Maricela Lizcano

Glenn Research Center, Cleveland, Ohio

Jonathan A. Mackey

University of Akron, Akron, Ohio

Status and Evaluation of Microwave Furnace

Capabilities at NASA Glenn Research Center

NASA/TM—2014-218349

November 2014
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Maricela Lizcano

Glenn Research Center, Cleveland, Ohio

Jonathan A. Mackey

University of Akron, Akron, Ohio

Status and Evaluation of Microwave Furnace

Capabilities at NASA Glenn Research Center

NASA/TM—2014-218349

November 2014

National Aeronautics and

Space Administration

Glenn Research Center

Cleveland, Ohio 44135
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This report contains preliminary fi ndings, 

subject to revision as analysis proceeds.
Status and Evaluation of Microwave Furnace Capabilities 

at NASA Glenn Research Center 

Maricela Lizcano 

National Aeronautics and Space Administration 

Glenn Research Center 

Cleveland, Ohio 44135 

Jonathan A. Mackey 

University of Akron 

Akron, Ohio 44325 

Abstract

The microwave (MW) furnace is a HY-Tech Microwave Systems, 2 kW 2.45 GHz Single Mode 

Microwave Applicator operating in continuous wave (CW) with variable power. It is located in 

Cleveland, Ohio at NASA Glenn Research Center. Until recently, the furnace capabilities had not been 

fully realized due to unknown failure that subsequently damaged critical furnace components. Although 

the causes of the problems were unknown, an assessment of the furnace itself indicated operational failure 

may have been partially caused by power quality. This report summarizes the status of the MW furnace 

and evaluates its capabilities in materials processing. 

Status

The MW furnace and the lab in which it is housed have been fully upgraded. The MW furnace was 

upgraded with the installation of a new isolator and circulator (Gerling Applied Engineering Inc., GAE, 

Modesto, CA). The power supply and the magnetron were sent to GAE for repair and returned. 

Additionally, in the event that an arc is discharged within the length of the waveguide during operation, 

GAE installed an arc detector in the magnetron that shuts power off and prevents damage to the 

components such as the isolator, circulator, magnetron or power supply. To address potential problems 

with power quality, a new power line and electrical receptacle were installed in the lab. A doubleconversion Universal Power Supply (UPS) and power conditioner were also implemented. The MW 

power supply, the water cooler and computer are directly plugged into the conditioner and UPS. The MW 

furnace is configured to operate under a controlled atmosphere and vacuum. Since these upgrades and 

modifications have been implemented, the status of the MW furnace is operational as of May 2013 with 

no other failures noted to date. 

One additional upgrade/repair needs to be completed. The furnace pyrometer seems to be working but 

data acquisition is not possible. It is unclear whether the problem is related to software, cabling or the 

pyrometer itself. Several attempts to repair this problem have been unsuccessful. Precise monitoring of 

temperature is an important part of material processing. It is recommended that a new temperature 

monitoring system be purchased and implemented for controlled material processing experiments. Two 

systems are currently being evaluated: (1) IR pyrometer or (2) IR Camera. A supplementary report with a 

recommendation for a temperature acquisition system will be submitted at a later date. 

Evaluation of Capabilities 

The MW furnace was utilized in various experiments. The in-house MW furnace has demonstrated 

capabilities in materials alloying, melting, sintering, nanofiber growth, and conversion of organicinorganic polymer to ceramic material. The following paragraphs describe these experiments. 

