; the remainder is cellulose. When the 

pellicules are dried to remove water, the layers of 

cellulose collapse on top of each other to produce a 

very thin membrane (<50 μm thick). 

Of particular interest to the DOE fuel cell 

program is the development of thermostable 

membranes that will facilitate the transfer of protons 

from the anode to the cathode during operation of a 

PEM fuel cell at high temperatures (>120EC). At 

higher operating temperatures, the electrode kinetics 

are improved, resistance to poisoning by carbon 

monoxide is increased, and the catalyst cost is 

minimized. Bacterial cellulose has several unique 

properties that potentially make it a valuable 

material for the development of PEM fuel cells: 

(1) it is a cheap and nontoxic natural resource, (2) it 

has good chemical and mechanical stability, (3) it is 

very hydrophilic, and (4) it does not re-swell after 

drying.1

 Additionally, its thermal stability and gas 

crossover characteristics are superior to those of 

Nafion 117, a material widely used as a protonconductive membrane in PEM fuel cells. 

Approach

There is a wealth of data, in both the scientific 

and patent literature, on the chemical modification 

of plant cellulose. All of these methods are equally 

applicable to bacterial cellulose, given that the two 

types of cellulose are chemically identical. However, 

it is the physical structure of bacterial cellulose 

membranes that makes it a potential material for 

PEM fuel cells. Therefore, the aim is to modify 

bacterial cellulose pellicules in such a manner that 

the structure of the cellulose is retained and the 

physical properties, such as thermal stability, gas 

crossover characteristics, and resistance to reswelling after drying, are not compromised. 

Results

Several strategies were employed to modify 

bacterial cellulose with ion-exchange groups. Of the 

methods attempted, modification of native bacterial 

cellulose with phosphate groups was most successful 

(Figure 2). The properties of the native and modified 

membrane compared with those of Nafion 117 are 

presented in Table 1. 

Cellulose phosphate had 2.7-fold greater thermal 

stability and 7.6-fold lower H2 permeability than 

Nafion 117. This marked increase in the thermal 

stability of cellulose phosphate was not unexpected, 

given that this material was first developed as a 

flame-retardant material. Unlike Nafion, cellulose 

phosphate is prone to swelling in H2O. However, at 

temperatures of more than 120EC, this characteristic 

may not pose a problem during operation of the fuel 

cell. The density of ion-exchange groups available 

(a) (b) 

Figure 1. Scanning electron microscope micrographs of freeze-dried bacterial cellulose: (a) transverse section and 

(b) top view. 
Propulsion Materials FY 2002 Progress Report 

69 

Figure 2. Synthesis of cellulose phosphate. 

Table 1. Comparison of the properties of cellulose phosphate with native bacterial 

cellulose and Nafion 117 

Membrane characteristics Native 

cellulose 

Cellulose 

phosphate Nafion 117 

Physical properties 

 Dry membrane thickness (mm) 0.010 0.023 0.199 

 Wet membrane thickness (mm)a

 0.032 0.081 0.225 

 H2O content / g dry membrane (g/g)a

 3.47 3.16 0.31 

 Thermal stability (o

C) 130 245 <90 

 Ion exchange capacity (mequiv/g) 0 1.3 0.9 

 H2 crossover (nmol.mil/h.cm2

.atm)b n.d. 267.2 2039.4 

Mechanical stability 

 Resistance to crease/crack: 

 dry Yes No Yes 

 hydrated Yes Yes Yes 

 Resistance to tearing: 

 dry No No Yes 

 hydrated Yes Yes Yes 

 Resistance to gas pressure (dry) n.d. 30 psi >50 psi 

Chemical stability 

 Acid stability (% weight loss)c

 12 39 2.5 

a

Determined after heating to 99oC for 2.5 hours in H2O. 

b

Measured at 20 psi H2 (100%) and 25oC. c

Determined after incubation in 0.5M H2SO4 at 95oC for 45 hours. 

for proton transport is similar in both materials. The 

superior mechanical properties of Nafion are 

probably due to the difference in thickness between 

the materials. 

After incubation of the cellulose phosphate 

membrane at 95EC for 45 h, the cellulose phosphate 

lost 39% of its original weight. This increase in 

sensitivity to acid attack is probably an artifact of 

the reaction conditions employed in the synthesis. 

Modifications of the reaction procedure will be 

investigated to minimize this unwanted side 

reaction. 

Conclusions

Several properties of cellulose phosphate have 

been evaluated. The material has good thermal 

stability and low hydrogen crossover, two 
FY 2002 Progress Report Propulsion Materials 

70 

requirements that are important to meet DOE fuel 

cell program targets. Further characterization of the 

material is required, especially the determination of 

proton conductivity. In addition, testing of the 

material in a membrane electrode assembly will 

allow the effect of acid stability and swelling 

properties of cellulose phosphate to be evaluated 

under typical PEM fuel cell operating conditions. 

References

1

H. O’Neill, B. R. Evans, and J. Woodward, 

“Metallized Bacterial Cellulose Membranes in Fuel 

Cells,” pp. 141–145 in Fuels Cells for 

Transportation Annual Progress Report, 2001. 

Publications/Presentations

B. R. Evans, H. O’Neill, V. P. Malyvanh, and 

J. Woodward, “ Palladium-Bacterial Cellulose 

Membranes for Fuel Cells,” submitted to Biosensors 

and Bioelectronics. 

B. R. Evans, H. O’Neill, and J. Woodward, 

“Bacterial Cellulose in Energy Conversion 

Applications,” poster presentation at the 24th 

Symposium on Biotechnology for Fuels and 

Chemicals, April 28–May 1, 2002, Gatlinburg, 

Tenn. 

B. R. Evans, H. O’Neill, and J. Woodward, 

“Micro-Fuel Cell Development Based on Bacterial 

Cellulose,” oral presentation at the 14th World 

Hydrogen Conference, June 9–13, Montréal, 

Canada, 2002. 

Patents Issued

B. R. Evans, H. O’Neill, V. P. Malyvanh, and 

J. Woodward, “Metallization of Bacterial Cellulose 

for Electronic and Electrical Devices,” patent 

pending, invention disclosure 0869, S-96, 631, 2001. 

H. O’Neill, B. R. Evans, J. Woodward, 

“Synthesis of a Novel Ion-Exchange/Proton 

Conductive Membrane,” invention disclosure 

submitted, ID 1099, S-99, 279, 2002. 
Propulsion Materials FY 2002 Progress Report 

71 

G. Carbon Foam for Radiators for Fuel Cells 

A. D. McMillan and J. W. Klett 

Carbon Materials Technology Group 

Oak Ridge National Laboratory 

P.O. Box 2008, MS 6087, Bldg. 4508 

Oak Ridge, TN 37831-6087 

(865) 241-4554; fax: (865) 576-8424; e-mail: mcmillanad@ornl.gov 

DOE Technology Development Manager: Nancy Garland 

(202) 586-5673; fax: (202) 586-9811; e-mail: nancy.garland@ee.doe.gov 

ORNL Technical Advisor: David Stinton 

(865) 574-4556; fax: (865) 241-0411; e-mail: stintondp@ornl.gov 

Contractor: Oak Ridge National Laboratory, Oak Ridge, Tennessee 

Prime Contract No.: DE-AC05-96OR22464 

Objectives 

• Develop compact, lightweight, more efficient radiators for fuel-cell–powered vehicles using unique highconductivity carbon foam. 

• Evaluate materials issues (e.g., vibration, erosion, corrosion, plugging, thermal shock) for fuel cell cooling 

systems. 

• Work with radiator manufacturer to develop and test fuel cell radiators. 

Approach 

• Study fundamental mechanisms of heat transfer using the carbon foam. 

• Develop a testing method to evaluate the foams and designs using the foams. 

• Work with industrial partners to develop a complete understanding of fuel-cell–related issues. 

Accomplishments 

• Modified the heat transfer test rig to accommodate subscale prototype radiators. 

• Implemented new engineering designs, resulting in high heat transfer with an acceptable pressure drop. 

• Conducted a collaborative effort with Georgia Tech Research Institute (GTRI) in which the foam integrated into 

an airfoil showed excellent heat transfer with very low drag. 

Future Direction 

• Model further engineering designs for even better heat transfer and decreased pressure drop; use them in 

airfoils. 

• Complete evaluation of materials-related issues such as corrosion, erosion, and vibration. 

• Complete evaluation of alternative precursor materials. 
FY 2002 Progress Report Propulsion Materials 

72 

Introduction

Dissipation of heat from fuel cells is more 

difficult than from internal combustion (IC) engines 

because fuel cells operate at lower temperatures. The 

smaller driving force to disperse the heat results in a 

design problem—that is, excess size and weight of 

the radiator. Unless more efficient and compact 

thermal management systems can be developed, 

radiators on fuel-cell-powered vehicles will need to 

be significantly larger and heavier than those on 

conventional vehicles. 

The development of a high-thermal-conductivity 

graphite foam1–3 will lead to novel solutions for 

thermal management problems. The extremely high 

thermal conductivity of the ligaments combined with 

the very high surface area (4 m2

/g) make carbon 

foam an ideal material for heat transfer. This 

material is an enabling technology for thermal 

management problems ranging from heat sinks to 

radiators. For example, with the foam used as a heat 

exchanger and air used for cooling, heat transfer 

coefficients over two orders of magnitude greater 

than those of current metallic finned designs have 

been measured. This result is particularly important 

with regard to fuel-cell-powered vehicles, as the heat 

generated by the stack is difficult to dissipate 

because of the low operating temperatures. 

Approach

Material Testing 

A primary concern for potential users of the 

graphite foam is its durability. Previous work has 

exhibited its superior thermal properties and the 

material’s excellent response to thermal cycling; 

however, how the material behaves in certain 

environments is still a concern. This issue is being 

addressed by tests being conducted under Society of 

Automotive Engineers (SAE) J1211 as 

recommended by the Electrical and Electronics Tech 

Team. A matrix test plan has been developed and 

implemented to test the foams under thermal cycling 

of joined unit(s), corrosion, salt spray, erosion, 

debris fouling, and vibration. The test plan calls for 

using three different forms of the graphite foam in 

each test (control, nickel-plated, and polymercoated), each of which is joined to a variety of 

substrates (copper, aluminum, stainless steel, and 

brass). Each sample will be characterized both 

physically and thermally prior to testing and posttesting. Compression testing will then be conducted 

to determine effects on mechanical properties of the 

foams. 

