• • HAS CR 72493 . - 14 'ERIALS FOR ELECTROCHEMICAL CELL SEPARATORS FI NAL REPORT lS December 1968 Prepared for: \ , \ NATIONAL AERONA UTICS and SPACE ADM INISTRATION LE WIS RESEARCH CEN TER Under Contract N AS 3-8522 ~_.~ N 6 · 1~'t"6456> : 9 - 1 G 1 '.,. t' <' • ~. c~ ! _::s/)lr~DERJ _---;;:'T~HtU~' __ • r ::" F[81969 ~ ! t R'1I'12 /-/n ;D'~ N INASA CR OR TMl( O~ AD NUMBERJ -~== __ ICATEGORY, 'AND, OHIO https://ntrs.nasa.gov/search.jsp?R=19690006769 2020-03-12T08:16:11+00:00Z NA[; CR-72493 Final Report ilArr'ERIALS FOR ELEC'l'ROCHEI1ICAL CELL SEPARATORS Prepared by J. \·Y. Vogt for National Aeronautics and Space Administration December 1968 Contract iJo. ~jl\S 3-8522 Technical Hanagcnent NA~A - Lewis Research Center Electrochemistry Branch Daniel G. Soltis Materials Technology TRW Equipment Laboratories TRi': Inc. 23555 Euclid Avenue Cleveland, Ohio 44117 I FOREWORD This is the final report on contract NAS 3-8522 initiated June 16, 1966~ A First Summary Report NAS-CR-72l48 was issued December 28, 1966, and a Second Summary Report NAS-CR-72267 was issued July 3, 1967. The purpose of the work was to develop improved matrices for electrochemical cellso Chrysotile paper and millboard were first studied and characterized in terms of properties related to the function of matrix in alkaline electrochemical cells4' The study was then extended to other natural fibrous materials, to synthetic inorganics, and finally to synthetic inorganics bonded by organic fibersm The best composites emerging from this study were processed into full size matrices and delivered to NASA for subsequent performance evaluation in electrochewical cells. This work was carried out in The Materials Technology Laboratory of The TRW Equipment Group. The principal investigator for this program was Dr. J. W~ Vogt, and Dr. Do P. Laverty served as the program manager. The bulk of the specific process development work was carried out by R. A. PI:osek .. Daniel G~ Soltis and Meyer R~ Unger of Lewis Research Center were the NASA technical directors. For internal TRW distribution, this report has been assigned the number ER-7055-4. i 1.1' I ". ! \ f i , I, ! ;'l\ 111 i 'I~ I, j I' I; :1 ~ :i :~ " G u ,", n f I \ 1 . I -- .-~... ;'1."~ ,,' ,,~~_ ,>"~-"~- ~, .---.. --.--~--~------... --- II ABSTRACT A t\-lo-year, five-part program has been carried out to deter- mine the properties of Fuel Cell Grade Asbestos and of alternate materials for application in alkaline-electrolyte electrochemical cell separators .. The first part of the program consisted of examining 20-mil thick and 60-mil thick chrysotile asbestos mats produced by Johns Manville especially for fuel cell application. The tests were designed to assess those attributes of the mats particularly pertinent to cell separator application, and they included physical properties f chemical and electrochemical compatibilitYf electrolyte absorption and retention, bubble pressure, and electrolytic resistance.., The chrysotile a,sbestos mats were excellent in most of these properties 0 Their main shortcoming was lack of chemical corr.pa·tibility with the KOH electrolyte at temperatures over 100oC~ The second part of the program studied other types of asbestoses and alternate fibrous inorganic materials in a search for improved cell separatorso Of the dozen or so materials studied in this part of the program, none yielded a significant improvement over the chrysotile asbestos mats in overall properties" However, potassium titanate (PKT) and fibrous zirconia were identified as showing marked improvements in chemica 1 compa tibili ty.., The third part of the program was aimed at exploiting the good chemical resistance of PKT, zirconia (both in fiber and powder form), and ceria (available as powder and known to be compatible with KOH) by forming mats of these materials using organic bindersv The organic binders examined included Teflon and polypropylene" The most promising separator mats developed in this phase of the program consisted of the base materials (ei·ther PKT, ceria powder, or zirconia powder) composited with a small percentage of Teflon powder which was formed into a fibrous network by repeated rolling treatments during the processing of the mat", The fourth part of the program consisted of preparing and testing full-size (8-inch square) mats of 20, 30, and 60-mil thicknesses made by this fibrilated-Teflon-bonded approach .. Three mat compositions (95% PKT + 5% Teflon, 99% .ceria + 1% Teflon, and 99% zirconia + 1% Teflon) were examined to determine the best one for :se in the last phase of the programo Since all three mat compositions appeared promising and there was no clear choice of the best one, the final part of the program consisted of producing, for delivery to NASA, 100 each of the three types of mats,. A selected number of each thickness ii r-.i c _________ O_< ... tfl _____ _ (20, 30, and 60 mils) were included to provide mats of each material for evaluation in the various types of electrochemical cells of possible applicationo I I ! Y iii I II. TABLE OF CONTENTS I . FOREWORD II. ABSTRACT III. TABLE OF CONTENTS I V. LI ST OF FIGURES V. LIST OF TABLES VI. INTRODUCTION V II. WORK PLAN OF THE PROGRAM VI I I. TASK I. PROPERTIES OF FUEL CELL ASBESTOS A. Procurement and Preparation of Specimens' B. Tests and Results 1. Asbestos Properties a. Chemical analysis b. Photographic and electronmicrographic examination c. Surface area 2. Dry Mat Properties a. Tensi!e tests b .. -\ 'Dens i ty and poros i ty c. Gas permeability d. Thickness variation 3. Mat Properties - Wet with KOH a. Electrolytic absorption and retention b. Liquid permeability c. Electrolytic resist~nce d. Gas pe rmeab iIi ty of wet mat 4. Chemical Degradation 5. Electrochemical Degradation C. Conclusions of Task I Work IX. TASK 2. TESTS OF ALTERNATE MATERIALS A. Materi a 1 Selection B. Chemical Degradation C. Tests of Selected Compatible Materials 1. Starting Materials a-. Chemical composition b. Fiber structure c. Surface area 2. Preparation of Mats iv Page No. i i i v vi i 2 5 5 5 5 5 6 6 9 9 18 19 19 24 24 27 30 33 38 43 45 47 47 48 52 52 52 53 53 53 I I. -. '--'""--'--""--.--~--'-~-""'-'" TABLE OF CONTENTS (Cont'd) 3. Dry Mat Properties a. Tensile strength b. Density c. Thickness variations d. Pore size distribution 4. Electrolyte Absorption and Retention 5. Electrolytic Resistance 6. Gas Permeability 7. Liquid Permeability 8. Electrochemical Degradation D. Conclusions from Task 2 Results --t--- -;:.., X. TASK 2a. MATRICES INCORPORATING ORGANIC BINDERS A. Composition of Mat Components B. Chemical Degradation Tests C. Properties of Pressed Matrices 1. Mat preparation 2. Selection of Matrices for Testing 3. Electrolyte Absorption and Retention 4. Gas Permeabi lity Tests (Bubble Pressure) 5. Electrolytic Resistance 6. Conclusions Pertaining to Pressed MatJ D. Matrices Bonded by Fibrilated Teflon 1. Mat Preparation 2. Composition of Matrices Prepared for Testing 3. Chemical Compatibility 4. Electrolyte Absorption and Retention 5. Gas Permeability (Bubble Pressure) 6. Electrolyte Resistance 7. Fiber Structure 8. Surface Area 9. Tensile Strength 10. Density and Porosity 11. Pore Size Distribution 12. Electrochemical Degradation E. Conclusions from Task 2a Work XI. TASK 3. FULL-SIZE MATRICES A. Equipment Changes and Technique Improvements B. Testing of 8-lnch Square Mats 1. Thickness Variation 2. Electrolyte Absorption 3. Bubble Pressure 4. Density C. Conclusions from Task 3 Tests v Page No. 60 60 60 60 60 66 66 69 72 72 75 76 76 76 77 77 84 84 85, 85 88 90 90 93 93 99 100 100 109 109 109 109 115 119 119 121 121 122 122 122 122 126 126 j I :j ,'Ii 1~ 1 I t - I TABLE OF CONTENTS (Cont'd) XII. TASK 4. PRODUCTION OF FULL-SIZE HATRICES IN QUANTITY XIII. CONCLUDING REMARKS XIV. APPENDIX - MANUFACTURE OF FUEL CELL ASBESTOS vi Page No. 128 133 135 ,Figure No. 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 IV. LIST OF FIGURES Ti tl e Chrysotile Asbestos Fibers; lOX Electronmicrograph of Chrysotile Fibers; 20,000X Tensile-Elongation Curves for 60 mil Fuel Cell Asbestos Board (1000 series) Tensile-Elongation Curves for 60 mil Fuel Cell Asbestos Board (2000 series) Tensile-Elongation Curves for 20 mil Fuel Cell Asbestos Paper (3000 series) Tensile-Elongation Curves for 20 mil Fuel Cell Asbestos Paper (4000 series) Tensile-Elongation Curves for 60 mil Fuel Cell Asbestos Board (no. 2701) Stress Applied Parallel to Processing Direction Tensile-Elongation Curves for 60 mil Fuel Cell Asbestos Board (no. 2702) Stress Applied Parallel to Processing Direction Tensile-Elongation Curves for 60 mil Fuel Cell Asbestos Board (no. 2702) Stress Applied Transverse to Processing Direction. Relationship of Air Permeation Rate and Pressure Differential Across 20 mil and 60 mil Dry Fuel Cell Asbestos Mat Thickness Distribution of 60 mil Fuel Cell Asbestos Board and 20 mil Pa~er Specimen and Holder for Electrolyte Absorption and Retention Test Centrifuge for Electrolyte Retention Test Schematic of Specimen Holder for Liquid Permeabi lity Tests a) Diagram of Cell used for Electrolytic Resistance Measurement b) Electrical Schematic of Resistance Apparatus View of Specimen Holder for High Temperature Chemical Degradation Tests vi i Page No. 7 8 11 12 13 14 15 16 17 20 "f, L,,_ 25 26 29 32 39 .1 y , j. t . Figure No. 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 35 36 LIST OF FIGURES (Cont'd) Title Page No. Chrysoti1e Before and After Chemical Degradation Test (lOX) 43 Schematic Diagram of V Cell for Electrochemical Degradation Tests. 44 Amosite (lOX) 54 Anthophylite (lOX) 54 Tremolite ('OX) 55 Crocidolite (lOX) 55 TX Fiber (lOX) 56 Zirconia E Fiber (lOX) 56 Potassium Titanate (PKT) lOX 57 Potassium Titanate (PKT) 10,000X 57 Mat Casting Apparatus 59 Tensile-Elongation Curves for Pressed Mats 61 Pore Size Distribution Curves for Pressed Mats 64 Electrolytic REsistance Cell-Modified 68 Teflon 6 Powder and Fibers 91 Fibers in Teflon-Bonded Matrix 110 Tensile-Elongation Curves for Teflon-Bonded Matrices 112 Tensile-Elongation Curves for Teflon-Bonded Matrices 113 Pore Size Distribution of Teflon Bonded Matrices 117 Apparatus for Vacuum Impregnation of 8-lnch Square Matrices 123 vii i Table No. 2 3 4 5 6 7 8 9 10 1 1 12 13 14 15 16 17 18 19 20 IV. LIST OF TABLES Title Tensi1e Tests of Fuel Cell Asbestos Gas Permeability of Dry FueJ Cell Asbestos Electrolyte Absorption and ReteM";'Jn Liquid Permeability Tests Electrolytic Resistance of Fuel Cell Asbestos Gas Permeability of Wet Asbestos Chemical Degradation Tests Chemical Degradation Tests Tensile Tests of Pressed Mats Density of Pressed Mats Electrolyte Absorption and Retention Electrolytic Resistance of Pressed Mats Gas Permeabi Jity of Dry Pressed Mats Gas Permeabi lity of Wet Pressed Mats Liquid Permeability of Pressed Mats Chemical Degradation Tests of PKT Chemical Degradation Tests of Ceria Chemical Degradation Tests of Zirconia Chemical Degradation Tests of Titania Chemical Degradation Tests of Polypropylene Felt ix Page No. 10 21 28 31 34 36 & 37 40 & 41 49,50 & 51 62 63 67 70 71 73 74 78 79 80 81 82 , ;1 '. ~ :J -I l -I ~ i H t Table No. 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 LIST OF TABLES (Cont1d) Title Electrolyte Absorption and Retention of Pressed Matrices Gas Permeability of Pressed Matrices Electrolytic Resistance of Pressed Matrices Chemical Degradation Tests of PKT-Teflon Matrices Chemical Degradation Tests of Ceria-Teflon Matrices Chemical Degradation Tests of Zirconia-Teflon Page No. 86 87 89 94 95 Matrices 96 Chemical Degradation Tests of Magnesia-Teflon Matrices 97 Chemical Degradation Tests of Magnesium Titanate- Teflon Matrices 98 Electrolyte Absorption and Retention of Teflon Bonded Matrices 101 Gas Permeability of Teflon Bonded Matrices 102-103 Electrolytic Resistance of Preliminary Teflon Bonded Matrices 105-106 Electrolytic Resistance of Teflon Bonded Matrices 107 Surface Area of Teflon Bonded Matrices 111 Tensile Tests of Teflon Bonded Matrices 114 Density and Porosity of Teflon Bonded Matrices 116 Pore Size Distribution 118 Tests of Full-Size Matrices 124-125 Data for Full Size Matrices PKT:Teflon 129 Data for Full Size Matrices Ceria:Teflon Data for Full Size Matrices Zirconia:Teflon x 130 131 it .\ ;i ,1 ~i j~ \l ; ~ ., ,] iJ " " :1 ;i i1 ji ~~ j{ " ., :'i. ~ i ,I Ij ;~ lJ I :"5' H n " I" ·1 1; l~ H ~ t~ J:! II :li lri 11 I ii ( f} rl i~ Ii li :.:f l~ h I VI INTRODUCTION Development of alkaline fuel cells and electrolytic cells has depended to a considerable degree on the use of pure chryso- tile paper as the electrolyte matrix and electrode separator~ Chrysotile is a natural asbestos, a hydrated magnesium silicate, and with the exception of incidental impurities, it is electro- chemically inert in an aqueous alkaline medium~ The chrysotile paper is manufactured as a special product by specially refined commercial equipment, and consequently, its physical properties are quite uniform~ Most of these properties - dry strength, fibrous structure, porosity, wettability, pore size are eminently appropriate for service as an electrolyte matrix~ Unfortunately, the chrysotile, being a magnesium silicate, reacts with alkali to form a soluble silicate und the gelatinous magnesium hydroxidec At moderate alkali concentrations and low operating temperatures, the chrysotile matrices will survive several thousands o£ hours in service.. But in very concentrated alkali, and at 150 or 200 0 Cy the chrysotile is rapidly degraded, and the service life is drastically shortened., The purpose of this project is to improve the chrysotile matrices or develop alternative matrices with better service capabilities... Commercially available chrysotile paper was taken as the reference material, and selected physical and chemical properties were measured~ Prospective new rraterials and material composites were evaluated then by comparison of the selected properties with those of chrysotile o In order, the materials tested were, natural asbestos other than chrysotile, synthetic inorganics, blends of synthetic inorganics with chrysotile, blends of synthetic inorganics with synthetic organic binders, and finally, synthetic inorganics bond~d by fibrilated Teflon., Matrices of the latter type were prepared in full matrix size and in quantity for performance testing in electrochemical cellsG ./ 1 VI.! .•'. n r ;-1 " 11 Ii H VII WORK PLAN OF THE PROJECT Task 1. Evaluation of Fuel Cell Asbestos Board Fuel Cell Paper (0.02 inch thick) and Millboard (0.06 inch thick) were procured from Johns Manville and subjected to the following tests: A. Asbestos Properties l~ Chemical composition 2. Fiber structure 3~ Surface area (per unit weight) B. C .. Dry 1. 2., .3., 4., 5 .. Wet 1 .. 2 .. 3~ 4~ Mat Properties strength Porosity Density Thickness variation Pore size distribution Mat Properties (wet with Electrolyte absorption Electrolyte retention Electrolytic resistance Gas permeability 30% KOH) D. Chemical Degradation in KOH Solutions E,.. Electrochemical Reactivity Task 2 .. Investigation of Other Asbestos Forms Other asbestos fibers and selected synthetic inorganics were tested as was the chrysotilec Those materials with satisfactory resistance to chemical attack by KOH solution and satisfactory physical properties were to be incorporated in matrices and tested for matrix properties 0 Those synthetic inorganics of non- fibrous structure were to be blended with sufficient chrysotile fiber to provide the necessary matrix strength~ The asbestoses to be tested were: 1... Chrysotile 2.. Tremoli te 3. Anthophylite 4.. Amosite 5~ Crocidolite 2 jl The synthetic inorganics specified for t~st were: 10 Zirconia paper 2~ Hydrated magnesia 3~ Potassium titanate 4~ Beryllium oxide 5c Zirconium silicate 6~ Titanium oxide 7~ Boron nitride Project Extension The work described above in Tasks 1 and 2 comprised the work to be performed in the original one-year contract~ When it became evident that useful matrices could not be prepared from synthetic inorganics alone, the project was extended for a second year's work, as follows, to include the use of organic binders. Task 2a~ Matrices Incorporating organic Binders The following materials, alone, and in the specified combin- ations were testedo 1. Potassium titanate - Teflon emulsion 2~ Ceria - Teflon emulsion 3.. Potassium titanate - Teflon fiber 40 Zirconia E fiber - Teflon emulsion 5~ Zirconia E fiber - Teflon fiber 6~ Zirconia powder - Polypropylene fiber 7~ Zirconia powder - Teflon fiber 8.. Potassium titanate - zirconia E fiber - Teflon fiber. On the basis of partial testing, the three most promising matrices were to be selected for complete property testsG Task 3.., Preparation and Evaluation of Full,-Sized Matrices The three best compositions were to be selected, and 8-inch square matrices were to be made in accordance with the following schedule.., six matrices of each composition were to be made in each of the thicknesses., 0.020 ± 0..,002 inch 0 .. 