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Propulsion Materials FY 2000 Progress Report

19

C. Mechanical Reliability of Electronic Ceramics and Electronic Ceramic

Devices

M. K. Ferber and A. A. Wereszczak

Mechanical Characterization and Analysis Group

Oak Ridge National Laboratory, P.O. Box 2008, MS 6069, Bldg. 4515

Oak Ridge, TN 37831-6069

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

DOE Program Manager: Patrick Davis (202) 586-8061; fax: (202) 586-9811; e-mail:

patrick.davis@hq.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

• Develop testing algorithms that can be used to assess electronic ceramic (EC) and electronic ceramic device

(ECD) mechanical reliability.

• Mechanically characterize EC and ECD alternatives that are less expensive and that can be used to promote

device miniaturization.

OAAT R&D Plan: Section 3.5: Task 4; Barriers A, D

Approach

• Utilize micromechanical testing and ceramic-specific-characterization testing facilities to measure in-situ

mechanical properties of ECs in the ECDs.

• Characterize presently used and developmental EC and ECDs supplied from their manufacturers or their endusers.

• Use existing ceramic component prediction codes (whose development was funded by the Office of Transportation Technologies for structural ceramics) and their statistical analysis capabilities in the mechanical strength

and fatigue analyses of ECs and ECDs.

• Provide results and insights back to manufacturers that will result in the improved reliability of ECs and ECDs.

Accomplishments

• Measured the thermal expansion and thermal conductivity as a function of temperature (–50 to 200°C) for

monolithic BaTiO3 and a variety of multilayer capacitors (MLCs). These data will be used to model and predict

thermal shock susceptibility.

• Completed the mechanical testing of three aluminas during FY 2000; the data will be used by Motorola to

design a more thermal-shock-resistant exhaust gas sensor.

• Fabricated special fixturing that will be used in concert with Raman spectroscopy to non-destructively measure

the in-situ residual stresses of MLCs.

• Extended the mechanical testing algorithms, which were developed to characterize the mechanical robustness

and reliability of small capacitors, to larger dc-buss capacitors.
FY 2000 Progress Report Propulsion Materials

20

Future Direction

• Develop the Raman spectroscopy technique to measure residual stresses as a function of position in MLCs.

• Develop quantifiable thermal shock methodology for MLCs to establish guidelines concerning soldering conditions and maximum allowable temperature excursions.

• Develop micromechanical tests to directly assess the strength of MLCs.

Introduction

A lack of mechanical reliability of ECs in ECDs

will limit the life of their electronic functioning. The

primary effort in FY 2000 involved the thermal

property characterization of BaTiO3 ECs in power

electronic capacitor ECDs. Work was completed as

well in FY 2000 on oxide ECs for automotive

exhaust gas sensor ECDs. The service life of both

these ECDs can be limited by their mechanical

reliability, so it is essential that that limitation be

understandable and predictable.

Ceramic MLCs for Automotive Power

Electronics

Manufacturers must exercise caution during

their fabrication of MLCs because these ECDs are

relatively large (Figure 1), and experience has

taught manufacturers that MLCs can be susceptible

to thermal failure if thermal gradients become sufficiently high. Likewise, end-users of these ECDs

must minimize the possibility of thermal excursions

to avoid producing failures induced by thermal

shock. A goal of this project is to help MLC manufacturers quantify thermal properties so that they

and their customers may quantitatively predict

allowable thermal excursions that do not produce

thermal fracture.

To understand and predict thermal shock susceptibility, three property sets must be known as a

function of temperature: thermal expansion, thermal

conductivity, and mechanical strength. Thermal

expansion and thermal conductivity were measured

between –50 and 200°C (a temperature range of

interest to the automotive industry). Their dependencies on temperature are shown in Figures 2 and 3.

In both graphs, the thermal expansion and conductivity of monolithic BaTi03 are compared with

apparent values of some capacitors shown in

Figure 1. Thermal expansion of the SM02 MLC

(the largest capacitor shown in Figure 1) and that of

BaTi03 are arguably equivalent. The thermal

Figure 1. Example of multilayer capacitors of various sizes.
	

