t.G

do p Ee 4 trr toa

rash 't 0 ANL -84-9o Y es" ___

Distribution Category:Energy Conversion

(UC-93)

DE84 014347

ARGONNE NATIONAL LABORATORY9700 South Cass Avenue

Argonne, Illinois 60439

ADVANCED FUEL CELL DEVELOPMENT

Progress Report forJuly-September 1983

Chemical Technology Division

DISCLAIMER

This report was prepared as an account of work psordby a gnyo h ntdSaeGovernment. Neither the United States Government nor any agency of the United Statesemployees, makes any warranty, express or implied, or asu agency thereof, nor any of theirbility for the accuracy, completeness, or usefulne, of anymes any legal liability or responsi-process disclosed, or represents that its use would not infringe ration edprts R eference herein to any specific commercial product o nr( privately owned rights . rutr-ence~~~~~~~

heent n pcfccm eca rdc, process, or service by trade name, trademark,manufacturer, or otherwise does not necessarily constitute or imply tsadnorsme recoikmendation, or favoring by the United States Government or imply its endorsement, recom-and opinions of authors expressed herein do not necessary any agency thereof. The viewsUnited States Government or any agency thereof.

June 1984

ANL---84-9

LIST OF CONTRIBUTORS

The following is a list of contributors to this report. Included areChemical Technology Division personnel, as well as contributors with otheraffiliations as indicated.

T. D. Claar (Materials Science and Technology Division)T. Fannon (Student researcher, Tennessee Technological University,

Cookeville, TN)R. J. Fousek (Materials Science and Technology Division)T. D. KaunN. Q. MinhJ. R. MoreschiF. C. MrazekJ. J. Picciolo (Materials Science and Technology Division)R. D. PierceD. Pickrell (Undergraduate research participant, Ohio State University,

Columbus, OH)R. B. Poeppel (Materials Science and Technology Division)V. L. Richards (Asst. Professor, Illinois Institute of Technology,

Chicago, IL)J. L. SmithJ R. StapayE. H. Van DeventerS. A. Zwick

ii

TABLE OF CONTENTS

ABSTRACT . . . . . . . . . . . . . . . . . . . . . . .

SUMMARY . . . . . . . . . . . . . . . . .

I. INTRODUCTION . . . . . . . . . . .

II. CATHODE DEVELOPMENT . . . . . . . .

A. Alternative Cathode Materials

1. LiFeO 2 . . . . . *.**.*. .2. Li2 MnO3 * . . .. . . .3. ZnO . . . . . . . . . . . .4. Li2TiO3 . .* . . . . . . . . ..

B. Cathode Material Stability . .

C. Cathode Material Solubility . .

1. Cyclic Voltammetry .2. Pot-Type Studies

D. Cathode Material Migration . .

III. ANODE DEVELOPMENT . . . . . . . . .

A. Fabrication Development . . .

B. Anode Superstructure Creep Test

IV. COMPONENT FABRICATION DEVELOPMENT . . . . . . 0.. . . . . . .A. Cathode Structures . . . . . . . . .

B. Electrolyte Matrix . . . . . . . . . . .

V. SYSTEM CODE DEVELOPMENT . . . . . . . . . . .

A. New Thermodynamic Data Files . . . .

B. Comparison with NASA Program Calculations

C. System Updates . . . . . . . . . . .

D. Boudouard Tests . . . . . . . . . . .

REFERENCES

iii

Page

1

. .0 .0 .0 .0 .0 .0 .0 .0

. . . . . . . 41

. . . . .

. . . . ."

. .a ." ." ."

1

4

5

5

588

12

12

14

1419

23

24

24

25

28

28

33

38

39

40

40

40

.w

"

*"

."

"

a

."

*f

."

."

"

"

."

."

r

."

"

a

."

"

.

"

."

"

"

."

."

"

*r

."

."

"

*r

."

*"

e

."

*"

."

."

."

"

*"

."

"

.r

."

."

"

*"

."

"

."

.a

."

"

."

"

."

. ." ." ." .s ." ." ." ." ." ." . ." ."

. ." ." ." ." ." ." ." ." ." ." ." ." ."

. .r ." ." ." ." ." ." .r ." ." ." .r ."

. . . . . . . . .

. . . . . . . . .

. . . , . . . . .

."

."

."

."

.

."

."

."

."

."

."

."

."

.r

."

."

."

."

."

."

."

."

."

."

."

.s

. . ." ." ." ." ." s ." ." ." ." ." ." ." ." ." . ." ." .s ."

LIST OF FIGU!AES

No. Title

1. Resistivity of Manganese-Doped LiFeO2 Prepared underDifferent Conditions . . . . . . . . . . . . . . . . . . . .

2. Resistivity Measurements on Manganese-Doped LiFeO2 . . .*. . .

3. Photomicrograph of Two Phases in Manganese-Doped LiFeO2 .*.

4. Resistivity of Chromium-Doped ZnO . . . . . . . . . . . . .

5. Resistivity of Gallium-Doped ZnO . . . . . . . . . . .

6. Resistivity of Zirconium-Doped ZnO before and afterLithium Addition . . . . . . . . . . . . . . . . . . . . . .

7. Cyclic Voltammograms in Carbonate Melt IllustratingLiFeO2 Solubility Current Peaks . . . . . . . . . . . . . .

8. Calibration Curve of Reported Iron Concentrations andCurrent Values Found by Cyclic Voltammetry . . . . . .

9. Solubility of LiFeO2 Cathode in 62 mol % Li2CO3-K2C03Carbonate Melt as a Function of Temperature in thePresence of a 2/3 C0 2-1/3 02 Gas Atmosphere Using PhysicalData Analysis . . . . . . . . . . . . . . . . . . . . . . .

10. Comparison of Solubilities by Cyclic Voltammetry under Dryand Humid Conditions Using Experimental Calibration Factor

11. Cyclic Voltammogram Illustrating a Detectable Anodic Peak atabout -0.7 V due to Li2MnO3 Addition to the Carbonate Melt

12. Solubility of Li2MnO3 in 62 mol. % Li2CO3-K2CO3 in a1/3 02-2/3 CO2 Atmosphere . . . . . . . . . . . . . . . . .

13. The Influence of Acid Concentration Used in Preparing the

Carbonate Samples for Analysis on the Results . . . . . . .

14. Arrangement of Pot-Type Solubility Apparatus . . . . . . . .

15. Photomicrograph of Anode Composite Cross Section: BipolarPlate Brazed to Foam Metal, Which Has Nickel AnodeEmbedded in It . . . . . . . . . . . . . . . . . . . . . .

16. Change in Thickness of Ni-Cr Retimet as a Function of Time

17. Thickness of Ni-Cr Retimet vs. Heating Time . . . . . .

18. Percent Deformation vs. Pressure . . . . . . . . . . . .

Page

6

* * 7

7

9

. . 10

. . 11

. 15

. . 15

. . 16

.. 17

18

18

20

21

24

26

26

27

iv

. .

. .0

.".

. .

. ."

. .

LIST OF FIGURES (contd)

No. Title P

19. Scanning Electron Micrograph of Fracture Surface fromGreen Nickel Oxide Tape N-5 . . . . . . . . . . . . . . . . . . 32

20. Particle Size Distribution of As-Received Lithco LiA102 a - - * - 35

21. Particle Size Distribution of Lithco LiAlO 2 Milled inDonaldson Mini-Grinder/A12 Classifier System . . . . . . . . 35

22. High-Temperature Equilibrium Regions..... ......... .. 38

23. Low-Temperature Equilibrium Regions . . . . ........... 39

V

LIST OF TABLES

No. Title Page

1. Properties of Doped LiFeO2 Samples Made from CoprecipitatedMaterials . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

2. Lithium Content of Doped and Undoped ZnO Exposed for 100 hto Cathode Conditions ......... . . . . . . . . . . . . 10

3. Stable Compounds of Selected Transition Metals in75% N2-21.8% CO2-3.2% 02, Humidified to >40% H20 . . . . . . . . 13

4. Stable Compounds of Selected Transition Metals in76.7% N2 -3.4% C0 2 -14.6% 02-5.3% H20 . . . . . . . . . . . . . . 13

5. Results of NiO Solubility Tests in 62 mol % Li2CO3-K2C03with Dry 30% CO2-Air Purge . . . . . . . . . . . . . . . . . . . 21

6. Effect of Acidity Level in Sample Preparation upon SolubilityTest Results of Alternative Cathode Materials in 70 mol %Li2CO3-K2C03 under 30% C02-Air at 923 K for 100 h . . . . . . . 22

7. Electrolyte Analyses for Selected Cations . . . . . . . . . . . 23

8. Creep Test Summary . . . . . . . . . . 25

9. Tape Casting of Alternative Cathode Materials . . . . . . 29

10. Nickel Oxide Tape-Casting Formulations. . ......... . . 31

11. Burnout Studies on Nickel Oxide Tapes.............. . . 33

12. Jet Milling of Lithco LiAIO2 Powder........ . . . . . 34

13. LiA1O 2 Tape-Casting Experiments................ . 36

vi

ADVANCED FUEL CELL DEVELOPMENT

Progress Report forJuly-September 1983

ABSTRACT

This report describes fuel cell research and developmentactivities at Argonne National Laboratory (ANL) during the periodJuly through September 1983. These efforts have been directedprincipally toward seeking alternative cathode materials to NiOfor molten carbonate fuel cells. An investigation was made of thethermodynamically stable phases formed under cathode conditionswith a number of transition metal oxides. Prospective alternativecathode materials are being synthesized and doped to promote elec-tronic conductivity. Three materials--LiFeO2 , Li2MnO3 , and ZnO--have been doped to give suitable conductivity. These materials arebeing further tested for solubility and ion migration in the cellenvironment. Techniques are being studied for the preparation ofthin electrode and electrolyte materials by tape casting, and acreep-resistant superstructure for the anode is under development.

SUMMARY

Cathode Development

Because of the problem of NiO cathode dt- solution in molten carbonatefuel cells, the experimental work at ANL has concentrated principally on theinvestigation of alternative cathode materials, namely, LiFeO2, Li2MnO3 ,ZnO, and Li2TiO3 .

Alternative Cathode Materials

Procedures for producing doped LiFeO2 with a resistivity of v6 Acmat 650*C have been established. Modifications to these procedures are beinginvestigated, and changes in resistivity of more than an order of magnitudehave been observed. These conductivity changes correlate with lattice param-eter measurements obtained by X-ray diffraction (XRD). In some preparationsa second phase was present.