030 ± 00003 inch 0~060 ± 00004 inch From the 9 composition-thickness groups, three matrices of each type were selected for testing., The full-size matrices were tested for density, electrolyte absorption, and gas permeability (or bubble pressure).. On the basis of these properties tests, the best matrix composition was to be selected for Task 4. 3 Task 4" Matrix Fabrication Two hundred matrices in 8-inch square size were to be made of the best matrix composition as follows: ae 100 matrices of 0~03 inch thickness b. 50 matrices of 0~02 inch thickness c~ 50 matrices of 0~06 inch thickness When the property tests of Task 3 demonstrated that three matrix compositions were reasonably similari' the provisions of Task 4 were modified to specify the manufacture of matrices as follows: Compositions a) Potassium titanate (PKT) 95% - Teflon 5% b) Ceria 99% - Teflon 1% c) Zirconia 99% - Teflon 1% One hundred matrices of each composition in 8-inch square sizeo a) 25 matrices 00020 inch thick ± 0~002 inch b) 25 matrices 00030 inch thick ± OQ003 inch c) 50 matrices Oc060 inch thick ± Oc004inch The matrix weights, according to the original specificationsi' were to deviate no more than ± 205% from the average of the compositions thickness groupo This was subsequently changed to prohibit deviations of matrix density greater than ± 5% of the average for the composition thickness group ... The finished matrices were also to be free of visually de- tectable surface defects and pinholes~ These finished mats were to be delivered to NASA-Lewis for subsequent evaluation including actual operation in electrochemical cells~ 4 ---- -- ~--,,--- ~~+-;:......---.-.-~~,- - ".----~~-.--~,.---. --- VIII TASK 1 PROPERTIES OF !VEL CELL ASBESTOS A~ Procurement and Preparation of Specimens The chrysotile sheet stock to be tested was selected from the warehouse stocks on hand at the Johns Manville Tilton planto One 25-sheet lot was cut from the leading end of a roll of 20-mil paper; another similar lote from the trailing enda One 25-sheet lot of 60-mil millboard was cut from the start of a production run; another lot from the end of the same run", These four lots were given special care in handling and were specially packaged to prevent damage during shipping", Upon receipt at TRWo the four lots were identified numer- ically as follows~ 1000 series 60 mil rnillboard~start of run 2000 series ~. 60 rril mil1board-end of run 3000 series = 20 mil paper = start of run 4000 series 20 mil paper = end of run From each of the lots v 5 sheets were selected at random and identified numerically. for example. 1100. 1200$ 1300 q 1400, l500~ Each sheet was then cut into sections and identified for testing (1101, 1102, etc~)a In each case, a one=inch margin was trimmed from each edge of the sheet in order to remove material that may have suffered physical damage~ These trimmed edges were then used for some of the tests of properties that are independent of fiber packingu Bp. Tests and Results l~ Asbestos ~operties ao Chemical analysis~ ~ Two oven~dried chrysotile speci- mens were analyzed by standard wet methods~ The specimens were digested for several hours with hydrochloric acid and filtereda The residue was ignited. weighed o and heated with HF to volatilize the silica., After weighing. the n9n~vola tile residue was dissolved in Hel and added to the filtrate containing the acid solubles", The iron group ions were double-precipitated with NH4 OH-NH4 Cl and ignited"" From the filtrate. calcium was precipitated as oxalate and ignited p and magnesium was precipitated as the arrmonium phosphate and ignited~ No attempt was made to resolve the R203 group into the usual constituents Fe, AI" etc", 5 ( Following are the results of this analysis: Si02 MgO CaO Fe203 The remainder (about 12%) is high temperature treatment~ Noo 1 41,,86% 42~78 2.,19 0.,85 water which Specimen can be No. 2 42.14% 42.80 1 .. 70 0.87 driven off by b.. Photographic and electronmicrogra,phic examination. A piece of black vinyl "Electricians" tape was pressed lightly against the surface of a piece of the 60-mil millboard, and the fibers adhering to the surface were photographed at lOX (Figure 1)., There are visible many very fine fiber bundles, several evident stalks of unresolved fibers r and several wads of very fine fibers", The electron micrographic specimen was prepared by lm- pressing the plastic replica material against an asbestos sheet. Fibers of the asbestos were retained by the plasticc The replica sheet was shadowed with chromium on carbon at about 20 0 angle. The photographs (Figure 2) made at 20,000X reveal that fibers of 0 ... 01 mil diameter are bundles of many smaller fibers" These photographs do not permi1: an estimate of ultimate fiber diameter, but they do suggest the enormous porosity potential of the natural material., c~ Surface areao - These measurements were made with the Perkin Elmer Sorptometer,Model 2l2B., The instrument was standardized against materials obtained from American Instrument CO,o and standardized by the Bone Char Research Project, Inc. (originated by The National Bureau of standards) .. Following are the average surface areas reported by the Bone Char Project and the val ues obtained by TRW Inc~ Reference Absorbent No" 2 Reference Absorbent Noo 6 Reference Absorbent No., 8 Bone Char Project TRW 10 .. 3 m2/gm 69~ 2 560 10.38 m2/gm 75 .. 6 515 The TRW values compare favorably with the span of values upon which the Bone Char Project averages are based .. One specimen of each of the asbestos stocks yielded the following values: 6 , .. , ( ! I I 1 ( Figure 1. Chrysotile Asbestos Fibers: lOX ..]14'+' 7 Figure 2. Electronmicrograph of Chrysotile Fibers; 20,OOOX 8 Specimen Number 1200 2400 3100 4100 Surface Area 5007 m2/gm 48 .. 5 55 .. 5 48 .. 3 These values are in very close agreement, and they indicate that the property is not significantly dependent on the variables in the processes of converting suspended chrysotile pulp into paper and millboard", 2~ Dry Mat Properties a 4 Tensile testsa Instron Tensile Tester~ x 3 inches) mounted to head speed was 0050 inch - Tensile tests were performed on an The specimens were die-cut rectangles (2 provide a gage length of 1 inch a Cross- per minute., In one set of tests, one specimen was taken from each of twenty test sheets., There were five sheets each of the material designated as 1000, 2000, 3000, and 4000 series. The tensile specimen were cut at random angles with respect to the processing direction 'of the material., The results are summarized in Table I and the load-elongation curves are presented~ superimposed, in Figures 3 # 4, 5 g and 6 -0 For the 20- mil paper, the values of load at failure and the curve shapes are reasonably simil,~lr. For the 60-mil millboard, however, the values of load-at-failure differ widely, and the elongation curves reveal different modes of failure., Some specimens failed after moderate extension while others stretched much more before failure. These tests did not reveal a clear relationship between mode of failure and angle of loading relative to processing direction. A second set of tests was conducted to clarify the influence of direction of loading on the shape of the elongation curves. Two presumably similar sheets of the same stock {2000 series) were cut into specimens., One sheet (2701) furnished nine specimens g all with the loading direction parallel to the processing direction 0 The other sheet furnished six specimens parallel (2702A) and four specimens transverse (2702B) to the processing direction~ The elongation curves for these tests are presented in superimposed groups in Figures 7, 8, and 9. The curves reveal that loading in the transverse direction causes about 0., 07 inch extension before abrupt failurE~. Loading in the parallel direction causes about 0015 inch extension at a much lower stress level" This probably reflects a preferential orientation of the asbestos fibers parallel to the processing directiono Parallel loading apparently involves considerable slippage between the parallel oriented fibers. In transverse loading, less slippage of the fibers occurs. It is interesting 9 Table 1 Tensile Tests of Fuel Cell Asbestos Specimen No. Loading Angle Load (1 bs . ) ~.~ 1100 45° 21 .675 1200 0 18.975 1300 30 19.675 1400 50 16.575 1500 20 19.80 2100 60° 10.05 2200 30 9.475 2300 45 16.95 2400 90 10.75 2500 0 10.75 3100 0 6.625 3200 0 6.325 3300 45 6.650 3400 45 7.25 3500 90 8.90 4100 0 6.05 4200 45 6.725 4300 45 7.35 4400 90 6.95 4500 0 6. 175 * This is max~mum load for specimens with a cross-sectional area of 2 inches times the thickness of the asbestos mat (0.055" for the 1000 and 2000 series specimens and 0.020·· for the 3000 and 4000 series). 10 L 1 f 1 j A 20 15 (/) 0 z ::::) 0 Cl. -Q « 10 0 -.J 5 o -05 ·10 ELONGATION (INCHES) A B C 0 E 1100 1200 1300 1400 1500 45° 0° 30° 50° 20° ·15 Figure 3. Tensile-Elongation Curves for 60 Mil Fuel Cell Asbestos Board (1000 series) 1 1 ( . 1 ! L 20 0 15 f/) 0 z ::J 0 Q" 0 « 10 0 ...J 5 o ·05 A 2100 60" B 2200 300 C 2300 900 0 2400 45 0 E 2500 OJ) ·10 ELONGATION (INCHES) ·15 Figure 4. Tensile-Eiongation Curves for 60 Mil Fuel Cell Asbestos Board (2000 series) 12 h302A 1 {; " I' i! h n !l 1i t\ n II " H ti 11 j; H n ;,1 " " lj f ~ ~ " " q It II ;1 11 " 'I U ~ i n U l' ,I Ii H t! H p n n H it ii " " Ii H l: If U IT " li Ji }~ i! " ,,' ( .. ",,1 15 t t '" !i " - II C/) H 0 k Z if :::) r 0 H a.. 10 n 0 i~ / / / 27 ij I" iI I li " n ( Table 3 Electrolyte Absorption and Retention Wt. of Spec. Wt. of Absorbed Wt. Rat i 0 Wt. of Retained Wt. Ratio Spec. No. gm So 1 n., gm Absorbed So 1 n., gm Retained 1100 0.5674 3.3970 5.98 2.9034 5. 12 1200 0.5250 3. 1424 5.99 2.7855 5.31 1300 0.5491 3.0519 5.56 2.6844 4.89 1400 0.5371 2.7296 5.09 2.5925 4.83 1500 0.5470 3.0531 5.57 2.5955 4.74 Average 5.64 4.98 2100 0.4611 2.5515 5.53 2.2699 4.93 !i 2200 0.4411 2.4,119 5.46 2.2976 5.22 2300 0.4499 2.6325 5.84 2.3367 5.20 j; h 2400 0.4535 2.6473 5.84 2.3108 5.09 ~ ! ", 2500 0.4148 2.3924 5.76 2. 1640 5.22. n ,) " jf H Average 5.69 5. 13 :1 , 3100 0.2245 0.8534 3.80 0.8534 3.80 d if 3200 0.2280 0.8980 3.94 0.8633 3.79 Ii it 3300 0.2207 0.7999 3.63 0.7852 3.56 !f j: 3400 0.2186 0.8520 3.90 0.8512 3.89 ,! I! 3500 0.2301 0.8978 3.90 0.8978 3.90 n ji I:! n 3.83 ,~ Average 3.79 f' 4]00 0.2]~7 0.8425 3.86 0.8443 3.86 4200 0.2153 0.8013 3.73 0.8015 3.73 4300 0.2229 0.8526 3.82 0.8327 3.74 4400 0.2163 0.8035 3.71 0.7957 3.68 ( 4500 0.2138 0.8452 3.95 0.~076 3.77 Average 3.81 3.76 ! ' 28 REFERENCE MARKS , . , SPECIMEN WIRE SCREEN CLAMPING PLATE Figure 14. Schemati~ of Specimen Holder for Liquid P~rmeabil ity Tests. 29 As described by Cooper and Fleischer, if one assumes that asbestos mat is essentially a packing of cylindrical tubes with axes all transverse to the plane of the mat, then, with incorpor- ation of additional data g one may compute a numerical value of porosity of the specimen. However, this computation involves several idealizing assumptions that are not even remotely realized in a sbestos mat, and consequ2ntly the porosity value so derived is ficti.tious. Since the liquid permeability test is being surveyed in this program merely as a convenient means of comparing specimens of asbestos for service as a matrix, we believe that the computation of porosity va:ues is an unwarrented elaboration, and we report only the raw data~ The first tests with asbestos specimens yielded grossly erratic results, evidently because of entrapment of air pockets. When the specimens were permitted to saturate by capillary absorption upward from the lower surface, the data became much more coherent., The data (Table, 4) reveal that the specimens of the 1000 series (production start) are much less permeable and much more variable than the specimens of the 2000 series (production end)., Roughly, the measured times of permeation correlate with the measured thickness of the dry specimens, although in the case of the 1000-series specimens v the permeability variations seem disproportionately great. Moreover, the slight difference in general thickness of the 2000 and 1000-series specimens cannot account for the notable difference between the permeabilities of the two groups .. For comparison, three sheets (8..,5 x 11 inches) each of the 1000-series and the 2000-series material were weighed, and the following results were obtained: 1000 series 2000 series Difference 214.,Og l81.,3g 32.,7g (or about 15%) Thus, the weight difference corresponds roughly with the differ- encein thickness between the two lots of millboard., However, the variation in water permeation rates is greater than that predicted from an exponential dependence on mat thickness. Evidently, the water permeation rate does reveal mat differences more significantly than simple thickness or geometric density differences .. c~ Electrolytic resistance~ - Electrolytic resistance of the saturated mat was measured with a cell similar to that des- cribed by Cooper and Fleischer., The cell (diagrammed in Figure 15) splits into two identical halves., Each of these pieces was machined from a Teflon block. When the specimen, with edges 30 ., .•... , I I I 1 I Specimen 1100 1200 1300 1400 1500 2100 2200 2300 2400 2500 3100 3200 3300 3400 3500 4100 4200 4300 4400 4500 Table 4 Liquid PermeabilitY'Test~ Specimen Thkns. (inch) 0.0565 0.0538 0.0537 0.0532 0.0550 0.0494 0.0470 0.0506 0.0478 0.0483 0.0208 0.0208 0.0201 0.0206 0.0203 0.0198 0.0194 0.0195 0.0205 0.0192 .. - ,~- --=; .~- - .-.~-. ~ -~ ~--- ---~- ,-.- .-.- _. - Flow Time (sec.)* 978 719 586 732 795 362 317 352 365 323 42 .. 5 39.7 39.4 40.7 41.3 43.8 41.0 38.8 39. 1 39.2 * Time required to flow 1.12 ml. of water through a 1/2 inch diameter circular area of asbestos mat under an average head of 119.4 em. of water. 31 I: Figure 15 1U151 a) I I I' I I I I I I I I I I : I I I, I " I I L J I "-< J "~" I , I ,~, L ______ :.. .... I I: I I I I I I I I ': l ) I '>/ I /'", I II "'''' I ","','" : ~~ _______ J I I I I I : :: I I I I I I I I I I l) I I ... " I I II I I II I I ~ i L _________ _ ~ ~ ~ ~ __________ J I,, __ v ___ ) ~ ______ J~i ___ ~ _______ J~ ____ .~ ________ ~ ~ SPECIMEN R;FERENCE ELECTRODE WELL :---n ~ -- -------- (a) WORKING ~ ELECTRODE V,........ CHAMIER RlTENTIOIoETER 'REFERENt:E HYDROGEN ELECTRODES +-I---,r---' '------I POTENTloSTAT (b) - + I WORKING ELECTRODES Diagram of Cell Used for Electrolytic Resistance Measurements. b) Electrical Schematic of Resistance Apparatus. 