 





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Propulsion Materials FY 2000 Progress Report

23

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

Tom M. Mulcahy and John R. Hull

Energy Technology Division, Argonne National Laboratory, Bldg. 335

Argonne, IL 60439

(630) 252-61451; fax: (630) 252-5568; e-mail: mulcahy@anl.gov

DOE Program Manager: Patrick Davis (202) 586-8061; fax: (202) 586-9811; e-mail:

patrick.davis@hq.doe.gov

ORNL Technical Advisor: David Stinton (865) 574-4556; fax: (865) 574-6918; 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 NdFeB permanent magnets with up to 25% higher strengths. The

higher-strength magnets will replace ones made by traditional powder metallurgy and enable significant size and

weight reductions in traction motors for hybrid vehicles.

• Use high-strength superconducting magnets to improve the magnetic alignment of grains prior to pressing and

sintering, therefore producing higher-strength permanent magnets.

OAAT R&D Plan: Section 3.5: Task 3; Barriers B, C, D

Approach

• Develop facilities to align magnetic domains of NdFeB powders within a high-strength magnetic field, created

by a superconducting solenoid, during forming operations.

• Collaborate with ORNL to 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 insertion of loose and compacted magnet powder into and out of the steady

field of a superconducting solenoid.

Accomplishments

• Established facilities at Argonne National Laboratory to handle pyrophoric NdFeB powder during its processing

into green compacts, which the industrial partners will sinter into permanent magnets.

• For the first time, made axial-die-pressed permanent magnets that used a superconducting solenoid [9-Tesla (T)]

for magnetic alignment of the powder.

• Characterized magnetic properties of the first permanent magnets made in the Axial-Die Press Facility and those

provided by the industrial partners.

Future Direction

• Report on the optimization of the fabrication processing and powders using axial-die pressing in batch mode

operation.
FY 2000 Progress Report Propulsion Materials

24

• Design, fabricate, and operate a reciprocating press in a continuous mode to demonstrate the feasibility of competitive factory operation.

• Optimize fabrication processing and powders from different industrial partners, using transverse-die pressing

and a reciprocating press.

• Provide design rules for the fabrication of permanent magnets, including knowledge for scale-up to larger magnets at commercial rates of production.

Introduction

For the first time, a superconducting solenoid

(9 T) was used as part of an axial-die press to compact permanent magnets. (Argonne’s new facility is

shown in Figure 1.) The solenoid aligns the magnetic domains of NdFeB powder during pressing

into green compacts for sintering into permanent

magnets by industrial partners. Industrial electromagnets are limited to 2 T.

The installation required shielding of sensitive

equipment in an adjacent laboratory from stray

magnetic fields. Two layers of shielding that now

cover the wall between the laboratories are shown in

Figure 2.

Magnetic code analysis was helpful in the

design of the wall shielding to reduce the level to

~10 Gauss. But to shield below the 5-Gauss

threshold sensitivity levels of computer monitors

would have been difficult. Shielding enclosures

were purchased for two computer monitors.

Figure 1. The Axial-Die Press Facility. Press tube is

remotely moved along a track into the horizontal bore of the 9-T superconducting solenoid.

Figure 2. Wall shielding. Press tube fully inserted in

bore of superconducting solenoid.

Results

The innovative press-in-tube device for axial-die

pressing magnet compacts in a batch mode was

made operational by pressing 25 pure-iron powder

compacts. Bronson and Bratton, Inc.’s 5/8-in.-

diameter axial-die and punch set, which is similar to

the 3/8-in.-diameter set shown in Figure 3, was

used. The die/punch set is shown being hand-loaded

Figure 3. One punch removed from 3/8-in.

diameter die/punch set.
Propulsion Materials FY 2000 Progress Report

25

Figure 4. Die/punch insertion (right) into press tube,

rotated into loading position. Hydraulic cylinder on left end of press tube.

into the press tube in Figure 4, and the press tube is

shown in Figures 1 and 2 being moved into the

solenoid along the motorized track of the press

insertion mechanism. A local manufacturer of diepressed parts provided the 25-micron-size pure-iron

powder, whose grains had no preferred magnetic

orientation and were coated with a pressing lubricant. Following procedures developed for processing NdFeB magnet powder, no difficulties were

encountered in fabricating compacts over the entire

range of expected press and extraction pressures.

