1 ligh “J’cmperat[]re Stability of l)otassi~]m Rcta’’-Ahm]ina

Roger M WilliamsAdam Kisor

Mar{:arct A. Ryan

.lel Propulsion 1 ,aboratolyCalifornia institute of I’cchno]ogy

MaIeI i21S ad I )CViCC TCC]mO]O&’ (houp}Hcclric Power Scc[ion

nigh “]’empcratmj Stability of ]’otassim 13cta’’-Ahm)illa

object ivcs:

Evaluate the stability ofpotassimn beta” alumina under potassium AMTHCopwating conditions.

13valuate the stability regime in which potassium beta” alumina can befabricated.

Materials and Device q’cch]lology CiroopIHcctric ]’owcr Section

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J. f Idrochm. SOC., VOI. 142, No. 1P, [)ec~nlt)cr 1995 (C The E kxtroctwroical Society, IIIC. 4?47

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Fig. 1. Schernc,tic diagram, not to scale, of the olkoli metol vaporexposure test chambel.

at 1425 K it) vacuum or at 1625 K in a KIIASJI; ])owdm bedfrl air at 1 atfl~. ‘J’}tc iw,o K} IA,SF, c,x(hnngc ])mccsses })]c)-duc(L(l Sonwwllat dissinlilar ccunlics. ‘1’hcsc ale i(lwltifl(d:islfllAS}:1425a~)(l KIIASIL1625 hc](>.

l~’olit.t }litl-filt ]l]))c~l:ll c,lcc,t]oclC*s,sl):I}Ic’Cl ascit}l(,rril)p,sc)lrwtanflalar })atchw with areas fmm 4 to --5 cm?, W’cr(’(1(, ])ositd on Nail ASK a n d KF!ASE tube sdio])s. I{h:tWel(xtro(lcs were (Ic’})osiid cm NaI’IASl; using a ])hotolyticct](,l])ical va})[)r d(,])ositio~l ])mcess, S]) L]tt(~r-(lc~)c) sitecl MO

fl]nis WC]( US(CI as elcctro(ics on KIJAS1:. ~:tw’tmdcs W’Cf’C

contacted with Moo]Ni n)cshmtid ot) \\rith Molcads a n d

\\, (,l(,s(’]) :i]’:itc,clL )}~l(’[[ic))]sof unccraterll{AS1’:. l)ctailsof theW/ltl I l)hotolytic de])osition IItocc$s, tlw KIIASE mchan~c1)10(,(ss, at](l AM’1’1~:(: clccirwde stu(lim am }]]xwntc(l(~ls(~\vll(m’. G ““)”34

S()(lillnl and ])ot:issiul)) W(,IC (]l)tain(d as magcni {:la(lc]nct:ils aI](lct ar{:oll, arl(l wcm ])urifid t)y hcatin:! th(, liquid

i[](,till \vith })i(lc(~s of NallASI’: and Kli ASI’; , rml)(,cti\’vly,;{t](l filt(, ] 1!)[: tlIc liclui(l metal t)]rol]{:li .sc(]uc]]ti:il 7 a]](l:? Ill]) st; ~i!llcssst ccl filt(~~'s .'J`lli stccll] li(]tl(, ]'cit)) c)vcs}):i]`tlcil -Iatcs al)(l Iow,(lx th( co])t:i]~lil]:ltiorl” l(vcI of th(, alkali metalt)y (2{, t,}r(,tnovin~ CaO])ariicJcs (..]‘-?’ sul)stitutcs for ttk(a lkal i iol)s ill thcccmmics and reduces t})ci]cc )r]cl~lcti\’ity.‘I’h(, \~a]ml ])lcss[]rc( )ft})c: ilkalil l)(t:ilwr:isca lc~]latccl~[sll]f:(,stal)lish(d (xl)mssim]s for the satamtd vapor ])rcssar(’alx)\Ic t}lc li(luid at t})v cold md ancl correcting for atomic

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\K,l[K,lt,v L’tlall[ {r’ (IUL’ to Lho t(’n)})m’ata[c dlff(~)l>tl (x’ 1)(, t\\, (’enttl(, [)001 l(,p, ion and the (’lectrolytc rq{iol l.’” ‘{H

‘I’tl(, t(,st:l] )}]:] ):]t L]s(I’if;. l)\\tlsz istaifll(,sss t((\lt(il)c\\’itl)f((d throll@ fm’ ICads, t}lcl’ll)(lc(lll j)l[’s, }Iulnlmllt, ar::ont)a(kf}ll, :in(l intlo(iuction of a cmntrollmi qaant It,Y of alkaliIl)ctal S;iln})][’s WL’l L’ lnoullt(,ci on a LY’ntral Su})}mlt tui)L’

witl] (r-al ll]l)ina st:ir](ioffs over a M(1 foil wtai). l~; lcct]icaiI(>ads atld sl)icl(imi tyI)(’ K t}](’lrllc)coli])l(’s WCIC i)ls\]lat(Yiwith (t-alumina tui)ing: illsicic tllc test a])~)aratus. 1~’illally,]cfractoty ])lctsrl foiis (Y,r, Mo,’J’a) were inscrtc(i insl(ic t h estair )i(xs st(, (~l tul)c for@tming ar}d l)]otcction of the sarm])lcs flonl hi@ vai)or ])rcssulc cornI)oncnts of t}lc stwl, such;IS l))arlp,ancse. ‘1’hc mtim assclnt)ly was wcl[ie(i shut ‘J’hc

!‘nlali {:ai)s bc’tu’em} thr’ Out[’r’ Str’cl f[’[’(i thr’mlg}ls a n t i [Y-Ilulnirla insal atom WC](’ h(~rme tically swllui wit}) a siow

JL4ti,,f: C,,oxy (E~JC,xi-1’titct,”) ‘1’hc :l})~):ll:lt US w’:l S S(’t Lll)u,it}t a t)()()l of alkali metal at ()]1(1 cr)(i c)f the tui)c asscml))y

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and KBASF. Stondord errors from the fits ore given in parenthesis.