NASA/TM—2014-218349 1
Alloying

The MW furnace has been demonstrated to be an effective processing tool for the alloying of 

thermoelectric powders. Thermoelectric composites consisting of a Si/Ge matrix with WSi2 nanoinclusions is desired. Direct mechanical alloying of the powders, in a planetary mill, was found to suitably 

alloy the Si/Ge matrix phase but could not react the W. A short 15 min exposure to microwave energy has 

been found to react the elemental W into the desired WSi2 phase. Figure 1 shows the XRD of the starting 

powder as obtained from mechanical alloying (black curve). The starting powder consists of an alloyed 

Si/Ge phase with an unreacted W phase. After 5 min at 500 W (orange curve) some of the W is reacted 

into a WSi2 phase. Exposure to 700 W for 15 min (green curve) consumes the entire W content to form 

the desired WSi2 phase. The final product of the experiment was a powder suitable for hot pressing or 

sintering by other means. The broad XRD reflections in the starting powder indicate nano-sized 

crystallites, while the sharp peaks after the MW heat treatment indicate crystallite growth. 

Melting and Sintering 

Systems with low processing temperatures such as Bi or Sb based skutterudite thermoelectrics can be 

easily sintered or melted with the MW system. Samples composed predominantly of Bi, melting point 

270 °C, were melted, and solidified in quartz (SiO2) crucibles within the MW cavity. The Bi based 

samples are found to directly couple with the microwave energy, these samples do not require a susceptor. 

The ingots release from the SiO2 crucibles and were easily machined into a number of samples required 

for thermoelectric characterization, Figure 2. 

Figure 1.—Demonstration of microwave alloying of powders. 

Figure 2.—Ni-Bi-Ge thermoelectrics prepared with microwave sintering. 

NASA/TM—2014-218349 2
Sintering of higher temperature materials like Si/Ge (melting range 937 to 1413 °C) has been 

attempted. The samples are found to directly couple with the MW radiation, and can reach stable 

temperatures in excess of 900 °C. At this time, the samples have not been successfully sintered to a 

suitable density. Instead local heating leads to melting identified as the spherical solidified phase in 

Figure 3. The local melting of the samples occurs before the bulk has the opportunity to sinter. Further 

experimental work needs to be conducted to prevent local heating and promote homogenous heating. 

A preliminary experiment was conducted to determine feasibility of an alternate sintering route for 

Aeronautical Sciences (AS) advanced SiC fiber development. A 1 1/2 in. tow was cut from a Sylramic 

spool and placed inside a small graphite tube. The sample was then placed vertically inside the furnace. A 

quartz tube was placed over the entire sample to control processing atmosphere. The Sylramic tow was 

irradiated for 20 min. Figure 4 shows an SEM image of (a) and (b) Sylramic (as received) fiber (c) and (d) 

Sylramic fiber that has been MW irradiated. Reduced porosity in the center of the fiber is noted for the 

fibers exposed to MW irradiation. In particularly, a reduction in pores d 50 nm can be observed (when 

comparing image (b) and (d). Additionally, a more uniform microstructure is observed which may 

provide an avenue to reduce core/shell effect often seen in in-house sintered SiC fibers. 

Figure 3.—Left: view of Si/Ge sample sintering in microwave. Right: final Si/Ge sintered sample, 

local heating leads to non-uniform melting of the sample. 

Figure 4.—SEM images of Sylramic fiber (a) and (b) as received and 

MW treated Sylramic fiber image (c) and (d).

NASA/TM—2014-218349 3
Nanofiber Fabrication 

Rapid growth of boron nitride (BN) nanofibers has been demonstrated with the MW furnace (Fig. 5). 

The BN nanofibers were grown from a BN stage in less than 1/2 hr. The morphology of the final BN 

consists of 1 μm diameter bundles of 100 nm fibers. Figure 4 shows the BN nanofibers at three 

magnification levels.

Polymer Derived Ceramics (PDC) 

The MW furnace was used to convert an organic-inorganic polymer material into ceramic SiC 

nanofibers demonstrating this capability. The spun pre-ceramic nanofibers were made from a polymer 

blend. The fibers were placed between two susceptor plates inside the MW chamber. The power was 

ramped up at 100 W intervals every 3 min, with an additional 3 min dwell time at 600 W. Temperatures 

of ~1140 °C were observed during the dwell time. The XRD result is shown in Figure 6. The peaks 

indicate conversion of precursor nanofibers to E-SiC nanofibers with 2T = 35.62°, 41.42°, 59.95° and 

71.74° ascribed to lattice planes (111), (200), (220), and (311), respectively. Figure 7 shows SEM images 

of (a) preceramic nanofibers, and (b) and (c) the MW converted ceramic SiC fibers. The uniform 

microstructure in the images demonstrates the advantage of MW irradiation as a rapid processing avenue 

for PDCs.

