1-18

ADVANCED FUEL-CELL DEVELOPMENT

Progress Report for

July-September 1980

by

R. D. Pierce, R. M. Arons, J. T. Dusek,

A. V. Fraioli, G. H. Kucera, R. B. Poeppel,

J. W. Sim, J. L. Smith, and B. S. Tail

ARGONNE NATIONAL LABORATORY, ARGONNE, ILLINOIS

Prepared for the U. S. DEPARTMENT OF ENERGYunder Contract W-31-109-Eng-38(i

A A

RA

ANL-81-16

*SO,

The facilities of Argonne National Laboratory are owned by the United States Government. Under the

terms of a contract (W-31-109-Eng-38) among the U. S. Department of Energy, Argonne UniversitiesAssociation and The University of Chicago, the University employs the staff and operates the Laboratory inaccordance with policies and programs formulated, approved and reviewed by the Association.

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Available fromNational Technical Information ServiceU. S. Department of Commerce5285 Port Royal RoadSpringfield, VA 22161

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This report was prepared as an account of work sponsored by anagency of the United States Government. Neither the UnitedStates Government nor any agency thereof, nor any of theiremployees, makes any warranty, express or implied, or assumesany legal liability or responsibility for the accuracy, com-pleteness, or usefulness of any information, apparatus, product,or process disclosed, or represents that its use would not infringeprivately owned rights. Reference herein to any specific com-mercial product, process, or service by trade name, trademark,manufacturer, or otherwise, does not necessarily constitute orimply its endorsement, recommendation, or favoring by theUnited States Government or any agency thereof. The views andopinions of authors expressed herein do not necessarily state orreflect those of the United States Government or any agencythereof.

Distribution Category:Energy Conversion

(UC-93)

ANL-81-16

ARGONNE NATIONAL LABORATORY9700 South Cass Avenue

Argonne, Illinois 60439

ADVANCED FUEL-CELL DEVELOPMENT

Progress Report forJuly-September 1980

by

*R. D. Pierce, R. M. Arons, J. T.

R. B. Poeppel, * J. W. Sim,

*Dusek, A. V. Fraioli, G. H. Kucera,J. L. Smith, and B. S. Tani

Chemical Engineering Division

July 1981

Previous reports in this series

ANL- 79-110ANL-80-33ANL-80-67ANL-80-9 8

July-September 1979October-December 1979

January--March 1980April-June 1980

*Materials Science Division, ANL.

DISCLAIMER

... , .14

S 'A .. (1 . " ., r ". '' .M ^ " ,,,.," I .Y -" -^ " -

L .. .'1 r " t

TABLE OF CONTENTS

Page

ABSTRACT . . . . . . . . . . . . . ....... ...0SUMMARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

I. INTRODUCTION . . . . . . . . . . . . . . . .9. . . .. 0.0.. . .

II. ELECTROLYTE DEVELOPMENT . . . . . . . . . . . . . .

A. Preparation of Sinters from -LiAl02 - - - - -

B. Alpha Lithium Aluminate Powder Production . . .

C. Characterization of Sintered Structures . .

D. Tape Casting Development . . . . . . .

E. Use of Spray Dried LiA102 in Electrolyte Tiles

III. TESTING OF ELECTROLYTE STRUCTURE . . . . . . . . . . .

A. LiA102 Thermal Stability/PolymorphicTransformation Studies . . . . . . . . . . . . .

B. Thermomechanical Tests . . . . . . . . . . . . .

C. Factors Influencing X-ray Interpretation in LIA102

1. Identification of - and y-LiA1O2. . . . .-. . .

2. Identification of a-LiA1O 2 and y-A1203 .---

3. Identification of y-A1 2 0 3 , LiA15 08 , and Al ON4. Discussion . .0. . . . .. 0 0 . . .

IV. CATHODE DEVELOPMENT.............. ................... 0.,....

A.

B.

C.

D.

Fabrication of Lithiated NiO Cathodes. . . . . .

Development of Laminated Cathode/ElectrolyteStructures . . . . . . . . . . . . . . . .

Nickel Aluminate . . . . . . . . . . . .

Electroless Nickel Plating . ..0 ..0 ..0 .V. CELL AND STACK DESIGN . . . . . . . . . . . .. . . . . . . . . .

APPENDIX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.REFERENCES..................... . . . . . . . . . . . . . . .

1

1

4

5

5

9

10

10

12

14

14

16

16

17171719

22

22

23

24

26

29

30

31

iii

--.,

--..

" ." .I ." ." ."

LIST OF FIGURES

No. Title

1. Micrograph of Sintered Pellet P-207-2-2 ShowingDestruction of Fine Microstructure by Excess LiOH

2. Micrograph of Sintered Peliet P-207-2-3 ShowingParticle Growth Caused by Excess LiOR

3. Micrograph of Sintered Pellet P-207-9-1Showing Normal Sintering Behavior .

4. Micrograph of Sintered Pellet P-134-147-3 ShowingNormal Sintering Behavior . . . . . . . . . . . . . . .

5. Micrograph of Spray Dried LiA10 2 afterImpregnation with Carbonates . . . . . . . . . . . . . . . .

6. Resistivity of Lithiated NiO Versus theTemperature of a 1-h Sintering Treatment . . . . . . . . . .

7. Catapal "SB" Hydrated Alumina Agglomerates . . . . . . . . .

8. Agglomerates of NiAl 2 04 Formed from Catapal SB at 1600*C . .

9. Faceted NiAl 2 04 from Catapal SB.. . .0 . 0. 0 . 0.0 .

iv

7

7

8

9

13

23

27

27

28

. . ."

. . ."

. . .

. . ."

LIST OF TABLES

No. Title Page

1. Summary of Spray Drying Experiments. .... . . ........ 6

2. Summary of Sintering Experiments . . . . 6

3. EstimatIon of Water in Spray Drying Reactants . . . . . . . . . . 9

4. Results of Mercury-Porosimetry Analyses of Sintered LiA102 . . . 11

5. Effect of Additives on the S- to y-LiA10 2 TransitionTemperature . . . . . . . . . . . . . . . . . . . . . . . . . . 15

6. Effect of Additives oil the a- to y-LiA102 TransitionTemperature . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

7. X-ray Powder Diffraction Patterns of Phasesin the Li-Al-O System . . . . . . . . . . . . . . . . . . . . . . 18

8. Density and Resistivity of Lithiated NiO as aFunction of Sintering Temperature after a 1-h Soak . . . . . . . . 22

9. Nickel Aluminate Summary Data . .............,............. 25

V

ADVANCED FUEL CELL DEVELOPMENT

Progress Report forJuly-September 1980

by

R. D. Pierce, R. M. Arons, J. T. Dusek, A. V. Fraioli, G. H. Kucera,R. B. Poeppel, J. W. Sim, J. L. Smith, and B. S. Tani

ABSTRACT

This report describes advanced fuel cell research and develop-ment activities at Argonne National Laboratory (ANL) during theperiod July-September 1980. These efforts have been directedtoward (1) investigating alternative concepts for components ofmolten carbonate fuel cell stacks and (2) improving our under-standing of component behavior.

The principal focus has been on the development of sinteredy-LiA102 for electrolyte support and sintered LixNil-xO forcathodes. In the electrolyte development effort, both a- andB-LiA102 have been synthesized as starting material for sinteredelectrolyte supports, and tape casting is being studied for pre-paring green bodies for sintering. A sintering procedure has beendeveloped which produces flat NiO cathodes with good conductivityand pore structure, and work has begun on sintering a lithiatedNiO cathode and LiA102 electrolyte support as one body.

Components are evaluated in bench-scale cell tests. A new

cell/stack design was completed in an effort to increase flexi-bility in our cell testing.

SUMMARY

Electrolyte Development

Both a- and S-LiA102 are being synthesized as starting material forsintered electrolyte supports.

A spray-dried material for synthesizing s- LiA102 was prepared from anaqueous slurry of Al(OH)3 and LiOH-H20. Results indicate that stoichiometricmixtures of these reactants produce S-LiA102 with good sintering properties,but that excess hydroxides result in S-LiA102 that will undergo excessivesintering and loss of fine pore structure. The spray-dried powders have the

reproducible surface areas needed for tape casting.