Another area of interest is decreasing the 

pressure drop in the system while maintaining a high 

heat transfer coefficient. Studies have been 

conducted in air and water using various geometries 

machined into the graphite foam. These samples 

have been compared with off-the-shelf metal foams. 

GTRI Collaboration 

GTRI has a patented aerodynamic heat 

exchanger (AHE), a high-lift airfoil section that 

incorporates a conventional radiator to provide heat 

transfer and cooling to an automobile (passenger or 

heavy vehicle). If flow is allowed through the airfoil, 

it can seriously degrade the aerodynamics of the 

system (Figure 1). Thus, a study jointly funded by 

OAAT and the Office of Heavy Vehicle 

Technologies was undertaken to determine the 

effectiveness of ORNL’s graphite foam in this novel 

airfoil design; the foam has excellent heat transfer 

characteristics, while engineering designs may allow 

tailoring of the porosity. Three AHEs—a 

conventional radiator manufactured by Visteon (like 

the one installed in the GT MotorSports Formula 

SAE race car), a solid graphite foam core, and a 

corrugated graphite foam core—were tested under 

the same conditions. Each core had cooling tubing 

passing through internal channels (Figure 2); and for 

all configurations, the airfoil was mounted on a 

strain-gage balance below the floor to measure 

forces and moments. Data were taken first to 

determine the aerodynamic characteristics of each 

core by monitoring the slot blowing pressure at a 

constant angle of attack, as well as the tunnel 

pressure. Then the thermal performance was 

measured by having a constant coolant flow rate for 

variable pressure; further, the tunnel speed was also 

varied. 

Milling Study 

While studies regarding areas of interest to fuel 

cell vehicles are ongoing, several issues continue to 

arise with regard to industrial use of graphite foam. 

Two areas of specific concern are being addressed: 

material isotropy and lower-cost precursor material. 

A milling study was conducted to address the 
Propulsion Materials FY 2002 Progress Report 

73 

isotropy issue, to determine the effectiveness of milling the existing precursor material in various 

Figure 1. Georgia Tech Research Institute’s patented aerodynamic heat exchanger. 

Figure 2. Solid graphite foam (left) and corrugated foam 

radiator cores. 

solvents before foaming. It was thought that in 

milling, some measure of solvent fractionation might 

occur and therefore refine the beginning material. In 

an effort to find a lower-cost starting material, 

several pitches were included in the milling study. 

Four pitches were evaluated: Mitsubishi AR (the 

current precursor), solvated Conoco, Mitsubishi 

A240, and Koppers. The AR and Conoco were 

subjected to three different solvents—EtOH, 

toluene, and xylene; the A240 and Koppers were 

subjected only to xylene in this study. Additionally, 

the addition of 5 wt % ground graphitized foam dust 

(GGFD) to AR milled in EtOH was evaluated under 

the same conditions. 

To avoid cross-contamination, Teflon mill jars 

were dedicated to a particular pitch. Each mill was 

loaded with 250 g pitch, 400 g solvent, and 800 g 

zirconia milling medium. Each mill was subjected to 

the same amount of milling time at the same speed. 

After milling, the solution was poured into drying 

pans and allowed to air-dry. After drying, a 5 × 7 in. 

pan was loaded with 400 g of pitch and placed in the 

furnace to be foamed at 1EC/min; to avoid any 

temperature variations, only the central loading slots 

in the furnace were used. Carbonization (0.2EC/min 

to 1000EC) and graphitization (1EC/min to 

2400EC—5EC/min to 2800EC/1 h) were carried out 

under normal conditions. Characterization of the 

foams was performed, including scanning electron 

microscopy, compression tests, electrical resistivity, 

and thermal conductivity. 

Results 

Material Testing 

The long-term durability tests were initiated in 

FY 2002 and are ongoing. The corrosion study was 

conducted in a 50/50 solution of ethylene glycol and 

water and was 6 weeks in duration. The completed 

tests were conducted at room temperature, 60EC, 

and 100EC, and are awaiting final thermal 

diffusivity measurements to determine any 

detrimental effects. Only one sample failed—the 

polymer-coated sample brazed to an aluminum 6061 

substrate in the 100EC oven. In this case, the joint 

failed after approximately 2 weeks, but the sample 

was subjected to the entire 6 weeks in solution. Until 

final characterization is complete, it is unknown 

whether the sample failed because of a galvanic 

reaction between the graphite and aluminum or 

because the braze was improperly applied. 

The SAE fine and coarse test dusts (NIST 

traceable) have been received and tests are under 

way for debris fouling. Although such a test is not 

part of the test standard, we will examine the 

possible utilization of the foam’s inherent electrical 

conductivity to discharge any debris buildup. This 

test should be completed during FY 2003. 
FY 2002 Progress Report Propulsion Materials 

74 

Vibration testing has been delayed because of 

some mechanical difficulties; however, tests are 

scheduled to be completed during FY 2003. 

In an effort to decrease overall pressure drop, we 

examined several engineering designs, including 

horizontal blind holes, vertical blind holes, and 

corrugation. We found that when the foam was 

machined into a “corrugated” structure (Figure 3), 

thereby modifying the flow length and web 

thickness, a pressure drop comparable to that of a 

copper or aluminum foam was achieved with a heat 

transfer nearly that of a solid block of graphite foam 

(Figure 4). 

GTRI Collaboration 

The heat transferred from the coolant can be 

expressed as 

Measurements were made for each configuration 

at several freestream velocities, coolant flow rates, 

and blowing rates. Figure 5 shows the comparison of 

the graphite foam cores to the conventional Visteon 

core. Interestingly, the solid graphite foam core 

performed as well as the conventional core but with 

significantly less drag (Figure 6). Thus, the dense 

graphite foam core has been shown to be an 

effective heat transfer medium that does not 

significantly affect the aerodynamic performance of 

the AHE. 

Milling Study 

Samples were cut into 5/8-in., 1-in., or 2-in. 

cubes. Two different techniques were employed for 

measuring density, as density is often the first 

measure of the isotropy of a graphite foam material. 

A traditional technique using Euclidean geometry 

was compared with an immersion density technique 

to validate the nondestructive technique; an 

acceptable variation of ± 5% or less was measured. 

Interestingly, it was found that the AR milled in 

EtOH with the addition of GGFD exhibited the most 

isotropic density measurements from top to bottom 

of the blocks of foam (z-direction). 

As expected, the compressive strengths varied 

directly with density. In agreement with previous 

work, the Conoco pitch exhibited significantly 

higher strengths, as samples prepared using this 

pitch have exhibited higher overall densities (Figure 

7). Additionally, the Conoco samples exhibited a 

better isotropy ratio than AR samples, albeit at a 

lower overall level (Figure 8). Note the AR+GGFD 

samples retain a high specific thermal conductivity 

in the z-plane, but more important, the x- and yplanes were increased. This result may be a 

reflection of the more homogeneous density. Further 

tests are being conducted with a more refined 

addition of the dust in an effort to exploit these 

promising preliminary data. Characterization of the 

dust particle size, the amount of dust added, and the 

proportions in which it was added are the variables 

in this ongoing study. 

Microscopy samples were taken from a slice 

through the thickness of a graphitized block. 

Micrographs were taken from the bottom of the 

sample up through the sample to the top, resulting in 

an evaluation of the entire thickness and any change 

( ) . c p cIN cOUT Q = m& C T −T
Propulsion Materials FY 2002 Progress Report 

75 

Solid Corrugated

Figure 3. Illustration of the decrease in flow length and web thickness achieved via corrugation.

0.0

20.0

40.0

60.0

80.0

100.0

120.0

140.0

160.0

180.0

0 5 10 15 20 25

Power Density [W/cm2]

Electronic Temperature [C]

no cooling

Aluminum Foam

Copper Foam

Graphite Foam

Corrugated Graphite Foam

Aluminum Foam 

∆P=0.03 psi/in. 

Copper foam

∆P=0.02 psi/in. 

Corrugated Graphite foam 

∆P=0.03 psi/in. 

Graphite Foam 

∆P=2.4 psi/in. 

Figure 4. Heat transfer properties of corrugated graphite foam and other foam heat sinks. 
FY 2002 Progress Report Propulsion Materials 

76 

Figure 5. Comparison of different radiator core heat

removal rates. 

Figure 6. Unblown airfoil lift/drag polars at different 

angles of attack with and without radiators 

installed. 

Figure 7. Compression strength of milled graphite foam 

samples. 

Figure 8. Specific thermal conductivity measurements of 

milled graphite foams. 

in structure (i.e., density gradient). These studies 

revealed a slight decrease in average bubble size for 

the Conoco. Also, the decrease in density gradient 

(as observed by Euclidean measurements) was 

obvious in the AR+GGFD sample (Figure 9). 

Conclusions

Although the data and discussion presented in this 

paper illustrate the potential of this material to be an 
Propulsion Materials FY 2002 Progress Report 

77 

enabling technology, further work is needed. Even 

though a design for an automobile radiator 

dramatically smaller than current systems has been 

developed, ongoing work will determine the effect 

of the interface at the joint as a function of thermal 

cycling. Additional studies on vibration, erosion, 

Figure 9. Through-thickness 

representation scanning 

electron micrograph of AR 

milled in EtOH + 5 wt % 

ground graphitized foam 

dust. Mag = 40×. 

corrosion, and debris fouling are coming to an end. 

Further, the potential to radically redesign the heat 

exchanger on a vehicle using the GTRI/ORNL 

airfoil is very promising. The milling study indicates 

that the starting material may be treated in such a 

way as to result in a more homogeneous product. 

Lower-cost precursor materials, such as Mitsubishi 

A240 and Koppers, are currently being evaluated. 