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Fig. 4. Ternperoture depen-dence of the conductivi~ ofNoBASE , KBASE 1425 , ondKBASE 1625, ofter >100 h expo-sure to olkoli metol vapor ot hightemperature. Initiol NaBASE dotofrom t < 100 h; ond some dataoutside the temperature rongesindicated by the solid line fits wosnot used in determining the fittingparcrmetcrs, but is shown. Onlythe 495 h doto wos used in fittingthe KBASE1425 date. The solidlines ore fits of the data to Eq. 1,and the dashed line is the fit to thedcrto in Ref. 21,43-45 to Eq. 2,

IFig. 5. Time dependence of tlw conductive of NcrBASE, 1028-

Y1201 K, at 0.3 to 2,0 Po N!,, with the dashe line s}lowing o fit toata as o linear function of time. The inset shows the initiol 100 h onn expended SCOIC with doshed line showing a fit of this dato to anxponcntml decrease.

., .

Wi(ll Ial)id ctrrlent increase Lit (he. potassium ionization}K)ttvllial, l’his effcd is impottrmt to applications ofseries co[l[lcctcd AM’I’IQ; in genrxal, series connczkdCC]]S should not CXCd 4.() V for potassium AM3”11CS or5 . 0 V fol sodiun] AM”l’l Kk, LIIIICM it can k a s s u r e d that

thm arc no possible vapor discharge palhway betwezncells with ]x>tcmtial di ffcrenczs greater than the.se valum

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J’@assilIIll. Ahf”l’l’:c.l’(st

I“hc. K-NASE tube, prcparw] as described above,was sucmssfully t)ra7f41 to a niobium tube transition,w i t h T’iCuNi filler lnctal, to a snlail stainle$s steelflange. “1’he tube was sputtc.red with Inolybdcnum thinfilm elw.trodcs for an potassium AM”l”I;C test.

llc c-en was operated at a nonlinal temperatureof 687 K (at the, bottom of the heater WCII), and onccurrent-voltage curve, shown in Fig. 7, of a 14.4 cm?e.lcctrode at an mtinratuf kmpcraturc of 725-750 K wasobtainul, with an open circuit voltage of 0.6 volts, shortcircuit current of 2.5 amps and a total power of 0.3watts. I’his performance is rncrckt, but substan( ia]lybetter than the pcrformancz of a comparable sodiumAM”J’l;C cell at this low tmnperaturc. I’hc sodium cellwould have a higher open circuit voltage, but current andpower densiti~s would k significantly lower at thiskmpcrature, J lowcvcr, this was an ear ly- in- l i fenml ybdcnum elect rode, probably containing substantialquantities of Kzhfo04, which wc would ex~t to be afairly good ionic conductor at e.lcvatwl temperature. ‘l”hisphase might persist for viable operation lifetimes atlower cdl tempcratums, as it is hig}lcr melting andsli~htly less volatile than Na2Mc04. Ba.scd on the resultsfrom both Ah41’IjC and vapor cdl tests, we wouldanticipate 1.0 Pm thick nmlybdcnurn e]cctrodcs to bcvt:ry useful at 9(X)K < “1’< 1100K in potassium Ahf ’1’IKkand molybdenum electrodes will not sintcr to a diameter

cxcczxlin,g 0.5 ~rn within Pcri[xls of years at the. lowerttmpcrat u res.

~X)NcI ,lJs~Q4s

Two low temperature routm to nearly phasepure K-RASIL (or Na-RASE) have been demonstrated andcharactcrimd. While not directly sintered to denseceramics exe+ for microscopic areas, this nratcrial isuseful in ion cxchangc via c.crarnic firing at controlledK?O activity ancl in potassium rrlctal purification,

Wc have demonstrated high temperature directsynthc.~is from aluminates which increases density of K-IIASI1. I’his technique could potentially provide hig}ldmsity ceramic with further rcfincmc.nt. Our results~e.nc.ral Iy confirm those of Sch.ifcl and Weppncr,although we did not achieve as high a ceramic density.[ig]

IIased o n i m p r o v e d undcrstajlcling of (hetcrnperaturc and K20 stabilit y regime of K-beta” -alumina,the. exchange process of Crosbic and l’cnnenhouse wasimproved by carrying out the exchange at a highertcrn}wraturc with better control of KZO activity. l’hcresulting ccrarnic shows the appropriate weight gain ofabout 4, S % a f t e r cxchangc, s h o w s only a +nallanontalous volurnc cxpansiorr ( <1 %) over the expd@edvolurnc e.xpansiorr due to increase. in the ]atticc

.

1 ligh Tempcratm-e Stability of ]~olassilnn Beta’’-Alun~ina

(kmclmions:

Potassium beta” alumina solid electrolyte ceramic shows improvecol~duetivity over 500 hours at potassium AMTEC operating conditions.

Potassium beta” alumina can be prepare by vapor exchange at temperatures10 about 1600K if K.20 act ivity is maintained,

l’olassium beta” alumina prepared by vapor exchange at higher tcmpcrat m-esis stronger, and has a higher ionic cond[lctivity at AMTljC operatingtclkq)cratm.x.

Materials and Dcvicc Tcclmo]ogy GroupFk3clric Power Scclion