A supply of a-LiA10 2 (%6 kg) has been produced for future use in pro-

ducing sintered electrolyte structures. Plans are for spray drying to beu43ed in the future production of this material.

1

2

Sinters prepared from a-LiA102 powders were examined. The starting

material--Degussa A1203 and Alcoa type-H7J.0 Al(OH)3--affected the final meanpore size; but, for both materials, the pore size was acceptably small incomparison to typical electrode pore sizes.

Investigations are continuing on the use of tape casting as a method ofproducing the green body for sintering. Progress has been made in producinga good slip with high-surface area LiA102 . The material can be successfullycast, but some problems yet remain with cracking during the drying operation.

Impregnation of spray-dried LiA102 powders with carbonates for hot-pressed tile production is being pursued. Spray-dried S-LiA102 has beenwetted with carbonates, and SEM photographs indicate that the particles werecompletely coated with carbonates. An attempt will be made to convert spray-dried S-LiA102 to y-LiA1O2 for impregnation and use in preparing tiles.

Testing of Electrolyte Structures

Further work has been done on defining the S- to y-LiA1O2 transforma-tion. Earlier work showed that carbonate eutectic promotes the transitionand that y-A1203 inhibits it. Results of the current work indicate that, ifnot catalyzed by an impurity, the a- to y-LIA102 reaction occurs between 1098and 1143 K; this transition occurs at about 1038 K when catalyzed. Additionof LiOH to the S-LiA102 produces a significantly lower transition temperature(981 K). Similar experiments with a-LiAl02 also showed L decreased transitiontemperature in the presence of carbonate eutectic; the effect was greaterwhen hydroxide also was present.

A creep test on a sintered LiA102 disc showed no measurable creep in200 h at 932 K under the conditions of the test. In addition, a thermo-mechanical test on a hot-pressed pellet of spray-dried S-LiA102 and 62.5 wt %carbonates was run and showed characteristics of a "dry" conventional tile,i.e., very little permanent deformation upon heating to 925 K.

Burn-off of some potential tape-casting binders was examined in athermogravimetric/iifferential scanning calorimetric analyzer. About 90 wt %of each specimen wz.s decomposed and vaporized at 735 K.

X-ray diffraction is a valuable tool in understanding the LiA102 mater-ials used in both tiles and sinters. It has limitations due to similarpatterns for different materials, especially with widened or overlappingbands. The details of these problems and their implications for quantita-tive measurements are discussed.

Cathode Development

Flat lithiated NiO cathodes with good conductivity, pore structure, andmachinability have been prepared by a sintering procedure. A group of NiOdisks (3.18-cm dia) were prepared by this procedure at sintering temperaturesfrom 800 to 1300*C and their resistivity measured. The optimal resistivitywas attained with a 1000-1100 C sintering temperature.

3

Work has begun on sintering a lithiated NiO cathode and LiA102 electro-

lyte structure as one body. Sintering characteristics are being tailored byusing different binders for the two parts of the body. Cold-pressed bodiesof 32 cm2 have been sintered with the required properties.

Nickel aluminate is being studied as a possible substrate material forthe electrolyte structure and electrodes. Four alumina precursors were usedin the preparation of nickel aluminate. The methods of preparation and finalproduct properties, surface area, and x-ray diffraction analysis are reported.

Cell and Stack Design

A preliminary laboratory cell/stack design has been completed that willallow considerable flexibility in operation. With this new design, anycombination of flow patterns and most potential component variations can beaccommodated with few if any modifications.

Electroless Nickel Placing

Electroless deposition of nickel alloys is being investigated as ameans of providing corrosion protection for structural hardware. Previouslyreported 752 Series Niklad* nickel platings were heat treated and the productswere analyzed. TAitially, these platings were diffusely reflective and weretarnished significantly after two hours at 650*C in air. They did, however,remain adhered to the substrate.

*Allied-Kelite Division, The Richardson Company.

4

I. INTRODUCTION

The advanced fuel cell studies at Argonne National Laboratory (ANL) arepart of the DOE Advanced Fuel Cell Program. A goal of this DOE program isthe earliest possible introduction of high-efficiency generating systemsbased on molten-carbonate fuel cells, which have the capability of operatingon coal or other fuels. At the present stage of development, the primarythrust of the ANL program is directed to development of the fuel cell itself.

A molten carbonate fuel cell consists of a porous nickel anode, aporous lithiated nickel oxide cathode, an electrolyte structure which sep-arates the anode and cathode and conducts only ionic current between them,and appropriate metal housing or, in the case of stacks of cells, intercellseparator sheets. The cell housings (or separator sheets) bear upon theelectrolyte structure to form a seal between the environment and the anodeand cathode gas compartments. The usual electrolyte structure, which iscommonly called "tile," is a composite of discrete LiA102 particles and amixture of alkali metal carbonates. The carbonates are liquid at the celloperating temperature of 925 K. At the anode, hydrogen and carbon monoxidein the fuel gas react with carbonate ion from the electrolyte to form carbondioxide and water while giving up electrons to the external circuit. At thecathode, carbon dioxide and oxygen react and accept electrons from theexternal circuit to reform carbonate ion, which is conducted through theelectrolyte to the anode. In a practical cell stack, CO2 from the cathodeprobably would be obtained from the anode exhaust.

The ANL contribution to the program is intended to develop improvedcomponents and processes and to provide understanding of cell behavior.Improvements are needed in the electrolyte structure and cathode, which arereceiving special attention at ANL. Electrolyte structures employing asintered LiA102 matrix are being examined as an alternative to tiles, whichare a paste-like mixture of fine LiA10 2 particles and carbonate salt.Characterization of electrolyte structure properties and the relation of theproperties to cell behavior is of major importance. Determination of thestability of the structure is also of high priority.

Current molten carbonate fuel cell practice involves assembling cellswith a sintered nickel cathode which reacts in situ with the oxidant gas ardthe electrolyte to form lithiated nickel oxide. The lithiation provides thecathode with adequate electronic conductivity. ANL is investigating prepara-tion of lithiated-nickel oxide cathodes for assembly in cells to improve cellperformance through better conductivity, strength, and dimensional stabilityof the cathode.

Cells are operated to assess the behavior of the electrolyte and othercomponents and to understand the performance and life-limiting mechanisms atwork within the cell. Cell operation is coupled with efforts on diagnosticsand materials development.

5

II. ELECTROLYTE DEVELOPMENT

For the past several years, we have been synthesizing mixtures of LiA102particles and carbonate salt, which were then pressed into a paste-like tilefor testing. Recently, we have shifted our attention to the development ofelectrolyte structures consisting of a sintered LiA102 matrix, which has theadvantages of being easily inspected to determine its acceptability, probablythermally stable, and compatible with fabrication of structures comprisingelectrod-electrolyte support laminates.

A. Preparation of Sinters from $-LiAlO2

(J. W. Sim, J. J. Slaga*)

During this quarter we investigated the use of LiOH-H2O in place of anhy-drous LiOH as a reactant in the synthesis of $-LiAlO 2 powders. The LiOH-H20reactant is less expensive than anhydrous LiOH, and it is also less hygro-scopic, which should permit better control of the reactant stoichiometry.Poor control of reactant stoichiometry can lead to the presence of excessLiOH in the LiA102 powder, which results in excessive densification andparticle growth by liquid-phase sintering (ANL-80-67, p. 8).

The experiments using LiOH-H20 as a reactant are summarized in Table 1,along with previous experiments using anhydrous LiOH. In these experiments,the reactants were mixed as an aqueous slurry, and then the slurry was spraydried using pneumatic atomization. After calcination of the spray-driedpowders at 875 K, the LiA102 powders were pressed into pellets and sinteredat 1275 K t', determine whether excessive densification or particle growthoccurred during sintering.