With a more complete understanding of materials 

properties, the full potential of this material may be 

realized. A design for a foam core radiator will 

probably be quite different from the current concept 

of a radiator. The data presented here illustrate that 

the foam will be most useful and efficient not when 

used simply as a replacement for existing thermal 

management materials, but rather when the full 

potential of its unique structure is used in out-of-thebox designs. 

References

1. J. Klett, R. Hardy, E. Romine, C. Walls, 

T. Burchell, “High-Thermal-Conductivity, 

Mesophase-Pitch-Derived Carbon Foams: Effect of 

Precursor on Structure and Properties,” Carbon

32(8), 2000. 

2. J. Klett, “High Thermal Conductivity 

Mesophase Pitch-Derived Graphitic Foams,” 

Composites in Manufacturing 14(4) (1999). 

3. J. Klett, C. Walls, and T. Burchell, “High 

Thermal Conductivity Mesophase Pitch-Derived 

Carbon Foams: Effect of Precursor on Structure and 

Properties,” p. 132 in Proceedings of the 24th 

Biennial Conference on Carbon, July 11–16, 

Charleston, S.C., 1999. 
FY 2002 Progress Report Propulsion Materials 

78 

FY 2002 Publications

J. Klett, A. D. McMillan, D. Stinton, “Modeling 

Geometric Effects on Heat Transfer with Graphite 

Foam,” 26th Annual Conference on Ceramic, Metal, 

and Carbon Composites, Materials, and Structures, 

Cocoa Beach, Florida, January 2002. 

A. D. McMillan, J. Klett, L. B. Klett, “The 

Effect of Thermal Cycling on Prototype Graphite 

Foam Heat Exchangers,” 26th Annual Conference 

on Ceramic, Metal, and Carbon Composites, 

Materials, and Structures, Cocoa Beach, Florida, 

January 2002. 

Patents Issued

J. W. Klett, “Method for Extruding Pitch-based 

Carbon Foam,” U.S. Patent Number 6,344,159, 

February 5, 2002. 

J. W. Klett, “Pitch Based Carbon Foam and 

Composites,” U.S. Patent Number 6,387,343, 

May 14, 2002. 

J. W. Klett, “Method of Casting Pitch-Based 

Carbon Foam,” U.S. Patent Number 6,398,994, 

June 4, 2002. 

J. W. Klett and T. D. Burchell, “Pitch-based 

Carbon Foam Heat Sink with Phase Change 

Material,” U.S. Patent Number 6,399,149, June 4, 

2002.
Propulsion Materials FY 2002 Progress Report 

79 
Propulsion Materials FY 2002 Progress Report 

79 

4. ADVANCED COMBUSTION 

A. Materials Improvements and Durability Testing of a Third-Generation 

Microwave-Regenerated Diesel Particulate Filter 

Dick Nixdorf 

Industrial Ceramic Solutions, LLC 

1010 Commerce Park Drive, Suite I 

Oak Ridge, TN 37830 

(865) 482-7552; fax: (865) 482-7505; e-mail: nixdorfr@indceramicsolns.com 

DOE Technology Development Managers: Nancy Garland 

(202) 586-5673; fax: (202) 586-9811; e-mail: nancy.garland@ee.doe.gov 

Kathi Epping 

(202) 586-7425; fax: (202) 586-9811; e-mail: kathi.epping@ee.doe.gov 

ORNL Technical Advisor: David Stinton 

(865) 574-4556; fax: (865) 241-0411; e-mail: stintondp@ornl.gov 

Contractor: Industrial Ceramic Solutions, Oak Ridge, Tennessee 

Prime Contract No.: 4000000723 

Subcontractors: Transportation Research Center, East Liberty, Ohio; Lydall Technical Papers, 

Rochester, N.H.; Northrop Gruman Electron Devices, Williamsport, Pa.; Lubrizol Corporation, 

Cleveland, Ohio 

Objectives 

• Design, fabricate, and road-test a pleated ceramic fiber filter system that has reduced engine backpressure 

compared with conventional particulate filters and will microwave-regenerate at all engine operating 

conditions. 

• Conduct a 7000-mile controlled track test of the filter system, including microwave regeneration at various 

operating conditions and Federal Test Protocol (FTP) emissions testing to verify filter durability during and 

after the test sequence. 

• Provide filter durability, fuel penalty, and particulate removal efficiency data from the diesel vehicle testing. 

Approach 

• Conduct papermaking, pleating, and filter cartridge testing to establish an acceptable prototype pleated filter 

cartridge. 

• Use finite element analysis of microwave fields and laboratory air flow/microwave heating tests to design the 

vehicle-ready test system 

• Validate the filter system’s particulate removal efficiency on a stationary diesel engine test cell. 

• Install and road test the improved microwave filter system on a 7.3-L diesel vehicle. 
FY 2002 Progress Report Propulsion Materials 

80 

Accomplishments 

• Installed and road-tested a microwave-regenerated filter system on a 1.9-L Volkswagen Jetta vehicle for 200 

miles and six filter microwave cleanings. (The testing of the Jetta was abandoned because of engine and exhaust 

system defects, unrelated to this work, on the vehicle.) 

• Developed a pleated ceramic fiber filter cartridge and demonstrated that it achieved 1/20 the exhaust 

backpressure of a conventional wall-flow particulate filter. 

• Tested the Industrial Ceramic Solutions (ICS) ceramic fiber filter cartridge for over 9 months on a Ford 7.3-L 

truck, under standard highway driving conditions, with no material failures. 

• Designed and laboratory-tested a pleated filter cartridge system capable of regenerating at any engine operating 

condition on a 7.3-L Ford F-250 truck. 

• Prepared to test the pleated filter system in a 7000-mile track test in FY 2003. 

Future Direction 

• Integrate the microwave filter particulate matter (PM) control unit with NOx, hydrocarbon, and CO emission 

devices to develop a total system approach to meet Environmental Protection Agency (EPA) Tier II 

requirements. 

• Continue on-road testing on the 7.3-L Ford truck for an additional 20,000 miles, under high-load conditions, to 

extend the durability performance database. 

• Enlist exhaust system, catalyst, engine, and vehicle manufacturers in a joint product development effort to 

move toward commercialization of the microwave-regenerated particulate filter in 2004. 

• Work with microwave suppliers and materials companies to further harden the microwave and filter media 

components of the pleated filter microwave system against vibration and exhaust forces. 

Introduction

Most current diesel engine particulate filter 

technologies depend on a catalyst to assist in the 

regeneration of the filter. Catalyst technology 

requires a minimum exhaust temperature of 

approximately 300EC to be effective. Small and 

medium-size diesel engines rarely achieve this 

exhaust temperature. The microwave-regenerated 

diesel particulate filter (Mw-DPF) has been 

developed to provide the required particulate 

removal efficiencies and regenerate at low exhaust 

temperatures. A catalyst can be easily applied to the 

Mw-DPF to allow regeneration at higher exhaust 

temperatures without microwave assistance. The 

Mw-DPF is a viable answer to the low-temperature 

urban driving cycle where catalyst technologies are 

ineffective (Figure 1). 

Engine backpressure created by particulate 

filters reduces engine performance and fuel 

economy. The ICS pleated ceramic fiber filter 

demonstrates 1/20 the backpressure on the engine 

that is exhibited by the standard wall-flow filter 

(Figure 2). This device will provide a major 

Figure 1. Microwave-regenerated diesel particulate filter 

regeneration at all engine operating conditions. 

breakthrough for customers concerned about 

optimum engine performance. 

Approach

The ceramic fiber wall-flow filter was tested on 

a Ford F-250 7.3-L compression-ignition, directinjection (CIDI) truck under routine highway driving 

conditions for approximately 2000 miles over a 

period of several months to demonstrate filter 

durability. The truck filter was removed and 

Cold-Start to Idle

0 – 100oC

Urban Driving

100-300oC

Full-Load Operation

300-500oC

Microwave Filter

Microwave-Assisted

Regeneration

Microwave Filter

Catalyst-Assisted

Regeneration

Extruded Wall-Flow

Catalyst

Regeneration (Uncertain)

Cold-Start to Idle

0 – 100oC

Urban Driving

100-300oC

Full-Load Operation

300-500oC

Microwave Filter

Microwave-Assisted

Regeneration

Microwave Filter

Catalyst-Assisted

Regeneration

Extruded Wall-Flow

Catalyst

Regeneration (Uncertain)
Propulsion Materials FY 2002 Progress Report 

81 

Figure 2. Exhaust backpressure of the ICS pleated filter 

cartridge vs conventional wall-flow filters. 

microwave-regenerated in the laboratory to enable 

understanding of the effects of microwave heating 

on the particulate-loaded cartridge. 

A second major project for 2002 was installation 

of a ceramic fiber, wall-flow microwave filter 

system on a 1.9-L TDI Volkswagen Jetta vehicle for 

a 7000-mile track test. Microwave regenerations 

were to be conducted at engine idle conditions. The 

Volkswagen Jetta, equipped with an onboard 

microwave regeneration system, was driven for 

approximately 200 highway miles with six idle 

condition regenerations conducted. The Jetta vehicle 

exhibited two preexisting severe mechanical 

problems. The EGR valve was uncontrollable, 

opening and closing at random during the engine 

idle microwave regeneration. This condition resulted 

in unacceptable exhaust flow variations during 

microwave regeneration. During stationary engine 

testing at Oak Ridge National Laboratory (ORNL) 

on an identical 1.9-L TDI engine, 3 hours were 

required to load the filter cartridge at normal engine 

speeds. The same size cartridge on the Volkswagen 

vehicle was found to load in less than 1 hour. This 

second problem was high inorganic ash 

accumulation in the filter, probably due to several 

years of being parked, as well as previous testing of 

unusual fuels and lubricants. ICS and DOE agreed 

that conducting the expensive track testing on such 

an unreliable test vehicle was counterproductive. 

Therefore, the 7000-mile track testing was 

transferred to the Ford F-250 7.3-L truck. 