Doped Li2MnO3 appears to be promising as an alternative cathodematerial, based on all tests performed to date including solubility, stabil-ity, conductivity, and migration. Therefore, plans are under way to producelarger batches of the material for cell performance tests. Work toward thisend has been initiated using spray drying instead of coprecipitation to formthe precursor material. Some effort is continuing on examining dopant con-centrations and the effects of the synthesis procedure.

Zinc oxide has proven to be a good conductor with Cr, Ga, and Zrdopants. Data are reported for these systems. A major concern is that thedoped ZnO will be doped in situ by lithium and cause a loss of conductivity.

I

2

Several experiments are under way to examine this potential problem. All aredirected toward establishing the equilibrium lithium dopant concentration inZnO in the cathode environment. To date, the results indicate a low level ofdoping, but testing will continue.

This quarter attempts were made to dope Li2TiO3 with La, V, and W.In all cases Ti02 was a starting material, and the dopant was mixed as asolution with subsequent drying. One pellet (La-doped) was tested for re-sistivity; it was too resistive for consideration as an alternative cathodematerial.

Stability Tests of Alternative Cathode Materials

Stability tests are run by synthesizing oxides of metals of inter-

est under cathode conditions to determine the thermodynamically stable phase.Two series of experiments were run at cathode gas outlet conditions selectedfrom systems studies. Most compounds identified earlier as stable under

cathode inlet conditions were also stable under these outlet conditions.

Cathode Materials Solubility Studies

The solubilities of alternative cathode materials (LiFeO2, Li2MnO3 ,and ZnO) have been examined for the effects of temperature (823-1023 K),electrolyte composition (70 or 62 mol % Li2CO3-K2C03), and humidified cathodegas. The solubility of LiFeO2 increased with temperature from 3 to 11 wppmiron. Under humidified cathode gas, the LiFeO2 solubility had an overallincrease of about 35%. The solubility of Li2MnO3 increased with temperaturebut was consistently low (0.3-0.4 wppm manganese at 823 K, about 1.0 wppm at923 K, and 4.0-5.0 wppm at 1023 K). Changes in electrolyte composition,humidity level, and CO2 partial pressure did not significantly alter thisrange of solubility. Zinc oxide solubility, on the other hand, tended to be

much higher. The preliminary results indicate solubility decreasing with

temperature from 170 wppm zinc at 823 K to 105 wppm at 1023 K and from 290to 135 wppm zinc under humid gas conditions. The solubility of ZnO alsoappears directly related to CO2 partial pressure.

Examination of lithiated NiO solubility under dry 30 vol % C02-air gas indicated a constant 7 wppm nickel level over the temperature range

823 to 1023 K. Two earlier independent tests conducted by the pot methodindicated both increasing and decreasing NiO solubility with temperature.Confidence in results by this approach was further lessened by difficultiesencountered in maintaining stable test conditions over long durations.Sample preparation methods (aqueous dissolution of carbonate samples foratomic emission spectroscopy analysis) were established which provided repro-ducible solubility results for the NiO and alternative cathode materials. Animproved procedure is still being sought. Under the 30 vol % C02-air gas in70 mol % Li2CO3-K2C03 at 923 K, solubilities of the alternative cathode mate-

rials were: 3.0 wppm iron for LiFeO2, 0.8 wppm manganese for Li2MnO3, and75 wppm zinc for ZnO.

3

Cathode Material Migration

Migration tests have been run for cells with NiO, LiFeO2, andLi2MnO3 cathodes. These cell tests are run for the exclusive purpose ofexamining cathode material migration They are run under open-circuit condi-

tions and with undoped cathodes. The results of tests completed to dateindicate very low rates of migration for LiFeO2 and Li2MnO3. These tests

will be continued, with gas composition as the primary variable.

Anode Development

Development of a creep-resistant anode structure is sought throughapplication of low-surface-area foam metal as a superstructure for theanode. Integrated structures have been fabricated with bipolar sheetbrazed onto the foam metal, which in turn has an anode embedded in it.

A 1-cm2 , 6.95-mm-thick piece of foam metal (Retimet") was tested undercompressive load. The load was increased incrementally to 0.4 MPa (60 psi)at 925 K over 400 h, and then the temperature was increased to 975 K. Overthe total test duration of 530 h, the sample compressed about 0.4%, which ismuch less than the compression of the best anode materials. The creep rate

is load dependent and decreases with time.

Component Fabrication Development

Cathode work this quarter has been directed toward preparation of sin-

tered discs for solubility measurements, preparation of cathode materialtapes for migration tests, and development of tape-casting techniques for

future work in cathode fabrication. In the absence of sufficient quantities

of proposed cathode materials, experience is being gained with INCO techni-cal-grade nickel oxide.

In matrix fabrication development, spray-dried LiAlO2 has been furtherexamined, and the use of commercial-grade LiAlO2 has been emphasized.

Because the commercial product is too coarse, a number of jet mills were usedto break the particles down to a sufficiently small size. The products withthe most suitable particle size were excessively contaminated by metals from

the milling/classifying equipment. The contamination problem may be overcomeby equipment modifications.

System Code Development

Development of an eight-species chemical equilibrium routine (CHEQ) was

completed. Tests indicate that the approximations used now converge rapidlyto the correct solutions for all points tested. New files of thermodynamicdata were constructed for the CHEQ routine and a 21-species properties code

(PROP) from the the SysLems Analysis Program (SALT). With the new thermo-dynamic data, CHEQ and PROP were found to compare favorably (to at least fourfigures) with chemical equilibrium distributions computed by a NASA programin a series of test runs. The CHEQ routine is now used in the SALT programto provide initial estimates for PROP calculations. Tests for carbon deposi-tion are now included in CHEQ and PROP.

4

I. INTRODUCTION

The advanced fuel cell studies at Argonne National Laboratory (ANL)are part of the DOE Advanced Fuel Cell Program. The objective of this DOEprogram is to reduce the technical uncertainties of fuel cells so that manu-facturers and users can introduce high-efficiency generating systems, whichhave the capability of operating on coal or other fuels. At the presentstage of development, the primary thrust of the ANL program is to providesupporting R&D that pursues fundamental understanding of fuel cell behaviorand investigates alternative stack concets.

The present molten carbonate fuel cells consist of a porous nickelanode, a porous lithiated nickel oxide cathode, an electrolyte structurewhich separates the anode and cathode and conducts only ionic current be-tween them, and appropriate metal housings or, In the case of stacks orcells, intercell separator sheets. The cell housings (or separator sheets)bear upon the electrolyte structure to form a seal between the environmentand the anode and cathode gas compartments. The usual electrolyte structureis a composite of discrete LiAIO2 particles and a mixture of alkali metalcarbonates. The carbonates are liquid at the cell operating temperature ofabout 925 K. At the anode, hydrogen and carbon monoxide in the fuel gasreact with carbonate ion from the electrolyte to form water and carbon diox-ide while giving up electrons to the external circuit. At the cathode, car-bon dioxide and oxygen react and accept electrons from the external circuitto form carbonate ion, which is conducted through the electrolyte to theanode. In a practical cell stack, CO2 for the cathode probably would beobtained from the anode exhaust.

It has become apparent that for pressurized operation, which is desir-able for large power plants, nickel dissolution from the NiO cathode anddeposition of metallic nickel in the electrolyte will preclude the 4 x 104-hlifetime desired for commercial cells. The evaluation of possible alterna-tive cathode materials is the group's principal current activity. We arealso considering ways to obtain satisfactory cell life with NiO cathodes.

Cells are operated to assess the behavior of components and to under-stand the performance of life-limiting mechanisms at work within the cell9Cell operation is coupled with efforts on diagnostics and materials develop-ment.

5

II. CATHODE DEVELOPMENT

Because of the earlier reported problem of NiO cathode dissolution inmolten carbonate fuel cells, the experimental work at ANL has concentratedprincipally on the investigation of alternative cathode materials, nauely,LiFer 2 , Li2 MnO3 , ZnO, and Li2 TiO 3 .

A. Alternative Cathode Materials

1. LiFeO 2(N. Q. Minh and E. H. Van Deventer)

Experiments have shown that the properties of a-LiFeO2 are sensi-tive to preparation procedures. The cause of the variation in pro, parties isbeing investigated. In addition to the changes in a-LiFeO2, it was foundthat some preparations resulted in two-phase products [e-LiFeO2 and(Mn,Fe)Fe 2 04 ]. The stability and significance of the second phase are beinginvestigated.

An earlier set of experiments1 produced Mn_ doped LiFeO2 with aresistivity of %6 rcm at 6500C. A series of syntheses based on this earlierwork was done this quarter and resulted in products with a wide variation ofresistivities and lattice parameters. A batch of iron and manganese hydrox-ides with an Fe/Mn ratio of 5/1 was prepared by precipitation from an iron/manganese(II) nitrate solution with ammonia (as in the earlier procedure).After coprecipitation, the material was filtered, water washed to a neutralpH, and air dried at 41500C. The succeeding steps to produce four differentspecimens for resistivity testing are summarized in Table 1. All pellets weresintered at 10500C for 1 h. Pellet C sintered to a higher density than theothers.

Figure 1 shows results of conductivity measurements. It should benoted that pellets A and B have the lowest resistivity and also have signif-icantly lower lattice parameters than C and D. The identifiable processingdifferences (Table 1) for A/B vs. C/D are: 12C03 vs. Li2C03-K2C03 eutecticfor the carbonate treatment; air vs. 30% C02/balance air for the carbonatereaction gas; 850C vs. 700*C; and-60 h vs. 100 h for the time of the reactionstep. Samples B and D underwent a heat treatment prior to the carbonatereaction, which appears to have caused slightly increased resistivity.

Another series of Mn-doped samples was prepared with propertiesgenerally similar to samples C and D, but an additional compound,(Mn,Fe)Fe 2 04, was present. These samples all underwent a heat treatment(1100C for 100 h and 15000C for 2 h) just prior to a reaction with Li2C0 3 /K2CO3. The material that was treated at 1500C had slightly lower resistiv-ity than the one treated at 1100*C (Fig. 2). They both contained a secondphase (Fig. 3), which, for the 1500*C sample, was identified as (Mn,Fe)Fe 2 04 .Based on optical examination, the second phase comprises about 5% of thesample and is evenly distributed as %4 pm crystallites. This is a spinelstructure that may have formed during the heat treatment and may not haveconverted to LiFeO2 due to kinetics. The stability of this compound in thecathode environment is being tested.