As shown in Table 2, pellets sintered from batches 134-1.48-600 and134-152-600 showed excessive densification and particle growth, and it wasconcluded that excess LiOH was present in the LiA102 powder. This particlegrowth is apparent in Figs. 1 and 2, which show the destruction of fineporosity due to liquid-phase sintering in pellets P-207-2-2 and P-207-2-3,respectively. The pellets sintered from batch 134-152-600 (see P-207-2-1and P-207-2-3 in Table 2) did not decrease in porosity as much as did pelletssintered from batch 134-148-600 (see P-134-149-2 and P-207-2-2 in Table 2).Comparison of Figs. 1 and 2 shows that the destruction of fine porosity ismore complete for P-207-2-2 than for P-207-2-3. These findings suggest thatbatch 134-152-600 ha(: less excess LIOH than batch 134-148-600; this wasexpected because less LiOH-H2O was used in preparing batch 134-152-600(see Table 1). When the amount of LiOH-H20 was further decreased, in batch207-7-600, the stoichiometry was finally corrected so that excess LiOH waseliminated. This is apparent in Fig. 3, which shows that the fine porositywas retained during sintering. Also, pellets made from batch 207-7-600(P-207-8 and P-207-9-1) maintained high porosity after sintering (Table 2).Thus, by controlling the stoichiometry of the reactant mixture, the presenceof excess LiOH in the LiA102 powder can be avoided.

To control the stoichiometry of the reactant mixture, the purity of thereactants must be known. The. major impurity in the reactants is probably

*Materials Science Division, ANL.

6

Table 1. Summary of Spray Drying Experimentsa

Product Corrected SurfaceRecovery, Li/Al Li/Al Area,

Batch No. Reactants % Ratiob Ratioc m2/g

134-144-600 305.3g Al(OH)3 46 1.055 1.011 2598.9g LiOH

134-145-600 305.Og Al(OH)3 83 1.057 1.013 2499.Og LiOH

134-148-600 305.Og A1(OH)3d 73 1.050 1.062 --172.2g LiOH-H20

134-152-600 305.Og Al(OH)3d 63 1.001 1.013 --164.2g LiOH-H20

207-7-600 305.Og Al(OH)3d 65 0.973 0.985 22159.7g LiOH-H2 0

aSpray dried powders were calcined at 875*C for 20 h.bAssumes 100% assay of Al(OH)3, LiOH-H2 0, and LiOH.cBased on estimates of water in reactants (see Table 3).dNew batch of Al(OH)3 .

Table 2. Summary of Sintering Experimentsa

Pellet No. Batch No. Green Porosity, % Sintered Porosity, %

P-134-145-1 134-144-600 72.4 64.1

P-134-145-2 134-144-600 72.2 63.6

P-134-147-3 134-145-600 71.2 62.4

P-134-147-4 134-145-600 70.4 58.8

P-134-149-2 134-148-600 67.2 25.0

P-207-2-2 134-148-600 63.4 31.2

P-207-2"1 134-152-600 71.6 45.6

P-207-2-3 134-152-600 72.0 49.8

P-207-8 207-7-600 72.9 71.0

P-207-9-1 207-7-600 72.6 66.2

aSintered at 1275 K for 1 h; pressed at 27.6 1Pa.

7

Fig. 1. Micrograph of Sintered Pellet P-207-2-2Showing Destruction of Fine Microstructure

by Excess T:iOH (sintered simultaneouslywith P-207-2-3)

Fig. 2. Micrograph of Sintered Pellet P-207-2-3Showing Particle Growth Caused by ExcessLiOH (sintered simultaneously withP-207-2-2)

8

Fig. 3. Micro;raph of Sintered Pellet P-207-9-1Showing Normal Sintering Behavior

water. Therefore, we attempted to measure the amount of water (ab. ,rbedor as hydrate) in each reactant by determining the weight loss upon heatingit in air. These results, which are summarized in Table 3, were then usedto calculate the corrected lithium-to-aluminum molar ratios given in Table 1.Although the corrected ratio was identical for batches 134-145-600 arn134--152-600, pellets from the former batch exhibited acceptable sinteringbehavior (see Fig. 4), while those from the latter batch sintered excessively(see Fig. 2). This suggests that there are additional impurities in thereactants. We have submitted samples of the reactants for analysis todetermine the level and type of additional impurities not accounted for bythe weight-loss experiments.

The specific surface areas of several samples of S-LiA102 powder pro-duced by spray drying were determined by nitrogen adsorption analysis.*These results, also given in Table 1, show that powders with reproduciblesurface areas can be obtained by spray drying. This is desirable if thepowder is to be used in tape casting (see Section II.D of this report)because the surface area of the powder can affect the viscosity of the tape-casting slip. Thus, spray drying is probably an effective method of pro-ducing LiA102 powder for tape-casting experiments.

*Analyses performed by R. Malewicki, Analytical Chemistry Laboratory, ANL.

9

Table 3. Estimation of Water in Spray Drying Reactants

Reactant Temperature, K Time, h Wt Loss, % Stoichiometric Wt Loss, %

LiOH 425 2 4.0 0

LiOH-H20 425 2 42.4 42.9

Al(OH)3a 1265 2 34.6 34.6

Al (OH) 3a 1265 2 34.4 34.6

aNew batch of Al(OH)3 .

. . :3. 3 m

Fig. 4. Micrograph of Sintered Pellet P-134-147-3Showing Normal Sintering Behavior

B. Alpha Lithium Aluminate Powder Production(R. M. Arons, J. T. Dusek, and W. Lloyd)*

We are engaged in producing a supply of a-LiA102 for use in developmentof a sintered electrolyte retainer. Powder is being prepared according to

the method described by Singh et al.1 in which Al203and Li2CQ3 are ball

milled in methanol, centrifuged, dried, screened, and calcined at 650*C for

four days. Up to the present time, we have produced about 6 kg of powder

*Materials Science Division, ANL.

10

in batches of 600 g each. X-ray diffraction (XRD) * shows the calcined productto be almost pure a-LiA102 , with possible traces of y-LiA102. A sample of themethanol supernate was evaporated, and a residue at Li2CO3 was identified byXRD--thereby showing that Li2CO3 has some solubility in methanol. We are nowrecycling used methanol and expect that it will saturate with Li2CO3. Inaddition, LiCl-H20 was identified as an impurity which extracts into themethanol.

We are now calcining larger batches of powder to assure ourselves thatno new problems will arise due to scale-up production-size runs.

Because the method described by Singh is fairly time-consuming andinvolves extensive material handling, we plan to spray-dry powder as a meansof attaining a fine-grained, highly homogenized mixture of A1203 and Li2CO 3for subsequent calcination.

C. Characterization of Sintered Structures(J. W. Sim)

Small pore sizes in the sintered LiA102 structuw are desirable forretaining the molten carbonates. Consequently, mercury-porosimetry analyseswere performed on several pellets that were sintered from S-LiA102 powders.The powders had been prepared by spray drying an aqueous slurry containingLiOH and either Degussa A1203 or ALCOA type-H710 Al(OH)3. The results ofthese analyses are given in Table 4. For comparison, typical results are alsogiven for a pellet prepared from a-LiAlO2 and another one prepared fromy-LiAlO2 powders. In this table, it is apparent that the first three pelletshave smaller pore sizes than those of the next four pellets. This wasexpected because the powder used in these first three pellets containedsmaller particles. (See ANL-80-67, p. 5 for a discussion of the character-istics of spray-dried powders as they are affected by the type of aluminaused.) As shown in Table 4, the pore sizes of the pellets prepared fromspray-dried 8-LiAlO2 powder are somewhat larger than those for pellets pre-pared from a-LiAlO2 powder; nevertheless, the pore sizes are considerablysmaller than those of typical a'.iodes and cathodes (about 5-um and 15-um manpore size, respectively). Thus, sintered structures prepared from spray-drieda-LiAlO2 probably have an accetable pore-size distribution for effectiveelectrolyte retention.

D. Tape Casting Development(J. T. Dusek and R. M. Arons)

Tape casting is under investigation as a method of producing the greenbody for sintered LiA102 structures. (See ANL-80-98, p. 5 for a descriptionof this process.) To this end, we have begun to formulate thick slurries(slips) which may be appropriate for the tape casting of LiA102. One radicaldeparture from the well-understood A1203 tape-cast systems is the extremelyhigh surface areas of the current LiA102 powders of interest. The appropriatevolume fraction of liquids added as vehicles and deflocculants for A1203 wasinsufficient to achieve the desired consistency when added to LiA102. Whenadditional solvent was introduced, the slip tended to separate. Consultation

X-ray diffraction analyses provided by B. S. Tani, Analytical Chemistry

Laboratory, ANL.