32 I f 1 t sealed by melted paraffin, is clamped between the halves, it presents a circular area of 1/2 inch diameter to the electrolyte. The reference electrodes in these tests were hydrogen- generating electrodes operating in the same electrolyte that filled the working celIe A Sorensen potentiostat furnished current controlled at ~41 rna (which is equivalent to 100 amp./sq. fto at the specimen surfaceo) The test procedure follows: with zero current between the working electrodes Q the rheostats in the reference electrode supply circuits were adjusted for gentle production of hydrogen and for zero potential _ difference between the two reference electrodes~ Then, with 141 rna passing through the specimen, the potential difference between the reference electrodes was measured" FinallY6 the electrolyte was removed, the specimen was flushed out of the cell by a stream of water Q the electrolyte was replaced g and the resistance of the electrolyte alone was measured.. The latter constitutes a blank measurement, but its relationship to the specimen measurement is very dubiousD The distance of separation between the two Luggin capillary orifices is determined by the thickness of the compressed rim of the specimen u whereas the rest of the specimen mat expands freely to several times its dry thickness., Therefore6 the mat resistance measured in this apparatus pertains strictly only to this particular condition Qf the mat and may not be applied unchanged to different situations. For that reason u the "blank" values are reported in Table 5, but are not incorporated in the measured values for the specimens~ Since the current density is regulated at 100 ASF 6 the potential across the specimen is converted to ohms per square foot by applying the factor 10-2~ The difference 1n resistance of the 1000 and 2000-series correlates qualitatively wi.th the measured thicknesses of the dry mat, and also with the measured weights of the dry mats (cfa thickness measurement and liquid permeability tests)., do Gas Eermeability of wet mato - The air permeability was measured for specimens of the asbestos mats containing absorbed 40% KOH solution in the w.eight rati.o 1: I and increasing to saturation~ For this purpose, the apparatus at hand was modified to improve its sensitivity~ The specimen g with edges sealed by melted paraffin g was mounted in a holder which supplied air under measured pressure to the lower surface of the specimen~ A 1-1/4 inch diarr'-;ter circular area of the specimen was exposed to the test ga~; The gas permeating the specimen ~'Jas contained by an upper chamber of the holder and conducted to a water bubbler, which served to indicate and measUre the gas flow., In the holder, the specimen was restrained against the pressure differential by a metal screen directly above it .. 33 1: ( Specimen 1103 1203 1303 1403 1503 2103 2203 2303 2403 2503 3103 3203 3303 3403 3503 4103 4203 4303 4403 4503 Blank Blank Blank Table 5 Electrolytic Resistance of Fuel Cell Asbestos b. E, Volts o. 1081 O. 1083 O. 1081 0.0835 0.1088 0.0891 0.0843 0.0905 0.0917 0.0874 0.0466 0.0695 0.0541 0.0667 0.0508 0.0400 0.0574 0.0445 0.0659 0.0561 0.0355 0.0350 0.0373 34 R, ohm/ft 10.81 x 10- 4 10.83 10.81 8.35 10.88 8.91 8.43 9.05 9. 17 8.74 4.66 6.95 5.41 6.67 5.08 4.00 5.74 4.45 6.59 5.61 l h , " It it p R H 11 I. ji ~ ( Preliminary experiments with bubbler design to achieve max- imum sensitivity as a gas flow meter revealed several interesting considerations. With decreasing orifice size, the bubble becomes smaller, but the capillary forces within the bubbler tube makes necessary greater gas pressures to expel a bubble of gas. In fact, with a very small diameter tube, the gas is released as a burs~ of bubbles" The optim\lm condi tion was attained by using a tapered polypropylene tube to minimize capillary effects and trimming off the tapered end to obtain the optimum orifice diameter" Press1.lre of the air supplied to thl~ specimen was measured by either a water manometer, a mercury manometer, or a Bourdon gage, depending on the pressure~ This provided accurate pressure measurements ra~ging from a fraction of an inch of water to 30 psig~ Very low pressures were corrected for the depth of immersion of the bubbler tip (about 1 inch)., The dat.a are recorded in Table 6... Probably the most significant yield from these tests is the gross difference between the paper and millboard... The 20-mil paper specimens consistently leaked gas at low pressure differentials (about 10 inches of mercury) even when saturated with KOH solution.. On the other hand, the 60-mil millboard usually was impermeable at 30 psi even at the minimum (1:1 weight ratio) content of KOH solution., We observed that in all cases the gas pressure forced KOH solution out onto the top surface of the specimen" When the pressure diff·erential was relaxed, the free solution was quickly reabsorbed into the specimen., We suggest the following tentative interpretation., At the 1:1 wei9ht ratio of asbestos to KOH solution, the paper contains only one-£ourth the saturating quantity of solution, the millboard contains only one-sixth. Evidently, the millboard structure is such that the pressure induced migration of some liquid produces a saturated and sealed zone near the low pressure sideo For some reason, the structure o:f the 20-mil paper or its lack of sufficient thickness does not permit a sealed zone to develop., 35 ! 1- , ( Table 6 Gas Permeability of Wet Asbestos Specimen Identity and Net Net Electrolyte Pressure ' . Flow Rate ~': Specimen Pressure Flow Rate ~': Rat io (ps i ) (Bubbles/Sec) Identification (ps i ) (Bubbles/Sec) 1201 1 : 1 6.958 .023 1501 2: 1 25.0 · 143 8.526 .025 25.0 · 125 9.065 .028 25.0 · 11 1 9.408 .045 2101 1 : ] 3.283 .059 2: 1 11 .270 .019 4.949 .083 14.308 .014 7. )-f48 · 125 15.500 .018 1~.005 .250 16.000 .014 2: 1 10.241 .050 3 : 1 25.000 .032 12.225 .071 30.000 .008 14.700 .091 1202 1 : 1 1 .421 .0]1 17.500 · 143 1 .667 .1,00 20.000 · 167 1 .764 .100 3: 1 17.500 .033 2: 1. 7.105 .038 20.000 .040 9.898 .043 25.000 .071 14.700 .067 4: 1 17.500 .016 15.000 .062 20.000 .023 17.500 .067 25.000 .045 20.000 .071 2102 1 : 1 21 .500 · 167 22.500 .083 18.000 .333 25.000 .091 2: 1 19.000 .01'7 27.5.00 · 100 3 : 1 30.000 0.000 30.000 · 111 2501 1 : 1 3.283 · 100 1301 1 : 1 1 .863 .020 2.009 .250 2.~91 .028 1 .911 .250 3.675 .037 2: 1 5.047 .050 t 4. 116 .037 25.500 .023 II ( 4.214 .040 3401 1 : 1 .418 .036 q ~ ~ 4.214 .042 .526 .034 Ii it 2: 1 30.000 0.000 .814 .050 II 1401 1 : 1 30.000 0.000 .900 .040 IT II 1501 1 : 1 3.773 .048 2: 1 1.176 .048 n II 2.646 .333 1 .372 .056 " Ii 3.773 .500 1 .372 .050 J 3.822 .083 3: 1 1 .519 ,.050 r 2: 1 6.223. · 143 1 .813 .053 I f 10.535 :125 .059 , 2.107 ; ! 18.500 · 143 4: 1 2.597 .059 I 21 .000 · 143 2.989 .062 I , 3401 4: 1 3.381 .067 4402 2: 1 12.250 · 143 5: 1 3. ) 85 .056 3: ., 7.840 .071 , .. 1 3.675 .056 12.250 · 143 4.018 .056 4: 1 12.000 .100 i ! 420) 1 : 1 .378 .067 12.000 · 100 I I :400 .067 20.000 .333 L, .428 .071 4403 1 : 1 .407 .024 l~-- ---,--- - -. I f 36 t ~ i f ~ F ~ -1 , 11 " __ ~:.-";-\"l:::,,=::::,,=,,--:;::;._ .• __ .- .;~="".'''-~ ~-.- .:..-~-.::.;..:=~~..:.:..:...::......:~-~,--.-,~,:,-~,-::,:"::".-.,,,,--,~~-------~.....:..--~ Table 6 (Cont'd) Specimen Identity and Net Net Elect ro I yte Pressure Flow Rate .'. Specimen Pressl1re Flow Rate " Ratio 14201 430] 4401 (ps i ) (Bubbles/Sec) Identification (ps i} (Bubbles/Sec) 2 : ] .875 .03] .684 .0'37 ] .001 .029 .B64 .043 ] .372 .031 4403 I : ] 2.450 · 143 3: ] ] .667 .033 7.350 .454 2. ] 56 .034 12.250 .B33 2.500 .034 2: ] 2.646 • 100 4: ] 3.234 .032 7.399- .333 3.578 0028 12.225 .556 4.655 .031 3: ] 4.753 .043 1 : ] . ] 19 .031 7.350 .077 .328 .042 ]2.225 .167 .911 .043 4: 1 5.978 .053 5.635 .200 7.350 0071 9.800 .500 12.225 .200 2: ] .846 .013 4501 ] : 1 .040 · 167 3.773 .040 .043 .333 7.350 . ] 25 2: ] .302 .091 12.495 .200 0367 0100 1 : , 2.009 .011 .60B · 143 4.900 .021 3: 1 0504 1 .667 7.350 .033 4402 ] : 1 .972 .016 9.800 .050 2.450 .040 12.250 .071 4.900 .OB3 2: 1 30.000 0.000 10.045 .250 3: 1 18.000 .143 2: 1 2.205 .020 lB.OOO . 125 4.900 .043 .,'; This is an arbitrary relative flow rate through a 1-1/4 inch diameter circular area of the mat. ,,, in ;.;j ;-'~ l'~ :~ !f I-t l~ i., !~ h ll!l! ~~ i< If p H ~ 11 " 11 ~I ~f If it il ji j ( :l 4", KOH for and and Chemical Degradation These degradation tests consist in maintaining specimens ln solution of 30 G 40 0 SO~ and 60 weight percent concentration 100 and 1000-hour periods at temperatures of SOl' 100, 150, 200oc~ Tests at SOoe in 50 and 60% KOH and at 200 0 C in 30 40% KOH are not required~ The tests were performed in ordinary laboratory ovens which incorporate thermostat controlso As containers g we used 4 ounce Teflon FEP bottles with screw caps~ These were satisfactory at the two lower temperatures g but would not retain the water at 150 and 200oF~ We then sealed each bottle individually in a capsule made from standard 2 inch threaded pipe nipples, closed with the threaded caps (Figure 16)0 We used Teflon pipe tape for a thread sealant g and learned that only certain premium brands of Teflon tape are effective~ and only when seven or eight laps of the tape are applied to the thread~ The caps were then tightened with a large pipe wrench p the handle of which was lengthened with a four- foot pipe., The ,Teflon bottles were weighed empty and with the specimens of asbestos~ A polonium=activated dust brush was placed in the balance case to speed the equalization of static charges which are specially troublesome with this plastic., A volume of 50 ml of the KOH solution was placed in the bottleD Where 60% KOH was to be usedo the appropriately weighed quantity of dry KOH pellets and volume of water were placed in the bottle Q At the end of the test g the contents of the bottle were transferred quantitatively to a 600 ml beakeru diluted with much water and permitted to settle~ The supernatant liquid was decanted through a sintered glass filteru and the washing was repeatedo The final wash was very slightly a.cidified with Hel to facilitate complete removal of KOH g and the solid was transferred to the fil·ter" dried" and weighedo For the lower temperature tests u the bottles were capped tightly and placed in the oven., For the higher temperature tests u the bottles were capped lightly and placed in the pipe capsuJ.€Q 1 ml of water was introduced to provide balancing vapor pressurep and the top cap was installed"" Each capsule was then weigh€d to the nearest O.,lg and placed in the oven", After several days/l the capsules were removed g allowed to cool.. and weighed again~ If there was any significant lossg the capsule was openedo a new sample was prepared and resealed in the capsule-<> Only those specimens that showed negligible weight loss were accepted as valid tests", trhe results of these tests are shown in TabJ.e 70 As expected Q the dissolution of specimens is greater with increasing timeQ temperature u and concentration of the KOH., However 0 with the exception of two tests and the results for the 38 "" .. _------ ! , i t i I if ., " It q ( ( Figure 16. View of Spec imen Hol de : for High Temperature Chemical Degradation Tests. 39 Test Time (HR) 100 100 100 100 100 100 1000 1000 1000 1000 1000 1000 100 100 100 100 100 100 100 100 100 100 100 100 1000 1000 1000 1000 1000 1000 1000 1000 1000 1000 1000 1000 Table 7 Chemical Degradation of Fuel Cell Asbestos KOH Cone. 30 30 30 40 40 40 30 30 30 40 40 40 30 30 30 40 40 40 50 50 50 60 60 60 30 30 30 40 40 40 50 50 50 60 60 60 Specimen Identification 1600 2600 4600 3600 3600 3600 2600 2600 4600 1600 1600 4600 Tests at 100 0 e 1600 2600 3600 1600 3600 4600 1600 2600 4600 2600 3600 4600 1600 1600 4600 2600 3600 3600 2600 3600 4600 1600 2600 4600 40 % Wto Loss 2.85 1. 14 6. 14 4.70 5.00 5.33 3.00 2.00 5.31 3.52 5.56 5.61 7.50 7.67 5.30 10.70 9075 10. 14 16.55 14.75 16035 15.90 32085 17.97 12.30 22.20 36.6 32.80 41.40 3002 41 .00 29.6 36.5 42.00 62.75 3609 ( Table 7 (Cont'd) Tests at 150°C Test KOH % Wt. Time (Hr) Cone. Specimen Identification Loss 100 30 1600 3.6 100 30 3600 16.9 100 30 4600 1504 ~oo 40 1600 2.0 100 40 2600 17.6 100 40 4600 22.4 100 50 1600 30.7 100 50 2600 3105 100 50 3600 39.9 100 60 2600 32.4 100 60 3600 38.8 100 60 4600 51.4 1000 30 1600 19.8 \ 1000 40 1600 30.6 1000 50 1600 .... q 5 :> .... 1000 40 2600 2e:' • ::> 0 I 1000 50 2600 3800 1000 60 2600 38.8 1000 50 3600 37.2 1000 60 3600 39.9 1000 30 3600 7.4 1000 60 4600 39.5 1000 30 4600 19.5 1000 40 4600 22.5 Tests at 200°C 100 50 1600 36.2 100 50 2600 36.5 100 50 4600 36.6 100 60 2600 37.6 ( 100 60 3600 38.6 100 60 ·4600 39.6 41 1000 hour, 40%.. This (44%) on pletely to assumption chrysotile 1000 hours 200 0F tests, the weight losses attain a limit of about value corresponds quite well with the values predicted the assumption that. the cbrysotile is converted com- insoluble Mg (OB) 2 and soluble silica te.. If this is valid, the data indicate the conversion of to Mg (OH)Z or hydrated MgO is virtually completed in at lOOOF and in 100 hours at lSOoC. Figure 17 shows the change in chrysotile caused by treatment with hot KOH so],ution.. The r~sidue from treatment retains some of the fibrous structure, but a large amount of granular material (dried Mg(OH)2) appears scattered across the micrOscope field and also filling the remaining fiber clusters. The data reveal that natural chrysotile is probably not a satisfactory matrix for long service at temperatures as high as 100oC~ The tests suggest, however, that the insoluble residue, if it retains a satisfactory structure, may be superior to chrysot ile,. S~ Electrochemical Degradation This test consisted essentially in subjecting the specjmens to a current density of 40 ASF in 40% KOH electrolyte at 1000C for 72 hours. At 24 hour intervals, I ml samples were drawn of the anolyte and catholyte, and the €lectrodes were washed with nitric acid to remove any deposits~ The electrolyte specimens and electrode washings were then analyzed spectrographically for identity and quantity of constituents of the asbestos mat~ These tests were performed in a V-shaped cell machined from a Teflon block (Figure IS) _ In one leg of the cell was a shoulder to support a platinum wire screen, on which the specimen rested~ since the specimen was located below the electrode level, the electrolytic gases escaped without entering the specimen .. . The cell was placed in a laboratory drying oven at 10Qoc. Electrolytic hydrogen was vented through a tube to the exterior of the oven, and oxygen was vented into the ovenD The requisite current (0027 amp) was provided by a Sorenson potentiostat~ The 40% KOH solution purified electrolytically for these tests contained, as revealed by spectrography, very small con- centrations of magnesium, calcium, and aluminum ionso These, of course, will not be removed by electrolysis., The several samples of used electrolyte analyzed were those taken at the ends of the 72 hour tests, when the soluble impurity concentrations were greatest. The concentrations of Mg, Ca, and Al ions were no greater than in the original electrolyte 0 Silicon was only barely detectable. ( (a) (b) Figure 17. Chrysotile Before and After Chemical Degradation Test. (lOX) 43 !. L ','~, n, i' ,.: .. ~.' .' I j SPECIMEN SCREEN .j , . .. ,.~:..,o_ • .,~ •• ::-:'.·~.~~._:::':.l' l. ; .... _ :;,:~-t;....!:~",~s...:....;;.,.~ .......... ,.. ..> • .:,...:;...;;..,.::.;.t ~ ->.<-:. ~" CATHODE ANODE , , , ..