6

Table L Properties of Doped LiFeO2 Samples Madefrom Coprecipitated Materials

Heat Carbonate Treatment Results of XRDaHeat Before Sintering/

Pellet Treatment Carbonate Temp., C Gas After Sintering

A None Li2CO3 850 Air LiFeO2 4.136 A/LiFeO2 4.138 A

B 1000 *C, Li2 CO3 850 Air LiFeO 2 4.138 A/60 h LiFeO2 4.140 A

C None Li2CO3/ 700 30% C02 / LiFeO2 4.144 AK2C03 Air LiFeO2 4.150 A +

(unidentified line)

D 1000 *C, Li2CO2 / 700 30% C02/ LiFeO2 4.153 A +60 h K2CO3 Air very minor LiFe508/

LiFeO2 4.144 A +minor LiFe5O8

aXRD = X-ray diffraction.

10,000 I I

OA

a

Ari

A

0

0

Pellet(see Table 1)

o A0 BA Co D

1.3 1.4

10'/T, K-'

1.5 1.6 12

Fig. 1.

Resistivity of Manganese-DopedLiFeO 2 Prepared under DifferentConditions

0

a

a

0 A

A

A

000 o

1,000

EV

cxS100~

10

1.0

0

0

~0

1.0 1.1 1.2.V I I 1_.._

I

I

I i 1.r

7

1.0 1.1 1.2 1.3 1.4 1.5

1000/T, K-

1.6

105

104

-v

V .,

ta 1;p;". k;i[ rY1"

Fig. 3.

Photomicrograph of Two Phasesin Mangauese-Doped LiFe02

SI

1 um

Norninii CompositionO LIMn 0 Fe0 740 2 (Ref. 1)

- o LiMno0 7Feo. 3O2 (Ref. 1)" LiMn0o1 FeooO 2 (Ref. 2) -o Li,.O.Mno.,SFeo02 O -

(1100*C interdiffusion step -

4- --

n Li104Mn028Feo. 7O2 (10'C interdiffusion step) -_ o Li 0 Mno.3 Fe 0 5 2 (1100"C interdiffusioii step) _

0 L 1 Mno02 Fe0 6702 (1500"C interdiffusion step)

Ea

0t

102

101

in

Fig. 2.

Resistiv.ty Measurements onManganes e-Doped LiFe02

Vii!': "ii ^ , fir,..

"'t 'z5:ly

%" l

8

2. L1 2MnO3

(J. L. Smith)

Materials have been received for preparing larger batches ofLi2MnO3 to be used to make cathodes for 100-cm cells. The coprecipitationprocess used for materials development is time-consuming and produces small

batches of material. Work has just been initiated on spray drying as a sub-stitute for the coprecipitation process used to date.

Some work is still being done on small samples for conductivitytests. Recently it was observed that some samples did not undergo completereaction to Li2MnO3 during the 100-h, 700*C carbonate treatment in 30% CO2-70% air. The incomplete formation of Li2MnO3 may be caused by a kineticsproblem due to the reactants having undergone particle growth during the1100 C heat treatment prior to the carbonate reaction step. The result is

that after sintering the samples are a mixture of Li2MnO3 and LiMn204 .Several samples are being prepared for examination of both the effect ofdopant concentration and the cause of the incomplete reaction.

3. ZnO(N. Q. Minh)

Our short-term (100-h) tests indicated the stability of ZnO to theLi2CO3 -K2C03 melt under the cathode conditions. To evaluate ZnO as a suit-able material for use as an MCFC cathode, work has been carried out on syn-thesizing and doping ZnO and determining the electronic conductivity of dopedcompounds. The effects of various dopants, dopant concentrati in, preparationprocedures, and lithium incorporation on the conductivity of ZnO are cur-rently under investigation.

a. Cr203-Doped ZnO

The electronic conductivity at different temperatures of threepellets sintered at 1300 C (about 45% porous) of ZnO doped with 2, 3, and4 mol % Cr203 was reported previously (ANL-83-89, pp. 9-11). It was foundthat the conductivity (at the same temperature) of doped ZnO decreases withincreasing chromium oxide content from 2 to 4 mol %. To determine t1.e chro-mium dopant concentration for the optimum conductivity of Cr203-doped ZnO,samples of ZnO doped with less than 2 mol % Cr203 were prepared and testedfor conductivity. The electrical resistivity results for ZnO doped with 0.5and 1 mol % Cr203 are given in Fig. 4. The porosity is about 18% for a0.5 mil % doped sample, while it is about 26% for a 1 mol % sample. Theresistivity of each of these two samples is much higher than that of 2 mol %Cr203-doped ZnO (Fig. 4.). This indicated that the optimum chromium concen-tration for the conductivity at 650*C is around 2 mol %.

b. Ga203-Doped ZnO

Samples of gallium-doped ZnO were prepared from ZnO powderplus gallium nitrate solution and tested for conductivity during thisreporting period. Figure 4 gives the resistivity of five pellets, sinteredat 1200 C, consisting of ZnO doped with 0.5, 1, 2, 3, and 5 mol % Ga2 03.

9

1,000

/O

E/100 -

100- 0E ,' o"o

/a A 7Fig. 4.$ AA/

10 ~ KResistivity of Chromium-Doped ZnO

10-

0.5 mol % Cro3o 1.0Omol %

2 mol %3 mol %

------ 4 mol %

1.0 a a a i1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7

103/T, K-'

The data show that the resistivity increases with increasing gallium concen-tration. While the measured conductivity of 0.5 mol % doped sample is muchbetter than the others, this sample is about 13% porous, whereas the porosi-ties of the others are about 40%. Thus, it appears that 1 mol % or less isthe optimum gallium oxide content. Within the temperature range investigated(300-700 C) the resistivity-temperature characteristics of Ga203-doped ZnOshow a maximum at about 468 C (1.35 x 10-3 K-1) (Fig. 5). A similar behaviorwas also observed for Al-doped and Zr-doped ZnO samples. Syr.thesis of Ga-dopedZnO by coprecipitation is in progress.

c. Zr02-Doped ZnO

A batch of about 100 g of Zr-doped ZnO was prepared and deliv-ered to T. Claar of the Materials Science and Technology (MST) Division fortape making for cell performance and migration tests. The Zr02 content inZnO is 3 mol %, and the material was prepared from ZnO powder + zirconiumnitrate solution and heat treated at 1300 C for 5 h.

d. The Effect of Lithium Incorporation

The introduction of lithium has long been known to lower theconductivity of ZnO. The lithium incorporation may occur when ZnO or dopedZnO is in contact with the carbonate electrolyte. During this reportingperiod, the introduction of lithium into ZnO in contact with Li2CO3-K2C03melt is being investigated.

Doped and undoped ZnO samples were exposed to carbonate meltsat 700 C in a cathode gas environment for 100 h. The samples were analyzedfor lithium contest after being washed free of carbonates. The results forseveral doped and undoped ZnO samples are shown in Table 2.

0O G

o 0e

aA0

A

S

0

A

10

:-

-o~ o

DA

A

00

o 0.5 mo % Ga203A 1 mol %o 2 mol%* 3 mol %0 5 mol %

0 -

0 -o o -0 -

0 oA

o o 0 -0

I I I 1 I1.1

0 0

1.2 1.3 1.4

1031T, K-1

0

a

A

0

Fig. 5.

Resistivity of Gallium-Doped ZnO

1.5 1.6 1.7

Table 2. Lithium Content of Doped and Undoped ZnOExposed for 100 h to Cathode Conditions

Sample Batch:

Lithium Content, ppm

1 2 3

Blank ZnOa

11

The high lithium content observed for Zr- and Ga-doped ZnO isprobably due to the presence of an insoluble compound formed by the reactionbetween Li2 CO 3 and excess dopant (i.e., dopant which had not been success-fully incorporated into ZnO during preparation). In the case of Cr-dopedmaterial, excess Cr203 probably reacted with Li2 CO 3 to form a soluble com-pound. This was indicated by the yellow color of the solidified carbonateafter each experiment.

The effect of lithium content on the conductivity of doped ZnOwas investigated. The desired amount of lithium ('350 ppm) was added to sin-tered pellets of known conductivities by filling the pores of the pellets withsolution of known LiQH concentration. The pellets were Then heated at 700*Cunder CO2 partial pressure. The result for a Zr-doped ZnO pellet is shownin Fig. 6. Although it appears that the lithium content has a negligibleeffect on the resistivity of the sample, further experiments are being car-ried out to confirm this result. The Cr203-doped pellets with lithium addi-tion showed a color change (brown to brown plus yellow) after being heatedunder CO2 partial pressure. The samples also became too soft to be pressedinto the resistivity apparatus. It is possible that excess Cr2 0 3 (not incor-porated into ZnO) present in the sintered pellets reacted with Li2 CO 3 duringthe heating under 02 and formed the yellow compound that destroyed thestructural integrity of the pellets.

100

"E d o0A

10o0bFig. 6.10 -

* Resistivity of Zirconium-Doped ZnO* before and after Lithium Addition

o No lithium additionWith 350 ppm lithium addition

1.0 I . I1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7

10'IT, K

Further experiments on the incorporation of lithium are inprogress. In these experiments, doped ZnO powder, after being exposed to thecarbonate, will be formed into pellets, and conductivity tests will be per-formed on those pellets. Pellets will be embedded in powder of the samematerial to minimize lithium loss (the lithium content of the ifllets beforeand after sintering will be analyzed). The conductivity of these pellets willbe compared with that of material untreated with carbonates and sintered underthe same conditions.

An experiment to evaluate the lithium content of ZnO at celloperating conditions will be done. Zinc oxide will be doped with lithiumto a high level and will then be exposed to the cathode znvtrznment.

12

Previously, undoped ZrO was exposed to the cathode environment, and thelithium content was evaluated. By approaching the equilibrium content fromboth higher and lower values, an equilibrium value should be determinableindependent of the kinetics of the process.

4. Li2TiO3(R. B. Poeppel,* Tu D. Claar,* V. L. Richards,tand J. J. Picciolo*)

Lanthanum-, vanadium-, and tungsten-doped Li2TiO3 have been pre-pared. Lanthanum doping at 0.1, 0.2, and 0.3 mol % was achieved by wet ballmilling mixtures of lanthanum nitrate, lithium carbonate, and titanium oxide,then dryirg and reacting them for 2 h at 1200 C. Analysis by X-ray diffrac-tion indicated lithium titanate with no "extra" lines in the pattern.Vanadium doping was achieved by wet ball milling vanadium oxide with titaniumoxide, drying, and firing at 1200*C. The doped titania was then wet ballmilled with lithium carbonate and dried. A mixture doped to 3 mol % V02 wasreacted at 1200 C. The product appears to have been at least partiallymelted. The X-ray diffraction pattern shows large-grain Li2TiO3, plus onevery weak line which was not identified. Materials doped to 1 and 2 mol %V02 will be reacted. Tungsten doping was achieved by wet ball milling mix-tures of metallic tungsten and W0 3 with titania in proportions to yield 1,2, 4, and 6 mol % W02 doping levels when dried and fired. The 4 and 6 mol %doped titania was reacted with lithium carbonate for 2 h at 1200*C. TheX-ray diffraction pattern of the 6 mol % tungsten-doped lithium titanateshowed lithium titanate with four weak unidentified lines. A pellet of La-doped Li2TiO3 had too high a resistivity in air at 650C to be measured on

the conductivity measurement apparatus. The conductivity of Li2Ti03 withother dopants will be determined next quarter.