Figure 5.—Demonstration of BN nanofibers rapidly grown in a microwave cavity. Final BN product consists of 1 μm 

diameter bundles of 100 nm fibers. 

Figure 6.—XRD of precursor nanofibers and MW energy converted nanofibers. 

NASA/TM—2014-218349 4
Figure 7.—SEM images of (a) preceramic nanofibers, (b) and (c) MW ceramic converted SiC nanofibers. 

Summary

The 2.45 GHz single-mode microwave furnace located at NASA Glenn Research Center has been 

upgraded and is operational. The furnace is fitted with a quartz tube and vacuum for environmental 

control during operation. Variable power output is in the range of 100 W to 2 kW. The unit has 

demonstrated capabilities in materials processing such as alloying, melting, sintering, nanofiber 

fabrication and ceramic conversion of polymeric materials. 

NASA/TM—2014-218349 5

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APPENDIX 1

1

National Aeronautics and Space Administration

www.nasa.gov

A Preliminary Study in The Use of

Microwave Energy To Produce

Microstructure Uniformity in SiC Tows,

Maricela Lizcano, PhD

NASA Glenn Research Center

04/24/2014

NASA/TM—2014-218349 7
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Objective and Task

Introduction: Microwave sintering offers an advantage over

conventional heating due to rapid molecular heating as

opposed toconvection and conduction heating using an

electric furnace. This translates to reduced heating

temperatures as well as reduced heating times and a cost

saving route for SiC towprocessing.It is expected that uniform

heating will produce uniform microstructures.

Objective: Determine feasibility of alternate sintering route for

UHT SiC fiber development.

Task: Use microwave energy to irradiate SiC (sintered) tow and

determine effects on microstructure using SEM.

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Experimental

A 2.45 GHz microwave furnace was used during this

experiment to determinethe feasibility of using microwave

energy for rapid sintering of SiC fiber.

A 1 1/2 in. tow was cut from a Sylramic spool and placed

inside a small graphite tube. The sample was then placed

vertically inside the furnace. A quartz tube was placed over

the entire sample to control processingatmosphere. The

sample was irradiated for 20 min.

Processing Time: Start to finish, < 1 hr.

NASA/TM—2014-218349 8
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Preliminary Results

Sylramic (Off Spool)

Microwave Irradiated (MW)

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A Closer Look

MW

Exposure to MW energy resulted in a more uniformmicrostructure with

reduced porosity.

Image 1 Sylramic off Spool Image 2 MW treated fiber

NASA/TM—2014-218349 9
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A Closer Look

MW

Two pore shapes and sizes are noted. Rounded pores (~100 nm )

and much smaller irregularly shaped pores (ч50 nm ). Both pore

types seem to diminish throughout the cross section of the

sample under MW irradiation.

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Conclusions

8

• Microwave irradiation of a Sylramic tow shows

promising results as a heat treatment method

to reduce porosity and produce uniform

microstructure in SiC tows.

• Further analysis of pore size and pore size

distribution is necessary to confirm

observations. New porometer is available onsite, however, a location for the instrument has

not been determined.

NASA/TM—2014-218349 10
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Future Work

9

• Grain size evaluation

• Processing temperature data acquisition upgrade

• Strength Testing

• Problem: current MW furnace restricts tow

length that can be irradiated and then tested.

• Solution: design a tow feed-through with step

motor.

• Lox M sintering experiments.

NASA/TM—2014-218349 11