Gaur, H. C.

Jain, S. K.

English

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Indian Journal of ChemistryVol. 15A, July 1977,pp.579-581"."0:_::1\\ElectricalConductancein Molten Salts: Part V - Mixturesof Lithium,Sodium,Potassium& Thallium Nitrateswith CadmiumNitrate*S. K. ]AINt & H. C. GAURDepartmentof Chemistry,Universityof Delhi,Delhi110007Received17 September1976:accepted9 February 1977The non-Arrhenianbehaviour,observedfor low-temperatureconductancedatafor binarymoltenmixturesof cadmiumnitratewith lithium,sodium,potassiumandthalliumnitrates,hasbeensuccessfullyinterpretedin termsof thefreevolumemodel. Thezeromobilitytem-peratureparameter(To) increaseswiththeaveragecationfieldstrength(:En;;,) of themediumandis seento begovernedbytheaveragecationicmassandthenatureof bondingbetweenthemetalandthenitrateion. Analysisof theresultssupportstheusefulnessof To in interpretingthe compositionandtemperaturedependenceof electricalconductivityandin establishingacorrespondingtemperaturescalein fusedsaltsystems.175 225 275 325Temp.:CFig. 1- Plotsof specificonductance(k) versustemperaturefor KNO.-Cd(NO.).mixtureswhere!1. is the coefficientof expansionof the melt.The valuesof !1. in thepresentstudywereapproxi-mated~to thosefor puresaltsat TITm=I'I; thesewere3·12X 10-4,3,85X 10-4,3'98X 10-4and3·31X 10-4~Althoughat showsa slight decreasewith additionofdivalention into the melt of monovalentnitrate;thesechangesdonot influencetheresultssignincantly.... (1)0.40f- " "O,CdINO"2 jl0.35f- j 2Cd (NO) ,.•E 1:: 0,4-00 3 2. "030 2=0·519 f.• 3=0'630 I;: '="'10 i!J' ,,5~0.25 5=0·170 • Jc ~'to." Ii .,Io .j ~J'U 0'15 j,'0100·05I_t.~/y"into ED valuesusing Eq. (1),ED=Ek+RT +!1.RT2ResultsandDiscussionSpecificconductanceis seen to have positivetemperaturecoefficientin all the casesstudied.Typical plots of specific conductanceversustemperaturein the caseof KN03-Cd(N03)2 mix-turesareshownin Fig. 1; for brevitysimilarplotsfor otherelectrolytemixturesusedin this investi-gationarenot included. Plots of log k versusliTare invariably curved. Typical plot for TIN03-Cd(N03)2 mixture containing 0·571 eq. ofCd(N03)2 is shownin Fig. 2. Curvaturein theseplotsindicatesanincreasein theapparentactivationenergy(Ek) withthedecreasingtemperature.Valuesof Ek were determinedthrough the derivative(0 In k) b . d b d'ff .. hI' h .3(IIT) 0 tame y 1 erenhatmgt e ogant nucformof variousmathematicalexpressionsemployedin describingthe specificconductance-temperaturedata. The averagevaluesof Ek weretransformed*part IV, seeref. 3.tpresentaddress:Hindu College,Universityof Delhi,Delhi 110007,MaterialsandMethodsAll the saltsusedwereof AR (BDH) gradeorof equivalentpurity. Details regardingtheir pre-treatment,samplepreparationand other experi-mental techniqueshave already been reported2•The specificconductance-temperaturedata in theform of least-squarequationshavebeenreportedelsewhere2,As a part;of investigationsonelect!icalconduc-tancem supercooledglass-foITmngmeltsl-4,the interpretationof the temperatureandcompositiondependenceof electricalconductancefor binary moltenmixturesof Li, Na, K and T1nitrateswith cadmiumnitratein termsof the zeromobility temperature5(To) is presentedin thispaper.579, --INDIAN J. CHEM., VOL. 15A, JULY 1977dcgr~e·Ifor LiN03, NaN03, KN03 and TIN03resp¢ctively.Accordingto free.volumemodel5ED-tQRT~BR[Tj(T _To)J2 ... (2)Renfc,Eeorr!=E,,+!RT +(J.RT2=BR[Tj(T _To)J2 ... (3)T~'1S,Eeorr mustb~a linear functionof [Tj(T-To)J~ I'll:: Eeorr-tempcratur,'data were analysedfor tho best To valuesas di.;cw'scdcarlier4. Thecomputc:dTo ard B valuesarl;recordedin Table1.Theiusdulnessof To in describingthe temperaturedcp~nd"nceof specificconductanceis seenthroughthe l ub,crvation that the curvilinear Arrheniusplot~sllc.wnil? Fig. 2, becomelinearwhen.log kIS plottprlagamst(T -Totl for the best chOlceofTo. i To vahl"sfor themeltsof monovakntnitrates,to \'./'hichcadmiumion" in the formof nitratewereadd¢d,are'in qu.alitativeaccordwith the expecta-tionhb s don the notionthat the averagecationfieldstreflgthin mixturesrisesin a regularmannerwhenthe ionsof lowerZ;'ri values(Li+=1·67;Na+=1·05; K+ 0·75;TJ+=0·69)are replacedby Cd2+with higher (2·06)charge-radiusratio. The plotscf To againstthe molepercentageof Cd(N03)2andaveragecationicfield strengthof the melt (shownin Figs. 3 and 4) could be regardedas linear.Extrapolatedvaluesof To fc.rLiN03, NaN03, KN03andTIN03 