During the test vehicle change, ICS was able to 

complete the development of a low-backpressure 

pleated filter cartridge to replace the wall-flow 

design for the 7000-mile durability track testing. The 

pleated filter system for the Ford truck will allow 

microwave regeneration at conditions other than 

engine idle, which is a requirement of the diesel 

engine manufacturers. ICS is currently testing the 

microwave-heating properties of this system in the 

laboratory. Particulate emissions testing will be 

conducted on the pleated filter on a 1.7-L Mercedes 

engine at ORNL. The 7000-mile track test will be 

performed at the Transportation Research Center in 

East Liberty, Ohio. The data from this test will 

verify system durability using filter efficiency 

performance in FTP chassis dynamometer testing 

and will accurately measure the fuel penalty of the 

Mw-DPF. 

Results

Data verifying the durability of the filter 

cartridge in the Ford truck highway testing are 

shown in Figure 3. Note how the backpressure of the 

same cleaned filter increases very gradually over a 

9-month period. That testing is still proceeding on 

the same ceramic fiber filter cartridge with no 

apparent mechanical damage to the filter cartridge. 

Figure 3. Backpressure increases on a single ICS fiber 

filter during 9 months of semi-continuous 

loadings and cleanings on a Ford 7.3-L CIDI 

vehicle. 

The ability of the microwave to clean a 

particulate-loaded filter to within 95–100% of its 

clean condition has been demonstrated in engine 

testing for the last 3 years. Similar results of 

microwave regeneration on the Volkswagen Jetta 

vehicle are shown in Figure 4. Again, note how the 

backpressure of the cleaned filter is approximately 

constant from regeneration to regeneration. The 

1.8

1.6

1.4

1.2

0.8

0.6

0.4

0.2

Cleaned Filter Backpressure at Engine Idle

0

1

6-14-01 7-24-01 8-6-01 9-13-01 10-8-01 4-8-02

Date

Pressure (in.H2O)

1.8

1.6

1.4

1.2

0.8

0.6

0.4

0.2

Cleaned Filter Backpressure at Engine Idle

0

1

6-14-01 7-24-01 8-6-01 9-13-01 10-8-01 4-8-02

Date

Pressure (in.H2O)

Pleated Filter vs. Wall-Flow Filter

Backpressure Comparison

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

50 cfm 100 cfm

Exhaust Flow

Inches of Water

Pleated Filter, 5.2 sq. ft.

Wall-Flow Filter, 6.9 sq. ft.

0.5 in. H2O

20.8 in. H2O

1.7 in. H2O

60.0 in. H2O
FY 2002 Progress Report Propulsion Materials 

82 

Figure 4. Microwave filter cleaning efficiency using the 

onboard system of the Volkswagen Jetta 

vehicle. 

design of the new pleated ceramic fiber filter 

cartridge is displayed in Figure 5. The 

commercialization plan for the pleated filter is to 

produce the same size cassette for all vehicles, using 

multiple cassettes as the engine size increases. The 

design of the pleated particulate filter system will 

accomplish microwave regeneration at all engine 

conditions, as shown in Figure 6. The onboard 

generator supplying power to the microwave system 

on the Ford truck is shown in Figure 7. The new 

uniform-sized pleated cassette concept, using 

multiple cassettes as engine size increases, will 

maintain the price of the Mw-DPF below that of 

current particulate control technologies while 

providing significant advantages in engine 

backpressure. Materials improvements in the 

ceramic fiber filter system have continued in 2002, 

including filter media burst strength increases from 

the 6 psi achieved in 2001 to 10 psi in 2002. The 

application of an inexpensive silicon carbide coating 

Figure 5. ICS pleated ceramic fiber particulate filter 

cartridge cassette. 

Figure 6. ICS pleated particulate filter system 

microwave regeneration design. 

Figure 7. Onboard generator to supply power to the 

microwave system for the microwaveregenerated diesel particulate filter on the Ford 

7.3-L test truck. 

to the filter cartridge has improved the microwave 

heating ability, as well as the diesel exhaust 

corrosion resistance. The use of silicon carbide 

structural members to frame the pleated filter also 

ensures stability during high temperature excursions. 

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

6.0

6.5

7.0

7.5

1a 1b 1c 1d 1e

Run #

Pressure (in. H2O)

Loaded Filter Pressure

Cleaned Filter Pressure

2”

8”

12”

First Prototype

Cartridge Design

2”

8”

12”

First Prototype

Cartridge Design

Exhaust Out

Exhaust In
Propulsion Materials FY 2002 Progress Report 

83 

Conclusions

Filter backpressure and the ability to regenerate 

a particulate filter at low exhaust temperatures are 

significant issues with diesel engine manufacturers 

preparing for the 2007 EPA standards. Laboratory 

and stationary engine testing of the ceramic fiber 

microwave-regenerated filter system have shown 

meaningful progress in those areas. The 7000-mile 

track test on the Ford 7.3-L vehicle will begin 

durability verification. Continuation of the 

development of the pleated cassette system in 2003 

will lead to a commercially viable product for 

mobile sources by 2004. 

FY 2002 Publications/Presentations

R. Nixdorf, “In-Situ Microwave Cleaning of 

Silicon Carbide Fiber Filtration Media,” TechTextile 

Symposium North America, Atlanta, April 2002.

Propulsion Materials FY 2002 Progress Report

85

B. Rapid Surface Modifications of Aluminum Automotive Components for

Weight Reduction

C. A. Blue, R. D. Ott, P. J. Blau, P. G. Engleman, and D. C. Harper

Oak Ridge National Laboratory

P O. Box 2008, Bldg. 4508

Oak Ridge, TN 37831-6083

(865) 574-4351; fax: (865) 574-4357; e-mail: blueca@ornl.gov

DOE Technology Development Managers: Nancy Garland

(202) 586-5673; fax: (202) 586-9811; e-mail: nancy.garland@ee.doe.gov

Kathi Epping

(202) 586-7425; fax (202) 586-9811; e-mail: kathi.epping@ee.doe.gov

ORNL Technical Advisor: David Stinton

(865) 574-4556; fax: (865) 241-0411; e-mail: stintondp@ornl.gov

Contractor: Oak Ridge National Laboratory, Oak Ridge, Tennessee

Prime Contract No.: DE-AC05-00OR22725

Objectives

• Further develop durability-enhancing coatings on steel for environmental protection and wear resistance.

• Develop a method to dramatically reduce the time required to cure an epoxy used to join automotive body

panels.

• Develop a procedure for selective heat-treating of aluminum automotive body construction parts in order to

soften selected areas to serve as built-in crumple zones.

Approach

• Fuse abrasion-resistant coatings in air to steel using the high-density infrared (HDI) plasma arc lamp.

• Use a focused tungsten halogen lamp line heater to rapidly cure epoxy used for joining body panels.

• Use the HDI plasma arc lamp to soften selected areas of extruded aluminum tubes used as automotive frame rail

structures.

Accomplishments

• Successfully fused onto steel abrasion-resistant coatings that show a reduction in porosity, an increase in

hardness, and appropriate bonding characteristics.

• Successfully developed the tungsten halogen lamp line heater for the rapid curing of epoxy resin, a process

currently being used on the production line at Ford.

• Developed heat flow models to determine the temperature profile during the pulsing of extruded aluminum

tubes with the HDI plasma arc lamp, making it possible to predict the degree of hardness reduction achieved.
FY 2002 Progress Report Propulsion Materials

86

Future Direction

• Further develop durability-enhancing coatings for the compression-ignition direct-injection (CIDI) exhaust gas

environment to improve the corrosion and wear resistance of relevant components and accommodate the more

aggressive environment of exhaust gas recirculation (EGR).

• Resolve accelerated corrosion and wear concerns associated with EGR, especially the use of coatings to prolong

the life of critical components such as the intake manifold and EGR valves.

• Use the HDI plasma arc lamp for rapid surface modification of discrete areas to eliminate fatigue-related

problems in cast aluminum engine blocks.

Introduction

Three research projects were associated with

FY 2002. The first one encompassed the further

development of durability-enhancing coatings; this

work was performed in conjunction with Caterpillar.

Caterpillar was looking for a way to fuse abrasionresistant coatings to steel with appropriate densities,

hardness, and bonding strengths. The HDI plasma

arc lamp was used to achieve the required

properties. These coatings are potential candidates to

enhance the life of exhaust gas components. Because

a larger amount of exhaust gas must be combined

with the intake mixture to reduce emissions,

components such as EGR valves and intake

manifolds will see accelerated corrosion and wear.

The abrasion-resistant coatings are able to withstand

the more severe environment, thus protecting the

steel components from premature failure.

The second research project was an effort to

reduce the curing time of automotive body filler

epoxy. Ford wanted to replace the joining material

for body panels with a one-component epoxy, but

curing the epoxy took too long for the production

line. A focused tungsten halogen lamp line heater

was developed at ORNL to help reduce the curing

time. Implementing use of the line heater allowed a

2-min reduction in cycle time, eliminated five

grinding steps, provided a safer, more

environmentally friendly process, reduced energy

consumption, and saved $28 per vehicle.

The third project involved working with Ford on

preferential heat treating of extruded aluminum

tubes intended for use as automotive frame rail

structures. The preferential heating was performed

to introduce crash triggers so that the structure

would collapse on itself in a controlled manner

during impact. Using the HDI plasma arc lamp, it

was possible to selectively soften the essential areas,

eliminating the need to introduce the crash triggers

mechanically and thus reducing cost. The

introduction of aluminum frame rail structures can

lead to a significant reduction in the weight of the

vehicle, increasing the fuel efficiency.

Results

Abrasion-Resistant Coatings

Caterpillar was interested in evaluating the

capability of the HDI plasma arc lamp to fuse

abrasion-resistant coatings to steel components. The

essential purpose of these coatings is to increase the

wear resistance and corrosion resistance of

components exposed to exhaust gases, such as EGR

valves and intake manifolds. One of the coatings the

company was interested in was an Fe-Cr-B-Mn-Si

wire arc-sprayed coating. Caterpillar’s main

concerns were associated with the porosity and the

hardness of the coating and the bonding

characteristics of the coating to the substrate.