PPrPellet

P-134-129-1A

P-134-131-1

P-134-138

P-134-147-4

P-134-145-2

P-134-129-2A

P-134-131-2

37

43

Table 4. Results of Mercury-Porosimetry Analyses of Sintered LiA102

10% Pore Volume 50% Pore VolumeC 90% Pore Volume?owder Smaller Than This Smaller Than This Smaller Than Thisrecursor Diameter, pm Diameter, pm Diameter, pm

a 0.04 0.26 0.76

a 0.04 0.11 0.66

a 0.05 0.08 0.67

b 0.23 0.65 1.36

b 0.11 0.39 1.28

b 0.11 0.34 0.71

b 0.11 0.28 0.66

-LiA102 0.09 0.12 0.16

-LiA102 0.17 0.30 1.28

Porosity, %

42.4

48.3

62.8

60.2

63.6

64.1

64.5

58.4

54.8

as-LiA10 2 powder obtained by spray

b O-LiA102powder obtained by spraycCommonly referred to as mean pore

drying

dryingsize.

of Degussa A12 0 3 /LiOH slurry.

of ALCOA type-H710 Al(OH) 3/LiOH slurry.

I-'N-

a-

Y-

12

with R. Mister (Plessey Corp.) led to the conclusion that more fish oil wasneeded in our system to wet all the particles and that an increase in solventfraction should parallel the fish-oil increase. Mistler recommended that ourfinal slip have a viscosity of 2 to 4 Pa-s. As a result of these recommenda-tions, a stable slip was produced, and preliminary casting experiments wereinitiated.

Thirteen trial runs on batch preparati.on for LiA102 tape casting weremade by varying the amount of components (including LiA102, fish oil, solvent,lubricant, plasticizer, and binder) in an attempt to produce a satisfactoryslip for taping. The doctor blade was set to produce a tape casting of 1.9-mmthickness. After drying, the tape casts varied in thickness from 0.7 to 0.8 mm.None of the formulations tried produced a good tape; each had some type ofcracking problem. Some dried very rapidly and formed cracks within minutesof taping; other dried more slowly and did not crack until essentially dry.

The mix of components and the preparation conditions must be carefullyadjusted to achieve simultaneously (1) proper wetting of the powder, (2) suffi-cient binder strength, (3) the ability to control drying time, and (4) propertape release from the substrate. The sequence of the steps in mixing thematerials also is important to obtain a good slip. If the solvent and fishoil are mixed first and then the LiA102 powder is added, the powder will wetmore readily. The plasticizer and lubricant can then be added withoutincreasing the viscosity too much. The binder is added last. This sequencerequires the minimum amount Of solvent. The fraction of solvent used canbe influential in determining the d-ying rate. Mistler has found similarbehavior in the tape casting of A1 203 .

E. Use of Spray-Dried LiA102 in Electrolyte Tiles

(J. ;. Sim)

We are considering the use of LiA102 produced by spray drying in thefabrication of hot-pressed electrolyte tiles. Consequently, we have performedsome preliminary experiments to obtain a uniform mixture of spray-dried LiA102and alkali carbonates. A portion of batch 207-7-600 (37.5 Uit %) was mixedwith Li2C03 (28.8 wt %) and K2C03 (33.7 wt %), and this mixture was heated to650*C for 1 h to impregnate the LiA102 with the carbonates. Microscopicexamination of the powder after impregnation revealed no evidence of separatecarbonate crystals, as shown in Fig. 5. The hollow spherical agglomerates ofLiA102 , produced by the spray drying, were covered by a film of carbonates,thereby indicating that a uniform, intimate mixture of LiA102 and carbonateswas obtained.

We plan to continue investigating the use of LiA102 produced by spraydrying in hot-pressed electrolyte tiles. We will attempt to convert thespray-dried 8-LiAl02 to y-LiA102 without decreasing the surface area of thepowder below that required for electrolyte tiles (about 17 m2/g). If theconversion is successful, we will impregnate the y-LiAlO2 with the Li2CO3 -K2C03 eutectic and use the resulting mixture in electrolyte tiles.

13

Fig. 5. Micrograph of Spray-Dried LiA102after Impregnation with Carbonates

14

III. TESTING OF ELECTROLYTE STRUCTURE

A. LiA102 Thermal Stability/Polymorphic Transformation Studies

(G. H. Kucera)

In the previous quarterly (ANL-80-98, p. 8), we reported that differentialthermal analysis (DTA) measurements on specimens consisting of 8-LiA102 rodsand varying amounts of the impurity y-A1203 (about 2-30 wt %) showed anincrease in the temperature of the $- to y-LiA102 transition directly relatedto the amount of y-A1203 in the mixture. We suggested that (1) a coating ofLi2CO3-K2C03 eutectic or a solid solution of eutectic in LiA102 on therelatively "pure" aluminate particles acts to promote the 8- to y-LiA102transition and that (2) the y-A1 203 reacts with the coating and inhibits thetransition. Analytical data showed the presence of potassium (A1/K=5/1), thuslending support to our speculation. However, the credibility of this hypo-thesis would be increased if it could be demonstrated experimentally thatthere is an amount of y-A1 203 that does not cause a further increase in thetransition temperature.

During this reporting period, we assessed the effect of adding largeamounts of y-A1 203(>30 wt %) to O-LiA102 rods on the 8- to y-LiA102 transi-tion temperature. In addition, we investigated the transition temperatureof pure a- to y-LiA1O2, and studied the effect of the additives--Li2CO3-K2C03eutectic, LiOH, and LiOH/eutectic--on the B- and a- to y-LiA102 transitions.

The thermogram obtained in a previous DTA experiment (ANL-80-98, p. 9)on a specimen containing about 30 wt % y-A1 203 and 0-LiA102 rods showed onlya weak endotherm indicative of the 0- to y-LiAl02 transition; therefore, DTAmethods could not be used to study the effect of greater amounts of y-A1203on the S- to y-LiA102 transition. Frm these data, however, it was estimatedthat The transition occurred at about 1106 K. In the current studies,mixtures containing 8-LiA102 rods and 29, 39, and 51 wt % y-A1203 were heldat 1098 and 1143 K in air for 3 and 1 1/2 h, respectively. Small samples ofeach mixture were analyzed by X-ray diffraction analyses.* The data show noevidence of the a- to y-LiA102 transition in any of the mixtures at 1098 K;however, the y-LiAlC2 phase was present in all three mixtures at 1143 K. Thesedata offer further support to the contentions that (1) some substance actingas a catalyst is destroyed by the presence of y-A1203 and (2) the transitionof S-LiA102 rods devoid of a catalyst to y-LiAl02 faces an energy barriersignificantly higher :han that of O-LiA102 rods with a catalyst. From theseexperiments, we estimate that the uncatalyzed O-LiA102 transforms to y-LiA102at a temperature >1098 and <1143 K; in contrast, the catalyzed O-LiA102transforms to -LiAl02 at 1038 10 K.

The effect of other additives on the 8- to y-LiA102 transition wasassessed also. Table 5 is a summary of the DTA transition-temperature resultsfor the addition of both 26 wt % Li2CO3-K2C03 eutectic and 15 wt % LiOH toS-LiA102 reds. The thermal measurements were made in air at heating rates of5 K/min for the eutectic additive and at 5 and 10 K/min for the LiOH additive;the transition onset temperature was obtained by extrapolation to a zeroheating ':ate. The data in Table 5 show little or no change in the onset tem-perature as a result of the eutectic addition; however, the addition of LiOHproduced a significantly lower onset temperature.

*X-ray diffraction analysis pe-cformed by B. S. Tani, Analytical ChemistryLab3ratory, ANL.