( ) I " I, ...... , I ..J I I / ~, " I "' I I .... }./ \ I I \ I \ I \ , \ I \ / \ I \ I \ , \ I L...1 " o 6" Figure 18. Schematic Diagram of V Cell for Electrochemical Degradation Tests. ~'.". In the first test" the speci.men was the 20-mil ~hrysotile paper" At the end of the first 24 hours, there was a visible mottled grey deposit on the anode surface., The deposit did not dissolve In nitric acid., At the end of the test (72 hOUr9) the deposit was apparently unchanged and still insoluble in nitric acid~ After standing overnight in the KOH electrolyte, the grey material changed to a golden brown color which dissolved in nitric acid" Upon evaporation to dryness a very small quantity of brown residue appeared~ It dissolved readily in a drop of hydrochloric acid g which was then analyzed and proved to contain iron.., Three subsequent tests were pelcf~~n:'med with 60-mil millboard specimens~ During the first two of these te$ts~ the electrodes remained bright and cleano and the electrolyte specimens revealed no significant concentrations of constituent elements of asbestoso During the last test (specimen 2600), very small amounts of brown deposit were formed on the anode" This material was readily soluble in nitric acid., Analysis of this also showed the presence of lronu These data seem to indicate the deposi.tion on the anode of the black Fe3 04 which 0 upon standing at room temperature for several hours" converts to the red Fe203 ~ The appearance of iron at the anode is remarkable in view of our observation that i,ron is not present in the anolyte in spectrographically significant concentration~ c~ Conclusions of Task 1 Work The properties of chrysotile asbestos, already well known, are that it is fibrous,. very porous" readily wettable .... and moder- ately resist.ant to attack by alkaline solutions., It was well- chosen for matrix service in alkaline fuel cells~ However, our tests revealed that some of the very small percentage of iron oxide normally present in chrysotile is transferred through the electrolyte and deposits on the anode in an electrolytic cello It remains to be determined whether the deposited iron adversely affects the electrode operation~ The major deficiency of chrysotile revealed by these tests is its reactivity in alkaline electrolyte~ The fibrous magnesium silicate is converted to a soluble silicate and geletinous magnesium hydroxide" The chemical compatibility tests demonstrated the degradation of chrysotile which occurs more rapidly with increasing temperature and KOH concentration., Evidentlyu 1000c is near the maximum temperature for 1000-hour survival of chrysotile in KOH solution., 45 ( The dry mat property tests did not produce any novel infor- mationo When the chrysotile mat absorbs KOH solution, it swells appreciably and loses much of its dry strength. The retention of electrolyte under 25G acceleration is excellent, and the gas- se&ling capabilities of the wet mat is adequateo At sub-saturation proportions of absorbed electrolyte, the thicker mat seals more effectively against gas transfer, evidently because the electrolyte pushed toward the low-pressure side is able to develop a completely saturated layero The 20 mil thick mat does not seal under a similar pressure differential. In general, the wet mat properties, as measured in this project, cannot be ~pplied quantitatively to the same material in an electrochemical cell. In a eell, the matrix is compressed between rigid electrodes, whereas, in the tests they were not confined., If the test data are to be related to the (';el1 environment, the degree of restraint of the specimens must be specified for tests like gas permeability and electrolytic resista nce 0 The fundamental and inherent limitation of chrysotile as- bestos is its chemical reactivity with alkaline solutions. At low temperatures and alkali concentrations, the low rea_etlon rate may permit its use as matrix for a reasonable timeD But at higher temperatures and electrolyte concentrations, the matrix life will be short 0 46 r IX TASK 2. TESTS OF ALTERNATE MATERIALS Au Material Selection The materials selected for test in this task of the program consistt~d of the following: Asbestoses: 1.. Leached chrysotile 2. Tremolite J... Amosite 40 Anthophylite Sa Crocidolite other inorganic materials: l~ Zirconia E fiber (neodymia stabilized) 20 TX fiber - nemolite (Hydrated magnesia) 30 Potassium titanate fiber (PKT) 4.. Boron nitride· fiber 5.. Beryllium oxide 6~ Zirconium silicate 7~ Titanium oxide Several tests of leaching treatments of chrysotile demon- strated that chrysotile is not improved by a preliminary chemical treatment... Leaching with concentrated Hel dissolves the magnesium constituent g leaving fibers of nearly pure silica. The silica fibers are readily soluble in KOH solution.. Leaching with sequestering agents has a similar effectu Pre-treatment with a surfactant converts the chrysotile fiber into an agglomerated, slimy, i.ntractable mass having no apparent advantag'e over the original material .. Acid leaching anthophylite, and cations, leaving a alkali .. of the other asbestoses - tremolite, amosite, crocidolite also dissolves the constituent fibrous silica which dissolves readily in As a result of these tests with leached asbestos, the long- time compatibility tests of leached material were omitted. Examination of the reported reactivities of beryllium oxide showed that it will dissolve in hot KOH solutions. Chemical attack of KOH on zirconium silicate was also expected,. Consequently, these two materials were omitted and the more promising materials, ceria and silicon carbide fiber were sub- s tituted~ The following three proprietary matrices were also tested .. 47 i l Acco-l (American Cyanamide company) Ace-Sil (Amerace corporation) Chrysotile-PKT-Neoprene (Pratt & Whitney Aircraft) B~ Chemical Degradation The compat.ibility tests were conducted by the techniques described earliero The test result was the quantity of insoluble aolid, in terms of the percentage of the original sample weight, recover'ed from the KOB solution.. Table 8 reports the test resultsQ Many materials were submitted to only part of the specified testing schedule - sufficient to demonstrate failure of the material., These test results can be summarized as follows: 1., The asbestoses~ being silicates, are inherently rea active with KOH and are, therefore, unsuitable. Pretreatment of the asbestos with dilute acid or sequestering agent removes the metallic cations from the fiber p leaving silica, which is readily soluble ln alkali., 2", TX fiber is superior in resistance -to KOH, but its high iron content renders it unsuitable for matrix service. 3., The three proprietary mats are pooro 4~ Boron nitride dissolves completely, and silicon carbide fiber is poor .. 5.., Zirconia E fiber and ceria powder are virtually unc changed.., 6 .. PKT and titania change only slightly during the 100 hour test, but both gain weight significantly during the 1000 hours.. The titania developed an insoluble, gelatinous filmy which may be a hydrated titania, but we have not established a chemica,l identification. The materials selected for further study on the basis of the initial chemical degradation tests were Zirconia E, PKT fiber, ceria, and titania., It should be noted that two forms of potassium titanate were tested., A long-fiber form, "Tipursul", is desirable for matrix application, but the production of Tipursul has been discontinued., The short-fiber form, "PKT', is being produced commercially for use principally as a paint pigment., The Tipursul -tested initially was from a small quantity at hand in the laboratory., Later, the PKT was used exclusively. 48 / I' Table 8 Chemical Degradation Tests Test Test KOH % Wt. Specimen 'ldentificati6n Time (Hr) Tem~ (OC) Cone. Loss " t: ACE-SIL 100 100 30 27.9 " I! ACE-S I L 100 100 50 27.7 l' p ACE-SIL 100 150 30 27.7 h li ACE-S I L 100 150 50 25.3 I, " " :1 ~f i: Potassium Titanate with u ji Asbestos and Neoprene " ~ \ Binder 100 100 30 7.2 iI 100 100 50 8.4 II 100 150 30 10.7 II 100 150 50 17 . 1 .' , ACCO No. 100 100 30 3.0 f ,~ 1 ACCO No. 100 100 50 11.2 I.) ,", , ACCO No. 100 150 30 19.9 ;j '-~ AceD No. 1 100 150 50 45.5 ;J " 1000 150 30 35.4 ;3 ACCO No. 1 ,! ;~ ACCO No. 1 1000 150 30 33.2 :J i.\ ',r ;J ACCO No. 1 1000 150 50 71.0 i'{ " ACCO No. 1 1000 150 50 76.9 !,~ it io( :;1 .', 'U Boron N tr de 100 100 30 93.4 1~ t'l Boron N tr de 100 100 50 98.3 if i1 de iOO 150 30 99.8 ~ 'f Boron N tr ~1 Boron N tr de 100 150 50 99.9 ~ ~ Boron N tr de 1000 150 30 I' !~ Boron N tr de 1000 150 30 f1 ii Boron N tr , 1000 150 50 ft ae jj Boron N de 1000 150 50 u tr x !\ Potassium Titanate 1000 150 30 2.7 '/ H (T i persu 1 PUlp) I II 1000 150 30 8.6 II 1000 150 50 13.4 II 1000 150 50 7.2 II 100 100 30 4.0 II 100 100 50 8.2 II 100 150 30 0.4 II 100 150 50 0.6 z rcon a E 1000 150 30 0.2 Z rcon a E 1000 150 30 0.3 z rcon a E 1000 150 50 0.7 z rcon a E 1000 150 50 0.6 ··1 Z rcon a E 100 100 30 ! O. 1 Z reon a £ 100 100 50 O. 1 Z rcon a E 100 150 30 0.4 z 100 150 .-,,- rcon a E 50 0.3 i 49 ! i ti ~ 1~ Table 8 (Cont'd) Test Test KOH % Wt. ~~i~en Identification Time (Hr) Temp (OC) Conc. Loss TX Fi ber 1000 150 30 20.5 TX Fiber 1000 150 50 3.6 TX Fiber 1000 150 30 Lost Sample TX Fiber 1000 150 50 37.3 TX Fi ber 100 100 30 5.5 TX Fiber 100 100 50 1.5 TX Fiber 100 150 30 1.6 TX Fiber 100 150 50 1.7 Amos i te 100 100 30 6.8 Amosite 100 100 50 30.3 Amosite 100 150 30 9.7 Amosite 100 150 50 39.2 C roc i do 1 i te 100 100 30 7.0 C roc i do 1 i te 100 100 50 26.9 C roc i do 1 i te 100 150 30 37.2 C roc i do 1 i te . 100 150 50 47.4 An thophy 11 i te 100 100 30 3·0 Anthophy 11 i te 100 JOO 50 7.5 Anthophyllite 100 150 30 9.0 Anthophyllite 100 150 50 25:6 Tremo 1 i te 100 100 30 4.6 Tremo 1 i te 100 100 50 5.5 Tremo 1 i te 100 150 30 7.5 Tremolite 100 150 50 12.9 Sil icon Carbide (woo 1) 100 150 50 14.6 Cer i c Ox de 1000 150 30 1.9 Cer c Ox de 1000 150 30 1.2 ,( Cer c Ox de 1000 150 50 0.6 Cer c Ox de 1000 150 50 1.8 Cer c Ox de 1000 100 30 1.5 Cer c Ox de 1000 100 30 1.6 Cer c Ox de 1000 100 50 1.8 Cer c Ox de 1000 100 50 1.2 Potass urn Titanate PKT 1000 100 30 4. 1 Potass urn Titanate PKT 1000 100 50 3.0 Potass urn Titanate PKT 1000 150 30 8.4 Potass urn Titanate PKT 1000 150 30 No Loss or Gain Potass urn Titanate PKT 1000 150 50 32.7 Potass urn Titanate PKT 1000 150 50 Lost Sample Potass urn Titanate PKT 1000 100 30 9.8 Potass urn Titanate PKT t_OOO 100 50 5.8 ~. ____ 0-,_- 50 Table 8 (Cont1d) Test Test KOH % Wt. Spec i ment Identification Time (Hr) Temp (OC) Cone. Loss Titanium Oxide 1000 150 30 34.3 Titanium Oxide 1000 150 30 30.4 Titanium Oxide 1000 150 50 60.4 Both had a thin Titanium Oxide 1000 150 50 87.7 film of transparen material present Titanium Oxide 1000 100 30 6.8 Titanium Oxide 1000 100 30 6.3 Titanium Oxide 1000 100 50 41.3 Titanium Oxide 1000 100 50 44.8 ( 51 f' , C.. Tests of selected ~ompa·tible ~.terials The four materials (zirconia fiber, PKT, ceria and titania) selected in the chemical compatibility tests were evaluated by the full complement of tests in this part of the program. This included a further study oft.he as-received fibers or powders, the preparation of 20-mil and 60-mil thick mats from these materials, the study of the dry mats, and an evaluation of the mats when wet with KOH. For the preparation of mats from these materials, 10% chrysotile fiber was added to the base constituent to help improve the structural integrity of the mats. 1m Starting Materi~~s a. Chemical compositi?nG - The chemical composition of the four materials used in mat preparation are listed below. These analyses have been supplied by the vendors of the respective materials '" PKT (Pigmentary Potassium Titan~te from dUPont) Ti02 K2 0 K2 S04 KCI Fe 85% 11 3 .. 0 0.1 100 ppm Titania (Ti02) (Fisher Scientific Co., Certified Anhydrous) Water soluble salts Arsenic (As) Iron (Fe) Lead (Pb) Zinc (Z) 0.05% 0 .. 00024 0.01 0 .. 002 0.,01 Zirconia Fiber (H~ I .. Thomas Fiberglass Co.) This material is basically zirconium oxide, stabilized by 10-15% neodymiao Semiquantitative spectrographic analysis by a commercial laboratory yielded the following results: Zirconium Hafnium Magnesium Titanium Silicon Calcium 52 73% 0 .. 74 0,,012 0..,068 0.13 0 ... 003 ceria (ceric ox.ae - Fisher Scientific coo Certified Grade) Ce02 Fe203 P?05 Rare Earth Oxides 99 .. 5% mine 0 .. 003 0 .. 005 0 .. 05 max .. Ou:..- spectrographic analysis revealed appreciable calcium, bu"t no quantitative estimate was attempted., bo Fiber structure., ~ The natural asbestoses amosite, anthophyllite; trernolite g and crocidolite - and TX fiber were photographed at lOX magnification (Figures 19, 20, 21, 22,and 23)~ Although these materials were not selected for the comprehensive testing program D the phot:>graphs reveal the wide difference in character of the materialo The fiber length and degree of fiber separati'Jn are largely determined by the processing each one has r~~ceivedf' but some inherent differences are evident., Tremolite is en. vel:y SOftD "ropey" fiber, while TX fiber is fineD looseD and trmds to be brittleG The anthophyllite fibers are short and poorly resolved., The Zirconia E fiber is evidently a smooth surfaced fiber, tends to curl,. but the fibers tend to remain separated (Figure 24)~ The potassium titanate (PKT) is a short straight fiber that tends stongly to clump together (Figures 25 and 26)0 The ceria and titania are not included here since they were purchased as powders and , therefore g have no fibrous structureo . c.. Surface area., - Surface areas ials selected for incorporation in adsorption technique D with the Perkin 212B., ceria Chrysotile Potassium Titanate Titanium oxide Zirconia E 2 .. 08 50 10.,2 8016 2085 of the component mater- mats were measured by the Elmer Sorptometer, Model m2/g m2/g m2/g m2/g m2/g The manufacturer g H., Ie Thompson Fiberglass Coo, reports the value of lOOm2 /g for Zirconia E fiber., The relatively smooth appearance of this fiber as shown in Figure 24, however, indicates that our experimental value of 2085 m2/g is more nearly the true value", 2~ Preparation of Mats Because mats composed individually of the four selected materials - PKT p ceria, zirconia, and titania - are too weak and brittle to be tested g these materials were blended with 10 weight percent of chrysotile asbestos fibers to add structural integrity 53 ) ~, , '·I.'~·' I ; t . 1 ;"·1 1 ~~ :.l.~'·'·' .. . ,; f" \ f ,- ~ Figure 19. Amosite (lOX) / Figure 20 . Anthophyl ite (lOX) 54 Figure 21. Tremolite (lOX) Figure 22. Crocidolite (lOX) 55 ~igure 23 . TX Fiber (lOX) Figure 24. Zirco n ia E F ibe f" ( lOX ) ; . 56 Fiq ure 25. Putassium Titannte (PKT) lOX Figure 26. Potassium Titanate (PKT) lO,OOOX 57 to the mats~ The components for each mat were weighed separately and then blended together in water by prolonged gentle mechanical stirring" Chrysotile fiber, when well dispersed, forms a very slowly- settling aqueous sllspensionQ Mats are best prepared with a sheet mold which consists essentially of a reservoir equipped with a fine screen bottom and a water column drain to generate about 30 inches of hydrostatic pressure at the screen., The dilute suspension of fiber is poured into the reservoir, agitated, allowed to become quiescent g and then quickly sucked down against the screen., The mat is t.hen lifted off the screen, pressed between absorbent paperu and dried Q A sheet mold was built in this laboratory to make mats of chrysotile and similar fibers (Figure 27) 0 The reservoir was made unusually tall to contain q in one filling, the quantity of dilube suspension needed for a 6 O~'mil thick mata The screen was replaced by a layer of l~inch thick g fine-pore polyurethane sponge on a perforated Plexiglass plate supportu The sponge was an effective non~clogging filter bed u from which the mat c':)uld be cleanly separated., The wet mat was then sandwiched between layers of absorbent paper and plastic plates and compressed by rolling with a 20 lb o steel cylinder g aftex which it was dried in a laboratory oven~ The she'2t !:T:old cannot be used wi,th the other selected mater- ials", In contrast with chrysotile fibere the other materials are more dense and settle much faster from a dilute suspensionn When mixed with chrysotile in dilute suspension Q the great disparity in settling rates causes gross stratification in the mat that is formed.., In order to preserve the desired homogeneity in the mat, the suspension must be made quite concentrated. and it must be cast quickly., The polyurethane sponge" which served so well as a bed for the casting of fibrous chrysotile g is unable to retain the small particle powders" ' Consequently u we used a standard laboratory Buchner funnel with filter paper for preparation of the composite mats.,. Af·ter being formed in the funnel u the mat was placed on paper towels to remove most of the water by capillarity~ Finallyu it was placed between paper ~owelsg and compressed in a small manual hydraulic press~ Composites with zirconia fiber were completely crushed by the hydraulic pressingu and therefore required more gentle treatment.., We compacted the zirconia composite mats by placing them between layers of absorbent paper sandwiched between Lucite plates (wj_th metal shims to establish the final mat thickness) and rolling manually with a 20-1b~ steel cylinder~ The mats prepared for testing were to be of two thicknesses: 0~020 ± Oc002 inch and O~060 ± 0~004 inch~ The mats containing PKT, ceriaj7 and titania were made conforming to the thickness 5CJ ( +-- ._n ~ __ .... ___ ~, __ _ i ( Figure 27. Mat Casting Apparatu s 59 requirements by maintaining a constant molding technique and final compaction pressure, and by controlling the weight of material in a mato In the case of the zirconia fiber composites, the weight of material per mat was adjusted to permit the final compaction without incurring undue destruction of the brittle fibers~ In all cases, the mats of each composition produced for test were uniform in thickness and weight. Dry Mat Propertie~ a~ Tensi~e strength" - Tensile tests were performed on the Instron Tensile Testero The specimens were die-cut rectangles, 2 x 3 inches, mounted to provide a gage length of 1 inch. Cross- head was 0.,50 inch per miEute" Typical extension curves are presented in Figure 28, and the tensile strength results are recorded in Table 9" It is noted that these mats are approximately only 10-15% as s·trong as the Fuel Cell Asbestos mats., It is likely, therefore, that most of the strength of these mats can be attributed to the 10% chrysotile fibers added to the mat" b~ Density~ - True densities were measured with the Beck- mann Air comparison Pycnometer", Values for the mat components separately are:: ceria Chrysotile Potassium Titanate Titania Zirconia E G., 93 g/cc 2 .. 