B. Cathode Material Stability(E. H. Van Deventer and J. Moreschi+)

Stability testing of a number of transition metals is continuing. It isimportant to identify compounds that are thermodynamically stable under allanticipated cathode conditions. Results are reported for various materialsin Tables 3 and 4. Testing is continuing with other possible outlet cathodegases, based on results of systems studies. Tests will be performed at both1 and 10 atm (0.1 and 1 MPa) pressures. Tests in a number of anode gaseswill be run at these pressures to define the potential sink materials.

Materials Science and Technology Division, ANL.

Argonne summer faculty research participant, Dept. of Metallurgical and.Materials Engio: ring, Illinois Institute of Technology, Chicago, IL.

?Ugh School Faculty Research Program participant.

13

Table 3. Stable Compounds of Selected Transition Metals in75% N2-21.8% C02 -3.2% 02, Humidified to >40% H20

Y.aterial ChargedFe203

Fe304 (ore)

ZnO

Ta'05

Mn02

T102 (anatase)

TiO2 (rutile)

Nb205Ga2 03

Zr02

SnO2

V2 05

MgO

W403

Reaction Products (XRD)

aLiFeO2

Fe3 0 4 , Fe 2 0 3 , a-LiFeO2 , 8-LiFeO 2 , LiFe5 O 8

ZnO

Li3 TaO4 + unidentified minor phase

Li 2MnO3

Li 2Ti03

Li2TiO3

Li 3 NbO4, KNb03 + unidentified minor phase

Ni 5 A14 02 (OH)18'6P 2 0 type pattern

Li2ZrO 3 , Zr02 + unidentified minor phase

Li2SnO3 , Sn02

Li3VO4 , a-LiA1O 2

MgO, Mg(OH) 2Water soluble material (probably K2W04 )

Table 4. Stable Compounds of Selected Transition Metalsin 76.7% N2 -3.4% C02-14.6% 02-5.3% H20

Material Charged Reaction Products (XRD)

Fe2 03 a-LiFeO 2

ZnO ZnO

Ta205 Li 3TaO4

MnO2 Li 2MnO3

TiO2 Li2Ti03 (monoclinic)

Zr02 Li2ZrO3 (monoclinic)

SnO2 Li2Sn03

V205 Li3VO4:4g0 MgO

W03 K2W04

..

14

C. CatMde Material Solubility

' . D. Kaun and T. Fannon*)

The discovery of metallic nickel deposits in the electrolyte structuresof molten carbonate fuel cells raised concern over the solubility of lith-i.ced NiO in the cathode environment. Cyclic voltammetry (CV) has been usedto investigate the effects of temperature, electrolyte composition (Li/Kratio), humidity in the cathode gas, and CO2 partial pressure on cathodesolubility.3 In addition, current peak height arising from NiO solubility

were calibrated with physical sample analyses. These two analytical tech-niques proved useful in the difficult determinations of parts per millionlevels of metals in carbonate melt. Th? determination of the solubility of

alternative cathode materials is now under way. The relative solubility ofalternative cathode materials is indicative of their potential for acceptablemass transfer rates and the stability of their electrode microstructures.

Another concern is the stability of their doped forms.

1. Cyclic Voltammetry

a. LiFeO2

Cyclic voltammetry was used to study the solubility of LiFeO 2in a 62 mol % Li2CO3-K2C03 melt. Tests were conducted between 850 and 1050 Kin a 1/3 02-2/3 CO2 cathode gas environment. (This carbonate composition hasa liquidus at approximately 763 K.) Tests were made under both dry andhumidified (room temperature) gas conditions, with physical samples beingtaken in conjunction with CV measurements at each temperature tested. Theanalyses of these samples provided a calibration of the CV current peaks.

Tests were controlled in a voltage range of +0.2 to -1.6 V vs.the reference electrode (gold in 1/3 02-2/3 C0 2) by a PARC Model 175 Univer-

sal Programmer driven by a Model 8C1200 Potentiostat (Stonehart Associates).

Operating parameters for the CV measurements were established experimentally.

The potential of a clean iron wire (vs. the gold in 1/3 02-2/3 Co2 reference electrode) was -0.9 V, with CVs on blank solutions pro-ducing no distinguishable current peaks. However, after electrochemicaldischarge of iron into the carbonate melt, an anodic peak arose at about-0.4 V (see Fig. 7). Introduction of LiFeO2 to the carbonate melt resultedin two sets of current peaks. One set of peaks occurred at -1.0 V and waslater associated with zinc, which had been the dopant of the LiFeO2 material

used in the CV. The set of peaks at about -0.8 V cathodic and -0.4 V anodicwas representative of LiFeO2 solubility.

About thirty physical samples (100-300 mg of melt) were taken

subsequent to a CV run. These samples were analyzed for iron by Inductively

Coupled Plasma/Atomic Emission Spectroscopy (ICP/AES)t to provide a cali-biation curve of the peak currents found by cyclic voltammetry (Pig. 8).

Student Researcher, Tennessee Technological University, Cookeville,'Tennessee.

tAnalytical results by E. A. Huff and A. Essling, Analytical Chemistry

Laboratory, ANL.

15

-1.5 -1.0 -0.5

Potential (V) vs 1/3 02-2/3 CO 2 on Gold

0.0

O mA

Fig. 7. Cyclic Voltammograms in Carbonate MeltIllustrating LiFeO2 SolubilityCurrent Peaks

0.25 0.5 0.75 1.0 1.25 1.5Peak Current, mA

1.75

Fig. 8.

Calibration Curve of ReportedIron Concentrations and CurrentValues Found by Cyclic Voltam-metry (A 20% level of error isexpected.)

62 mol % L12 CO 3-38 mol % K 2C0 3 W-100 mV/s Scan Rate

a-000 1 mA

-------. --- Blank Carbonate(903 K)

--- With LIFeO 2 (873 K)

15

10

E0.

0.

lop.2"

0C-)

1 I

o Samples prepared for analysis by old method (no filtra-tion step). Expected to produce high values.

o Samples prepared for analysis by new method with -filtration step to give more-reliable results.

0

0

0

0 -

0

0 A

A-

000o9A

A 00-eA

5

16

Concern over the reproducibility of analytical results, due to carbonate sam-ple contamination by fine particulates, led to the development of a revisedsample preparation procedure. Results from both procedures are presented.*The calibrating factor ias 5 1 wppm iron per milliampere of the anodic peakfor dry gas conditions. Each sample was drawn after at least 1 Ii of gas purgeat a set condition. Hurldified conditions were attained by bubbling purge gasthrough water at room temperature.

The voltammograms were recorded on 50- and 250-mV/cm scales,corresponding to 0.5 and 2.5 mA/cm. The current peak heights were measuredvertically from the baseline for cyclic voltammograms (-1.6 V cathodic limit)and had about 10% error.. including a 10% error in iron concentration for thesample analyses, an overall error of 20% could be expected for the solubilityvalues.

The solubility of LiFeO2 as a function of temperature for drycathode gas conditions, as obtained through actual physical sample analysis,is shown in Fig. 9. The solubility of LiFeO2 increases with temperature fromabout 3 wppm at 850 K to around 11 wppm at 1050 K. Results from old and newpreparation methods are included in Fig. 9. The old-method results proved tobe comparatively high.

Temperature, "C750 650 550

a Samples prepared for analysis by old method (no fUltra-tion step). Expected to produce high values.

20 o Samples prepared for analysis by new method withfiltration step to give more-reliable results.

0

" a Fig. 9.

E 10

Solubility of LiFeO2 Cathodeg *a- in 62 mol % L1 2 CO 3-K2C03s- Carbonate Melt as a Function of5

CO 4 0 Temperature in the Presence of a2/3 C02-1/3 02 Gas Atmosphere

a-- Using Physical Data Analysis

2

1

0.9 1.0 1.1 1.2

1031T, K

The effect of humidity upon LiFeO2 solubility is illustratedin Fig. 10 and correlates well with the CV findings. Room-temperature humid-ified 1/3 02-2/3 CO2 cathode gas increased LiFeO2 solubility by approximately35%, from 5 wppm iron at 850 K to 17 wppa at 1050 K.

*The revised sample preparation procedure is described later in this report.

17

Temperature, *C750 650 550

o Dry Conditionso Humidified at Room Temperature

2 - 0

E o Fig. 10.

9 --

S-- Comparison of Solubilities by

Cyclic Voltammetry under Dry*N_ and Humid Conditions Using

Experimental Calibration Factor

3-

2-

0.9 1.0 1.1 1.2103(T, K'

Appreciable levels of zinc (150-300 wppm Zn) were found in thecarbonate melt that had been contacted with this Zn-doped LiFeO2. In compar-ison, the solubility of undoped LiFeO 2 determined by the pot-type studies indi-cated less than 20 wp-m zinc present. Analysis by X-ray diffraction* of thisZn-doped LiFeO 2 after exposure to humid cathode conditions revealed no signif-icant change in lattice structure.

b. Li2MnO3

In the manner described above, the solubility of Li2 MnO3 wasexamined by CV; 35 physical samples taken subsequent to CV were also analyzedfor solubility product. (The sample preparation procedure is described inthe next section.) A temperature range of 823 to 1023 K was examined. Ananodic peak indicating Li2 MnO3 solubility was identified at -0.7 vs. the1/3 02-2/3 CO2 reference electrode (Fig. 11). Current peak heights weremeasured from voltammograms having a -1.6 V cathodic limit. Below 923 K,solubility was apparently quite low, and analysis of the physical samples byICP/AES was relied upon. The CV resulted in negligible peak heights in someof these cases. The results of the CV and physical analyses correlated well.The solubility of Li2MnO3 in dry 62 mol % Li2C03 -K2C03 is presented inFig. 12. Increasing with temperature, the manganese level is 0.3-0.4 wppm at823 K, about 1.0 wppm at 923 K, and about 5.0 wppm at 1023 K. The compoundLi2MnO3 has consistently been found to show very low levels of solubility andhas the lowest solubility of materials tested to date.