15

Table 5. Effect of Additives on the S- toy-LiA1O2 Transition Temperature

Composition Onset Temperature,a K

$-LiA102 rods (washed) 1038

S-LiA102 rods + 26 wt % Li2CO 3-K2C03 eutectic 1028

8-LiA102 rods + 15 wt % LiOH 981

aExtrapolated to a zero heating rate

The transformation temp :rature of a- to y-LiA102 was determined by DTAmethods. The a-LiA1 2 used in these studies was prepared by reacting Degussa

y-A1203 with a stoichiometric amount of Li2CO3 at 873 K (batch no. 18-38).X-ray diffraction -nalyses showed only two phases, a-LiA102 (major) and Li2CO3(very minor); nevertheless, a portion of this batch was mixed with an equalweight of Li2CO3-K2C03 eutectic and heated at 843 K in air for about 90 h(sample no. 18-63A) to ensure complete reaction of the y-A1203 and to promotecrystal growth.

Table 6 presents the extrapolated onset temperatures for the phase transi-

tion (at a zero heating rate) of pure a-LiA102 (sample 18-63A washed free ofcarbonates), a-LiA102 plus Li2CO3-K2C03 eutectic, and a-LiAlO2 plus theeutectic plus LiOH. The data show that the pure a-LiA102 transformed toy-LiA10 2 at a temperature about 200 K higher than the a-LiA10 2 in thealuminate/20 wt % eutectic mixture. This large difference in transitiontemperature suggests that the catalyzing agent present in pure 8-LiA102rods was not present in the specimen of pure a-LiA102. Energy dispersivex-ray fluorescence analysis* of the pure a-LiA10 2 showed little potassium;the Al/K ratio was assessed to be 25:1. The addition of LIOH (about 6 wt %) toan aluminate/6 wt % eutectic mixture resulted in a further decrease in the

extrapolated onset temperature of the a- to y-LiA1.02 transition. This trendis similar to that reported above for the 8-LiAlO 2/LiOH mixture.

Table 6. Effect of Additives on the a- to

y-LiAlO2 Transition Temperature

Composition Onset Temperature,a K

a-LiA102 (washed) 1208

a-LiA102 + 20 wt % Li2CO3-K2C03 eutectic 1009

a-LiA102 + 6 wt % eutectic/6 wt % LIOl 953

aExtrapolated to a zero heating rate.

Analysis performed by E. T. Kucera, Analytical Chemistry Laboratory, ANL.

16

B. Thermomechanical Tests(G. H. Kucera)

The creep behavior of a LiA102 sintered disc was monitored for about 200 hat 923 K in a CO2 environment. This disc had dimensions of 2.542-cm dia by0.312-cm thick and a porosity of 63.4%, was not impregnated with Li2CO 3-K2C03 ,and was supported by a high-purity, high-density, 2.43-cm ID A1203 ring. Inaddition, a load of 940.7 g was applied to a 0.635-cm dia A1203 rod whichrested on the center of the sinter. No creep occurred under these conditions.

The thermomechanical behavior of a small (1.26-cm dia by 0.401-cm thick)hot-pressed pellet consisting of spray-dried a-LiA102 and 62.5 wt % Li2CO 3-K2C03 eutectic was monitored in a dilatometer; this pellet was subjected tothermal cycles from about 300 to 933 K in a dry CO2 environment and under astress of 98.5 kPa. In general, this pellet exhibited the characteristicsof a "dry" tile, i.e., very little permanent deformation upon heating toabout 925 K. Specifically, a 1% slump was observed at the melting of theeutectic (764 K), and an additional 1.7% compression took place during theinterval required to reach the cell operating temperature (about 925 K).The creep behavior at 925 K was monitored for about 60 h; it was estimatedthat about 1% creep occurred during the first 10 h at this temperature, withno apparent creep occurring thereafter. It appears that the use of a highercarbonate content with the spray-dried S-LiA102 would be desirable to increaseits flow characteristics under moderate stress (about 100 kPa).

Studies have been initiated to determine the weight loss during heatingof potential binders, ?lasticizers, and wetting agents that are used in prepar-ing slips for tape casting. The thermogravimetric behavior of specimens ofpolyvinyl butyral resin (BUTVAR 79 and 98) were monitored in a Rigaku simul-

taneous thermogravimetric-differential scanning calorimetric (TG-DSC) analyzer.The data show that about 90 wt % of each specimen had decomposed by about735 K.

C. Factors Influencing X-ray Interpretation in LiA102

(B. S. Tani*)

X-ray diffraction (XRD) patterns have been used as a means of identifyingthe components in the matrix material of the fuel cell electrolyte structure.The powders under analysis can be simple, containing only one crystallinephase of LiA10 2 , or more complex, containing any of the LiA102 forms incombination with each other as well as with the reactants and other productsof the syntheses, i.e., unreacted y-A1203, LiA1508, or "AlON" (A1(8/3 + x/3)

O4-xNx where x ranges from 0.22 to 0.50). This section discusses some ofthe difficulties encountered in the interpretation of the diffraction patternsand in the quantification of the constituents of the powders.

Analytical Chemistry Laboratory, ANL.

17

1. Identification of s- and y-LiA1O2

The x-ray patterns of the s- and y-LiAlO2 in fuel cell samples aredistinct. Because both phases tend to be very crystalline, the line-broadening effect arising from small crystallite size (<200 A) is minimal;therefore, these phases are easily identified, even in mixtures.

2. Identification of a-LiAl02 and y-A1203

Structurally, y-A1203 is related to a-LiAlO2. The hexagonal a-LiAl02has octahedral packing, while the cations in cubic y-A1203 are distributed inboth the octahedral and tetrahedral sites. Table 7 presents the JCPDS (JointCommittee on the Powder Diffraction Standards) diffraction patterns fory- A1203 (column 3) and a-LiAl02 (column 4); the patterns are seen to besimilar, differing slightly in line position (d) and intensity values. Thex-ray diffraction identification of Degussa y-A1203 .in mixtures containinga-LiAl02 is more complex than might be surmised from the JCPDS patterns.Column 1 of Table 7 shows that the Degussa y-A1203 in fuel cell samples ischaracterized by a very broad diffraction profile; there are several diffusebands with no sharp definitions of lines. This is typical of small crystal-lite size and/or disorder; i.e., line broadening occurs over several tenthsof angstroms, with the weak lines becoming scattered into the background andthe strong lines appearing as a heavy and diffuse band.

The effect of thermal history is illustrated in column 2 of Table 7,which gives the diffraction patterns for Degussa y-A1203 that had been heat-treated at 900 C for about 7 h. These diffraction lines are better definedand less broad than those for untreated Degussa (column 1). The a-LiAl02in su'ne fuel cell samples also has exhibited this line sharpening; however,this effect occurs to a lesser degree than it does with Degussa y-A1203 .Well-cristallized materials (particles >10-5 cm dia) have narrow half-heightmaxima, while those comprised of small crystallites show large peak widths.

3. Identification of y-A1203, LiA1508 , and AlON

The x-ray diffraction patterns of Degussa y-A1203, AlON and LiA1508 ,given in columns 2, 5, and 6, respectively, of Table 7 are very similar. Allthree phases are based on the cubic spinel-type structure. The lattice con-stant of both AlON and LiA1508 are reported to have a range; hence, withinthe error of measurement, all three phases could have a common latticeconstant at a = about 7.91 X. If a lattice parameter is common to two ormore phases and the intensity corresponds as well, x-ray data alone will beinsufficient to resolve the individual phases.

Two forms of LiA15O8 , based on the spinel-type structure, have beenreported. The x-ray pattern of Form II (column 7), although similar to Form I(column 6), shows the presence of additional weak lines. This difference inx-ray patterns has been reported to be caused by a different ordering of thecations and anions on sites in the basic spinel-type structure.