Pressing operations included extraction of the iron

compacts from the superconducting solenoid operating at 8 T, an operation necessary for simulation

of compact pressing during automated production

using reciprocating feeds. Large extraction forces

(up to 750 lb) can occur between the solenoid and

compacts.

UGIMAG routinely ships its hazardous NdFeB

magnet powder in vacuum-sealed metal pouches.

However, requirements for storing the powder at

Argonne and shipping the compacts back to

UGIMAG for sintering had to be established, using

Argonne specialists in waste management and

transportation. Material handling of the powder is of

critical importance because it can oxidize readily.

Oxidation not only is hazardous, but also reduces

the percentage of hard magnetic material in the

compact and therefore the strength of the sintered

magnet. In factory operation, the powder is made

into compacts and sintered within two days, all the

while being handled in an argon atmosphere.

Since Argonne operations with a batch of powder would extend over weeks, additional handling

procedures were identified and implemented in

consultation with UGIMAG. Also, press operation

in the superconducting solenoid could take tens of

minutes, instead of an instant, because of the slow

ramp times of the superconducting solenoid’s

magnetic field. A powder-handling facility to load

and eject the compact from the die/punch set with

the pyrophoric NdFeB powder was established

using a glove box built to fabricate fuel elements for

breeder reactors. (See Figures 5 and 6.) During

compaction, the press tube is maintained under an

argon atmosphere.

Originally, the glovebox was intended for use at

oxygen levels of less than 10,000 ppm and with a

Figure 5. Glovebox to store and load magnet powder in

die, then eject compact.

Figure 6. Glovebox powder weighing and die filling.

Vacuum storage desiccators in rear.
FY 2000 Progress Report Propulsion Materials

26

nitrogen cover gas. It was overhauled and improved

with a new oxygen sensor that extends measurement

capability to 1 ppm. Now the glovebox operates at

350–600 ppm during powder handling operation. To

avoid an oxidation buildup over time, the magnet

powder and compacts are stored in the vacuum

(~30 in. mercury) containers (dry-seal desiccators;

Figure 6) during processing and before sintering.

Although no problems were encountered in

pressing the pure iron powder, many unexpected

hurdles had to be overcome in pressing the smaller

5–10 μm powder into green compacts. Magnetically

anisotropic powder was found to be difficult to

process because the grains tend to form in chains.

The negative magnetic pole of one grain is attracted

to the positive pole of another grain. The magnetic

bonding between grains inhibits pouring and creates

bridging during filling operations, which results in

voiding that is difficult to remove prior to pressing.

Exacerbating the bridging phenomenon are lubricants added to the powder to facilitate rotation of

the grains (easy magnetic axes) into alignment with

the orienting magnetic field that is applied during

pressing. If gas is trapped in voids as the powder is

pressed into a compact, elevated gas pressures may

cause internal cracking and promote end capping.

End capping begins at the die wall under the

punch when pressure on the punch is reduced to

zero, usually as part of the compact ejection process.

Friction between the die wall and the compact,

developed during pressing, may exceed the forces of

elastic rebound during punch unloading and initiate

a crack that causes a thin lens of the compact to

delaminate under the punch. End capping is not an

uncommon problem in the industry, but it is not one

of which Argonne was made aware of during the

design of the press-in-tube device. The industrial

solution of maintaining some pressure on the

punches as the compact is ejected from the die

cannot be accomplished with the current press

design. Control of the other processing parameters

was investigated to eliminate compact cracking.