73 g/cc (PKT) 30 32 g/cc 4003 g/cc 4 .. 70 g/cc True densitieS of the finished mats were also determined, the results are recorded in Table 10., The mat porosity was also cOl~iputed from a comparison of true density with the geometric density., Porosity in the 70-85% range was obtained in these mats.. This appears favorable compared to the 70% porosity typical of the standard asbestos mats" c.. 1J:'hickness variationsc> - Thickness was measured with a dial gage instrument equipped with a 1/2-inch diameter foot and dead-weight loaded to 5 lb per square inch. Only those mats were retained for testing which fulfilled the thickness tolerance requirements, namely ± 00002 inch for the 0.,020-inch mats and ± 0,,004 inch for the DoDGO-inch mats" d~ Pore size distribution" - The pore size distribution of these mats was measured by the mercury intrusion method using an Aminco-Winslow Porosimetero The intrusion curves are shown in Figure 290 These results show that the titania and the PKT mats contain pores mostly in the sub-micron range.. The ceria mat has most of its pores in the 1-1~5 micron range, and the zirconia mat 60 ( 3 -(I) 0 2 Z ::» 0 Q. -0 c( 0' 0 ..J o A ·05 A TI TANIUM OXIDE - CHRYSOTILE B CERIC OXIDE - CHRYSOTILE C ZIRCONIA E - ',":,HRYSOTILE o POTASSIUM TIT ANATE PKT" CHRYSOTILE ·10 ELONGATION (INCHES) '15 Figure 28. Tensile-Elongation Curves for Pressed Mats. Table 9 Tensile Tests of Pressed Mats Specimen Ceric Oxide-Chrysotile Cer i c Oxide-Chrysotile Cer i c Oxide-Chrysotile Cer i c Oxide~Chrysotile Titanium Oxide-Chrysotile Titanium Oxide-Chrysotile Titanium Oxide-Chrysotile Titanium Oxide-Chrysotile Potassium Titanate PKT-Chrysot i 1 e Potassium Titanate PKT-Chrysoti le Potassium Titanate PKT-Chrysot i le Potassium Titanate PKT-Chrysot i le Zirconia E-Chrysot i 1 e Zirconia E-Ch rysot i 1 e Zirconia E-Chrysot i le. Zirconia E-Chrysotile Fuel Cell Asbestos ** Fuel Cell Asbestos ** Thickness .020 " .02011 .06011 .06011 .020" .020" .06011 .06011 .020" .020" .06011 · 06011 · 02011 .02011 · 060'1 · 060'1 .020" .06011 Load (lbs.),I, .715 .895 4.06 2.295 . 71 .54 3. 18 2.89 .550 .505 1 .955 1.615 .620 .725 2.305 2.20 ," Load on a 2" wide cross-section of the listed mat thickness ** Results from Task 1 of the program. 62 Tensile Strength 17.9 22.4 33.8 19.2 17.7 13.5 25.6 24. 1 13.7 12.6 16.3 13.5 15.5 18. 1 19.3 18.4 150 80-170 (ps i ) { " '"- .. ~ -.~-. --'-~-".-, --~""-- -~-.. - -,-'"-- Table 10 Density of Pressed Mats Actual Apparent % Void Specimen Identification Density Density Vol ume i l~ Ceri e Oxide-Chrysotile u l' it .020" Thickness 6.24 glee 1.64 glee 74 d u ;\ .060" Thickness 6. 18 glee 1.80 glee 71 ;l it q ,l !l I{ Zirconia E-Chrysotile q i! .020" Thickness 4.97 glee 0.67 glee 86 Ii ~ !~ .060" Thickness 5.39 glee 0.72 glee 87 !J j:i i, ;', !i H Potassium Titanate PKT-Chrysot i le t"[ l.; 11 .060" Thickness 3.59 glee 0.47 glee 87 H Ii :p Titanium Oxide-Chrysotile .020" Thickness 3.67 glee 0.98 glee 73 .060. 1 Thickness 3.85 glee 1. 16 glee 70 ( 63 PORE-DIAMETER ·MIGRONS 100 20 10 2 1-0 0-2 0·10 0·02 0-01 0-20~--~----------~----~----------~~--~------------.---~~----------~--~ A POTASSIUM TITANATE PKT - CHRYSOTILE B TITANlUM OXIDE" CHRYSOTILE 0-16 C CERIC OXIDE - CHRYS OTILE D ZIRCONIAE - ICHRYSOTILE (.) 0·12 (.) .------------ A z 0 -0'\ .... ,J::- c ax .... 0·08 '" z III D- o-o~ o 10 100 1000 10000 ABSOLUTE PRESSURE PSI Figure 29. Pore Size DistrioutionCurves for Pressed Mats. ! ~-. contains pores mostly in the lO-micron range. As will be seen later, this relatively large pore size of the zirconia mat results in poor gas-sealing behavior compared to the other mats. Mercury intrusion curves could not be obtained on the new Fuel Cell Grade Asbestos mats studied in Task 1 because their flexibility caused them to collapse under the mercury pressure. 65 ( , , i : ,1 , ' : ) i 4 ! ~ 1M ;i ;~ 4~ Electrolyte Absorption and Retention The technique used for this test was essentially that des- cribed in the Task 1, except that in the recent tests all the manipulations - weighing, saturating centrifuging, etc. have" been performed without transferring the specimen from its supporting screen.. The mats, when saturated with KOH electrolyte, are too fragile to permit such a transfer. The results from these tests are summarized in Table 11. As a basis on which to compare these results, it is recallec that the 20-mil asbestos absorbed 308 times its weight in KOH, and the 60-mil mat absorbed 5.,6 times its weightc On this basis, the zirconia mat and the PKT mat compare favorably with the standard asbestos in ability to abosrb electrolyte" The mat~ made from the powders (ceria and titania) do not compare as favorably with the asbestosc> Part of this difference is due to the higher density of the powders compared with the chrysotile asbestos~ If this density difference is corrected for, however, these mats still have only about one half the absorbancy of asbestos on a volume-to-volume basise The ability of the mats to retain electrolyte under the action of an acceleration force of 25g compares well with the asbestos mats. The mats made from the zirconia fiber lose significantly more than the ctherse However, the ability of the 60-mil zirconia mat to retain 78% of the electrolyte during the test is about the same as was experienced with the 60-mil asbestos mats., 5., Electrolytic Resistance The measuring cell was changed to ~ccommodate the pressed matrix specimens", When the chrysotile ma~"riceswere tested, the spec'"'1lens were simply clamped between t.he cell halves and perm:-ted to expand freely., However, ti'1ese pressed matrices disintegrate when saturated with electrolyte, and consequently, a physical support was required for this test.. The cell was modified by installing between the cell halves a Plexiglass sheet (1/8 inch thick) with a 5/.8 inch hole bored coaxial with the 1/2" diameter hole that forms the electrolyte channel, Figure 30. This arrangement provides a chamber in which the specimen can be mounted between double layers of supporting metal screen. Under these conditionsI' the specimen can attain a maximum thickness of about 60 milso A question of data interpretation arises 0 The exposed diameter of the specimen is now 5/8 inch rather than 1/2 inch. This constitutes an area increase of 56%.. However, this increased area is a rim 1/16 wide lying outside the region of rectilinear electrical flow linesc> The degrees to which this rim area contributes to the.total specimen conductivity is not known. 66 J f j j ( , . Table 11 Electrolytic Absorption and Retention Weight Weight of Weight % Th i rk. Wt. of Wt. of Absorb. Ratio Retained Ratio Re-S .. I.nches Spec . .J!!!!. Solution, pee I roi'~fi . .~~ gm Absorbed Soln. gm Retained tained Ceric Oxide-Chrysoti1e .020 .4090 .4884 1. 19 .4755 1. 16 Ceric Oxide-Chrysotile .020 .3856 .567i 1.47 .5218 1.35 Average 1. 33 Average 1.26 95 Ceric Oxide-Chrysoti1e .060 1 .5494 1 .6199 1.04 1 .4770 .95 Ceric Oxide-Chrysoti1e .060 1.3713 1 .4249 1.04 1 .3153 .96 Average T:04 Average .96 92 Titanium Oxide-Chrysotile .020 .2351 .4189 1. 78 .4088 1. 74 Titanium Oxide-Chrysotile .020 .2215 .4172 1.88 .4055 1.83 Average 1.83 Average 1. 78 97 Titanium Oxide-Chrysotile .060 .7374 1 .0564 1.43 1.0439 1.42 0'\ Titan i urn Ox i de-Chrysot j 1 e .060 .7589 1 .0930 1.44 1 .0809 1.42 '-J Average T:1i4 Average 1.42 98 Zirconia E-Chrysotile .020 . 1273 .7966 6.26 .6295 4.94 Zirconia E-Chrysot i le .020 . 1702 .8589 5.05 .6525 3.88 Average 5:b6 Average 4.38 77 Zircon·j a E-Chrysot i le .060 .4871 1. 6911 3.47 1 .3520 2.78 Zirconia E-Chrysotile .060 .4802 1 .6374 3.41 1. 2513 2.60 Average 3.44 Average 2.69 78 PKT-Chrysot i 1 e .020 .0941 .6201 6.59 .5367 5.70 PKT-Chrysot i le .020 .1029 .6639 6.45 .6171 6.00 Average 6.52 Average 5.85 90 PKT-Chrysot i 1e .060 .3546 1.6558 4.67 1 .6310 4.60 PKT-Chrysot i 1 e .060 .3494 1 .6310 4.67 1.5856 4.54 Average r;-:r;=; Average 4.57 98 SPECIMEN -- I I I I I i I : L J I ,< I ' , " I ,,, " I , , L ____ _ . __ _ L_~ __ -. ____ _ REFERENCE ELECTRODE WELL 1/8" PLEX'IGLAS SPACER I I I I I I - i 1 l. ) >/ '" " " " I , " I'>" I -------~ ----.-.--- ...... -~ 2 SUP,PORTING SCREENS EACH SIDE ..... --, .... ------~ WORKING ELECTRODE CHAMBER Figure 30. Electrolytic Resist~nce tell - Modified. , i t I J - I • • & • J I 1 I " ) I 1 ..... , I I I I I I I I I I I I I I I I J Also,. the effective performed geometric specimen .. degree to which the supporting screens reduce the specirren area is not known. A test was therefore to provide a factor of relationship between the total area and the effective conducting area of the supported For this test we selected Ace-sil, a well-bonded non- swelling microporous rubber separator material of 27-mil thickness" A piece of this material was first tested without, and then with, the Plexiglass separator and supporting screens. First, the specimen was mounted directly between the test-cell halves so that a 1/2 inch diameter disk of surface was fully exposed to the electrolyte~ Data from this ~~st yielded the true electrolytic resistance of the specimenG In the second test, the specimen, trirr-lf~ed to 5/8" diameter, was mounted between the double layers of supporting screen in the Plexiglass recess between the test cell halves. The results of this test indicated just about four times the resistance of the unsupported specimen~ Accordingly, in the data reported for electrolytic resist- ance (Table 12), the computations are based on the full specimen area (1 ... 98 cm2) and the final value of resistance is reduced by the factor of four. In order to establish a basis of relationship, specimens of chrysotile were also measured and the data are included in Table 12~ Incidentally, inasmuch as the supporting screens are used in pairs on each side of the specimen, the question arose, whether the orientation of the contiguous screens influences the effective conducting area" Tests were., therefore, performed using the Ace-Sil membrane with the screens oriented wires- parallel and the wires-crossed 4500 The data were practically . identical, and we conclude that screen orientation is not criticalo The data listed in Table 12, show several significant things.. First, the resistance of the Fuel Cell Asbestos as measured by this modified test rig was about one-half of that determined by the original test rig in Task 1 of the program. This probably can be attribute0, to the restricted degree of swelling that can take place in the modi filed test rig.. The second observation is that all the mats tel3ted in this part of the program showed less resistance to ionic c()nduction than the Fuel Cell Grade Asbestos mats .. 6. Gas Permeability The gas that permeates the specimen under a pressure differ- ential is measured by a water bubblerc As expected, all the dry mats are permeable (Table 13). The ratio of pressure 69 ( ~ - .~, - - ~ -._._.-._------ ---~-.".,-,- .---~-,- Specimen Table 12 Electrolytic Resistance of Pressed Mats (Current 87 ma, Specimen Area 1.98 cm2 Thickness (inches) R of Mat'l't (ohm-cm~ Potassium Titanate (PKT) 0.020 0.020 0.209 0.218 Zircon i a E Titan i um Ox i de Cer i c Ox i de Fuel Cell Asbestos 0.020 0.020 0.020 0.060 0.060 0.060 0.020 00020 0.060 0.060 0.020 0.020 0.060 0.060 0.020 0.060 o. 198 0.181 o. 180 0.228 0.226 0.226 O. 170 o. 176 0.285 0.260 0.213 0.202 0.319 0.306 0.24 0.36 Specific Resistances (ohm-cm) 4. 13 4.30 3.90 3.58 3.55 1.50 1.49 1. 49 3.36 3.47 1.87 1. 71 4.20 3.98 2.10 2.01 4 74""" . ,,, ,,, 2 37""" . ,,, ,,, * These derivod values of resistance incorporate the assumption that all specimens $weJI to fill completely the O.060-inch thick space between the supporting screens and, therefore, replace a O.060-inch thick layer of KOH solution. This may account for the general difference between the computed values for the 0.020-inch and O.060-inch thick mats. ** These values compare with values of 9 ohm-em for the 20-mil paper and 5.5 ohm-em for the 60-mil mat determined during Task 1 of the program on the unmodified test apparatus. 70 I I I f 1 ( ... "'<-«- Chemical Degradation Tests 'rhe prospective matrix component materials individually and in the proposed mixtures, were tested as described previously. Those materials with better resistance to ROH were carried through the entire range of tests. Others were tested only sufficiently to demonstrat€ their inadequacy_ 76 ( In view of the fact that Teflon is the material adopted for the matrices with the best promise, it should be noted that in most instances, the material under test was contained in a Teflon bottle.. Therefore, the tests of materials indi.vidually are really tests-of that material with Teflon .. Like the mat materials tested previously, mats formed from these materials disintegrated completely in the KOH. ~"he insolubles were recovered by filtr(.'tion, washed, dried and weighed~ The weight change is reported in terms of percent of the original specimen weight~ Results of these tests are reported in Tables 16, 17, 18, 19 9 200 Figures in the rectangles are the percent changes in weight.. Data for the 100 hour tests are recorded above the slash lines: data for 1000 hour tests are below.. Where tests were duplicated, the results are recorded individually .. ceria and zirconia were virtually unchanged during these testsC) PKT lost weight slightly in the more moderate tests, but then gained weight in the more severe tests.. The gain suggests reaction with the KOH to form an insoluble higher titanate, or perhaps an insoluble hydrate., This change also seems to modify or destroy the short-fiber aspect of the PKT crystalso Magnesia was converted completely to a gelatinous hyr-ate~ Magnesium titanate reacted to form, probably, an inso~uble potassium titanate and insoluble hydrated magnesia.. Titanium dioxide apparently formed a potassium titanate" Polypropylene felt was tested at temperatures including lSODC, which exceeds the recommended service limitG In all tests, the polypropylf.:.'ne seemed entirely unchanged" C~ Properties of Pressed Matrices 1. Mat Preparation Our first attempts to prepare composite matrices with organic binders were adaptations of the "sheet casting" methods described previously" The components, with sufficient water to form a mobile slurry" were mixed'in an electric blender .. The slurry was then quickly suction filtered in a BuchnEI funnel, and the moist cake was finally compadted in a hydraulic press .. The organic binders specified for test were Teflon fiber, Teflon emulsion, and polypropylene fiber 0 Teflon fiber and polypropylene fiber were procured as floc, in 6G7 denier and 1.8 denier, respectively, and chopped to several lengths.. The one- 77 '( ( --- ---~- Table 16. Chemical Degradation Tests of PKT WEIGHT CHANGE OF SPECIMENS IN PERCENT Specimens: Potassium Titanate (PKT) 100 Hr. Hr. lS0°C +28. 