1. Degussaa

I/I1 d, A

4.7

"470

2.65

2.45(2.38

,L70 12.007 1.94

Table 7. X-ray Powder Diffraction Patterns of

2. Degussa-900b 3. y-A1203c 4. a-LA102d

I/I1 d, A I/I1 d, A hkl I/I d, A hkl

2 14.8 40 4.56 111 70 4.72 0033.1

15 2.85-2.70 20 2.80 220(10 2.60-2.57)

25 2.46-2.40 80 2.39 311 40 2.386 10120 2.29-2.26 50 2.28 222

60 2.00-1.94 100 1.977 400 100 2.000 1045 1.844

Phases in the

5. A10Ne

I/I1 d,

15 4.57

30

10010

60

155 1.54-1.52 30 1.520 511 40 1.556 107 35

60 1.432 018

100 1.41 100 1.41-1.385 100 +.395 440 60 1.399 110 8511.38

aDegussa y-A1203 ; I - visual estimate. !See also y-A120 3, JCPDS 29-63.)

bDegussa y-A1203 heated to 900*C; I - visual estimate.

cJCPDS 10-425; f.c. cubic; a - 7.90 A.

dJCPDS 19-713; rhombohedral, hexagonal axis; a - 2.800 A; c- 14.22 A.

eJCPDS 18-52; f.c. cubic; a = 7.92 A, x - 0.22; to a - 7.950 A, x - 0.50, A1(8/3 + x/3)04-xNx.

Dtatta and Roy;2 f.c. cubic; a - 7.921 A, form I, spinel type. formed above 1290 C.

Lejus;3 f.c. cubic; a - 7.910-7.925 A, disordered spinel type.

gDatta and Roy;2 primitive cubic; a - 7.907 A, form II ordered.

2.801

2.3892.287

1.980

1.6171.525

1.400

Li-Al-O System

6. LIA15 08 (I)f

I/I1 d, X

9 4.57

40

10019

69

642

68

2.80

2.3922.285

1.981

1.6181.526

1.403

7. LA1508 (II)g

I/I1 d, A hkl

31 5.57 11010 4.56 11121 3.53 21019 3.22 21149 2.791 220

100 2.380 31115 2.28 222

60 1.974 4004 1.723 420

10 1.61 42236 1.52 511

70 1.39 440

19

4. discussion

The data given in Table 7 show that a number of phases in theLi-Al-O system have similar x-ray patterns. It is imperative that theexperimental conditions of a sample be known so that an ambiguous interpreta-tion of the x-ray diffraction data is avoided. In addition, knowledge of thetemperature of phase formation and analytical analyses will aid in the identi-fication of the phases present.

The quantitative determination of a specific phase in a mixture can

be determined from a measurement of intensities of the diffraction lines. Theintensity is dependent on the sample being irradiated and includes theabsorption of radiation by the sample, the diffracting angle, the crystalstructure of the phases in the sample, the span of time that the sample isexposed, the temperature, and the experimental arrangement used to collect thedata. Currently, the diffractometer arrangement is used because of its speed,accuracy, and the independence of the absorption factor with 26, the scatteringangle.

The relative intensity of a reflection (line) using the Debye-Scherrer powder diffraction technique is given by:

I = Lp-m-A.IFhklI 2.T-V

where I = intensityLp = Lorentz polarization factorm = multiplicity (i.e.,number of faces in crystal form)A = absorption factor

I hk1 2= structure factor FT = temperature factorV = volume of sample irradiated

In the above equation, Lp, A, and T vary monotonically with angle e, and

FhklJ2 and m vary greatly with the atomic positions of the crystal and theparticular Miller indices (h, k, 1). To achieve a quantitative assessmentof the components in a mixture, however, measurement of the integratedintensity rather than peak intensity is essential.

The small crystallites in Degussa y-A1203 (which is nearly amorphous,i.e., <200 X) result in large peak widths which are difficult to separate fromthe background and which overlap with the peaks of other components. Otherfactors affecting quantitative analysis include preferred orientation,

absorption, and extinction; these factors are discussed below.

Preferred Orientation. In the intensity equation for the powder

diffraction methods, it is assumed that the crystals making up the powderspecimen have completely random orientations. If the crystals tend tocluster to any degree about some particular orientation(s), then it issaid to have a preferred orientation or texture. The effect on t.he x-raypowder pattern is that certain classes of diffraction lines have intensities

that are abnormally stronger or weaker than those of the remaining diffrac-

tion lines. Preferred orientation is fairly common. It can usually be

20

expected if the crystalline samples have plates, fibers, needles, rods, ortneet-like aggregates. The effect of preferred orientation can be minimized

by reducing the particle size and by tumbling or rotating the sample as itis being exposed to the x-rays.

Absorption. The intensity of the diffracted beam is attenuated bythe mass of the sample. This attenuation is measured for each element interms of thc mass absorption coefficient for each type of x-ray radiation.If a sample is a mixture of phases, the intensities of the respective diffrac-tion patterns will be influenced by the particle sizes of the phases as wellas by the mass absorption coefficient of the elements of the phases. Absorp-tion becomes a significant factor when the particle sizes are larger than1 pm, with linear absorption coefficierns greater than 500 cm-1. In thiscase, it is important to grind the sample to a smaller and more uniform sizein order to derive representative intensities for assessment in quantitativeanalysis.

The Debye-Scherrer powder technique is subject to an absorptioneffect not present in the diffractometer technique. However, the loss inintensity can be corrected for by applying an absorption correction factor.

Extinction. The intensity equation for a theoretically perfectcrystal is different from that for real crystals. For a perfect crystalthere is an effect at the diffracting angle of reflection that is calledprimary and secondary extinction. These extinction effects act as anadditional absorption coefficient and result in an attenuated diffractedintensity. Extinction is more apparent for strong intensity reflectionsthan weaker reflections. Most crystals do not reach the perfect crystalstatus, and the intensity equation as written can apply. Grinding crystalsto powders below 10 pm reduces the extinction effect to insignificance.In comparison to preferred orientation and absorption, the extinction effecton intensity is relatively small.

In the quantitative analysis of the components of a mixture, asuitable diffraction peak of one component must be selected and compared tothe diffraction peak of another component or internal standard. Care must betaken to assure that the selected diffraction peak is free from overlap withother diffraction lines and superposition of amorphous materials. Further-mcre, the peak selected must be sufficiently intense so that it can be

followed in mixtures where it may vary from high to low concentrations.Finally, the peak must be free from preferred orientation, extinction, andabsorption.

The following summarizes some of the difficulties encountered in

the quantitative determination of Une components of the matrix material ofthe fuel cell electrolyte structure:

Peak overlap: Degussa y-Al2O3 with r-LiA102, LiA150p, AlON,

y-A12 03 (JCPDS)

Preferred orientation: a-LiAlO2 (high temp.), S-LiA102, y-LiA1O2

Identity problems: Form I LiA1508 , AlON, Y-A1203 (JCPDS)

21

The above brief discussion on the interpretation of XRD resultsshows that it is not always possible to identify an unknown phase by a simplematch of its diffraction patterns with the JCPDS x-ray file. A number offactors complicate the matching process; these include line breadth, whichvaries with crystallite size, disorder, preferred orientation, and extinction.Similarly, the quantitative assessment of a single phase in a mixture can behindered by the superposition of the broad diffraction lines of a materialconsisting of particles with a poor degree of crystallinity. Peak overlap,preferred orientation, and identity problems are also hinderances in thequantitative analysis of a single phase in a mixture. The molten carbonatefuel cell samples frequently consist of phases representing one or more ofthe factors which complicate identification/quantification.

22

IV. CATHODE DEVELOPMENT

In the molten carbonate fuel cell, the nickel oxide cathodes are normallyproduced by the in-cell oxidation and lithiation of a sintered porous nickelplate. However, this reaction results in cathode swelling and yields astructure with resistance to electron flow. We are working on the out-of-cell preparation of cathode plates of sintered Li0.05Ni0. 9 50. In addition,we are investigating the bonding of lithiated NiO to a sintered LiA102structure.

A. Fabrication of Lithiated NiO Cathodes(R. M. Arons, J. T. Dusek, and J. J. Slaga)

In this report period, lithiated (5 cation %) NiO disks (3.18-cm dia)

were prepared by the method described in ANL-30-98, p. 11 and were sinteredfor 1 h at a temperature in a range from 800 to 1300*C. Table 8 shows thedensity and resistivity of these disks. A plot of resistivity versus sinter-ing temperature is given in Fig. 6. The resistivity measurement is describedin the Appendix. Two factors are evidently involved in the variation ofresistivity with firing temperature. The optimal (lowest) resistivity occursat 1000 to 1100*C. At higher sintering temperatures, the resistivity increaseis due to volatilization of lithium, which profoundly affects the electricalproperties of NiO. We have yet to verify the lithium loss by an independenttechnique. At lower temperatures, the slight rise in resistivity is probablydue to the lower sintered densities and the associated poorer conduction paths.