*B. S. Tani, X-ray Diffraction, ANL Analytical Chemistry Laboratory.

18

-1.0 -0.5 0

-10 mA

-5 mA

0 mA

5 mA

10 mA

LI2MnO3 Present in62 mol % Li2CO-3 K2CO3 at 1023 K

In Dry 113 02-2I3 CO 2 Cathode Gas100 mVIs Scan Rate

Potential (V) vs 113 02-213 CO2 on Gold

Fig. 11. Cyclic Voltammogram Illustrating aDetectable Anodic Peak at about-0.7 V due to Li2MnO3 Additionto the Carbonate Melt

10231on.

5.0

Temperature, K923

2.0F-

1.0

0.5

0.11.0 1.1

103IT, K)

823

1.2

/I

Fig. 12.

Solubility of Li2 MnO 3 in 62 mol %Li2CO3 -K2C03 in a 1/3 02-2/3 CO2Atmosphere. The solubility ofLi2MnO3 in 70 mol % Li2CO3-K2C03in dry and humid conditions(60C H20) is not significantlydifferent.

.).o-1.6

0

C0.00

ECL

00

CS

C0V)SNca

a

\i2

-I

--\

I I I- J i

r J J J

.A,I

0.2F-

19

The effect of increased Li/K ion ratio was examined. Tn thetemperature range 823-1023 K, Li2MnO3 solubility in 70 mol % Li2CO 3-K2C03tended to be slightly lower than In 62 mol % Li2CO3. For example, at 923 Kthe detected manganese level was 0.8-0.9 wppm manganese, compared to1.0-1.3 wppm manganese in the 62 mol % Li2CO3 electrolyte. The analyticaluncertainty is rather high at these low values.

A slight increase in Li2MnO3 solubility due to humidity(20% H20) was indicated. Again, this apparent incrt.se is considered to bewithin the expected deviation of determined values. However, the L1 2MnO3solubility could be lower for the 1023 K temperature with humid cathode gasthan with dry cathode gas (4 vs. 5 wppm). Data indicating the effect of CO2partial pressure are rather limited, but results of a pot-type study at 923 Kand 30% C02-air cathode also indicated 0.8-wppm manganese solubility.

In summary, the solubility of Li2MnO3 appears rather insensi-tive to changes in the Li/K ratio of the carbonate melt, humidity level, andCO2 partial pressure of the cathode gas. All test produced consistentlylow (

20

carbonate sample was examined. Samples of identical carbonate were preparedwith HCl of 5, 2, 1, 0.5, and 0.25M concentration to achieve 0.3M final acid-ity after filtration. As indicated in Fig. 13, samples with

21

Sampling Tube

Purge Gas and Electrolyte -Circulating Pump

Molten Carbonate -

Cathode Material -

Thermocouple

Arrangement of Sample Crucibles-- Within Furnace. (All A1203

Crucibles and Tubes)

4

---- -

Fig. 14.

Arrangement of Pot-Type SolubilityApparatus. (Operated at 823-1023 Kwith 30% C02-air atmosphere.)

Table 5. Resultsa of NiO Solubility Tests in 62 mol %Li2Cu3-K2C03 with Dry 30% C02-Air Purge

Time at ,NiO Solubility, wppm ( 10%)Conditions,

h 823 K 923 K 1023 K

75 10.4 7.1 6.9

100 7.2 8.0 7.7, 6.9

aAnalyses conducted by E. Huff and A. Essling ofAnalytical Chemistry Laboratory, ANL.

b. Solubility of Alternative Cathode Materials:ZnO, Li2MnO3 , and LiFeO2

To make the pot-type solubility tests more analogous to themolten carbonate fuel cell environment, sintered pellet samples (pressing andsintering performed by T. Claar et al., MST Division) were attached to theend of the gas purge tube as a sparge frit (Fig. 14). This configuration isintended to fully wet the 60% dense sintered ZnO, LiFeO2 , and Li2MnO3 sam-ples with electrolyte as they are contacted by the purge gas of 30% C02-air.The initial testing was conducted in 70 mol % Li2CO 3-K2C03 . The followingexperiment was conducted to establish a sample preparation procedure. Alarge 5-g sample was collected after about 100 h at 923 K, ground, and split.

_1

22

From this large sample, four separate samples were prepared in 2, 1, 0.5, and0.3M HN03 and then subjected to filtering and ICP/AES analysis. Solubilityresults of this analysis are given in Table 6.

Table 6. Effect of Acidity Level in Sample Preparation uponSolubility Test Results of Alternative CathodeMaterials in 70 mol % Li2C03 KJC03 under30% C0 2-Air at 923 K for 100 h

Solubility, wppm 10%

Material 2.0M 1.0m 0.5M 0.3M HNO3

ZnO 136 145 124 118

Li2MnO3 1.0 0.9 0.7 0.8

LiFe02 2.9 4.4 2.7 3.0

aAnalyses conducted using ICP/A1S by E. Huff and A. Essling ofAnalytical Chemistry Laboratory, ANL.

The sample preparation method for L1 2 MnO3 and LiFeO2 was setusing the 1.0m HNO3 solution for dissolving the carbonates since the resultsvaried within expected error margins. On the other hand, the results of theZnO preparations were all quite high and tended to be lower with reduced acidconcentration. The development of the sample preparation procedure for theZnO solubility tests required added attention, since ZnCO3 and ZnO have simi-lar solubility in aqueous acid solutions. Because consistently high solu-bility values were obtained for preparations using dilute HNO3 and aceticacid, a method of preparation using a carbonic acid was examined. A "clean"sample was prepared by contacting the carbonate melt with ZnO for only 2 h atconstant cathode conditions. (The carbonate melt contained a 4-wppm zincbackground level.) Results of preparing a portion of a "clean" sample bythree different acid dissolutions are as follows: 1M and 0.5M acetic acid,178 and 188 wppm zinc, respectively; and bubbling 002, 193 wppm zinc. Zincoxide powder was then added to some "clean" carbonate sample, and the aceticacid and bubbling CO2 preparation procedures were again compared. The 0.5Macetic acid preparation resulted in 25,200 wppm zinc. Although selectivedissolution was possible with the bubbling CO2 method, it resulted in only75 wppm zinc (possibly indicating equilibrium was not attained). A sampleextracted after 100 h at similar conditions as the "clean" sample and pre-pared with carbonic acid was found to contain 150 wppm zinc. This prepara-tion method appears to produce ZnO solubility results that do not reflect thepresence of the ZnO particulate in the melt.

Because of the aforementioned problems of maintaining steadytest conditions over long time durations, these tests were abandoned beforethe full range of temperatures and levels of humidity could be examined.The data obtained generally confirmed the CV solubility results or providedan independent examination of the effect of C02 partial pressure. Althoughthe Li2 MuO3 test produced a pink carbonate melt, a low (

23

D. Cathode Material Migration(F. C. Mrazek, J. R. Stapay, and J. L. Smith)

Results from an apparatus for testing cathode material migration for NiOappear to duplicate the results observed in large-scale fuel cell assemblies.Modifications such as (1) humidifying the electrode gases (80% H2-C0 2 and33% 02-C02) to >20% moisture and (2) improving the electrolyte wet seal havebeen made to this apparatus to provide improved control of the environment.

A cell test was made in duplicate under these new conditions withLi2MnO3 as the cathode material. This test operated for 225 h and had anaverage cell voltage of 1.08 V. At least three 1-cm-long specimens of thefull electrolyte thickness were obtained from each cell. These samples wereprepared and examined first with a reflected light microscope in the ANL

Inert Atmosphere Metallographic Facility, followed by a Scanning ElectronMicroscopy-Energy Dispersive Spectrometry (SEM-EDS) examination. No manga-nese precipitates were observed in the electrolyte. Some small random areasin the electrolyte, mostly near the cathode side, contained a high chromiumcontent, presumably the corrosion product from one of the stainless steelstructural components.

A sample of the full thickness of the electrolyte from one of the cellswas cleaned of any residual electrode material and submitted for bulk chem-ical analysis. The results are presented in Table 7, along with some pre-viously obtained results for comparison. These results, along with themicroscopic examination, show that manganese from the Li2MnO3 cathode doesnot migrate to a measurable extent into the electrolyte during a 200-h test.

Table 7. Electrolyte Analyses for Selected Cations

Contaminants, ppma

Fe Cr Mn Ni

Electrolyte from NiO Cathode Cellwith Dry Gas 60 10 1 162

Electrolyte from LIFeO2 CathodeCell with Dry Gas 116 34 19 15

Electrolyte from Li2MnO3 CathodeCell with Dry Gas 120 38 10 18

Electrolyte from Li2 MnO3 Cathode

Cell with Moist Gas 64 150 19 30

aAnalytical results by E. Huff, ANL Analytical Chemistry Laboratory.

24

III. ANODE DEVELOPMENT

A. Fabrication Development(T. D. Kaun, F. C. Mrazek, and T. Fannon*)

Application of Ni-Cr foam metal Retimet" as a superstructure for theanode gives promise of alleviating design problems and performance degrada-tion associated with typical anode creep of 5-50% change in thickness. Ourapproach to anode development should lead to anode creep of

25

has also been sintered at 1220 K to the foam metal (examined metallograph-icalhy), but the conditions necessary to avoid coarsening of the electrodestructure have not been found. It is conceivable that the sintered attach-ment of the anode to the foam metal. may occur in cell operation due topressure loading at temperature.

Aside from solving problems of anode creep, the superstructure approachallows anodes to be developed for performance aspects independently of physi-cal strength requirements.

B. Anode Superstructure Creep Test

(J. Moreschi* and T. D. Kaun)

A 1-cm-square, 6.95-mm-thick piece of Ni-Cr Retimet" foam metal wastested for creep using a dilatometer (ANL-79-84, p. 27). The foam metal washeated to 650*C in a 3% H2-97% Ar atmosphere, then subjected to a series ofincreased pressures for extended periods of time. Immediately followingthis, the temperature was raised to 700 C and the foam metal was again sub-jected to a series of pressures. A summary of the test conditions and resultsappears in Table 8,

Table 8. Creep Test Summary

T, CPressure,psi (kPa)

Time,h

Thickness Change,amm

Avg. ZThicknessChange

13.7 (93.2)

27.5 (187.0)

45.2 (307.4)

27.5 (187.0)

13.7 (93.2)

27.5 (187.0)

45.2 (307.4)

59.3 (403.4)

59.3 (403.4)

45.2 (307.4)

27.5 (187.0)

13.7 (93.2)

90

100

70

3

55

8

16

48

30

66

24

24

-0.008 to -0.010

-0.012 to -0.016

-0.019 to -0.023

-0.023

-0.022

-0.022

-0.023 to -0.024

-0.024 to -0.026

-0.026 to -0.030

-0.030 to -0.032

-0.032 to -0.033

-0.030

to the original 6.95-mn thickness.