Experiments were conducted by varying the arc

lamp’s reflector geometry, amperage (i.e., power

density), and pulse or exposure time. The lamp

processing parameters were optimized to obtain the

desired coating properties.

It was shown that there was a significant

reduction in porosity, increased coating hardness,

and adequate metallurgical bonding. The

micrographs in Figure 1 reveals a cross-sectional

view of a coating, pre- and post-processing. It was

also shown that altering the processing parameters

could vary the degree of mixing between the

substrate and coating. This research demonstrates

the plasma arc lamp’s capability to rapidly fuse

coatings in an air environment. This capability leads

to a very robust fusing technique that makes it
Propulsion Materials FY 2002 Progress Report

87

(a) (b)

Figure 1. Scanning electron microscope micrographs of a cross section of an abrasion-resistant coating on a

steel substrate: (a) pre-processed by the HDI plasma arc lamp (note the porosity) and (b) postprocessed by the plasma arc lamp, revealing the densification of the coating.

suitable for high production volumes, ideal for

automotive components in the EGR system and

combustion chamber.

Rapid Curing of Automotive Body Filler

Epoxy

Ford was interested in replacing a welding

process for joining body panels with a onecomponent epoxy. The specific joint to be

considered was a welded seam in the C-pillar of the

Lincoln LS vehicle. Ford wished to eliminate steps

associated with the production of the body to reduce

cost. The process being used was operatordependent and thus susceptible to quality concerns

and throughput issues. The major challenge was to

develop a process that used a one-component epoxy

and a procedure for curing the epoxy in a timely

manner.

Ford pursued a collaboration with ORNL to

develop a method to rapidly cure the epoxy seam on

the C-pillar, since it was not cost-effective to heat

the entire component to elevated temperatures to

cure the epoxy. After several methods to heat the

seam were investigated, the focused tungsten

halogen lamp line heater showed the most promise

as a robust heating system. It was able to cure the

epoxy in approximately 20 s. The line heater is

capable of going to full power in less than 1 s and is

90% efficient in converting electrical power to

radiant power. Its inherent properties make it ideal

for industrial applications. Ford was able to realize a

$28-per-vehicle savings by using the epoxy filler

with the line heater curing method, as well as a

2-min reduction in cycle time. Figure 2 shows the

line heater lamp on the production line and the joint

after the curing process.

Preferential Heat-Treating of Aluminum

Tubes

In an effort to reduce the overall weight of an

automobile, Ford has been investigating the use of

aluminum for the frame rail structure. One of the

main purposes of this assembly, located in the front

portion of the body, is to absorb energy during an

impact. To do so, its structure must collapse in a

certain sequence. This process is accomplished by

built-in crash triggers, which are points along the

structure that allow the structure to collapse and

deform in a controlled manner.

Currently, front frame rail structures are

manufactured from steel. Replacing steel with 6063

aluminum alloy would result in considerable weight

savings. Extruded square aluminum tubes are more

cost-effective than stamped aluminum because of

their lower tooling costs. However, it is easy to build

crash triggers into stamped aluminum during the

manufacturing process; that is not the case for

extruded aluminum tubes. Therefore, the HDI

plasma arc lamp was used to soften (i.e., reduce the

hardness of) selected areas along the aluminum tube

to eliminate the need to introduce crash triggers

mechanically.
FY 2002 Progress Report Propulsion Materials

88

(a) (b)

Figure 2. The line heater lamp on the production line curing an epoxy seam (a) and the seam

after the curing process (b).

Experiments were performed at ORNL to

determine the necessary plasma arc lamp parameters

to achieve the required reduction in hardness. It was

shown that the required 50% hardness reduction

could be reached. From these experiments, a heat

flow model was developed to optimize the process,

and a microhardness map was developed to

determine the required hardness reduction along the

profile of the tube. Tubes are currently being pulsed

according to the optimized process and will be sent

to Ford for crumple test evaluation. Figure 3 shows

the crumple test setup.

Microstructural evaluation of the 6063 T-6

aluminum specimens revealed that Mg2Si

precipitates had gone back into solution in regions

that had been heat-treated. The microstructure

farther away from the heat-treated zone resembled

that of the overaged condition, a dense Mg2Si

precipitate matrix with precipitate-free zones at the

grain boundaries. The micrographs in Figure 4 show

these two regions.

Summary

Work is ongoing in the area of abrasion-resistant

coatings for steel and aluminum components. The

plasma arc lamp has shown great promise for

processing these coatings for numerous applications.

Work also continues on the preferential softening of

the aluminum frame rail structure tubes. Aluminum

tubes that have been heat-treated by the plasma arc

lamp will be crush-tested at Ford to evaluate the

optimal heat-treating process. Ford officials believe

that this is a viable technology and has a real chance

to be implemented into production.

The HDI plasma arc lamp has shown promise in

depositing wear- and corrosion-resistant coatings on

steel substrates intended for the gaseous oxidant

environment of the exhaust gases. The coatings

produced by this method have shown promising

properties in regard to adherence to the substrate,

reduction in porosity, and mechanical strength. They

can be deposited quickly in an environment suitable

for high production volumes, such as the automotive

industry. This process has been shown to be an ideal

technology for producing protective coatings to

reduce emissions.

Presentations

R. D. Ott, C. A. Blue, A. S. Sabau, T. Y. Pan,

and A. M. Joaquin, “Preferential Softening of

6063-T6 Aluminum Alloy Utilizing a High Density

Infrared (HDI) Plasma Arc Lamp,” The Minerals,

Metals & Materials Society Fall Meeting, 2002.
Propulsion Materials FY 2002 Progress Report

89

Figure 3. An aluminum tube undergoing a crumple

test.

(a) (b)

Figure 4. Micrographs of the (a) heat-treated region and (b) non-heat-treated region of 6063 T-6 aluminum.

Notice the lack of grain definition in the heat-treated region compared with the non-heat-treated

region. This is due to the dense Mg2Si precipitate matrix resembling that of the overaged

condition.

Propulsion Materials FY 2002 Progress Report

91

C. Material Support for Nonthermal Plasma Diesel Engine Exhaust Emission

Control

Stephen D. Nunn

Materials Processing Group

Oak Ridge National Laboratory

P.O. Box 2008, MS 6087

Oak Ridge, TN 37831

(865) 576-1668; fax: (865) 574-4357; e-mail: nunnsd@ornl.gov

DOE Technology Development Manager: Nancy Garland

(202) 586-5673; fax: (202) 241-0411; e-mail: nancy.garland@ee.doe.gov

ORNL Technical Advisor: David Stinton

(865) 574-4556; fax: (865) 574-6918; e-mail: stintondp@ornl.gov

Contractor: Oak Ridge National Laboratory, Oak Ridge, Tennessee

Prime Contract No.: DE-AC05-00OR22725

Objectives

• Identify appropriate ceramic materials, develop processing methods, and fabricate complex-shaped ceramic

components that will be used in Pacific Northwest National Laboratory (PNNL)-designed nonthermal plasma

(NTP) reactors for the treatment of diesel exhaust gases.

• Fabricate and ship components to PNNL for testing and evaluation in prototype NTP reactors.

• Develop a component design and establish a fabrication procedure that can be transitioned to a commercial

supplier.

• Assemble and test a prototype NTP reactor on a laboratory diesel engine.

Approach

• Evaluate commercially viable forming methods to fabricate complex-shaped ceramic components that meet

PNNL design specifications.

• Modify processing as needed to accommodate material and design changes.

• Evaluate bonding and sealing materials for preparing assemblies of the ceramic components.

• Investigate metallization materials and processes to apply electrodes to the ceramic components.

Accomplishments

• Modified the processing procedure for fabricating the ceramic components to improve reliability and simplify

the production.

• Identified a sealing glass composition for joining together the ceramic components that are used in the NTP

reactor assembly.

• Selected a preliminary NTP reactor design for conducting functional testing of the device on a 1.7-L diesel

engine in an engine test cell.
FY 2002 Progress Report Propulsion Materials

92

Future Direction

• Finalize the selection of sealing materials to bond and seal the various ceramic and metal components of the

NTP reactor into a complete assembly for functional testing.

• In collaboration with PNNL, select an NTP reactor design for assembly and testing to determine the operational

performance of the device.

• Fabricate an NTP reactor assembly and test the device in a diesel engine exhaust gas stream.

Introduction

NTP reactors have shown great potential as an

effective means for eliminating unwanted exhaust

gas emissions from diesel engines. In particular, the

NTP reactor is very effective in reducing NOx.

Researchers at PNNL are developing new,

proprietary design configurations for NTP reactors

that build on past experimental work. To improve

the effectiveness, these designs include ceramic

dielectric components having complex

configurations. Oak Ridge National Laboratory

(ORNL) has extensive experience in the fabrication

of complex ceramic shapes, primarily based on prior

work related to developing ceramic components for

gas turbine engines. The ORNL expertise is being

used to support PNNL in its development of the new

NTP reactor designs.

Approach

Collaborative discussions between ORNL and

PNNL are used to establish new ceramic component

designs for improved NTP reactors. The need to

meet NTP reactor design objectives is balanced with

the limitations of ceramic manufacturability to arrive

at a new component configuration. The ceramic

processing facilities and expertise at ORNL are then

used to establish fabrication capabilities and to

produce components for testing at PNNL. This is an

iterative process as both parties gain more

knowledge about fabricating the components and

about their performance in NTP reactor tests. The

ultimate goal is to identify a design that performs

well and that can be readily produced by a

commercially viable process.

Results

In the early stages of this project, complexshaped ceramic components were fabricated by the

gelcasting process. Although these parts performed

well in laboratory tests, it was decided that the

fabrication process was too complicated to be

feasible for commercial production. A new

fabrication process was developed that uses

commercially available tape-cast ceramic materials.