Two lithiated NiO cathode plates (10.8-cm thick) were fabricated by the

same method for cell testing. The as-sintered plate was cut to size using ahigh-speed (about 3000 rpm) diamond saw with a smooth, 12.7-cm-dia rotaryblade. The plate could be cut successfully over a wide range of feed rates,both with and without lubricant. We expect that any required machining, suchas cutting or drilling, of similar sintered cathode plates will pose noproblems.

Table 8. Density and Resistivity of Lithiated NiO asa Function of Sintering Temperattre after a1-h Soak (agglomerate mesh size of -200 mesh).

SinteringSpecimen Temp., Density, Resistivity,*Number *C g/cm3 ohm-cm

16-6 800 2.997 3.6516-1 900 3.382 2.8016-2 1000 3.907 2.3516-3 1100 4.319 2.3416-4 1200 4.376 4.5816-5 1300 5.338 22.9

*See Appendix for description of measuring technique.

23

24 Li0.05 Ni0 .95O

22 1 HOUR SOAK

20--

16-

14-

12Liic: 10-

8-

6

4

2

800 900 1000 1100 1200 1300

SINTERING TEMPERATURE (*C)

Fig. 6. Resistivity of Lithiated NiOVersus the Temperature of a1-h Sintering Treatment

B. Development of Laminated Cathode/Electrolyte Structures(R. M. Arons, J. T. Dusek, ar J. J. Slaga)

Work has been initiated on development of a bonded cathode/electrolytecomposite. For this structure, lithiated NiO is laminated to LiA102 and thecomposite is fired. Some basic problems need to be surmounted if one is toproduce such a laminate either by cold pressing or tape casting. First, oneneeds to develop powders and green-body fabrication techniques that yieldLixNii-xO and LiA102 bodies both of which fire under the same temperature andtime condition. The resultant fired bodies must possess the desiredporosity and particle morphology. This poses a problem since LiN_ Ogenerally requires a higher sintering temperature than does LiA102 to achievethe desired results. We are, however, sLriving to produce LixNii-x0 bodieswhich require lower sintering temperatures. To further complicate matters,the fabrication of a flat, laminated structure will require that both com-ponents have the same shrinkage characteristics upon firing. However,preliminary tests show that, with 3.18-cm-dia laminated disks, we can forcethe disk to warp into a concave, flat, or convex shape, depending upon whichside tends to shrink more. Another required improvement is reduction in thethickness of the electrolyte structure below the current average of about1.25 mm and optimization of the thickness of the cathode material based onin-cell performance. In the LiA102 side of the composite, it was found thatsoft binder promotes greater shrinkage, whereas a greater volume fraction of"fines" promotes higher porosity. Finally, we found that firing at 900*Cresults in a very friable LixNi-.x0, while firing at 1000*C results in amore strongly sintered material.

24

With a better understanding of the effect of some of the variables

described above, we have fabricated via cold pressing and sintering somecomposite LiA102 and LixNii..xO plates of roughly 12.7-cm square that had

almost no warping and the desired porosities, thickness, morphologies, etc.It is probable that only subtle variations are required to produce a compositeacceptable for in-cell testing in the near future.

C. Nickel Aluminate(A. V. Fraioli)

The purpose of this study is to develop sinter-resistant substrate mater-ials that may find application as electrode support or sinter plate in moltencarbonate fuel cells.

Four types of commercial alumina were obtained as substrate precursorsfor the formation of nickel aluminate. The physical characteristics of thesepowders are listed in Table 9 sampless 1. to 4), along with data of four setsof nickel aluminates formed from these precursors. The aluminates of samples

5 through 8 were formed by mixing the precursor aluminas with stoichiometricNi(N0 3)2 -6H20, heating the mixture for two hours at 250C to decompose thenitrate to NiO, and finally calcining it for an additional two hours at1000 *C. Since the nickel infusion was not complete, the bulk of excess NiOwas removed by immersing the sample in boiling concentrated HNO3 followed

by washing it in distilled water. The remaining three sets of nickel alumi-nate (samples 9 to 12, 13 to 16, and 17 to 20) were formed by partiallyreacting the respective substrates with a stoichiometric amount of NiO at1000*C as above, retaining the unreacted NiO, then dividing each substrateinto three aliquots to be refired an additional two hours at 1200, 1400 or1600*C. The table summarizes the analytical results* so far obtained. Thesurface area data represent single BET measurements. Duplicate surface areameasurements are being made to provide an estimate of the precision of thedata.

The data generally indicate that the more reactive the aluminas, interms of their surface areas, the more easily they form spinels. This isparticularly true for the hydrated y-alumina, whose large surface area(290 m2/g) provides short diffusion paths for Ni2+ migration in the infusionprocess. The reaction is essentially complete at the infusion temperatureof 1400*C, with the presence of unreacted (physically included) NiO decreasingin the treated samples as the infusion temperature is raised to that level.

The data for samples treated at the 1600 C infusion temperature show adecrease in the lattice parameter, which is probably due to elimination oflattice defects as the sintering process provides crystalline development.

The measured lattice parameter increases with the original precursor surfacearea (rather than the final surface area); this finding suggests a range ofNi2+ in the various aluminates formed, rather than the stoichiometric formulaindicated.

An anomaly is found in the data for Sample 20 (1600*C), which show NiOpresent in greater concentration than had been observed in Sample 16 (1400C).

B. S. Tani and R. L. Malewicki, both of the Analytical Chemistry Laboratory,

supplied XRD and BET surface area data, respectively.

Table 9. Nickel Aluminate Summary Data

XRD Analysis

No. Sample Dscrp. Infusion Surf. Area, Color >50% About 30-40% About 5%Temp., C m2/g Major Medium Minor Very Minor

1 C-5R (Unground)a Precursor 1.2 White a-A1 203 NaA170172 C-5R (Ground)a Precursor 2.0 White/Gray a-A1 203 NaA170173 C-70 bPrecursor 32.0 Off-White a-A1203 y-A1 2034 Catapal "SB"b Precursor 290.0 White y-A100H

5 C-5R (Unground)a 1000 1.2 Pale Blue a-A1203 NaA17017, NiAl2046 C-5R (Ground)a 1000 1.5 Very Pale Blue a-A1 203 NiAl2O4 NaA170177 C-70a 1000 20.5 Light Blue a-A12 03 NiAl2 048 Catapal "SB"b 1000 60.7 Blue Green NiA1 2 04, noal,a2 NiO

9 C-5R (Unground)a 1200 1.1 Light Blue NiAl204, noal,a2 a-A120310 c-5R (Ground)a 1200 1.2 Blue Green NiAl2 04, noai,a2 a-A1 2 0311 C-70a 1200 8.4 Blue Green a-A1 2 0 3, NiA120 4 NiO12 Catapal "SB"b 1200 1.0 Blue NiA120 4 (8.048 + 0.002)c NiO

13 C-5R (Unground)a 1400 0.56 Blue NiAl204 (8.046) NiO14 C-5R (Ground)a 1400 0.75 Blue NiA12 04 (8.046)15 C-70a 1400 3.2 Blue NiAl2 0 4 (8.048) NiO16 Catapal "SB"b 1400 0.70 Blue NiAl2O4 (8.050)

17 C-5R (Unground)a 1600 0.44 Blue NiA1204 (8.044)18 C-5R (Ground)a 1600 0.59 Blue NiA120 4 (8.045)19 C-70a 1600 2.1 Blue NiAl 2 O 4 (8.045) NiO20 Catapal "SB"b 1600 0.25 Dark Blue NiAl2 O 4 (8.049) NiO

'Product of Kaiser Chemical Co., Dolton, IL.bProduct of Continental Oil Co., Saddle Brook, NJ.CNumbers in parentheses here and below are NiAl2 04 spinel lattice parameter;

at stoichiometry, ao - 8.048 X.