A study was made to identify useable ranges of

more than 12 processing parameters. The compaction pressure, rate of loading and unloading, load

hold time, and amount of die lubricant were found

to be the most sensitive parameters for the control of

cracking. The rate of loading was greatly reduced

and load times increased by installation of velocity

control and shut-off valves in the hydraulic circuit

of the press. Success was achieved when the thickness of the die and punch lubrication (1% stearic

acid in IPA) was reduced to nearly zero by careful

buffing. All these modifications can be interpreted

as improving the venting of air during compaction.

Higher magnetic alignment fields may improve

the integrity of the compact, but the study results are

hard to interpret because the hold time of the load

increased, as well. Ramping up and down of the

superconducting magnet to 8 T took 90 min, and the

load was held during ramping down. Lower field

strength took proportionally shorter ramping-down

times.

Whole compacts can now be made in any

diameter-to-length ratio. However, all of the first 65

compacts made had some end capping and hairline

cracking. Fortunately, 38 were long enough for

UGIMAG to sinter, slice, and determine their standard B-H curves and magnetic properties. Seven

compacts were sintered for each of five different

strength alignment fields: 0, 2, 4, 6, 8 T. Table 1

shows selected measurement results for ten of the

compacts.

Table 1. Magnetic measurements of PMs

Sample H(T) Br(kG) MGOe g/cm3

2-4/25 0 7.24 10.72 7.583

1-5/2 0 7.28 10.82 7.582

2-5/2 0 7.32 10.95 7.593

3-5/12 2 11.47 29.94 7.558

4-5/12 2 11.19 28.15 7.561

5-5/12 2 11.76 31.58 7.553

1-5/15 4 11.86 32.14 7.580

2-5/15 4 12.25 34.73 7.587

1-6/5 8 12.15 33.91 7.557

1-6/6 8 12.67 37.19 7.583

Conclusions

For the first time, a facility has been established

for pressing permanent magnets in the high fields

(9 T) of a superconducting solenoid. The energy

product (MGOe) and remnant field Br(kG) showed

a strong dependence on the magnitude of the alignment field H(T). Improvements in permanent magnet strength of 25% were found by increasing the

alignment field to 8 T from the 2 T typically used in

industry. The 8-T magnet strengths are comparable

to those obtained in industry. The density (g/cm3

) of
Propulsion Materials FY 2000 Progress Report

27

the sintered magnets is typical of those produced in

the factory and is an indication that oxidation during

Argonne’s longer processing times is not a problem.

Now that compacts can be made in shorter lengths,

whose shape effect creates large distortions in alignment at current industrial fields (2 T), improvements

of alignment in the higher fields of the superconducting solenoid will be evaluated next.
FY 2000 Progress Report Propulsion Materials

28
	

 







	



	
	

	
		


		
	
	



	





	

 

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FY 2000 Progress Report Propulsion Materials

56

Figure 5. Photograph of radiator constructed which dissipates 7 kW of heat. Note that the

foam is epoxied to the aluminum tubes, rather than brazed or press-fit.

pressure drop, but the heat transfer coefficients were

reduced to about one sixth of the original value.

The data presented here illustrate that high-conductivity carbon foam has great promise for use in

fuel-cell radiators; however, much work remains to be

done. It appears that the foam will provide the greatest

benefit when it is used in innovative designs and not

used simply as a replacement for existing thermal

management materials. The technique used to join or

bond the foam to other materials has been proved to

have a dramatic effect on heat transfer.

References

1. J. Klett, R. Hardy, E. Romine, C. Walls, and

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, South Carolina, 1999.

FY 2000 Publications

J. W. Klett, C.-C. Tee, D. P. Stinton, and N. A.

Yu, “Heat Exchangers Based on High Thermal

Conductivity Graphite Foam, ” in Proceedings of the

1st World Conference on Carbon, July 9–13, Berlin,

Germany, 2000.