*High School Faculty Research Program participant.

650

650

650

650

650

650

650

650

700

700

700

700

0.12

0.20

0.30

0.33

0.32

0.32

0.33

0.36

0.40

0.44

0.46

0.43

aRelative

26

Figure 16 shows the percent thickness change from original size as afunction of time. From zero to 270 h, the percent thickness change increaseswith the pressure, from 0.15% at 13.5 psi (93.1 kPa) to 0.35% at 59.3 psi(408.9 kPa). From 270 to 350 h, when the pressure was reduced, the thick-ness remained virtually unchanged. An increase of pressure at 350 h againIncreased the change in thickness. At 400 i. the temperature was raised to700 C, and one can see that as the pressure was reduced in sequence, the rateat which the thickness changes diminished.

Total Heating Time, h

0 100 200 300 400 500 600

Lasz

wOV.

ILI-

a

=0.21

-0.4

-0.6

1 1 i 1 T TPressures

(!blIn2)I(kPa)" A = 11:11 9(13 )/(932)i

'-.."8= (27.5)!(1f'' --.. ........ C = (45.2)l(3C

D = (59.3)/(4C

A B C A DDDC B

"B sQT= 650C-T =700*C

87.0)07.4)03.4)

Fig. 16. Change in Thickness of Ni-Cr Retimet as a Functionof Time. Originally 6.95 mm thick, 3% H2-97% Ar.

Figure 17 shows changes in the thickness of the Ni-Cr foam metal as afunction of time, with the reference line showing the original thickness.One can see plateaus, again coinciding with reductions in pressure (at 270to 350 h and at 420 to 530 h). At the conclusion of the test, there was areduction in thickness of about 0.03 mm or 0.4%.

0 100 200Cumulative Time, h

300 400

Original Thickness = 6.95 mm

A B C A D D C

- BB BfC

500 600

Pressures(IbI in2)I(kPa)

A = (13.7)/(93.2)B = (27.5)!(187.0)C = (45.2)1(307.4)D = (59.3)1(403.4)

Fig. 17. Thickness of Ni-Cr Retimet vs. Heating Time

E 6.95Ei 6.00

j. 6.80

I.1

I

27

Figure 18 shows the percent deformation as a function of pressure. Thepoints are connected in chronological order. Once again, one can see thatwhen pressure is relaxed, the creeping essentially stops.

0.5

0.4- 12 11 10 g

4 T7

0.3 63

0.2 2

Points Are inn - Chronological Order

10 20 30 40 50 600 100 200 300 400

Fig. 18.

Percent Deformation vs. Pressure

P, Iblin2

P, kPa

C.20E0

0

c

VC.

I to 8 at 850*C9 to 12 at 700 C

.. ____ 1

.-I

28

IV. COMPONENT FABRICATION DEVELOPMENT

(R. B. Poeppel,* T. D. Ciaar,*R. J. Fousek, and D. Pickrellt)

Studies are under way on the fabrication of both cathode and electrolytestructures.

A. Cathode Structures

Activities under this task include the fabrication of porous pellets forstability testing of alternative cathode materials and development of pro-cesses for fabricating thin porous cathode plaques for in-cell testing. Thepreliminary cathode plaque specifications are a dual porosity structure thatis approximately 0.015-in. (0.38-mm) thick and has a total porosity of 55 to65%, approximately half of which is comprised of small pores (

29

have been prepared for cathode migration tests. The slip formulations usedin these tape-casting experiments are summarized in Table 9. The slips werevibratory milled in a methylene chloride/chloroform milling solution, usingZ-3 Menhaden fish oil as a deflocculant. The slips were milled further afteraddition of the Cerbind 73150" binder concentrate. After ultrasonic agita-tion and partial evacuation to eliminate entrained air bubbles, the slipswere cast onto a Teflon surface with a moving doctor blade set at an openingof 0.030 to 0.040 in. (0.76 to 1.02 mm). The LiFeO2 tapes were cast at0.030 in. (0.76 mm) and dried to thicknesses of 0.007-0.008 in. (0.18-0.2 mm),while the dried Li2MnO3 tapes were cast at the same thickness and dried tothicknesses of 0.012-0.013 in. (0.3-0.33 mm). Zinc oxide tape Z-1 was castto a thickness of 0.030 in. (0.76 mm) and dried to a thickness of 0.008-0.009 in. (0.2-0.23 mm). Tape Z-2 (ZnO-3 mol % Zr02 ; batch 256-ZZ-T-1) wascast at a thickness of 0.040 in. (1.02 mm) and dried to a thickness of0.015 in. (0.38 mm). The slip containing ZnO-ZrO2 powder required a higherpowder/solvent ratio to produce a castable slip; this was the result of thecoarser particles caused by the high-temperature calcining required to incor-porate the zirconium dopant into the ZnO lattice.

Table 9. Tape Casting of Alternative Cathode Materials

Slip No.

LIF-3

LIM-4

Composition

48 g LiFeO234 g Cerbind 73151" milling solution0.5 g Z-3 fish oil31 g Cerbind 73150" binder

48 g Li2MnO329 g Cerbind 73151" milling solution0.5 g Z-3 fish oil33.5 g Cerbind 73150" binder

48 g Li2MnO328.9.g Cerbind0.5 g Z-3 fish30.5 g Cerbind

45 g ZnO Powder30.5 g Cerbind0.5 g Z-3 fish31.7 g Cerbind

85 g ZnO-3 mol26.1 g Cerbind0.5 g Z-3 fish27.1 g Cerbind

73151" milling solutionoil73150" binder

73151" millinoil73150" binder

g solution

% Z10273151" milling solutionoil73150" binder

LIM-5

Z-1

Z-2

30

All of the tapes were very flexible and could be handled readily. Somemacroscopic voids were present in several of the tapes as a result of incom-plete removal of entrained air bubbles. Improved de-airing procedures toeliminate this type of defect are under investigation. No attempt was madeto produce the dual porosity typical of cathode structures in these tapes,which will be utilized in cathode materials migration tests.

As mentioned earlier, tapes of LiFeO2 and Li2MnO3 for migration testswere fabricated from undoped powders prepared by high-temperature calci2!-igof the appropriate oxides. However, cell performance testing of alternativecathode materials will be performed with doped materials having adequateelectrical conductivity, relatively high surface area, and particle sizedistribution consistent with the desired dual porosity microstructure. Thecoprecipitation process currently used to prepare doped LiFeO2 and Li2MnO3materials needs to be modified so that batches of material large enough(several hundred grams) to allow systematic development of tape-casting pro-cedures can be provided for each particular material. Spray drying andfreeze drying Aave been used to prepare high-surface-area (>10 m2/g) oxidecatalysts from a variety of precursors. These techniques are being con-sidered for preparation of alternative cathode powders for fabrication ofcathode structures by tape casting. The preparation of larger batches ofcathode material will be a cooperative effort between CMT and MST.

Until sufficient quantities of doped alternative materials are availablefor tape-casting fabrication studies, INCO technical-grade nickel oxide isbeing utilized for the evaluation of various binder/solvent systems, de-airing techniques, and binder burnout characteristics. This powder consistsof nearly equiaxed particlx2 or aggregates ranging in size from approximately5 to 20 pm, with a mean particle size of 10 pm. The aggregates were foundby SEM to consist of well-sinitered particles approximately 1 pm or less indiameter.

Tapes of nickel oxide were cast from the slip formulations listed inTable 10. The casting slips were prepared by mixing with either a 200-Wultrasonic probe or vibratory mill. After mixing, the slips were de-airedunder a partial vacuum (350-500 mm Hg) and cast on Teflon substrates by usinga moving doctor blade set at a 0.040-in. (1.02-mm) opening. The ultrasonicprobe did not provide adequate mixing to slip N-3-2, and the resulting tapecontained many agglomerates and inhomogeneities. Tapes N-3-2-A and N-3-2-Bdried to thicknesses of 0.012-0.013 in. (0.30-0.33 mm). Slip N-4, preparedby vibratory milling, produced a tape free of agglomerates. However, bindermigration to the surface of tapes N-4-A and N-4-B resulted in very stickysurfaces on these tapes, making them very difficult to handle. These tapesdried to thicknesses of 0.010-0.011 in. (0.25-0.28 mm). Slip N-5 was pre-pared with a lower binder/powder ratio than N-4, and no binder migration wasobserved with this tape. Tape N-5 dried to a thickness of 0.015 in.(0.38 mm) and was free of air bubbles, agglomerates and other defects. This

tape was also very flexible and strong and was easy to handle. Figure 19 isan SEM micrograph of a fracture surface of the green tape N-5, prepared byimmersing and fracturing a tape specimen in liquid nitrogen. The nickeloxide particles are costed and bound together with organic binders. Aninterconnected porosity of approximately 5-10 pm in size is readily apparent.Tape N-6 was fabricated using a methylene chloride solvent/acrylic bindersystem formulated to introduce high porosity levels in the resulting tapes.

31

Table 10. Nickel Oxide Tape-Casting Formulations

Slip No. Composition Mixing Met-hod

N-4

60 g INCO Nickel Oxide30 g Cerbind 73151" Milling Solution35.8 g Cerbind 73150" Binder

50 g INCO Nickel Oxide30 g CerbInd 73151" Milling Solution30.4 g Cerbind 73150" Binder

75 g INCO Nickel Oxide57 g Cerbind 73151' Milling Solution0.5 g Z-3 Fish Oil40.4 g Cerbind 73150" Binder

40 g INCO Nickel Oxide50 g Cerbind 73131" Binder

50.3 g INCO Nickel Oxide51.2 g Cerbind 73151' Milling Solution0.5 g Z-3 Fish Oil1.55 g Li2CO3-K2CO3a29.7 g Cerbind 73150a Binder

50.3 g INCO Nickel Oxide51.2 g Cerbind 73151" Milling Solution0.5 g Z-3 Fish Oil1.55 g Li2C03-K2CO3a26.3 g Cerbind 73150" Binder

50 g INCO Nickel Oxide35 g Cerbind 73151" Milling Solution30 g Methylene Chloride1.0 g Z-3 Fish Oil3.2 g Li2CO3-K2C03 a29.4 g Cerbind 73150" Binder

50 g INCO Nickel Oxide35 g Cerbind 73151" Milling Solution28 g Methylene Cnloride1.0 g Z-3 Fish Oil4.95 g Li2CO3-K2C03a28.7 g Cerbind 73150" Binder

62 mol % Li2 C03-38 mol% K2CO3.