Nf

26

Since NiO decomposes above 1500 C, it may have been effused from the lattice

at the higher temperature with the reversed concentration gradient, andreoxidized at the surface upon cooling below 1500*C. This material's resis-tance to solution in the acid wash is as yet unexplained.

The SEM analysis indicates that conversion to the spinel can be achieved

without alteration of the agglomerate morphology of the substrate aluminas.For example, Fig. 7 shows the relatively amorphous y-A100H (Catapal "SB")

with aggregates in the 50 um range, which contributes to the free-flowing

character of the powder. Figure 8 is an SEM of NiAl204 formed from thismaterial after infusion at 1600*C and shows that the aggregate dimension is

not visibly changed. Figure 9 is a photomicrograph of the material fired at

1600 C and shows the development of terraced facets of the highly densified

spinel; this is in agreement with the trend of the surface area data.

D. Electroless Nickel Plating(A. V. Fraioli)

The purpose of this study is to determine whether electroless deposition

of nickel alloys (e.g., Ni-P and Ni-B) provide adequate corrosion protectionto structural hardware. The electroless nickel coatings (752 Series Niklad*)with a low boron content (1%), whose deposition onto 316 stainless-steelcurrent collector strips was described in the last quarterly report (ANL-80-98,p. 16), were exposed to thermal treatments and evaluated by visual inspectionas well as scanning electron microscopy. The as-plated films have a mattefinish and are not as specularly bright as the 4% boron films of the Niklad 740Series reported earlier. They tarnished more rapidly under exposure to air for2 h at 650*C, with or without prior -educing-environment (film anneal/diffusion)heat treatment. Fissuring was not evident and the film-substrate interfacecould not be delineated, in contrast to the 740 Series photomicrographs reportedearlier.

*Richardson Co., Allied Keliti Division, Des Plaines, IL.

27

Figure 7. Catapal "SB" HydratedAlumina Agglomerates

Figure 8. Agglomerates of NiAl 2O4Formed from Catapal "SB"at 1600*C

28

Faceted NiA120 4 from Catapal "SB"Figure 9.

29

V. CELL AND STACK DESIGN(J. L. Smith, I. Pollack*, J. A. Kelley)

Preliminary engineering drawings of a test fuel cell stack have beencompleted. This test stack was designed to obtain maximum experimental flexi-bility using sheet-metal components that employ features expected on commercialcells. The initial stack will use a flat, bipolar separator sheet with corru-gated current collectors.

The flexibility of the design may be described by a listing of the optionsreadily available. Parallel, counter, or cross flow of the reactant gases maybe run with no hardware changes. With minor changes to some components,either a ribbed or flat separator sheet may be accommodated. Also with minoror no changes, ribbed anodes and/or ribbed cathodes may be used. Finally, avariety of anode and cathode thicknesses may be used with, at most, minorchanges to other components.

The basic design uses internal manifolding in stainless steel framesaround the active cell area. Zirconia felt provides the manifolding sealsand the sealing between the active cell area and the surroundings. This isnot a "wet seal" because the gasketing material, rather than a wet filmbetween the tile and housing, provides the seal.

*Engineering Division, ANL.

30

APPENDIX

Cathode Resistivity Measurement Technique(J. L. Smith and J. R. Stapay)

The technique being used for resistivity measurements is that reportedby L. J. Van der Pauw.'4 It is a four-probe measurement which is geometryinsensitive, but does require a constant thickness sample.

A

D

B

C

The procedure is as follows:

(1) Pass a current between points D and C;measure resultant voltage between points A and B;Calculate resistance R1 = V/I.

(2) Pass a current between points A and D;measure resultant voltage between points B and C;calculate resistance R2 = V/I.

The resistivity, p, is then calculated from

exp ( nRld) + exp (-rR 2d) 1

p p

where d is the sample thickness. This iterative calculation results in

the reported values for resistivity.

31

REFERENCES

1. R. N. Singh, J. T. Dusek, and J. W. Sim, Fabrication and Properties of aPorous Lithium Aiuminate Electrolyte Retainer for Molten Carbonate FuelCells, submitted to Bull. Am Ceram. Soc. (1980).

2. R. K. Datta and Rustum Roy, J. Am, Ceram. Soc. 46(8), 388-390 (1963).

3. Anne Marie Lejus, Rev. Hautes Temp. Refractaires 1(1), 53-95 (1964).

4. L. J. Van der Pauw, Philips Research Reports 13, 1 (1958).

32

Distribution for ANL-81-16

Internal:

J. P. Ackerman

R. M. AronsD. L. BarneyS. H. BarrR. L. Breyne

L. Burris

F. A. CafassoM. J. Caines

M. ContosJ. T. DusekP. A. FinnA. V. FraioliJ. E. HarmonJ. E. Herceg

C. E. JohnsonA. A. JonkeJ. A. KelleyM. Krumpelt

G. H. KuceraD. S. KuppermanN. P. LapinskiZ. NagyP. A. NelsonR. D. Pierce (35)R. B. PoeppelI. PollackJ. J. Roberts

L. J. Ryan

J. W. SimJ. L. SmithJ. R. StapayR. K. Steunenberg

R. SwaroopD. S. WebsterJ. E. YoungS. A. ZwickA. B. Krisciunas

ANL Patent Dept.

ANL Contract File

ANL Libraries (3)TIS Files (6)

External:

DOE-TIC, for distribution per UC-93 (165)Manager, Chicago Operations Office, DOER. J. Gariboldi, DOE-CHPresident, Argonne Universities AssociationChemical Engineering Division Review Committee:

C. B. Alcock, U. TorontoT. Cole, Jet Propulsion Lab.W. L. Worrell, U. Pennsylvania

Materials Science Division Review CommitteeE. A. Aitken, General Electric Co., SunnyvaleG. S. Ansell, Rensselaer Polytechnic Inst.A. Arrott, Simon Fraser U.R. W. Balluffi, Massachusetts Inst. TechnologyS. L. Cooper, U. WisconsinC. Laird, U. PennsylvaniaM. E. Shank, Pratt & Whitney, East HartfordC. T. Tomizuka, U. ArizonaA. R. C. Westwood, Martin Marietta Labs.

B. S. Baker, Energy Research Corp., Danbury, Conn.T. R. Beck, Electrochemical Technology Corp., SeattleA. Borucka, Borucka Research Co., Livingston, N. J.E. Camara, Inst. Gas Technology, ChicagoT. W. Carter, U. S. Coast Guard, WashingtonD. Chatterji, General Electric Co., SchenectadyL. 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.J. W. Harrison, General Electric Co., Wilmington, Mass.L. C. Headley, Morgantown Energy Technology CenterD. Johnson, Northwestern U.J. Kelly, Westinghouse R&D Center, PittsburghJ. M. King, United Technologies, Inc., South Windsor, Conn.K. Kinoshita, SRI International, Menlo Park

33

H. R. Kunz, United Technologies Corp., South Windsor, Conn.M. N. Mansour, Office of Fossil Energy, USDOEL. Marianowski, Inst. of Gas Technology, ChicagoH. Maru, Energy Research Corp., Danbury, Conn.

R. Matsuinato, Ceramatech, Salt Lake City

A. P. Meyer, United Technologies Corp., South Windsor, Conn.L. Nanis, Stanford Research Inst.

R. C. Osthoff, General Electric Co., SchenectadyJ. R. Peterson, General Electric Co., Schenectady

J. J. Rasmussen, MERDI, Butte, Mont.C. A. Reiser, United Technologies Corp., South Windsor, Conn.

J. Searls, U. S. Bureau of Mines, WashingtonR. Selman, Illinois Inst. of Technology

R. Sperberg, Gas Research Inst., ChicagoG. Tittemore, Office of Fossil Energy, USDOEG. Voelker, Office of Coal Utilization, USDOEP. Weaver, Stanford Research Inst.G. Wilemski, Physical Sciences Inc., Woburn, Mass.K. Wray, Physical Sciences, Inc., Woburn, Mass.

E. Yeager, Case Western Reserve U.

M. Zlotnick, Office of Fossil Energy, USDOE