J. Klett, A. McMillan, and R. Ott, “Heat

Exchangers for Heavy Vehicles,” in Proceedings of the

Society of Automotive Engineering Government/

Industry Meeting, June 19–21, Washington, D.C.,

2000.

J. Klett, L. Klett, T. Burchell, and C. Walls,

“Graphitic Foam Thermal Management Materials for

Electronic Packaging,” in Proceedings of the Society

of Automotive Engineering Future Car Congress,

Crystal City, Washington, D.C., April 2–6, 2000.

J. Klett and B. Conway, “Thermal Management

Solutions Utilizing High Thermal Conductivity Graphite

Foams,” in Proceedings of the 45th International

SAMPE Symposium and Exhibition, Long Beach,

California, May 21–25, 2000.

J. Klett, R. Hardy, E. Romine, C. Walls, and

T. Burchell, “High-Thermal-Conductivity, MesophasePitch-Derived Carbon Foams: Effect of Precursor on

Structure and Properties,” Carbon, 32(8) (2000).
	

 





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FY 2000 Progress Report Propulsion Materials

70

• Delivered nitrided Nb-30Ti-20W wt % (Tribocor) and Ni-10Ti-2.5W-0.15Zr wt % coupons to Los Alamos for

corrosion testing.

• Evaluated nitrided Nb-30Ti-20W wt % in the Los Alamos Corrosion Test Cell. It exhibited a 5-hour stabilized

corrosion current of 6.1 × 10–7 A/cm2

 at the air electrode potential of 0.98V vs NHE (data of Kirk Weisbrod).

This value meets current DOE corrosion goals. The nitrided Ni-10Ti-2.5W-0.15Zr wt % showed evidence of

local surface defects after a 5-hour potential hold that resulted in a transition to unacceptably high corrosion

rates.

• Down-selected the inward-growing nitrogen gradient zone protection mode (modeled by nitrided Nb-30Ti20W wt %) over the discrete TiN scale protection mode (modeled by nitrided Ni-10Ti-2.5W-0.15Zr wt %).

• Obtained preliminary findings that suggest that adding zirconium to titanium promotes the formation of a

corrosion-resistant inward-growing nitrogen zone. An optimized nitrided Ti-based alloy has the potential to

meet DOE performance/cost goals.

Future Direction

• Optimize composition and nitridation conditions for inward-growing nitrogen gradient zone Ti-Zr–based alloys

and evaluate their electrical conductivity and corrosion resistance (deliver coupons to Los Alamos and Plug

Power for evaluation). Include examination of alloying additions, such as V, that improve the cold-formability

of titanium. Evaluate alloying additions to promote an inward-growing nitrogen gradient zone in Fe-Ti and

Fe(Ni)-Ti alloys (much less expensive than Ti-based alloys).

• Obtain industrial input/collaboration with regard to alloy formability and cost to assist in down-selection of the

final alloy base.

• Evaluate the performance of optimized 1-in.-diameter nitrided bipolar plate in a single-cell PEM fuel cell test

rig at Los Alamos. Initiate scale-up to 4 in.× 4 in. plates and deliver them to industry for in-cell evaluation and

feedback.

Introduction and Approach

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 that currently are used, and the potential for 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 PEM. Metal

nitrides, carbides, and borides (e.g., TiN, NbC) offer

electrical conductivities of up to an order of magnitude greater than graphite and are highly corrosion

resistant. Unfortunately, conventional coating methods leave “pin-hole” defects in the nitride (carbide,

etc.) layers that result in accelerated local corrosion

and unacceptable performance.

The goal of this effort is to develop a titaniumcontaining bipolar plate alloy that will form an electrically conductive and corrosion-resistant TiN surface layer during thermal nitriding. There are three

advantages to this approach. First, because the

nitriding is performed at elevated temperature, 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 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.