In the green (unfired) state, the ceramic tape is

flexible (Figure) 1. The tape can be shaped and

laminated to form the ceramic dielectric components

for the NTP reactor. Figure 2 illustrates this process,

showing where grooves have been formed in the

outer layers that will be laminated with flat tape

layers to form the final assembly. Using a flat core is

a modification of the original process that simplifies

fabrication and improves yield. Silver electrodes are

applied to the insides of the grooved areas and then

extended to the outside of one end of the assembly.

A stack of sintered components is shown in

Figure 3. The individual dielectric plates are

separated by alumina ceramic spacers to produce a

precise gap between the plates.

In the NTP reactor assembly, the ceramic

components will be fixed in place in a metal

housing, with ceramic spacers used to maintain the

separation between the individual plates. To form

Figure 1. Photograph of pieces of the tape-cast ceramic

material showing the flexibility of the unfired

tape.
Propulsion Materials FY 2002 Progress Report

93

Figure 2. Examples of formed and flat tape segments

illustrating how they are assembled to form the

ceramic dielectric components.

Figure 3. Sintered dielectric plates assembled in a stack

with individual plates separated by alumina

ceramic spacers.

the assembly, a bonding and sealing material is

needed to fix the ceramic components in position

and to form a gas-tight seal to contain the exhaust

gases. The bonding/sealing material must be an

electrical insulator and must have an appropriate

thermal expansion match to maintain a tight bond

during thermal cycling. Several glass compositions

have been evaluated for use in joining the various

components. An example of a test sample is shown

in Figure 4, where pieces of the dielectric ceramic

and the spacer are bonded in a sandwich. A

photomicrograph of the bond is shown in Figure 5.

The glass wets and bonds the materials together and

forms a fillet of material at the outer surface to make

a gas-tight seal. Additional testing will be required

to identify an appropriate bonding material to join

the ceramic components to the metal housing.

Plans are now being made to make a complete

NTP reactor during the coming fiscal year and to

conduct tests of the performance of the device on a

1.7-L diesel engine in an engine test cell.

Figure 4. Test assembly for evaluating bonding and

sealing of the NTP reactor component

materials.

Figure 5. Micrograph showing the adhesive bond

between the dielectric material (top) and the

spacer (lower left). A smooth fillet has

formed where the outer portion of the two

materials join (center) forming a gas-tight

seal. The bar equals 50 microns.

Conclusions

The fabrication procedure for ceramic dielectric

components was modified to simplify the production

of parts for the NTP reactors. The new procedure

should be lower in cost and should improve the

reliability and yield of the components. A sealing

glass was identified for joining together the ceramic

components of the NTP reactor, but additional

testing is needed to find a material that will bond the

ceramics to the metal housing of the reactor.

Propulsion Materials FY 2002 Progress Report

95

D. Fabrication of Small Fuel-Injector Orifices

John Woodford and George R. Fenske

Argonne National Laboratory

9700 South Cass Avenue

Argonne, IL 60439

(630) 252-0910; fax: (630) 252-4798; e-mail: gfenske@anl.gov

DOE Technology Development Manager: Nancy Garland

(202) 586-5673; fax: (202) 586-9811; e-mail: nancy.garland@ee.doe.gov

ORNL Technical Advisor: David Stinton

(865) 574-4556; fax: (865) 241-0411; e-mail: stintondp@ornl.gov

Contractor: Argonne National Laboratory, Argonne, Illinois

Prime Contract No.: W-31-109-Eng-38

Objectives

• Develop a methodology for reducing the diameter of fuel injector orifices to 50 μm by applying material to the

internal diameter (ID) of a conventional 200-μm diameter orifice.

• Characterize the spray and combustion properties of the fuel injector systems so treated.

• Transfer the technology to an industrial partner.

Approach

• Identify and rate potential thin- and thick-film deposition technologies for reducing the diameter of diesel

engine fuel injector orifices.

• Perform laboratory-scale evaluations of the most promising technology or technologies.

Accomplishments

• Selected electroless nickel (EN) plating as the primary candidate, with electroplating and/or physical vapor

deposition (PVD) as possible secondary candidates.

• Began benchtop evaluation of EN plating for injector tips.

• Reduced orifice diameter from 200 μm to 100 μm with EN plating.

• Began forced-flow EN plating tests.

• Identified the critical role of particulates in EN orifice plating quality.

Future Direction

• Complete construction of forced-circulation multicomponent plating system.

• Analyze spray characteristics of coated injectors.

• Provide coated injector tips to Argonne National Laboratory (ANL) Energy Systems personnel for combustion

tests.
FY 2002 Progress Report Propulsion Materials

96

• Determine the vulnerability of EN-plated injectors to deposit formation. If necessary, vary plating chemistry to

ameliorate vulnerability.

Introduction

Recent work on the control of particulate matter

(PM) emissions and improvement of engine

combustion efficiency in diesel engines has shown

the effectiveness of reduced injector orifice diameter

in promoting fuel atomization, leading to more

complete combustion and reduction in soot

formation.1,2 Using electrodischarge machining

(EDM), the current method for fabricating injector

orifices, the minimum achievable orifice diameter is

on the order of 125 μm. To see significant

improvement, orifice diameter should be 50 μm or

less. Work toward refining EDM techniques to allow

economical large-scale fabrication of 100-μm

orifices is ongoing. In addition, two other

technologies may be used to manufacture small

orifices: laser drilling and LIGA. Both technologies

have disadvantages precluding their commercial use

in the near- to mid-term. Therefore, we propose

another method.

There are currently a wide variety of techniques

for depositing moderately thick (>10 μm) films onto

various surfaces. It may be possible to reduce the

diameter of an extant orifice by depositing material

onto its interior (Figure 1). We propose to select and

evaluate an appropriate technique for doing so, and

if it appears that this approach is successful, we will

develop a method and transfer it to an industrial

partner. We are currently working with Siemens,

which has provided us with sample injector tips and

information.

Approach

As mentioned earlier, there are a large number

of coating techniques to be considered. Our first

step, therefore, is to perform a survey of deposition

methods and determine which may be used to coat

orifice IDs. We will then rank those methods

offering a reasonable chance of success by ease of

overall implementation, taking into account such

factors as coating cost, startup cost, and

environmental friendliness.

Figure 1. Schematic illustration showing the proposed

method of reducing the orifice diameter.

With the ranked list in hand, we will work

toward implementing the easiest method on a

laboratory scale and examining the feasibility of

working on others. Our criteria for success are as

follows:

• The technique allows reduction in the orifice

diameter to at least 50 μm.

• The coating adheres well to the substrate.

• The coating is at least as damage-resistant as

the substrate.

In addition, we will consider the effort a limited

success if the surface chemistry of the (adherent,

damage-resistant) coating is such that deposit

formation is minimized, even if we are unable to

achieve the goal of an ID of 50 μm.

As part of the evaluation process, we will

examine the flow-through and spray characteristics

of coated nozzles and will provide them to industrial

partners or other collaborators for combustion

studies. Although our focus in this project is on
Propulsion Materials FY 2002 Progress Report

97

deposition methods, we understand that the overall

goal is to improve fuel combustion in diesel engines.

Following a successful laboratory-scale

demonstration of the coating technology, we will

work with Siemens or another industrial partner to

transfer the technology.

Results

We completed a process comparison in the

second quarter (Table 1). The most promising

candidate method was EN plating, which offered a

combination of rapid deposition rate, ability to coat

IDs, ready scalability, overall maturity level, lowexpense facilities, and durability of coating. We then

set out to evaluate the process according to the

criteria described earlier.

EN plating is a method of depositing

nickel/phosphorus (or nickel/boron) alloys (usually

Ni-P or -B solid solutions, with NiP or NiB

precipitates) onto metallic surfaces from an aqueous

solution. Samples are placed in a plating bath of the

appropriate composition, the bath is heated to

approximately 70–95EC, and the nickel/phosphorus

coating grows directly from the bath via a surfacecatalyzed chemical reaction.

Initial results have been quite promising. We

have coated the orifice IDs on sample injector tips

provided by Siemens (Figure 2) with reasonable

uniformity (Figure 3). We have also established the

adherence of the EN plating on the injector tips.

Although we have not yet achieved reduction to

50 μm, we have deposited an EN plate that is about

50 μm thick onto the ID of 200-μm diameter

orifices, reducing them to 100 μm in diameter.

In order to obtain greater uniformity, better

adhesion on the interior of the injector tip, and more

rapid deposition, we began to plate injector tips by

forcing the plating bath through the injector orifices

during the coating process. This approach

approximately doubled the deposition rate to around

50 μm/hour. However, we found that the bath

needed to be filtered to prevent clogging of the

nozzles with small nickel particles. In fact, if the

bath is not filtered, the nickel particles nucleate the

growth of metallic threads inside the body of the

injector tip. In addition, the pump we were using did

not develop enough pressure to force the bath

through the orifices once they had closed to around

100 μm in diameter. We are in the process of

constructing a larger-scale plating bath with a

capacity of several gallons, a more powerful pump, a

filter on the supply line, and a manifold for coating

multiple injector tips at a time.

Conclusions

EN plating has been shown to be an effective

method of reducing the ID of fuel injector tip

orifices. Further work toward improving the method

is ongoing.

References

1. John B. Heywood, Internal Combustion

Engine Fundamentals, McGraw-Hill, 1988.

2. Lyle M. Pickett and Dennis L. Siebers,

“Orifice Diameter Effects on Diesel Fuel Jet Flame

Structure,” Paper 2001-ICE-399, ICE-Vol. 37-1,

2001 Fall Technical Conference, American Society

of Mechanical Engineers, 2001, ed. V. W. Wong.

Table 1. Process comparison

Process MOCVD

(vacuum) PVD MOCVD(atmo)

Thermal

spray

EP EN

Inexpensive? No No Variable Yes Yes Yes

Reliable? Yes Variable Yes Yes Yes Yes

Green? Variable Yes Variable Yes Variable Variable

Adherent? Yes Variable Yes Variable Yes Variable

Uniform? Unknown Probably not Unknown No Unknown Yes
FY 2002 Progress Report Propulsion Materials

98

Figure 2. Micrograph of the cross section of the coated

fuel injector tip orifice. The nickel plate is the

lighter-colored ring around the orifice ID.