1 -4.0 -:-0.4 30% KOH +31 .2 +21 . 1 +9. 1 40% KOH +27.3 + 11 .4 50% KOH +47.2 -8.2 -0.6 60% KOH -1.6 +38.4 +33.0 +32. 1 +113.6 +33.4 +63.4 + O.lt +31.4 +58.3 "'''"-,,, ........ ' _ ...... - ''II'''Wlfilof' ., .... 't••• 1 'III'." ••• Table 17. Chemical Degradation Tests of Ceria WEIGHT CHANGE OF SPECIMENS IN PERCENT Specimens: eerie Oxide 100 Hr. 1000 Hr. 150°C -1.4 +0. J -1.4 30% KOH -0.7 .. J. 5 -4.3 ...... \.0 40% -1.9 - o. I -0.3 KOH -0.5 -0.5 -1 .6 50% KOH -3.0 -1.9 -O.B -1.1 -5.3 -1.0 -2.0 60% KOH -0.5 -1.6 , 00 o Table J 00 Hr. 1000 Hr. 30% KOH 40% KOH 50% KOH 60:t KOH Chemical Degradation Tests of Zirconia WEIGHT CHANGE OF SPECIMENS IN PERCCNT Specimens: Zirconium Oxide Fiber -0.3 -0. 'J -0.2 ; 0 -0.7 -0.4 -u.4 -0. I -0.4 -0.4 -5.6 -0.3 -1.4 -0.3 -1.5 -0.9 -5.3 -0.3 -3.0 -3.3 ,.'." Illtt Table 19. Chemical Degradation Tests of Titanium Oxide WEIGHT CHANGE OF SPECIMENS IN PERCENT Specimens: Titanium Oxide Ti02 100 Hr. Hr. +1.9 30% KOH +6.4 + 11 .7 +8.2 +29.6 40% KOH +8.4 +25.7 +50.4 50% KOH +77.7 +83.3 i +47.2 +31 .0 +36.3 +67.8 +77.7 +64.9 +113.6 +5.6 60% KOH +88.7 +48.0 rtlllii' ex> N , . Table 20. Chemical Degradation Tests of Polypropylene Felt 100 Hr. 1000 Hr. 30% KOH 40% KOH 50% KOH 60% KOH WEIGHT CHANGE OF SPECIMENS IN PERCENT 50"C Specimens: Polypropylene Felt (0 ) -2.6 (0 ) -2.7 (0.2) -2.9 (0.3) -3.2 ( ) insoJublE';s in the KOH (0 ) -2.4 (0 ) -0.2 (0 ) -1:8 (0 ) -2.3 eighth and one-sixteenth inch lengths seemed to be appropriate for this purposec When these organic fibers g both hydrophobic, were blended with hydrophyllic and more dense inorganic solids in a fluid slurry, upward segregation of the fibers began immediately upon cessation of vigorous mixin.g." consequently, the organic fibers were invariably concentra.ted in the upper levels of the filter cake and the final pressed mato This effect could be somewhat moderated by adding suitable surfactants to the mixturec However u being hydrophobic and also less dense than water u polypropylene floc segregates almost completely from the slurryC1 The polypropylene floc was therefore quickly rejected as a useful matrix COf.lpOnent" In mixtures with PKT and ceria u the segregation of Teflon floc was only partial u a small amount of the Teflon remaining in the bottom layers~ Several matrices were made by compressing two such filter cakes, face-to=face q so that the Teflon floc~rich layers formed the outer surfaces q support~ng the fiber-deficient middle layer.., As anticipated g these "sandwich" matrices had moderately good gas sealing properties when wetted with KOH electrolyte solutions u but they lacked the cohesion that is desired in an acceptable matrix., It should be expect,ed that these matrices u having so much Teflon fiber in the surface, would establish a discontinuous g high resistance. electrolytic interface at an electrode surface" This effect was not testeda It became evident t.hat the smooth-surface hydrophobic fibers of Teflon and polypropylene were not suited for matrix bonding. We made several attempts to produce a matrix by loading a polypropylene felt with inorganic powder., The felt is a random packed mat of fibers Q cross-locked by transverse fibers drc.~wn through by barbed felting needles" A polypropylene felt has excellent properties of strength and flexibilityu but the needle punctures g and the transverse hydrophobic fibers form paths for gas leakage~ We believed that q if such a fiber structure could be loaded with PKT or ceria u the composite might be sufficiently hydrophyllic to absorb electrolyte and seal against gas transfer., Several attempts to infiltrate a loose polypropylene felt with PKT were complete failures, and we desisted these efforts ln favor of a completely different and more promising techniqueo Teflon emulsion was tested as a binder for PKT g ceria, and zirconia fiberu Teflon 308 emulsion g sufficient to provide 5 weight percent of Teflon solids in the final composite, was dispersed in water and stirred vigorously in the blender until coagulation occurred.. The inorganic powder or fiber was then added and blended, The slurry was quickly filtered with suction and the moist cake was compacted with a small hydraulic press. 83 " , ( \ These composites were completely unsatisfactory; they were weak and brittle when dry and disintegrated when wet~ The several composites containing zirconia E fiber proved to be entirely unsatisfactory because of the pronounced fragility of the fibers.. Under very moderate compacting force, the zirc ,; Cj Jj. I Table 24. Chemical Degradation Test's of PKT - Teflon Matrices WEIGHT CHANGE OF SPECIMENS IN PERCENT Specimens: PKT Matrix - 5% Teflon J 00 Hr. 100'0 Hr. 30% KOH +6.5 '(0.0) +8.2 +7.3 (0.0) i +6.4 +4.5 i +7.6 +14.4 (0.0) ~ I 40% KOH +6.3 +5.9 +1.7 1 +4.2 +6.0 +2.9 +4~5 (0. [,)) . +5.5 +3.4 +118.0 (5.9) 60% KOH +29.4 +19.5 +4. 1 (0.3) +3.5 -5.6 - i i 1 ( ) insolubles in the KOH II Table 25. Chemical Degradation Tests of Ceria - Teflon Matrices ) 00 Hr. 1000 Hr. 30% KOH 40% KOH ·50% KOH 60% KOH WEIGHT CHANGE OF SPECIMENS IN PERCENT Specimens: Ceria Matrices - 1-2% Teflon ... 0.7 -1.0 -1.2 -1.9 100"C (0.2) -2.5 -1.5 ( o. 7) -1.7 -0.4 -1.0 -0.4 -1.3 ( L _ il}so 1 ubles in the KOH ,- 1 .8 -6.3 -1.6 -2. 1 -0.9 -1.5 -2.0 -3.4 (3.7) -1.4 (97.2) -100 (0.0) - 2. 1 -100 Table 26. Chemical Degradation Tests of Zirconia ~ Teflon Matrices 100 H r- • Hr. 30% KOH 40% KOH 50% KOH 60% KOH ", WEIGHT CHANGE OF SPECIMENS IN PERCENT Specimens: lrO - 1-3% Teflon Matrices 2 (0. 1) -0.6 ( ) insolubles in the KOH (0) +0.4 C4.n -].2 (7.3) -7.2 -100 ;1 I I , Table 27. Chemical Degradation Tests of Magnesia - Teflon Matrices 100 Hr. 1000 Hr. 30% KOH 40% KOH 50% KOH 60% KOH- WEIGHT CHANGE OF SPECIMENS IN PERCENT Specimens: MgO - 5% Teflon Matrices (0 ) +33 .. 7 (0) +34.2 (0 ) +34.5 (1. 0) +31.9 ( ) insolubles in the KOH NOTE: All Mats Disintegrated ( 7. fJ (10.5) +24. 1+28 . (J 36) -100 (132) -100 ( 132) -100 -100 " 1 i Table 28. Chemical Degradation Tests of Magnesium Titanate - Teflon Matrices 100 Hr. Hr. 30% KOH 40% KOH 50% KOH 60% KOH _,1_, _il _11_"_-_'_ .. IC ____ ~_-~<~'·-·----"~ WEIGHT CHANGE OF SPECIMENS IN PERCENT Specimens: Mg Titanate - 2% Teflon Matrices -0.6 -0.7 +4.7 +27.5 +1.1 - +1.6 - -0.7 +12.6 +18.3 + 1.7 +51 .6 +52.9 150°C I; ! I t somewhat and became stiff and brittlee The ceria specimens were apparently unchanged~ The dimensions were unchanged and the corners and edges of the specimen retained their original sharp angularity.. When rinsed and dried, the ceria specimens were still flexiblea The zirconia specimens were similar in this attribute to the ceria matrices. At 200 0 C and 1000 hours duration, the zirconia and ceria matrices began to fail by disint~grationG PKT matrices did not fail similarly, although the beginning of such failure may be indicated by the specimen weight loss in 60% KOH. When the specimens disintegrated, the Teflon fibers evidently dissolved completely in the concent~ated KOH.. This reaction of the Teflon was contrary to the previous test results and to the generally reported inertness of Teflon in aqueous alkaline solutionsG However, these tests were of very long dur~tion and the Teflon was in a state of extremely great surface exposure, conditions that might permit a very slow reaction to produce the observed effect., several short but severe tests were made of the ~eflon reactivity~ A matrix was prepared with calcium carbonate ,for the inorganic filler F and the latter was dissolved in dilute HCI, leaving a mat of fibrilated Teflon.. This mat was placed on molten KOH in a platinum dish and maintained above the melting temperature for about 1:-1/2 hours. The KOH slowly became golden yellow and finally black, and about 2/3 of the Teflon dissolved. After cooling, the KOH was dissolved in water, and a yellow insoluble solid was for~d. Tests of the solution and the solid for fluoride were negative", In another test, a small quantity of Teflon 6 powder was placed on the surface of molten KOH, which was then heated fairly strongly.. The Teflon ignited and burned vigorously.. After several repetitions of this test, the KOH (entirely black in color) was diluted and tested... Fluoride ion was present in abundance. ~.dl the compatibility tests of watrix specimens, failure by dissoL~;:..ion of the Teflon fibers appeared only at 200 oC. The tests of ISOoc for 1000 hours revealed no significant failure of the Teflon fiber.. Consequently, these tests indicate that the Teflon • bonded matrices may be satisfactory for long service at IS0oC, but not at 200o-Co They also show that fluoride ion may be formed in the electrolyte, and that a possible adverse reaction with cell components should be considered a 4,. Electrolyte Absorption and Retention The fibrilatedTeflon bonded matrices did not wet to satur- ation by spontaneous absorption. To ensure complete saturation of the specimens, they were vacuum impregnated with KOH solution. 99 ( Each weighed specimen was sandwiched between two layers of poly- prolylene screen, and after impregnation, the exce'ss solution was absorbed from the screen surfaces by filter paper.. The specimen \vas then weighed to determine the quantity of solution absorbed. The specimen was then bested for electrolyte retention under 25g accelerationo The test results are summarized in Table 29. From this data, it can be seen that the PKT mats have the greatest capacity of the four types for holding electrolyte. On a volume-to-volume basis, the advantage ofPKT is this respect is significanto On a weight-to-weight basis, the relatively low density of PKT increases its advantage even more., All the mats appeared satisfactory in retaining electrolyte after a 25g test. The main variation in this property appeared to be due to mat thickness rather than to the rrat material .. , The 20-mil mats retained 85-90% of the electrolyte after the test; the 60-mil mats retained 93-95%~ 5~ Gas Permeability (Bubble Pressure) The fibrilated Teflon matrices were tested by' essentially the same procedure described previously for the pressed matrices .. However, the data lacked the desired consistency" We attribute this to the fact that the hydrophobic Teflon in these specimens is so completely and intimately dispersed through the mass of inorganic particles that uniform distribution of aqueous electrolyte by capillarity alone may not occuro As expected u the specimens show no significant gas-sealing capability until they were saturated (or nearly saturated) with electrolyte (Table 30)0 Several matrices did not leak gas at 15 psi differentialo The 20 mil thick specimens generally leaked at a low pressure dif£erential y but the 30 mil mats were usually v€ry much superior~ 6,. Electrolytic Resistance The fibrilated Tef~on bonded matrices retain integrity and strength when saturated with electrolyte and swell only slightly. Consequently, these specimens were mounted directly between the halves of the measuring cell~ The net potential developed across the specimen {with correction for the blank) reflects the electrolytic resistance of the saturated specimeno Although these Teflon-bonded matrices will absorb KOH electrolyte spontaneously" the Teflon does reduce the absorbancy somewhat, and consequently we used vacuum impregnation to ensure complete flooding of the specimen., After clamping the dry specimen between the cell halves" the cell was evaluated, filled with electrolyte and then returned to atmospheric pressure. Usually, ~,~lectrochemical cells az:e charged with electrolyte by this procedure., 100 1 ( "'>" - •. -.- .. -,-.----,,~.-- -~"-> --.- --------".- , Specimen MgO 95% Ce02 99% Zr02 99% PKT 95% < -~-- ._. ~ -- -- ------ Table 29 Electrolytic Absorption and Retention of Teflon Bonded Matrices Thickness 0.0215 .0196 .0592 .0582 0.0188 .0189 .0573 .0580 0.0197 .0200 .0605 .0613 0.0200 .0189 .0560 .0563 inch Absorpt icm ~OH/g of Spec. 1.283 1.270 1.430 1 .434 0.328 .304 .321 .304 0.240 .244 .564 .492 3. 13 3. 11 4.06 3.80 101 9 KOo/ cm3 Spec. 0.85 .83 .86 .87 0.70 .65 .78 .77 0.645 .605 .625 .585 1 .317 1.574 1.138 1.140 Retention After 25 9 Test 89% 89 95 95 86% 86 94 93 87% 86 94 93 90% 91 95 95 I I :~ j .".: ;l ~ 1\ ,f, t , ~ '" " i: ";: ]. ( Table 30 Gas Permeabi lit of Teflon Bonded Matrices Specimen Diameter 1 inch Matrix Thickness Electrolyte: Bubble Pressure (psi) Composition inch Matrix Specimen 1 Specimen 2 PKT 95% Teflcn 5% PKT 95% Teflon 5% PKT 95% Teflon 5% PKT 95% Teflon 5% Cer i a 95% Teflon 5% Ceri a 99% Teflon 1% Ceria 99% Teflon 1% Ceri a 99% Teflon 1% Ceri a 99 3/4% Teflon 1/4% Ceria 99 3/4% 0.020 0.027 0.060 0.030 - - - 0.020 0.030 0.060 0.070 0.060 dry 1 : 1 2: 1 3:1 (sat'd) dry 1 : 1 2: 1 3: 1 dry 1 : 1 2:1 3 : 1 4: 1 (sat'd) sat 'd dry 1 : l' dry 1 : 1 (sat'd) (sat I d) dry (sat'd) dry (sat'd) (sat'd) 102 0.05 0.06 0.06 2.06 0~90 0.90 1. 51 15 0.02 0.04 0.06 7.40 9.75 13.23 14.00 0.24 0.33 0.04 1.42 11,,22 0.05 6.47 0.36 12.0 12.0 (no 1 eak) 15 (no leak) 0.26 10.88 , ... '1 ~ .,; ,,; ~! ~ '·f l~ ;1 lJ t", {! t L ( ,- ; , Table 30 Cont'd ~ ~ Matrix Thickness Electrolyte Bubble Pressure (~s j) Com~osition Inch Matri x S~ecimen 1 S~ecimen 2 Zirconia 99% 0.020 dry 0.04 Teflon 1% sat'd 1.96 Zirconia 99% 0.030 sat'd 15.0 (no 1 eak) i5 (no 1 eak) Teflon 1% Zirconia 99% 0.060 dry 0.04 Teflon 1% sat'd 15.0 (no leak) , c' , Magnesia 95% - - - dry 0.10 Teflon 5% 1 : 1 15.0 (no 1 eak) 15 (no 1 eak) Magnesia 95% 0.030 sat'd 15.0' (no 1 eak) 15 (no 1 eak) Teflon 5% Magnesia 95% 0,,060 dry 0.05 Teflon 5% 1 : I 4.90 sat'd 5.05 ( 103 The results of these measurements should be accepted with considerable reservationy inasmuch as the blank correction is very large~ The blank measurement is made with the cell halves clamped together~ with no specimen in place." and the Luggin capillary orifices brought togetherG with zero electrolytic flux, the reference electrode current supplies are adjusted to zero potential difference between the reference electrodes.. Then with a flux of 50 ASF" the potential between the reference electrodes is measured again9 The blank value thus obtained was in the order of 20 mV9 The values obtained with the specimen in place are, in most instances" not greatly different from the blank value, and -the net corrected potentials are very smallo The accuracy of the derived value of specimen resistance cannot be confirmed by the testing of standard materials since none of this type is available", The only opportunity for a corroborative test occurred in another projectc A matrix prepared for test in an acid electrochemical cell was also tested for electrolytic resistance by the procedure described aboveo The full matrix in the test cell had almost prec isely the resj.stance predicted from the resistance testu The results of the tests of matrix specimens are recorded calculation is presented below: the fibrilated Teflon bonded in Tables 31 and 32., A sample Specimen: ceria + 1% Teflon 0002 inch thick Current: 70 mao Potential measured across specimen: Potential (blank determination) Net potential for specimen 0.,0270 volts 000182 volts 0.,0088 volts Resistance of specimen = 0.0088 volts Ori07 amp Diameter of specimen face = 1/2 inch Area of specimen face = 1~269 cm2 - 0.126 ohm Unit area resistance of specimen - 0.,126 x 1.,269 = 0.,160 ohm cm2 Table 31 reports the tests of specimens prepared during the initial development of fibrilated Teflon bonded matrices .. Specimen thicknesses conformed only very roughly with those specified for acceptable matrices., Table 32 reports the tests of specimens of the correct thicknesseso In Table 32g the very high values of resistance for 0.06 inch thick ceria matrix are inconsistent with the other values .. We believe that these specimens were not completely saturated 104 1 { o V"1 Specimen Blank A B PKT - 5% Teflon A B Magnesium Titanate - 5% Teflon A B Table 31 Electrolytic Resistance of Preliminary Teflon Bonded Matrices Thickness (i nch) 0.029 0.029 0.024 0.024 30% KOH Electrolyte, I = 70 mao Potential Diff. (vo 1 ts) 0.0203 .0200 .0195 0.0199 avg. 0.0196 0.0217 0.0214 0.0209 avg. 0.0276 .0278 .0277 0.0277 avg . . 