Two protection schemes were identified: (1) a

discrete TiN surface layer and (2) an inward-growing nitrogen gradient zone. The discrete TiN surface

layer approach is highly amenable to the formation

of a corrosion-resistant TiN composition, but it can

be sensitive to the presence of surface defects (e.g.,

porosity, inclusions), edges, and corners. An

inward-growing nitrogen gradient zone is formed on
Propulsion Materials FY 2000 Progress Report

71

metals and alloys with a high nitrogen permeability

and, because of the inward nature of the growth

front, is not sensitive to surface defects, edges, or

corners. However, it can be difficult to form a

dense, continuous TiN surface layer to impart the

desired degree of corrosion resistance.

Results and Conclusions

Selected for study were a series of Ni, Ni(Fe),

and Ni(Cu)-Ti-based alloys with the potential to

form a discrete TiN surface layer, and Nb-30Ti20W wt %, which forms an inward-growing nitrogen gradient zone. Nickel was selected as an alloy

base because it does not form a stable nitride, has a

low nitrogen permeability, is reasonably low in cost

(≈$3 to 4/lb raw material cost) and is highly formable. Titanium is added because it is a strong nitride

former and is also reasonably low in cost (≈$3–4/lb

raw material cost). The Nb-30Ti-20W alloy, commercially known as Tribocor, was designed to form

a corrosion- and wear-resistant nitrogen gradient

zone during thermal nitriding. It is too costly for

transportation-related PEM fuel cell applications,

but it was selected as a model inward-nitrogen gradient zone-forming alloy.

The alloys were nitrided in N2-4H2 at 1000–

1100°C for 24–48 hours. To screen for corrosion

resistance and the presence of defects in the

protective layer, nitrided coupons were immersed in

5% HF for 24 hours. Post-exposure weight change

measurements and cross-section scanning electron

microscopy and EPMA were used to gage the protectiveness of the nitrided surface and to provide

feedback for modification and initial optimization of

alloy composition. Based on these studies, 1-in.-

square coupons of nitrided Ni-10Ti-2.5W-0.15Zr

wt % (Figure 1) and Nb-30Ti-20W wt % (Figure 2)

were sent to Los Alamos for evaluation of corrosion

resistance in simulated PEM fuel cell environments.

The nitrogen concentration for both alloys in the

near surface region was in the range 46–48 at. %,

which is in the range reported for TiN (Figures 1

and 2). The Ti-nitride formed on the Ni-Ti–based

alloy was present as a discrete, continuous layer on

the order of 5 μm thick (Figure 1). In contrast, the

nitrogen gradient zone formed on the Nb-30Ti-20W

alloy extended tens of microns into the depth of the

alloy (Figure 2). The bulk electrical conductivity of

Ti-20.5N-0.8Ni-0.3Zr wt.%

Ni-5.5Ti-3.3W-0.8N wt.%

Ni-10Ti-3W-0.15Zr-0.8N

TiN (48 at.% N)

Alloy

10 μm

Figure 1. SEM cross-section micrograph of Ni-10Ti2.5W-0.15Zr wt % nitrided for 48 h at

1100°C in N2-4H2.

decreasing nitrogen

Ti-47Nb-16W-14N wt.% (46 at.% N)

10 μm

TiN

 precipitate Alloy Matrix

Figure 2. SEM cross-section micrograph of Nb-30Ti20W wt % nitrided for 48 h at 1100°C in

N2-4H2.

nitrided Ni-10Ti-2.5W-0.15Zr was 1.47 ×

104 Ω1

 cm

–1, which exceeds the DOE goal by two

orders of magnitude (measured at room temperature

by dc 4-point probe). This value is consistent with

the bulk electrical conductivity of TiN, and similar

excellent electrical conductivities are expected for

all nitrided alloys examined under this program.

Nitrided Ni-10Ti-2.5W-0.15Zr wt % initially

exhibited a low corrosion current in a simulated

PEM fuel cell environment of 0.001 N H2SO4

(2 ppm Fl, 80°C, deaerated with N2) (Figure 3, data

of Kirk Weisbrod). However, after a 5-hour hold at

the anode and cathode potentials, the corrosion
	


 





















	

	

	

	


	




		

	 	 	 	 	 	







 



		 







		 




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