Ultrasonic Probe

Vibratory Mill

Vibratory Mill

Vibratory Mill

Vibratory Mill

Vibratory Mill

Vibratory Mill

Vibratory Mill

N-5

N-6

N-7

N-8

N-9

N-'0

32

Fig . 19.

Scanning Electron Micrograph ofFracture Surface from Green

Nickel Oxide Tape N-5

Disk specimens of 1-in. (25.4-mm) diameter were punched from nickeloxide tapes N-5, N-6, and previously prepared tape N-3-1 for binder burnoutstudies. The disks were placed on a high-density alumina plate and heatedslowly from room temperature to 650 C over a period of 12 h and held at thistemperature for 1 h. After the organics were burned out, the specimens werevery weak and fractured during handling for weight and dimensional measure-ments. The specimens showed negligible dimensional changes and weight lossesof 17 to 22%. As shown in Table 11, porosity levels of 57 to 77 were esti-mated from geometric considerations. As expected, the highest porosity wasobtained with the Cerbind 73131 binder, which is specially formulated to pro-duce high-porosity tapes.

A series of nickel oxide tapes (N-7 through N-10) has been fabricatedfrom slips of INCO nickel oxide powder containing 3, 6, and 9 wt % of the62 mol % Li2C0 3-38 mol % K2C03 eutectic salt. The Li2C03 and K2C0 3 powderswere preblended by wet vibratory milling in methanol. The purpose of thesetests was to determine whether carbonate added to the cathode tape would actas an effective binding agent for the porous cathode structure after heatingto -650*C for organic binder burnout and melting of the carbonaLe. This ap-proach may allow more-reliable characterization of the porous microstructuresby mercury porosimetry and scanning electron microscopy than is possible ondried green tapes or on the very weak structures obtained after organic burn-out without carbonate additions. Disk specimens were punched from tapes N-7and N-8 (3 wt % carbonate), N-9 (6 wt % carbonate), ard N-10 (9 wt % car-bonate) and heat-treated for organic burnout according to the scheduledescribed previously. Specimens containing 3 wt % carbonate (ti9 vol %) were onlyslightly stronger than those with no carbonate addition, after the burnouttreatment. Specimens with 6 wt % (-18 vol %) and 9 wt % (ti25 vol %) carbon-are were substantially stronger than those with 0 and 3 wt % carbonate.

33

Table 11. Burnout Studies on Nickel Oxide Tapesa

Weight Geometric EstimatedSpecimen Loss, Density, Porosity,

No. Powder Binder System % g/cm %

N-3-1-1 Fisher reagent Cerbind 17.2 2.95 5773151/73150"

N-5-1 INCO technical Cerbind 21.4 2.12 6973151/73150'"

N-6-1 INCO technical Cerbind 73131'" 21.8 1.54 77

aBurnout schedule: Heat from room temperature to 650 C during 12 h,hold 1 h at 650 C.

bBased on theoretical density of 6.807 g/cm3 .

The higher carbonate levels permitted handling of the 1-in. (25.4-mm) diam-eter specimens for weight and dimensional measurements without fracturing.However, stronger cathode structures will be required to permit handling oflarger sizes. Microstructural characterizations of these heat-treated speci-mens are in progress. Future efforts will address the tradeoffs involved inassembling cells with green cathode tapes vs. the use of sintered structures.

B. Electrolyte Matrix

The fabrication of LiA102 electrolyte matrices by tape casting was con-tinued during this quarter. Recent efforts have focused on Y-LiA102 elec-trolyte support materials synthesized by a spray-drying process or obtainedfrom commercial suppliers.

A new batch of r-LiAl02 powder prepared as tape-casting feed materialhas been characterized. Batch SLA-1 was processed by spray drying a slurryconsisting of 305 g Al(OH) 3 (Alcoa H710) and 162.1 g LiOHPH20 in 3 L of de-ionized water. The spray-dried powder was calcined 20 h at 600*C and 2 h at900C, Analy. is by X-ray diffraction of the calcined powder indicated thatall the material had been converted to Y-phase LiA102. The surface area asdetermined by BET was 10.5 m2 /g. Examination by SEM revealed that the spray-dried and calcined product consisted of porous, approximately sphericalagglomerates similar to those reported by Sim (ANL-80-67, pp. 5-11) rangingfrom 5 to 45 um in diameter. The ultimate particles within the agglomerateswere generally submicron in size. These particles appeared to be only weaklybonded together, and it is anticipated that vibratory milling during slippreparation will break up the agglomerates and disperse the LiA10 2 particlesthroughout the tape cast structure.

We are also continuing to evaluate the feasibility of using commerciallyavailable LiA102 powder as the electrolyte matrix material. Samples ofr-LiA102 powder supplied by Lithco (Gastonia, NC) have been milled in fourjet mills of various designs, with a target median particle size of 0.5 umafter milling. The jet-milling equipment under evaluation in this study

34

includes the Donaldson Mini-Grinder in series with the Model A-12 Classifier,the Trost TX Laboratory Mill, the Sturtevant 4-Inch Micronizer Mill, and theFluid Energy 4-Inch Mictojet System. Samples of the four jet-milled mate-rials have been characterized by particle size analysis, SEM, and chemicalanalysis. As indicated by the results in Table 12, the finest material wasobtained by milling with the Donaldson Mini-Grinder in series with the ModelA-12 classifier. This milling process reduced the median particle size from11.0 pm (as-received) to 0.96 um. The particle size distributions of the

as-received and Donaldson milled materials as determined by SediGraph 3000Eanalyses are shown in Figs. 20 and 21, respectively. The other milling pro-cesses investigated yielded median particles sizes of 1.9 to 3.2 jm. Becausemost of the powders became discolored from white to light gray after milling,

chemical analyses were performed in an effort to determine the source of con-tamination. Spectrochemical analyses indicated that iron concentration, andto a lesser extent that of chromium and nickel, increased as a result of

exposure to steel components, particularly in the Sturtevant and Donaldsonmills (Table 12). Further effort will be made in future work to minimize thecontact of the LiA102 with steel surfaces during the milling and classifying

operations. Donaldson personnel indicate they expect to have the capabilityof operating their classifier with a wear-resistant ceramic lining in thenear future. Further experiments with this modified system are under con-

sideration in an effort to reduce the median particle size to .0.5 pm and toeliminate the source of metallic contamination.

Table 12. Jet Milling of Lithco LiA102 Powder

Impurity Concentration,

Medium Particle wpmSample Size, Um Fe Cr Ni

--- received 11.0 200

35

I 1 1 1 1 i Ii 1I

100

90-

E80-

e 70-

E0-

:6a10

;.4073E 30-

20o

10-

0.605040 30 20 10 8 6 5 4 3 2 1

Equivalent Spherical Diameter, pm

Fig. 20. Particle Size Distribution of As-ReceivedLithco LiA1O2

C)10-90-

-

E 3o- -

E20- -

10-

038 20 10 8 6 54 3 2 1 0.8 0.60.5

Equivalent Spherical Diameter, pm

Fig. 21. Particle Size Distribution of Lithco L1A1O2

Milled in Donaldson Mini-Grinder/A12

Classifier System

Table 13. LiA102 Tape-Casting Experiments

Nominal Thickness Nominal Thickness

Tape No. Composition of Dried Tape, in. Tape No. Composition of Dried Tape, in.

LA-7 24 g LiA102a 0.018(k) LA-14 53 g LiA102c 0.017

0.6 g fish oil34 g 58% xylene-42% -thpnol3.4 g PX-3165.7 g UCON-20004 g B-98

10 g LiA102a50 g 73115 Cerbind0.32 g fish oil9 g methylene chloride

26 g LiA102a30 g 73115 Cerbind42 g methylene chloride

100 g LiA102b125 g 73151 mill solution1 g fish oil54.4 g 73150 binder

90 g LiA102b75 g isopropyl alcohol0.5 g fish oil50.1 g 73200 binder

130 g LiA102c105.1 g 73151 mill solution1 g fish oil35 g 73150 binder

56 g LiAlC2c41.1 g isopropyl alcohol0.5 g fish oil39.6 g 73200 binder

0.021(B)

0.008

0.031

0.021(A)0.020(B)

0.015(A)0.011(B)

0.024(A)0.023(B)

0.013

LA-15

LA-16

LA-17

LA-18

LA-19

LA-20

50.1 g 58% xylene-42Z thanol0.6 g fish oil5.7 g PX-31611.8 8 UCON-20008 g B-98

66 g LiA102c42.1 g isopropyl alcohol0.5 g fish oil46.5 g 73200 binder

92.6 g LiA102c40.4 g isopropyl alcohol0.5 g fish oil64.8 g 73200 binder

50 g LiA102d

20 g isopropyl alcohol0.5 g fish oil35.1 g 73200 binder

50 g LiA102d

19 g isopropyl alcohol0.5 g fish oil40 g 73200 binder

50 g LiA10220 g isopropyl alcohol0.5 g fish oil35.1 g Cerbind 73200 binder

50 g LiA102d

21.7 g isopropyl alcohol0.5 g fish oil35.1 g Cerbind 73200 binder

0.018

0.015(A)0.018(B)

0.019

0.015

LA-8

LA-9

LA-10

LA-1l

LA-12

LA-13

aSpray-dried LiA102 (SLA-1)bAs-received Lithco LiA1O2 .

g'rot-milled Lithco LiA102 (#3).

dTrost-milled Lithco LiA102 (#2).

0.020

37

air bubbles still remaining in the slip after de-airing using ultcasonicagitation/partial evacuation procedures. Improved de-airing techniques arebeing pursued, including fabrication of a filtering device for removal ofbubbles and any agglomerates that may be present in the castir:g slips.

Tape casting of LiAl02 matrices will be conducted at a reduced levelof effort during the next few months so that we can focus on development ofcathode fabrication techniques.