Orifice Diameter vs. Position

0

50

100

150

200

0 500 1000

Distance from outer surface, um

Orifice diameter, 

um

Run #3

Run #2

Run #1

Figure 3. Graph of coating thickness as a function of

position along the length of the orifice.
Propulsion Materials FY 2002 Progress Report

99

E. Technology for Producing Small Holes in Advanced Materials

Stephen D. Nunn

Materials Processing Group

Oak Ridge National Laboratory

P.O. Box 2008, MS 6087

Oak Ridge, TN 37831

(865) 576-1668; fax: (865) 574-4357; e-mail: nunnsd@ornl.gov

DOE Technology Development Manager: Nancy Garland

(202) 586-5673; fax: (202) 586-9811; e-mail: nancy.garland@ee.doe.gov

ORNL Technical Advisor: David Stinton

(865) 574-4556; fax: (865) 241-0411; e-mail: stintondp@ornl.gov

Contractor: Oak Ridge National Laboratory, Oak Ridge, Tennessee

Prime Contract No.: DE-AC05-00OR22725

Objectives

• Explore methods for producing ultra-small holes (<50 μm) in advanced materials for fuel injector nozzles.

• Evaluate carbide-based cermets and high-temperature ceramics as candidate materials.

• Devise methods to precisely produce a desired pattern of holes having a well-controlled size and shape.

Approach

• Form holes in situ during the sintering process by incorporating various pore formers in the green (unsintered)

body while it is being shaped.

• Use nickel alloy wires in nickel aluminide (Ni3Al)-bonded titanium carbide (TiC) to form holes during

sintering.

• Embed combustible organic fibers in gelcast ceramic materials that will vaporize during sintering at high

temperatures.

• Gelcast ceramic materials around metal wires that can be removed from the green body prior to sintering,

leaving a hole in the part.

Accomplishments

• Formed ~30-μm holes in gelcast alumina by embedding polymer fibers in the green body and sintering the

material at 1500EC.

• Formed ~35-μm holes in alumina that was gelcast around fine metal wires, which were removed prior to

sintering at 1500EC.

Future Direction

• Demonstrate the ability to form holes in cermets and additional ceramic materials.

• Evaluate techniques to form arrays of holes in precise locations in the sintered parts.

• Investigate microfabrication by coextrusion as an additional method for forming ultra-small holes in advanced

materials.
FY 2002 Progress Report Propulsion Materials

100

Introduction

To meet the ever-growing demand for improved

efficiency and reduced emissions, future fuel

injection systems will require improvements in both

design and materials. The objective of this project is

to explore new methods of forming ultra-small

(<50-μm) holes in advanced materials. Carbidebased cermets (ceramic/metallic composites) and

high-temperature ceramics are candidate materials to

be used in this study. These materials have the

desirable properties of high strength, high modulus,

and low density compared with steel. In addition,

they are corrosion resistant and, because of their

high hardness, also resistant to wear and erosion.

Currently, fuel injector nozzle holes in steel are

150 to 200 μm in diameter. This size is at the limit

for machined holes. One of the major challenges to

using advanced materials for improved nozzles is

the inability to manufacture very fine holes in the

densified material by conventional machining

processes. To overcome this limitation, this project

will explore methods for the in situ fabrication of

holes during the sintering step that is a normal part

of the advanced material fabrication process.

Various techniques for incorporating fugitive poreformers will be investigated. These pore-formers

will be incorporated in the green body during the

forming process and will be removed before or

consumed during the sintering step to leave

precisely controlled pores (holes) in the densified

material. If successful, this technique will not only

allow the formation of simple holes, but also add the

potential to form holes having a variable geometry.

Approach

It has been observed in past studies of the

cermet Ni3Al-bonded TiC that the presence of metal

particles in the unsintered powder compact can leave

voids in the sintered part as a result of the metal’s

being drawn into the carbide particle array by

capillary action when the metal becomes molten.

This tendency will be exploited in the present study

to intentionally form holes in predetermined

locations. Nickel alloy wires of the appropriate size

will be located in the unfired material to form fine

holes in the sintered part.

Several ceramic materials will be investigated in

this project. Among the ceramics being considered

are alumina (Al2O3), silicon nitride (Si3N4), silicon

carbide (SiC), and zirconia (ZrO2). The approach for

forming holes will be to incorporate fugitive pore

formers in gelcast ceramic green (unsintered)

bodies. Gelcasting is a method of forming powdered

materials into complex shapes. Organic monomers

are added to an aqueous slurry of the ceramic

powder. Through initiation of a polymerization

reaction, the organic molecules and the slurry are

transformed into a solid (gelled) body. Casting the

slurry in a mold and then gelling can form a

complex-shaped part. One approach to forming

holes in the gelcast ceramic part would be to place

fibers in the mold that would be trapped in desired

locations in the gelled part. These fibers would then

be burned away during the sintering process, leaving

holes in the densified part. The fibers can be

synthetic polymers (e.g., nylon, polyethylene),

natural fibers (cotton, silk), or even graphite. The

second approach to forming holes in gelcast ceramic

parts is to locate fine metal wires within the casting

mold. As with the fibers, the metal wires would be

trapped in the gelled part. But, rather than burning

out, the wires can be withdrawn from the green body

prior to sintering. Even very fine holes in the green

part can be retained in the sintered ceramic.

Another method being considered for later study

would involve the use of coextrusion to form

complex arrays of holes on a very fine scale.

Results

Funding for this project became available

midway through the second quarter of FY 2002.

Despite the short time available to conduct research,

some interesting results have been obtained. Tests

were begun with gelcast Al2O3, and the initial results

look very promising. Figure 1 shows micrographs of

holes that were formed by embedding metal wires in

a gelcast part. The wires, 38 μm (0.0015 in.) in

diameter, were removed from the gelled part before

sintering. The resulting holes are about 30 μm in

diameter. One of the holes is shown lengthwise in

the micrograph in Figure 2. The hole was exposed

by grinding away the ceramic material. The ground

surface is not quite parallel to the axis of the hole,

and the hole actually goes below the surface at the

location indicated by arrow 1. Some damage due to

the grinding operation is seen at arrow 2. Holes

more than 15 mm long were produced using this

method.

Figure 3 shows holes that were formed in

gelcast Al2O3 by incorporating polymer fibers in the
Propulsion Materials FY 2002 Progress Report

101

(a) (b)

Figure 1. Micrographs showing holes in sintered alumina ceramic that were formed by embedding metal wires

in the gelcast ceramic green body. The wires were removed prior to sintering, and the holes were

retained in the densified ceramic. The same hole is shown at (a) low and (b) high magnification.

Figure 2. Micrograph of a hole in sintered alumina

ceramic shown lengthwise by grinding away

the ceramic surface. The ground surface is not

quite parallel to the hole axis, and the hole

actually goes below the surface at the point

indicated by arrow 1. The chipping at the edge

of the hole shown at arrow 2 is due to grinding

damage.

gelcast material. The fibers burned away during

sintering and left well-defined holes in the ceramic.

These holes are also about 30 μm in diameter and

were as long as 20 mm. Both of these methods were

effective in producing ultra-fine-diameter holes in

ceramics and demonstrate the feasibility of using

these techniques to make fuel injector nozzles

having holes smaller than 50 μm in diameter.

Figure 3. Micrograph showing holes in

sintered alumina ceramic that were

formed by incorporating polymer

fibers in the gelcast ceramic green

body. The fibers burned away

during sintering, leaving holes in the

dense ceramic.

Conclusions

Preliminary tests to produce ultra-fine holes in

Al2O3 ceramic have been very successful. Holes that

are about 30 μm in diameter and as long as 20 mm

have been produced. Additional testing will be done

using other advanced ceramic materials and the

cermet compound. Future efforts will begin to focus

on producing arrays of holes in a predetermined

pattern.

Propulsion Materials FY 2002 Progress Report

103

F. Electrochemical NOx Sensor for Monitoring Diesel Emissions

L. Peter Martin and Ai-Quoc Pham

Lawrence Livermore National Laboratory

P.O. Box 808, MS L-353

Livermore, CA 94551-0808

(925) 423-9831; fax: (925) 424-3215; e-mail: martin89@llnl.gov

DOE Technology Development Manager: Nancy Garland

(202) 586-5673, fax: (202) 586-9811; e-mail: nancy.garland@ee.doe.gov

Contractor: Lawrence Livermore National Laboratory, Livermore, California

Prime Contract No.: W-7405-Eng-48

Objectives

• Develop a compact, rapid-response electrochemical NOx sensor for compression-ignition, direct-injection

(CIDI) exhaust gas monitoring.

• Fabricate a first-generation laboratory prototype for sensitivity/selectivity testing at Ford Research Laboratory.

• Continue the investigation of materials and sensing mechanisms to optimize performance.

Approach

• Utilize an ionic (O2−) conducting ceramic as an electrolyte and mechanical support (substrate).

• Use colloidal spray deposition to apply metal oxide electrodes to the electrolyte substrate.

• Evaluate electrode materials and processing conditions for sensitivity and response time.

• Test operating modes (potentiometric and amperometric) to optimize performance.

• Demonstrate stability and cross-sensitivity with interfering gases.

Accomplishments

• Developed a potentiometric sensor with high NO2 response, negligible NO sensitivity, and fast response time at

700°C.

• Identified a current-biased mode of potentiometric operation giving the best NO sensitivity and response speed

(~27 mV at 500 ppm NO, 10% O2, 650°C, 1.5 s response).

• Selected electrode materials for the current-biased NO sensor.

Future Direction

• Investigate sensor stability and oxygen sensitivity.

• Send the first-generation laboratory prototype sensor to Ford for sensitivity/selectivity testing.

• Continue to investigate electrode materials/microstructure (FY 2002, FY 2003).