0250 .0248 .0250 0.0249 avg. 0.0340 .0344 .0338 0.0341 avg. 0.0372 .0374 .0373 0.0373 avg. Net Potential Diff. (vo 1 ts) 0.0078 0.0040 0.0142 0.0164 Resistance (ohms) (ohm cm2 ) O. 111 O. 141 0.057 0.077 0.203 0.257 0.234 0.296 • i~ i'~ \i I,. .~ 1 , '. 1: I' Tab1e 31 (Cont'd) Thickness Potential Diff. Net Potential Diff. Resistance Specimen (inch) (vo 1 ts) (vo 1 ts) (ohms) (ohm cm2J Ceria .. 5% Teflon A 0.034 0.2211 .2200 .2150 0.2187 avg. o. 1988 2.84 3.60 B 0.034 0.1079 .1070 .1082 0.1077 avg. 0.0868 1.24 1. 57 Ceri a - 0.25~~ Teflon 0 A 0.084 0.0683 '" .0686 .0678 0.0682 avg. 0.0483 0.690 0.824 ~.0584 , B 0.077 I .0578 I .0580 .0585 avg. 0.0376 0.538 0.681 I I j, ' o -.....J Thickness Specimen (inch) Blank Ceria + 1% Teflon 0.02 PKT + 5% Teflon Zirconia + 1% Teflon Magnesia + 5% Teflon 0.03 0.06 0.02 0.03 0.06 0.02 0.03 0.06 0.02 0.03 0.06 Table 32 Electrolytic Resistance of Teflon Bonded Matrices 30% KOH Electrolyte; 70 ma current Potential Diff. (vo 1 ts) 0.0190) 0.0182 avg. 0.0175) 0.0270 .0256 .0256 .0210 .0316 .0475 0.0166 .0240 .0236 .0219 .0273 .0239 .0320 .0284 .0278 .0208 .0640 .0650 .0330 .0430 .0450 .0541 .0385 .0578 Net Potential Diff. (vol ts) 0.0088 0.0074 0.0074 .0024 .0134 .0293 - -;': .0058 .0054 .0037 .0091 .0057 .0138 .0102 .0096 .0026 .0458 .0468 .0148 .0248 .0268 .D359 .0203 .0396 Resistance (ohms) (ohm cm2 ) o. 126 .106 .106 .035 · 192 .420 0.083 .078 .053 · 130 .081 · 197 .146 · 137 .037 .655 .669 .212 .354 .380 .513 .290 .566 o. 160 · 134 · 134 .044 2.43 5.32 o. 105 .099 .067 · 165 .103 .249 · 185 · 173 .047 .830 .846 .268 .448 .481 .650 .367 .716 :': Measured potential is less than blank value. flo tenable explanation can be offered. 1 t HI , , - with electrolytec In general, the values of specimens resistance correlate ~lery poorly with thickness .. 108 ., i ( I I 7 .. Fiber Structure Although these matrices contain only a small relative amount of Teflon, the fibers are apparently the sole basis of matrix integrity~ Whereas compacts of the inorganic components alone are rigid and brittle, these matrices are very flexible and can be stretched considerably before parting. Since the inorganic particles do not adhere strongly to the Teflon fiber surfaces, it is presumed that each inorganic particle is trapped in the random network of fibers .. When a specimen of matr~x is carefully stretched to failure, and the specimen is examined at about 30X magnification under re- flected light, £ibrous composites can be seen bridging the new voids (Figure 32)... Under greater optical magnification, these can be identified as st,rings of inorganic particles incorporated in f~ber bundlese Sometimes under properly directed illumination, individual fibers (or probably fiber bundles) can be seen across the void. 8~ Sur£ace Area ---- Measurement of surface area of matrices by the BET method produced the values lis ted in! Table 33... The PKT and MgO matrices are clearly of greater area than the ceria and zirconia matrices, but these differences do not correlate with properties of immediate concern in matrix performance .. 9 .. Tensile Strength Specimens of the Teflon fiber bonded matrices were measured with the Instron Tensile Tester.. The elongation curves are presented in Figures 33, 34 and the interpretations in Table 34. The specimens \t7ere die-cut rectangles, 2 x 3 inches. They were mounted in the tester to present a gage width of 2 inches and gage length of 1 incho Crosshead speed was 0.5 inch per minute. The Teflon-fiber bonded matrices are all very flexible and will stretch inelastically., The low-density PKT matrices may be handled without significant danger of distortion. However, the more dense ceria and ~irconia matrices, in the full size and especially in the 20-rrclJ.thickness, are much more susceptible to stretching by incautious handling... It is advisable to support these matrices on paper or cardboard .. When these matrices are saturated strenth remains virtually unchanged. increased weight, greater handling care distortion of 'wet matricese 109 with electrolyte, the However, because of the is required to avoid , I .~ ~ 4 Figure 32. Fibers in Teflon-Bonded Matr ix. • 110 Table 33 Surface Area of Teflon Bonded Matrices Specimen Area (1) Area (2) PKT 95%; Teflon 5% 8.52 m2/g 8. 19 m2/g Ce02 99%; Teflon 1% 1. 55 1. 50 11 MgO 98% Teflon 2% 10.55 10.55 Zr02 98%; Teflon 2% 1. 41 0.87 j, fl ( 111 2.JJ2" 7 .>!~ ~ 9 PKT 0.0211 ';t'~ :it 10 II JI :~ :~l J1 .. 0-.06 "F 12 II II , 3 I i lif , 'i;! 13 Zr02 0.02 .W 14 II .. I~ ~- 15 .. 0.06 "iii Ii. S ~ 16 .. .. i ~ j,"'" t: I " ;1 '# >- 1 - Iff t: ,j 0 4 l! ,..... ..0 l " :-=: -- t c;, 1ft .a :~ - , ~ Lt\ - .' "It: '" I i N ~ • L- 0 0 ~ ~ - -1ft, .Q.. - "'0 2 1 "' ; ; 0 t .... , __________________________ ~--~------~----~----------~--~----~--__ ----.. -----------__ --__ o 1.5 1.0 O.S EJongat lon( Inches) Figure 33. Tensile-Elongation Curves for Teflon-Bonded Matrices U-(((~ MgO 0.02" 2 II II 3 II 0.06 4 " II S Ce02 0.02 6 II " 7 " 0.06 8 II " 2.0 3 2 8 1 If" 1.5 1.0 0.5 o Elongation (In~hes) Tensile-Elongation Curves for Teflon-Bonded Matrices. r- o .. A. - -.,. lit - i i i j! Specimen MgO 95% Ce02 99% PKT 95% Table 34 Tensile Tests Apparatus: Instron Tester Gage Length: 1. i ncb; Gage Wi dth: 2 inch Crosshead Speed: 0.500 in/min Thickness (nom i na 1) ( in) 0.02 .02 .06 .06 .02 .02 .06 .06 .02 .02 .06 .06 .02 .02 .06 .06 Elongation % 62 90 152 50 67 90 80 30 27 72 57 72 62 97 112 114 Load (1 bs) 0.30 .59 .655 .715 . 203 .345 1.605 1. 715 .203 .265 1 .395 1 .360 .995 1.075 5.33 7.74 Tens i 1e Strength psi 15 30 10.9 11.9 10 . 17.2 28.7 28.6 10. 1 13.2 23.2 22.7 49.7 53.7 88.9 129.0 , J } 1 I, 'f • ,. ,0 ~ (.1' " ~ I ~ ~ " ~ j~ Jt ~ !" ;~ :t 'f " " t .~ 1 1 , I t .t t f I t <: , r 1: J f :f :, " . ,if ~' f 'I .1 j! " ( 100 Density and Porosity The average density of a matrix j.s derived from the geom- etric volume and ''''eight of a specimen. The percent void volume is the difference b tween the theoretical density and actual density, expressed as percent of the theoretical density of the matrix materialc Because of the very minor contribution of Teflon to the matrix volume, the calculations are based on the inorganic component alone. Absolute densities of PKT, ceria~ and zirconia were measured in the air comparison pycnometer, w~,th the following results: PKT Ceria Zirconia 3.,426 g/cc 6.85 g/cc 5.,367 g/cc The relative void volume is calculated from the relation: reI., void vol .. = 1 - actual density theoretical density The specimens measured were those prepared for the electro- lyte absorption and retention testsc They were rectangular pieces 1 inch x 1/2 inch~ Thickness was meas~red with a dial gage equipped with a 1/2 inch diameter "point" loaded only by its own weight and the light internal return spring., The data and results from these tests are recorded in Table 35., 110 Pore Size Distribution Matrix specimens of the Teflon fiber bonded matrices were tested by the mercury intrusion method. As expected, these specimens were compressed by the surrounding mercury before actual penetration occurred., This is manifested by the long gradual rise of the curve preceding the pronounced upward deflection (Figure 35) 0 Although the data do not permit a quantitative description of the specimen compression~ it may be concluded that the PKT and MgO matrices are much more compressible than ceria and zirconia matrices", Penetration of the inter-particle voids is understood to begin with the upward inflection of the curve and approach com- pletion at the limiting pressure., The curves do not indicate a significant porosity of the particles., The numerical interpretation of the penetration curves given in Table 36 is based on arbitrary estimates of the beginning and end of the steep rise and the total penetration at limiting 115 ·or ) ( i l l I " ! : Composition 99% Ceric: Oxide 1% Teflon 99% Zirconium Oxide 1% Teflon 95% Potassium Titanate 5% Teflon Table 35 Density and Porosity of Matri~ Specimens Thickness (inch~ .0188 .0189 .0573 .0580 .0197 .0200 .0605 .0613 .0200 .0189 .0560 .0563 Weight 0.3941 .4002 1.1263 1 • 1347 0.4636 .4370 1 .5450 1 .5955 0~0735 .0676 . 1257 . 1350 116 Geometric Density (g/cc) 2.46 2.49 2.31 2.30 .J. 11 2.89 3.37 3.44 0 .. 485 0.556 O~296 0.317 64. 1 63.6 66.3 66.4 42. 1 46.2 37.2 35.4 85.9 83.8 91.4 90.7 c o 2 3 It 5 100 PKT PKT Zr02 Ce02 HgO Pore Diameter (Microns) 10 LO 0.1 All Specimens 0.060 inch thick Mercury Intrusion Curv~s Figure 35. Pore Size Distribution of Teflon Bonded Matrices. i:i ,I \' r.: , iii i~ ! ' However Q there is a prospect that they may be improved by refinement of particle size of;the inorganic component 0 and possibly by the addition of sealing ;.: :1 " i ,.r..-"-£'~ ag ts.,? .~~. ( ,...(.1'1,,,"("'" 4 .. Dens it Y ~.""", jJ:" .... '~- The geometric volume of each matrix was calculated from ,the face area and the average of sixteen thickness measurements across the face~ Weight of each matrix was measured to the nearest Oalg. The densities are recorded in Table 37~ ;{ .. il' Ij i 11 ~ !, C~ Conclusions From Task 3 Tests'" ~ C The tests revealed that no one of the matrix composi1ions is. _~t.' distinctly superior to the others. Zirconia mats htve l~ i capacity' for absorbed KOH solutiono but the gas ls~~~~ng ; capabilities are comparable to the others 0 with the NASA ~roject managers, we concluded that these tests were indecisive and that all three types of matrices should be prepared in quantity in Task 4 of the program for further evaluation by testing in electrochemical cellso 126 Figure 37. Bubbl e Pres sure Appara t us for 8-inch Sq uare Matrices. 127 -----==~-------=~-~========~==~~~~~====::==----~---------------- i I ; j i ~ I 1 XII TASK l PRODUCTION OF FULL SIZE MATRICES IN QUANTITY Our experience with the Teflon-bonded matrices revealed that those based on PKT~ ceria and zirconia are quite similar and that the selection of the one superior composition would be most arbitraryo Evidently, cell performance test of these matrices was required before a selection could be madee Accordingly, Task 4 was revised to require the preparation of 100 matrices of each composition - 50 to 60 mil thickness, and 25 each of 30 mil and 20 mil thicknessc The two component materials, PKT and zirconia are manu- factured primarily for use as pigment and in ceramics, respect- ively, and particle size is therefore a matter of ordinary concern to the vendor~ Ceria, on the contrary, is produced for the chemical tra.de" and partic::le size is not specified by the manufacturers or vendors., In preparing for the \Olork of Task 4, we obtained a bulk quantity of ceria from a vendor other than the original~ Although the new rna.terial was, in terms of purity specifications" superior to what we had used previously, the matrices based on this new ceria were unsatisfactory., evidently, because of the smaller particle size of the new material., Fortunately, the original vendor was able to supply our require- ments of c€:'Lia for Task 4 from the single production batch of the mat,erial# -t.llU,:; assuring us of average uniformity of particle size for the ceria matrices~ Some consideration was given to methods of improving the speed, and efficiency of production" but none seemed appropriate., Bulk weighing and dry blending of the components was rejected because of the tendency of the Tef.1on powder to smear and to form coherent clumps 0 wet mixing in the electric blender seems more certain to achieve a thorough distribution of Teflon through the masse We attempted to increase our production rate by stirring the heated blend (with mineral spirit lubricant) un'til fiber development started, but the uniformity and strength of the final rolled mat were poor., We discovered that the entire hot rolling treatment must be performed without significant interruption, otherwise the final mat will be non-uniform and weak~ This precludes the prospect of processing a large batch of mixture to some desired state of development and then taking portions for final rolling., The matrices 'lere ther!efore compounded and processed in- dividually" The components for each mat were weighed aIld blended, and the entire fiber-forming process was performed without interruption., Each matrix was heated at 1000c in a vacuum oven for about 30 minutes to expel any residues of the mineral spiritsc> After a fina'l cold-rolling treatment to adjust 128 .;1 I ( ~ I ~ u > . ~ i l f , I , , i I f • l I ! f ; i r ! f I ! ! II v R ~ ~ j -I : t.he mat thickness I! it was trimmed to the 8 inch square thickness was measured with a dial gage at nine places surface; if any single measurement fell outside the range of thickness latitude, the matric was rejectedo size. The across the specified The work statement originally specified that the weights of all matrices of a composition-thickness group must be within + 2 .. 5% of the average of that group. Th'is requirement was changed to speci£y that a matrix density must be within ± 5% of the average for its group~ The finished 8-inch square matrices were measured for thickness at 9 locations across the surface and weighed to the nearest Oel gram~ The record of individual thickness measurements, average thickness, weightr and calculated density was attached to the envelope of each matrix.. A summary of these data is contained in Tables 38, 39 and 40 .. 129 ( . - ---~-~~-- --~---. ,--- -~ - --::-.--::':::::"':";::;::;-;;"'::::"':;:;:~:"'\~-"::"-'-"'"' :- ::::.-::./'t:~ __ ~_ , ., _ ~.;:.::.:::::::::...::::::-..~-~--..... " " POTASSIUM TITANATE (PKT) ~ 20 Mil Mats 60 Mi 1 Mats :1 No. Thickness Weight Density No. Thickness Weight Density I Mil s ~ms g/cc Mil s gms g/cc ' -f " 1 19.3 6.4 .316 51 61.2 14.5 .226 . , , 2 2:1.5 7.2 .319 52 62.7 14.6 .221 i ' I 3 20.3 6.8 .319 53 62.6 13.8 .210 ,It 4 21.1 7.0 .316 54 57.6 13.0 .215 J 5 20.7 6.4 .309 55 61.3 13.4 .208 ;1 6 20.2 6.8 .321 56 60.8 13.8 .2i6 if 7 19.9 6.2 .312 57 62.6 13 .6 .207 I' \ 8 19.0 5.7 .300 58 61.3 14. 1 .219 ! ; 9 19.4 6.5 .320 59 57.6 12.5 .207 ill ;4 10 " 20.8 6.9 .302 60 62.6 14.2 .216 :, 11 20.4 6.5 .303 61 56.2 12.2 .207 1 J ' ~ 12 20.7 6.7 .308 62 62.8 14.2 .216 :1: j 13 19.7 6.3 .304 63 58.9 13.0 .211 ,.{ 14 19.4 6.2 .304 64 56.9 12.3 .206 .~ 15 19.2 6.2 .308 65 57.8 13 .4 .221 11 , " 16 20.9 6.9 .314 66 62.3 13.7 .210 i~ !t'~ lif 17 19.4 6.2 .304 67 62.7 13.7 .208 ' ? , i 18 20.0 6.7 .319 68 57.4 12.7 .21 1 : ~ I, ;~ 19 19.7 6.3 .305 69 60.7 14. 1 .221 '.I L;l 20 20.3 6.7 .314 70 57.6 12.7 .210 rj ,. " 21 20.3 6.6 .310 71 62.3 13.9 .212 ~ , , 22 19.0 6.2 .311 72 58.1 13.3 .218 ;.; '., 23 19. I 6. I .300 73 62. I 13.7 .210 :;,!,.1 " R 24 19.2 6.2 .308 74 62. 1 14.2 .217 \~ . , 2~ 18.9 6.2 .312 75 61.3 13.9 .216 .;; ;.!~ :.\ 76 63.6 14.8 .221 ' '~ Average Dens i ty = .310 g/cc ij 77 62. 1 14.7 \",\ Range @ ± 5% .294 g/cc to .326 g/cc .225 .1: = ,~~ 30 Mil Mats 78 61.0 13.7 .214 '.J 2b 31.0 8. 