38

V. SYSTEM CODE DEVELOPMENT(S. A. Zwick)

Development of an eight-species chemical equilibrium routine, CHEQ, wascompleted in this period. The CHEQ routine a )unts for N2 and seven activespecies-CO, C02, CH30H, CH4, H2, 20, and 02, its purpose being to constructrapid first estimates for the larger equilibrium code, PROF. The procedurein CHEQ is to divide the (C, H2, 0) phase region into zones where only threeor four species are dominant (see Figs. 22 and 23). These species can befound quickly. Subsequently, the equilibrium relations are iterated to findother species. Special approximations are required for boundaries betweenzones, which change character between 700 and 1100 K from the low- to high-temperature limiting cases. The calculations now used in the CHEQ routineyield convergence to the correct solutions within about five iterations forall interior and boundary zone points tested, over the complete range of tem-peratures considered (now 100 to 2500 K).

C

Excess C

CO

CH4~ti0

CH4 Reform CO2

CO2 , H20 O 11Shift H2, CO, CH44 ~ 0

L / \I/ -Oxide -

H2 IH 2O0

Fig. 22. High-Temperature (above 1100 K) EquilibriumRegions. Each region contains as principalspecies the components named at the regioncorners, except for the oxide region whichcontains free 02 (not 0). At very hightemperatures, the boundaries, shown here aslines, broaden into finite zones. Below1100 K, the equilibrium species are a com-bination of the high- and low-temperature(Fig. 23) components. Because of theBoudouard (soot deposit) reaction, theactual Excess C zone extends somewhatbelow the CH 4 -CO line.

39

Co, CO

C

Excess C

Co

Monox H2, H2 0 ~O

CH4 C2CO, H2 *

Water A H2, CO,Fuel Oxide

H2 H2O 0

0CH 4 ~u 0

Fig. 23. Low-Temperature (below 700 K) EquilibriumRegions. Principal species in each regionare the components named at its corners,except for the oxide region which containsfree 02 (not 0). Above 700 K, the equi-librium species are a combination of thoseshown here and the high-temperature(Fig. 22) components. The Excess C regionactually extends somewhat below the CH4-COline due to the Boudouard (soot deposit)reaction.

A. New Thermodynamic Data Files

Earlier runs involving CHEQ and the System Analysis (SALT)* program' sproperties code, PROP, showed deviations from chemical equilibrium distribu-tions predicted by a modified NASA program 4 by a few parts per thousand insome cases. This variation was ascribed in large part to interpolationerrors in equilibrium constants computed by CHEQ and PROP. To avoid sucherrors, the thermodynamic files were reconstructed to give data values each100 K for the enthalpy, entropy, and heat capacities over the rage 100 to2400 K, instead of each 500 K over 500 to 3500 K ao in the original files.Data entries from the JANAF (1971) tables 5 were checked, and in some casescorrected or smoothed, by plotting the heat capacity (Cp) for all speciesin interpolation steps of 25 K and adjusting entries to give smooth seconddifferences. Values of Cp and Cp/T were then integrated numerically andcompared with the enthalpy and entropy tables. Finally, adjustments in the

*SAT is a systems code under development at ANL.

40

last places were made to give exact fits at 298.15 K and approximate extrap-olations through 2500 K or 2600 K. The interpolation routine uses hyperbolicspline segments adjusted for matching value and slope at each data point(100-K steps) and overall minimum curvature, so that extrapolations outsidethe tables are asymptotically linear.

B. Comparison with NASA Program Calculations

As a final test, predictions by CHEQ and PROP using the 100-K data werecompared with selected NASA program results and found to correspond throughthe fourth significant figure. The CHEQ and PROP programs differ from NASAin that the NASA code uses polynomial interpolations for the thermodynamicdata and accounts for dozens of trace species, whereas CHEQ and PROP usehyperbolic spline interpolation. The PROP routine computes equilibria forseven elements (Ar, C, H, K, N. 0, S) and 21 active species.

C. System Updates

The SALT program has been made interactive as a means of simplifyingfuel cell plant system design and adjustment. If input from a terminal isdesired, the user can insert PL/I Get-statements in his Struct (SALT input)files. These statements will halt a systems run until appropriate inputhas been entered at the terminal. To prompt the terminal user or report oncurrent calculations, a PL/I Put-statement, Put File(TERM).., should bewritten into the Struct file. Regular printouts still appear in file SPR2OUTP.

The NASA program will now accept input from files with names such asMYDAT DATA (MYDAT being an arbitrary name of 8 letters or less). To call fora NASA run in CMS, the user can enter NASA MYDAT at the terminal. Results ofthe run will then be sent to 0MS file MYDAT OUTP and, after the run is com-pleted, will be printed at the terminal. The terminal printout can be can-celled by pressing the (Break) key and typing HT, followed by (Return). ifno name is given after the NASA command, or if the statement LOAD NASA isentered, file GAS6 DATA will be used as default data file name.

D. Boudouard Tests

Carbon is not actually considered an equilibrium species by CHEQ andPROP, but its equilibrium constants are used to test for possible soot depositdue to the inverse Boudouard reaction (2CO A C02 + C), methane cracking(CH4 +' 2H2 + C), or CO decomposition (CO + H2 + H20 + C). A warning isprinted out if this appears likely.

Inert species (as defined by the user) are handled in PROP by withdraw-ing the inert fraction before an equilibrium calculation and adding it backafterward. The equilibrium constants are reduced to suppress production ofthe species. The CHEQ routine has been adjusted so that its equilbriumconstants will match those of PROP when it is intended for input to PROPequilibrium calculations.

41

REFERENCES

1. R. D. Pierce et al., Advanced Fuel Cell Development Progress Report forJanuary-March 1983 (in preparation).

2. C. E. Baumgartner, Cathode Material Development for Catbonate Fuel Cells,Oak Ridge National Laboratory Report ORNL/FMP-83-2, pp. 389-397(May 1983).

3. T. D. Kaun, Solubility of the NiO Fuel Cell Cathode in Li2CO3-K2C03

Melts as Determined by Cyclic Voltammetry, Fourth Int. Symp. on MoltenSalts, 163rd Electrochem. Soc. Meeting, San Francisco, CA, May 8-13,1983.

4. Sanford Gordon et al., Computer Program for Calculation of ComplexChemical Equilibrium Compositions, Rocket Performance, Incident andReflected Shocks, and Chapman-Jauget Detonations, National Aeronauticand Space Administration Report N78-17724 (NASA SP-273), March 1976.

5. JANAF Thermochemical Tables, 2nd ed., D. R. Stull and H. Prophet, ProjectDirectors (June 1971).

42

Distribution for ANL-84-9

Internal:

J. P. AckermanP. A. BlackburnR. L. Breyne

L. BurrisT. D. ClaarG. M. CookD. W. DeesJ. T. DusekD. C. FeeP. A. FinnB. K. FlandermeyerA. V. FraioliJ. E. Harmon

A.T.V.M.G.N.F.

Z.P.J.R.R.

A. JonkeD. KaunM. KolbaKrumpeltH. KuceraQ. MinhC. MrazekNagy.. NelsonJ. PiccioloD. Pierce (25)B. Poeppel

J. J. RobertsJ. L. SmithJ. R. StapayR. K. SteunenbergB. S. TaniE. H. VanDeventer

J. E. YoungS. A. ZwickA. B. KrisctunasANL Patent Dept.ANL Contract FileANL Libraries (3)TIS Files (6)

External:

DOE-TIC, for distri t "tion per UC-93 (130)Manager, Chicago Opecations Office, DOER. J. Gariboldi, DOE-CHM. Zahid, DOE-CHChemical Technology Division Review Committee Members:

S. Baron, Burns and Roe, Inc., Oradell, N. J.W. L. Worrell, U. PennsylvaniaE. B. Yeager, Case Western Reserve U.

Materials Science Division Review Committee:C. B. Alcock, U. TorontoA. Arrott, Simon Fraser U.

R. C. Dynes, Bell Labs., Murray HillA. G. Evans, U. California, Berkeley

L. M. Falicov, U. California, BerkeleyH. K. Forsen, Bechtel Group, Inc., San Francisco

E. Kay, IBM San Jose Research Lab.M. B. Maple, U. California-San DiegoC. L. McCabe, Cabot Corp., Kokomo, Ind.P. G. Shewmon, Ohio State U.J. K. Tien, Columbia U.

B. S. Baker, Energy Research Corp., Danbury, Conn.R. W. Barta, General Electric Co., Ballston Spa, N. Y.

J. L. Bates, Pacific Northwest Lab.

T. R. Beck, Electrochemical Technology Corp., Seattle

R. Bradley, Oak Ridge National Lab.E. Camara, Inst. Gas Technology, Chicago

P. T. Carlson, Oak Ridge National Lab.T. W. Carter, U. S. Coast Guard, WashingtonD. Chatterji, General Electric Co., Schenectady

J. Cuttica, Gas Research Inst., ChicagoW. Feduska, Westinghouse R&D Center, PittsburghL. M. Ferris, Oak Ridge National Lab.A. P. Fickett, Electric Power Research Inst.

E. Gillis, Electric Power Research Inst.J. Giner, Giner, Inc., Waltham, Mass.

43

F. Gmeindl, Morgantown Energy Technology CenterG. L. Hagey, Div. Advanced F:Lergy Conversion Systems, USDOEJ. W. Harrison, General Electric Co., Wilmington, Mass.L. C. Headley, Morgantown Energy Technology CenterD. T. Hooie, Gas Research Inst., ChicagoW. Huber, Morgantown Energy Technology Center

A. 0. Isenberg, Westinghouse R&D Center, PittsburghB. Jackson, Tennessee Valley Authority, ChattanoogaD. Johnson, Northwestern U.

J. Kelly, Westinghouse R&D Center, Pittsburgh

C. Kinney, Office of Fossil Energy, USDOEK. Kinoshita, Lawrence Berkeley Lab.M. Kresge, Mitsubishi International Corp., New York CityH. R. Kunz, United Technologies Corp., South Windsor, Conn.A. R. Maret, Gas Research Inst., ChicagoN. Margalit, Combustion Engineering, Windsor

L. Marianowski, Inst. of Gas Technology, ChicagoH. Maru, Energy Research Corp., Danbury, Conn.

R. Matsumato, Ceramatech, Salt Lake CityA. P. Meyer, United Technologies Corp., South Windsor, Conn.C. A. Reiser, United Technologies Corp., South Windsor, Conn.

F. Salzano, Brookhaven National Lab.J. Searls, U. S. Bureau of Mines, WashingtonR. Selman, Illinois Inst. of TechnologyJ. Sholes, Morgantown Energy Technology CenterP. Stonehart, Stonehart Associates, Inc., Madison, Conn.

G. Wilemski, Physical Sciences Inc., Andover, Mass.K. Wray, Physical Sciences Inc., Andover, Mass.C. Zeh, Morgantown Energy Technology Center, USDOE