areshownin Table2. A notablefeatureofTo parameteris thatthecomputedvaluesforTo liecloseto the exprerimentallydeterminedvaluesofglass-transitiontmpcratures{Tg)7.Exchangeof K+ by TJ+,whichis almostof thesame size but heavier and more polarizable,produceda drop of about 30-350in To vall1es4,7.This couldbe rationalizedin termsof correlationalreadyobservec18•9betweenTg, Debye-temperature(8D) and Dcbye-frequency(VD), which postulatesa m-1dependenceof To. ChangingK+ by Na+causeda drop of about 10-24°,but when Li+TA~LE 1- COMPUTEDPARAMETERSFOR Li, Na, K AND'1'1NITRATES-CADMIUMNITRATE MIXTURESTABLE 2- EXPERIMENTALMELTINGANDGLASS-TRANSITIONtEMPERATURESAND EXTRAPOLATEDTo VALUES FOR, SOMEMONOVALENTNITRATES*Qveral1uncertainty in To values is ±5 degrees.f'1aluesin the parenthesesare the extrapolatedvaluesofeXpejrimentallymeasuredTg values (ref. 7).802000-5250350'"c:.J-44000'2 0-24r:}TFig. 2 - Plots of log" k versus liT (dotted) ancl liT - To(solid line) for TlNOa-Cd(NOal. mixturesX: 3001::020 40 60Cd(N~)2,mOle%Fig. 3 - Plots of To versusmole percentage(Li, Na, K, Tl)NOa-Cd(NOa)2 systems0'95591·06411·23801·79291·80221·87841'35531·40581·52701·58751·07941·21031·35441·47231·5719B917'8535'4766'6546'6460,5305'2541'9520'7549'3KNOa-Cd(NOa)2NaNOa-Cd(NOa)2To (K)*TlNOa-Cd(NOa)2250 (257) 514·2276 (270) 406'6285 (290) 512·0295300310325LiNOa-Cd(NOa),365 511-6350 402'2420 562-8305 (300lt321 (320)315 (330)345 (340)365 (355)To (K) To (K) T m (K) Tg (K)*Extrapolated values mean31 i5341353i630'035:047105310251035rO46>0551062,619!-4271'34~0SaltCd(N/03),(mol~%)Fig. 3Fig. 4LiNP,2622882755Narta54505236KN' 306 061TI , a326479*Re£. 11.580:JAIN & GAUR: ELECTRICAL CONDUCTANCE IN MOLTEN SALTS n! iTI KFig. 4 - Plots of To versus~nizi (Li, Na, K, TI)NOa-Cd-'Yi(NOa)2 systems400300;;:200f-!ooentropyof the melt,whichchangeswith tempera-ture, accordingto the relation (3).Sc(T)=ACp loge(TITo) ... (3)Since, ACp is unlikely to vary greatly amongthesemelts,low temperatureresultsmay be usedto establisha correspondingtemperaturescalebasedon thestateof equalconfigurationalentropy.An interstingfeaturewhichemergesout fromthedatarecordedin Table2 is that the dependenceofTo (andhenceTg) Oncationis unexpectedlysmalll1,This near identity of To values,comparedwithwidelyscatteredmeltingpoints,whencoupledwiththecorrelationsalreadydiscussed,leadoneto believethat To mayproveto be a moresatisfactorybasisfor correspondingtemperaturesin fusedsaltsthanthe meltingpoint, usedin past. However,muchremainsto bedoneto provegeneralusefulnessofTo,AcknowledgementThe authorsthank CSIR, New Delhi, for thefinancialassistanceand fellowshipto oneof them(S.K.].).ReferencesreplacesK+, thereis a sharprise in To valuesby2-70°dependingupon M2+/M.f mole ratio. It isnot clearat this stagewhetherthesechangescouldbe attributedto thechangesin the averagecationicmassof the medium,in the bond type betweenmetaland the nitrate ion or the combinedeffectof the two.Further,whenthe correctedactivationenergies,after allowingfor the variationof B (Eq. 2) withthe compositionof the melt (E'=EcorrIBR), areplottedagainstTIT 0' theentiredatafallon a singlecurve (figurenot included)speciallyin the lowertemperatureregion,wherethe instantaneouslopeis a near universalfunctionof TIT o. Accordingto Adam and Gibbs10the instantaneouslopeinsuch plots is proportionalto the configurational1. GAUR, H. C. & JAIN, S. K, J. chem.Engng Data, 17(1972),200.•2. JAIN, S. K & GAUR, H. C., J. chem.Engng Data, 21(1976),284.3. JAIN, S. K & GAUR, H. C., Indian J. Chem.,15A (1977),447.4. JAIN, S. K &. GAUR, H. C., Rev. RoumaineCkim., (inpress).5. COHEN, M. H. & TURNBULL, D., J. chem.Phys., 31(1959),1164.6. ANGELL, C. A., J. phys. Chem.,68 (1964),1917.7. RAO, K J., HELPHREY, D. B. & ANGELL, C. A., Phys.chem.Glasses,14 (1973),26.8. ANGELL, C. A., J. Am. ceram.Soc., 51 (1968),117.9. COLE, R. H. & DAVIDSON, D. W., J. chem.Phys., 20(1952),1389.10. ADAM, G. & GIBBS, J. H., J. chem.Phys., 43 (1965),139..11. ANGELL, C. A. & HELPHREY, D. B., J. phys. Chem.,75(1971),2306.581

Electrical Conductance in Molten Salts: Part V- Mixtures of Lithium, Sodium, Potassium & Thallium Nitrates with Cadmium Nitrate

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Electrical Conductance in Molten Salts: Part V- Mixtures of Lithium, Sodium, Potassium & Thallium Nitrates with Cadmium Nitrate

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