• Design and build integrated (self-heated) prototype sensor (FY 03)

• Perform fundamental investigation to identify NO sensing mechanism (FY 03)
FY 2002 Progress Report Propulsion Materials

104

Introduction

The most promising NO sensors for exhaust gas

monitoring are based on ionically conducting solid

state electrochemical devices.1,2 These devices

typically consist of a solid ceramic electrolyte onto

which two or more metal or metal-oxide electrodes

are deposited, and they can be operated in either

potentiometric or amperometric modes. Significant

progress has been made toward the development of

deployable sensors using yttria-stabilized zirconia

(YSZ) as the electrolyte and catalytically active

metal oxides as the sensing electrodes.3

 However,

improvements are still needed in sensitivity,

response time, reliability, and cross-sensitivity.

The current work is directed toward the

development of a fast, high-sensitivity

electrochemical NOx sensor. Target operating

parameters for the proposed sensor (based on

discussion with Ford collaborators) are sensitivity to

the total NOx content in the range of 1 to 1000 ppm,

operating temperature of >600°C, and response time

≤1 s. The elevated operating temperature is to ensure

compatibility with a possible conversion catalyst

that will convert the total NOx to one species,

probably NO. In addition, the sensor should be

simple and reliable, and cross-sensitivity with other

oxidizing/reducing gases should be minimized.

Finally, it should be noted that the relative merits of

NO2 versus NO selective sensors are not clear at the

present time.

Approach

The proposed approach is to develop a sensor

using catalytic metal oxide electrodes on a solid

ionic conductor electrolyte. Similar technology has

been widely investigated for various gas sensing

applications and has been successfully developed for

use as exhaust gas oxygen sensors. The current

effort approaches the problem by the application of

novel materials and fabrication processes designed

to optimize electrode microstructures. In addition, a

potentially novel mode of operation has been

identified that yields enhanced NO response

amplitude and speed.

Sensors were prepared by spray deposition of

metal oxide electrodes onto YSZ electrolyte

substrates, followed by sintering at 1000–1100°C.

NOx sensing experiments were performed in a quartz

tube inside a furnace. All tests were performed using

500 ppm NO or NO2 in 10% O2, balance N2, at a

flow rate of 1000 mL/min. The design of a typical

sensor and test apparatus are shown schematically in

Figure 1. All tests were performed in the

temperature range of 600 to 700°C.

Figure 1. Schematic of the experimental test setup

showing: (a′, a′′) wire leads, (b) YSZ

electrolyte, (c) metal oxide electrode,

(d) platinum or metal oxide electrode, (e) test

gas flow, (f) quartz tube, and (g) furnace hot

zone.

Results

Figure 2 shows the mixed potential response

from a sensor using a composite YSZ/dopedlanthanum manganate sensing electrode and a

platinum metal reference electrode. The data show a

baseline near 0 mV when the gas stream is

composed of 10% O2, balance N2, at 700°C, and a

response in excess of 40 mV when 500 ppm NO2 is

introduced. The 90% recovery (turn-off) time for

this sensor is 2.5 s, which approaches the target 1 s

(the datum points in all figures are spaced 0.5 s

apart). The sharp peaks at the beginning of each

response result from a transient overpressure when

the NO2 is introduced into the gas stream. The

sensor has negligible NO sensitivity, making it

highly selective for NO2. It was observed that

potentiometric sensors that provided reasonable

sensitivity to NO at temperatures >600°C—for

example, sensors with NiCr2O4 as the sensing

electrode—had recovery times that were much too

long (>10 s). Thus alternate modes of operation

were investigated.
Propulsion Materials FY 2002 Progress Report

105

Figure 2. Potentiometric response of a NO2 sensor,

operated at 700°C, with a composite sensing

electrode (YSZ and doped-lanthanum

manganate). The gas contains 10% O2 and

500 ppm NO2.

Since the electrochemical sensing mechanisms

for the NOx species involve oxidation/reduction

reactions, it is logical to think that one could modify

the kinetics, and perhaps speed up the response, by

appropriately biasing the sensor electrodes. Other

investigators have attempted to correlate the gas

composition with the current resulting from a fixed

potential-bias across the electrodes. In the 10% O2

environment, however, this biasing causes a high O2

pumping current that overwhelms the NOx sensing

response. To correct for this high O2 current, it is

generally necessary to pump out the oxygen from

the sample gas stream using, for example, a YSZ

pump. This requirement contributes to the

complexity of the sensor and to concerns relating to

the possible decomposition of the NOx during the

pumping operation. We have developed a related

technique in which a fixed current, rather than a

fixed potential, is applied between the sensing and

reference electrodes. The potential required to

maintain this current is then measured and correlated

to the gas composition. Figure 3 shows data from a

sensor using an NiCr2O4 sensing electrode and a

YSZ/doped-lanthanum manganate reference

electrode at 650°C. The response is +27 mV when

500 ppm NO is introduced into the gas stream, and

the 90% recovery time is 1.5 s. It is interesting to

note the positive sign of the response, which is

indicative of the reduction of NO and is consistent

with the direction of bias of the electrodes. Under

the current-biasing conditions shown in Figure 3, the

sensor has high NO2 sensitivity (~3× the NO

sensitivity).

Figure 3. Response of the current-biased sensor to

500 ppm NO in 10% O2 at 650°C. The sensor

uses an NiCr2O4 sensing electrode and a

composite reference electrode.

It is possible, by operating under different

biasing conditions, to make the sensor shown in

Figure 3 insensitive to NO2. Under those conditions,

the sign of the response becomes negative,

indicating that the sensor response comes from the

oxidation of NO to NO2. Thus, changing the biasing

can actually change the operating mechanism of the

sensor. In addition, the sensitivity nearly doubles (to

45 mV for 500 ppm NO), but the response time

becomes slower (90% recovery increases to 7 s).

Conclusions

We have developed a potentiometric NO2 sensor

with high sensitivity, selectivity, and speed at

700EC. We have developed an alternative mode of

operation for NO detection that uses a current-bias

across the electrodes. This mode of operation gives

good NO sensitivity (~27 mV at 500 ppm NO) and

response speed (1.5 s) when operated at 650°C in

10% O2. When operated under different biasing

conditions, this mode of operation gives enhanced

NO response and negligible NO2 sensitivity at the

expense of response time. To the best of our

knowledge, this mode of operation has not been

reported in the literature pertaining to

electrochemical NOx sensors. Continued

investigation is necessary to optimize the
FY 2002 Progress Report Propulsion Materials

106

performance, quantify the cross-sensitivity, and

establish the stability of the sensor.

References

1. F. Menil, V. Coillard, and C. Lucat, “Critical

Review of Nitrogen Monoxide Sensors for Exhaust

Gases of Lean-Burn Engines,” Sensors and

Actuators B, 67, pp. 1–23 (2000).

2. N. Miura, G. Lu, and N. Yamazoe, “Progress

in Mixed-Potential Type Devices Based on Solid

Electrolyte for Sensing Redox Gases,” Solid State

Ionics, 136–137, pp. 533–542 (2000).

3. T. Ono, M. Hasei, A. Kunimoto, T.

Yamamoto, and A. Noda, “Performance of the NOx

Sensor Based on Mixed Potential for Automobiles in

Exhaust Gases,” JSAE Rev., 22, pp. 49–55 (2001).

Publications/Presentations

L. P. Martin, Q. Pham, and R. S. Glass,

“Electrochemical NOx Sensor for Monitoring CIDI

Vehicle Emissions,” presented at National

Laboratory CIDI and Fuels R&D Merit Review and

Peer Evaluation, Argonne, Illinois, May 14, 2002.

L. P. Martin, Q. Pham, and R. S. Glass, “Effect

of Cr2O3 Electrode Morphology on the NO

Response of a Stabilized Zirconia Sensor,”

submitted to Sensors and Actuators B (June 2002).
107

APPENDIX A: ACRONYMS AND ABBREVIATIONS

AHE aerodynamic heat exchanger

ANL Argonne National Laboratory

ASTM American Society for Testing and Materials

CIDI compression-ignition direct-injection

CO carbon monoxide

CVI chemical vapor infiltration

DF dissipation factor

DOE U.S. Department of Energy

EDM electrodischarge machining

EDX energy-dispersive X-ray spectroscopy

E/E Electrical and Electronics

EGR exhaust gas recirculation

EN electroless nickel

EPA Environmental Protection Agency

F fluorine

FTP Federal Test Protocol

GGFD ground graphitized foam dust

GM General Motors

GTRI Georgia Tech Research Institute

HA-ADF high-angle annular dark-field

H+ hydrogen ion

H2 hydrogen gas

HDI high-density infrared

HEPA high-efficiency particulate air (filter)

IC internal combustion

ICS Industrial Ceramic Solutions

ID internal diameter

LANL Los Alamos National Laboratory

L/D length-to-diameter

MEA membrane electrode assembly

MLCC multi-layer ceramic composite

MDM mechanical properties microprobe

MW-DPF microwave-regenerated diesel particular filter

NEP National Energy Policy

NFC near-frictionless carbon

NIST National Institute for Standards and Testing

nm nanometer, 10–9 meters

NOx oxides of nitrogen
108

NSA National Security Agency

NTP nonthermal plasma

OAAT Office of Advanced Automotive Technologies

OEM original equipment manufacturer

OHVT Office of Heavy Vehicle Technologies

OM optical microscope

ORNL Oak Ridge National Laboratory

OTT Office of Transportation Technologies

PEM polymer electrolyte membrane

PEMFC polymer electrolyte membrane fuel cell

Pd palladium

PM permanent magnet

PNGV Partnership for a New Generation of Vehicles

PNNL Pacific Northwest National Laboratory

POEM porous oxide electrolyte membrane

PPS polyphenylene sulfide

Pt platinum

PVD physical vapor deposition

PVP hydroxylated polystyrene

R&D research and development

S sulfur

SAE Society of Automotive Engineers

SEM scanning electron microscope

SHE standard hydrogen electrode

SNL Sandia National Laboratories

SO3

2– sulfonate group

STEM scanning transmission electron microscope

T Tesla

TEM transmission electron microscope

TiN titanium nitride

TIVM toroidal intersecting vane machine

WC tungsten carbide

YSZ yttria-stabilized zirconium

Z characterized by a high atomic number