1 .249 79 61.3 14. 1 .219 'I 27 31.2 8. 1 .247 80 60. 1 14.2 .225 28 27.4 7.5 .261 81 59. I 13.3 .214 ~l 29 31.8 8.3 .249 82 58.8 12.7 .206 if 30 27.4 7.5 .261 83 60.9 13.9 .217 if 31 28.4 7.9 .265 84 59.6 13.3 .213 32 29.0 7.5 .246 85 61.0 13.5 .21 I ( 33 31.2 8.6 ,263 86 59.9 14.3 .227 1 87 60.8 14.4 i 34 28.8 7.6 .251 .226 I 88 59.6 13.6 ; 35 30.5 8.4 .262 .217 f 36 28.7 7.8 .259 89 60.7 13.8 .217 37 30.0 8.2 .260 90 59., 14.0 .223 38 31.3 8.7 .265 91 63.8 15.2 .227 39 27.0 7.0 .247 92 6}'3 14.5 .225 40 29.0 7.4 .243 93 60.4 14.3 .225 41 28. 1 7.4 .251 94 59.4 13.9 .223 42 31.7 8.5 .256 95 58. 1 12.9 .212 43 31.6 8.2 .247 96 61.4 14.6 .227 44 31.2 8.0 .244 97 58.0 12'.9 .212 45 32.7 8.8 .257 98 58.4 13.4 .218 1 46 32.0 8.3 .248 99 60. 1 13.2 .209 47 31 .3 8.5 .259 100 57.7 13.7 .226 48 32. 1 8.7 .258 Average Density = .216 g/cc 49 32.6 9. I .266 50 32.4 9.0 .265 Range @ ± 5% = .205 g/cc to .227 g/cc Average Density = .255 g/cc Range @ ± 5% = .242 g/cc to .268 g/cc 130 __ >_ ~ .: • .".,. ~:::"""". ____ " ___ .,_."_.-." •• __ ':::::.-=3:-...:':'~7_-:-"::::::::"'~~~-:;,.~_:::~ ':':-"~"'::"---'-:_~_"_' -" "--.;;......;:::;:....~---~~'''''" CERIC OXIDE " t 20 Mi 1 Mats 60 Mil Mats No. Thickness Weight Density No. Thickness Weight Density Mil s gms g/cc Mil s gms g/cc ~ 101 21.6 60.7 2.68 151 60.7 153.7 2.41 102 21.6 60.5 2.67 152 59.6 151 .3 2.42 _ .. 103 21.6 64. 1 2.83 153 59.8 158.8 2.53 104 21.6 61.5 2.71 154 58.9 148.7 2.41 105 20. 1 56.5 2.68 155 60.6 163.7 2.57 l06 21.7 66.8 2.93 156 58.2 156~3 2.56 107 21.4 65. 1 2.90 157 57.6 146.1 2.42 108 21.8 62.2 2.72 158 59.9 150.9 2.40 109 21.6 65.3 2.88 159 58.9 161 .5 2.61 1 10 21.3 65.3 2.92 160 57.2 148.0 2.47 I 1 1 21.7 67.3 2.95 161 63. 1 174.6 2.64 'f -~ 1 12 21.8 65.3 2.85 162 60.4 161. 3 2.55 I 1 J 3 21.2 63.if 2.85 163 60.0 162.3 2.58 ... ~ 1 14 19.8 56.7 2.73 ]64 61.8 166.2 2.56 't1 'r: 1 15 21.3 63.5 2. 8.1~ 165 62.6 -167.8 2.55 1 1 16 20.2 59.0 2.78 166 61.4 165.5 2.57 ~, i. 1 17 18.7 53.5 2.73 167 61.4 169.8 2.64 l i 1 18 20.9 59.8 2.73 168 62. 1 16B.o 2.58 :jj 1 19 21.7 65.8: 2.89 169 62.8 171 .9 2.61 i 120 20.8 61.9 i 2.84 170 59.8 163.9 2.61 ; l.. 121 20.6 61.6 ~~~,Q~, 171 63.4 170.6 2.56 , } 122 19.6 56.7 2.75 172 61.1 165.8 2.59 , , 123 21.6 65,5 2.89 173 61.9 168.6 2.60 124 21.6 67.0 2.95 174 59.8 150.7 2.40 125 20.0 57.6 2.74 175 56.3 143.2 2.42 Average Density = 2.81 glee 176 63.0 167.9 2.54 177 61.2 167.4 2.61 Range @ ± 5% = 2.67 glee to 2.95 g/ec 178 60.8 163.7 2.57 30 Mi 1 Mats 126 28.9 74.5 2.46 179 62.9 171 .2 2.59 127 28.6 74.4 2.49 180 62.4. 166.8 2.54 I , .. , 128 28.8 74.6 2.47 181 60.3 167.3 2.64 129 27.6 71.7 2.48 182 62.0 169.0 2.60 .. 183 62.4 164.9 2.52 130 31 .3 79.3 2.42 ] 3 ] 28.7 72.9 2.43 184 57.2 145.6 2.43 ]32 30.8 82.3 2.54 185 63.2 170.6 2.57 '( 133 30.8 83.2 2.58 186 62.4 168.1 2.56 134 29.9 77.8 2.48 187 56.6 155.2 2.61 135 30.4 79. 1 2.48 188 56.6 142.6 2.40 136 30.4 79.5 2.49 189 56.3 141 . 1 2.39 'f. 137 27.4 71.2 2.48 190 56.3 142.0 2.40 ] 38 29.9 79,,9 2.54 191. 61.2 167.4 2.61 139 29.4 76.,6 2.48 192 56.9 145.6 2.44 140 31.7 85.8 2.58 193 61.6 154.4 2.39 }·41 29.6 78.9 2.54 194 61.2 160.9 2.51 142 27.9 73.9 2.52 195 56.2 141 .3 2.39 143 31.3 84.3 2.56 196 57.2 144.6 2.41 144 31.6 86.3 2.60 197 58.8 154.2 2.50 145 29.6 77. 1 2.48 198 57.3 144.9' 2.41 146 29.6 . 79.2 2.55 199 58. 1 146.7 2.41 - • ,- 1 147 30. 1 75.8 2.40 200 63.6 170.6 2.55 148 31.3 80.7 2.46 Average Density = 2.52 glee 149 29.4 75.6 2.45 150 30.8 79.6 2.46 Range @ ± 5% = 2.39 g/cc to 2.65 g/cc Average Density = 2.50 g/cc Range @ ± 5% = 2.38 g/cc to 2.62 g/ce 131 ;i _ _ _ ____ "~" .::,:~,u ~::. ~~-. :A::::.:-..: ,. ,,;...._,,.::.::;:-:..--=.:::.:;:;.:.::..--_-'~ It Ii ZIRCONIUM OXIDE 20 Mil Mats 60 Mil Mats L No. Thickness Weight Density No. Thickness Weight Density \~ 11 Mil s g/cc Hi 1 s g/cc l~ gms 9ms '~ ,- ; ~! 201 20.7 69.2 3. 19 251 59.0 173.4 2.80 :1 202 21.4 68.7 3.06 252 60.0 178.2 2.83 .- 203 21.8 73.9 3.23 253 59.0 173.6 2.80 t' 204 22.0 75.7 3.28 254 59.3 176.2 2.83 'fl ", 205 21.7 73.2 3.22 255 58.9 176.4 2.86 fi 206 20.7 69.6 3.,20 256 59.9 180.7 2.88 1 207 20.6 69.0 3. 19 257 58.8 170.7 2.77 :1 208 21.0 72.5 3.29 258 59.2 169. 1 2.72 :1 209 20.9 70.5 3.22 259 59.4 172.3 2.76 '~ \ "1 210 21.4 70.3 3. 13 260 58.8 171 .0 2.77 21 1 21.7 70.9 3. 12 261 59. 1 169.2 2.73 ~i 212 20.0 65.6 3. 13 262 58.9 170.0 2.75 ';( j 263 t 213 20.2 67.2 3. 17 59.7 172.5 2.75 ! 214 20.7 67.7 3. 12 264 59.9 174.2 :.77 ,f i r~ 215 20.4 67.3 3. 14 265 59.6 170. 1 2.72 if 216 19.7 62.0 3.00 266 58.8 166.8 2.70 "! " , 217 20.4 65.3 3.05 267 59.3 169.7 2.73 '1"i .. 218 20.4 69.9 3.27 268 58.7 )67.2 2.72 ~~ 219 20.2 67.3 3. 18 269 57.7 167.0 2.76 :"~ , 220 21.0 67. 1 3.05 270 58.8 173.4 2.81 " ~i 221 20. 1 63.0 2.99 271 60.3 178.4 2.82 ~ J 222 20.0 63.8 3.04 272 60.3 172.8 2.73 ';1 '.::' 223 20.2 66.7 3. 15 273 58.9 170.5 2.76 f '/:1 ,l, 224 19.6 65.0 3. 16 274 59.2 169.5 2.73 ~ 225 18.9 62.5 3. 15 275 60.0 176.8 2.81 '~ Average Density = 3.15 g/cc 276 60.7 182.2 2.86 $1 277 57.4 169. 1 2.81 ' .. ' ·et Range @ ± 5% = 2.99 g/cc to 3.31 g/cc 278 60.2, 178.9 2.83 ~ 30 Mil Mats "'l 279 59.6 173.5 2.78 i l 226 30.6 94.0 2.93 280 59.3 170.0 2.73 i 227 29.8 88.8 2.84 281 60.0 172.3 2.74 228 31.1 99.5 3.05 282 60.7 177.7 2.79 ,I 229 30.9 93.3 2.88 283 60.3 169.7 2.68 230 30.8 93.2 2.99 284 59.8 176.6 2.82 231 31.6 95.3 2.88 285 59.6 172.3 2.76 ( 232 31.8 99.9 2.88 286 60. 1 168.7 2.68 . 233 29.2 90.4 2.95 287 60.4 170. 1 2.68 234 31.2 95.6 2.92 288 59.4 169.3 2.72 235 30.8 93. 1 2.88 289 59.4 170.4 2.73 ,236 31.1 97.4 2.99 290 57.9 168.8 2.78 237 30.3 93.3 2.94 291 60.2 171. 5 2.72 238 30.8 91.3 2.83 292 58.2 169.9 2.78 239 31.2 98. 1 3.00 293 59.4 169.6 2.72 240 31.3 92.4 2.81 294 59.6 172.0 2.75 :241 31.0 97.4 3.00 295 61.1 171. 9 2.68 ' .242 31.0 ~.' :J 2.86 296 59.0 165.4 2.67 :243 30.:4 9j.7 2.94 297 59. 1 167.5 2.70 244 30.3 89.7 2.82 298 59.9 170.0 2.71 ;245 30.1 92.0 2.91 299 59.7 170. 1 2.72 :246 31 .,3 97.5 2.99 300 58.9 170. ] 2.75 - :247 30.7 91.0 2.83 :248 30.3 89.6 2.82 Average Density = 2.76 g/cc :249 30·3 92.2 2.90 Range @ ± 5% = 2.62 g/cc to 2.90 g/cc 250 29.7 90.6 2.91 ~verage Density = 2.91 glee ' , " IRange @ ± 5% = 2.76 glee to 3.06 g/ce .' 132 .- ~-~ XIII CONCLUDING REMARKS - In many respectsy chrysotile asbestos is ideal as a matrix materialc A mat of the long, very porous hydrophyllic fibers is light and strong when dry~ When wetted with electrolyte, it is an excellent gas barrier, and it has a low electrolytic resistance~ Unfortunately y being a silicate, chrysotile is reactive with alkaline solutions., The asbestos fibers are destroyed in the formation of soluble silicate and gelatinous magnesium hydroxide~ At low tem~eratures and moderate alkali concentrations, the fiber destruction is slowg but at the conditions desired for ultimate fuel cell operation, the chrysotile will not surviveo Alternative mineral fibers are generally inferior to chryso- tile in both physical properties v impurity content, and prospects for survival in alkaline electrolyte~ The only synthetic inorganic fiber having adequate inertness in KOH electrolyte is zirconia fibero However u a mat of these fibers is very poor as a gas barrier and the fibers are extremely fragile., The. synthetic inorganic substances having adequate resistance to attack by KOH are PKT (a very short fiber) and the granular powders ceria and zirconia~ For the requisite matrix cohesion and strength, these matrices must depend on a suitable organic fiber.., Of the chemically compatible organic fibers, only poly- propylene and Teflon are suitable., O£ these, Teflon is distinctly superior because of its unusual ability to propagate very thin fibers under mild shear forces~ By a simple rolling technique, a mixture of Teflon 6 powder with an infusible powder is converted to a flexible· sheet a matrix of powder incorporated in a network of very fine Teflon fibers.. These matrices are spontaneously wettable by aqueous KOH and have a fair gas sealing capability" Chemical degradation tests show that these matrices will survive contact with 60% KOH at ISOOC for at least 1000 hours; ceria matrices are apparently completely unchanged by such a treatmento .. The most severe degradation tests {60% KOH at 200 0 C for 1000 hours) show that the Teflon fibers are attacked by alkali~ It is possible p alsop that the dissolution of Teflon may be faster in the persence of an oxidant., TherefQre p the details concerning the upper limit of application of these mats with regard to temperature 8 time p KOH concentration p etc., are not yet knownc The Teflon-bonded matrices produced in this program should be regarded as preliminary~ We are confident that they can be improved by several modifications such as the particle size or of particle size distribution, or the use of inorganic particle blends rather than a sin.gle species", Zirconia is now available 133 ( as a highly porous granular powder; this material should be evaluated as a way of overcoming the high density disadvantage of the zirconia mats produced in this programc These Teflon bonded matrices are inferior to asbestos as gas sealsc However they might be significantly improved by the addition of magnesia, which forms an aqueous gel filling the matrix pores.. Inasmuch as the chrysotile matrices become filled with hydrated magnesia without evident loss of performance, such a magnesia treatment of the Teflon bonded matrices merits attentiono It is anticipated that evaluation of these mats in cell environments will confirm the high-temperature advantages of these separators compared to the fuel cell asbestos mats.. such cell operating experience may also uncover some other limitations of these mats~ Such information can then serve as an intelligent guide for future efforts to improve even further this type of electrochemical cell separatoro 134 i ~ I ( -. - .... "' -~- ---- _,-...- ______ ~_._~v~_·_·~ __ · __ ~,_ .. ,,_ '. . -:."1 --~" ... "_ .. " .-._---_ .. _-,--- ". XIV APPENDIX At the beginning of Task 1, this author visited the Johns Manville development laboratories to confer with the personnel directly involved in the manufacture of Fuel Cell asbestos paper and millboardo The report of this tripv published in our First Summary Report {DecQ 28 q 1966)g emphasized those aspects of the technology deemed relevant to fuel cell development 0 Dro J<> S., Parkinson of Johns Manville subsequently prepared an amplified description of their process for manufacturing as- bestos papers and rnillboards for fuel cell application~ Dro Parkinsonvs description of the process is as follows: 135 J • i' Ii l¥ H !' ff t i j: PRODUCTION OF ASBESTOS FUEL CELL PAPERS AND MILLBOARDS BY JOHNS-MANVILLE Asbestos papers and millboards for alkaline, hydrogen oxygen fuel cell diaphragms have been in limited production at the Tilton, New Hampshire plant of Johns-Manville since June 1961. These are rrade on machines uniquely designed for the production of high quality asbestos electrical papers and millboards~ The Tilton plant site was selected to take advantage of an unusually pure source of water for these electrical papersti The fuel cell products are made ..;",i th carefully selected Ar.izona chrysotile asbestosc To data, standardization of the papers and boards has not been possible because customer use requirements are constantly changing~ Many of the NASA evaluations were made using materials on hand at the time the sample requests were submitted" The Tilton plant~s capabilities to modify these products to meet use reqUirements are quite extensiveo Control of raw m~terials and product properties can be made as rigid as the economics of the product will justify~ There appears to be no reason why a suitable product cannot be produced for fuel cell applications as long as the requirements do not exceed the chemical and physical capabilities of asbestos. Raw materials used to produce the paper are water and a low iron g low calcium~ low chloride u Arizona chrysotile asbestoso Only a small amount of fresh water is used aft~;:r: start up since there is extensive white water recycling., Although 1:he quaiit.y of the water does vary slightly with the season of the year, there has been no need to introduce any chemical treatment or suppressant to meet finished product s~~cificationsG The fresh water used is cleaned to remove suspended solids so that it contains only trace amounts of solubleso s·; \ck for fuel cell paper or millboard production is pre- pared in -equipment normally found in mills used to make fine paperc Asbestos and water are added to a pulper where the fiber is ground to reduce the size of the fiber bundles", Batch solids, temperature time, pulper rotor clearance u rotor electrical loading u and schopper-Riegler freeness are used to control the amount of grinding~ Periodic wet screen classification (McNett) of beater samples are also used as an additional check on grinding" No dry processing of fiber is carried outti stock from the pulper is dumped into a chest and diluted to a controlled solids content before being pumped to the stock chest.. From the stock chest" the slurry goes to a consistency regulator, is diluted with whi te water from the paper or millboard machineg and fed to a special cleaning system.. Stock finally goes to the millboard or paper machine where it is formed into the final product by normal paper making techniques~ 136 , ! I - -- "'- "--- ------~-- - ~ .----.-~.-.---. ,." - - stock flow to the machine, and stock and white water re- circulation are quite extensive. Control of stock solids, suspension and flow rates, uniformity of flow to the mold, control of liquid levels in the vat and mold, etc. are needed to form a ~niform sbeetc As stated before, the Tilton machines are unique in their ability to make uniform products from short fibered asbestos stocks. Sheet smoothness, density, and uniformity are also controlled by variations in machine speed, roll pressures, vacuum, and drying conditions~ Tests made by the Quality Control Laboratory depend on the paper's end use., At present, the laboratory is equipped to make the following tests on a routine basis as required; 1. Basis ':~Jeight; 2... Thickness; 30 Mullen (burst strength); 4... Tensile and elongation; 5. Elmendorf tear (secondary tear); 6., Curley densometer (air permeability) ; 7~ Williams penetrometer (resin penetration rate) ; 8., Organic content by ash tests; 9.. Magnetic rating (related to iron in fiber) ; 10. Breakdown voltage; II.. stock freeness and drainage; 12. McNe,tt classification of stock; 13.. Kerosene pick-up (saturant capacity); 14... Clark stiffne,ss" Normal weight and thickness tolerances on papers and mill- boards produced ,at Tilton are plus or minus ten per cent. Where required and justified by product cost, closer tolerances are maintained" Wool felts are used to carry the paper at various points in the process and these leave felt marks on the paper which can be lessening by using smoother felts and pressing or calendering the sheet during production., In no cases does the felt do more than mark the surface., It does not cause pe:rfora tions in the paper,J To da te, papers 10, 15, and 20 mils thick, and Jnillboards 30, 34" 40; 50, 60, and 70 mils thick have been produced~ At present q efforts are made to keep the iron content of the product below 0.,5 per cent, and the CaO below 1.0 per cent, the chloride content below 50 ppm Cl, and the organic content below 0.,04 per cent., Chemical analysis and sheet physical property tests requiring more sophisticated equipment are made at t;J.!E:! Johns-Manville Research Center in Manville, New Jersey., Although there are always small variations in the properties of the sheet during a run, these are never significant after standard running conditions are established and production of the product begins4) 137 (

Materials for Electrochemical Cell Separators

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