Nov., 1963
CORIJIUSICATIONS TO THE EDITOR
2505
measurements on the systems AgK03-KK03 and molten metal oxides-SiOz,sand liquid junction potential measurements on the system AgN03-CsN08, show the great dependence of the ionic mobilities on the composition and temperature of the system. Equalization of the mobilities of like charge ions in ionic melts, while occurring in many systems, is not a general phenomenon as stated by Laity and Moynihan.10 They report that data for a t least ten different systems are consistent with t’hehypothesis that the mobilities of like-charged ions in fused salt mixtures are equal within about 10 to 15% a t all concentrations.ll Many of the systems discussed by Laity and Moy:nihanlo were studied. by measurement of the liquid junction potential. No conclusion regarding the relative mobilities of cations can be drawn from zero values of the liquid junction. potentials15as was done by MurgulCHEMISTRY AKD MATERIALS SECTION F. G. STICKLAXD escu and Marchidan,l6since the assumption of constant AEI RESEARCH LABORATORY mobilities over the concentration range of the cell TEMPLE FIELDS, HARLOW necessary for integrating the equation relating transESSEX,ETGL’4ivD port numbers and liquid junction potentials is not RECEIVED AUGUST15, 1963 valid, as can be wen from mobility measurements on the systems AgNO8-Kn’OJ and NaN03-Kn’03.14 The observation of anionic migration for traces of certain metals strongly suggests that such ions form DIFFEREKCES I K THE MOBILITIES O F “complexes” in the melts. These “complexes,” being LIKE CHARGE I O N 3 IK MOLTEK SYSTEMS equilibrium phenomena, will depend on the composition Sir: and temperature of the system. For binary mixtures, We wish to report on some preliminary results, having one ion in common and of approximately equal which me have obtained on ionic mobilities of cationic molar composition, the relative mobility of two ionic traces in alkaline earth halide melts and in the eutectics species depends on the state of aggregation14 of the NaK03-KN03 and KaNOz-KX03-LiN03. system. As the temperature increases, the aggregates During the course of counter-current electromigration disappear, and the ions can compete for other species in experiments similar to the ones described previously,’ the nielt to form ‘Lcomplexes”which will determine the it was found that in SrBrz a t 770-800O the cationic migration velocity. Lantelme and Chemla have shown migration of the specie containing the strontium ion was how the variations in the self-diffusion coefficients aiid appreciably fa,ster than that containing calcium or magionic mobilities for the system NaNOrKN03 are nesium ions, while the specie containing barium migrated consistent with this explanation. The apparent actifaster in relation to strontium. I n CaBrz at the same vation energy for ionic mobility therefore will depend temperature, the species containing strontium and strongly on the state in which a given specie is to be barium migrated faster, and the ones containing found and, while it is possible that the ionic mobilities magnesium migrated slower than calcium. These become the same a t a given composition for one temphenomena were found to hold for concentrations of perature, they are most likely not to be the same a t traces of about 100 p.p.m. Direct measurements of another temperature due to differences in the activation these mobilities are made a t present on films of alumina energies. powder.2 We also wish to point’out that the observed mobilities Ionic mobility measurements of cationic traces in of alkaline earth ions in solution in an alkaline earth nitrate eutectics have been made on films of alumina bromide (Ca, Sr) art 770-800° and in SaSOz-KNOBa t powder under a flow of dry Nz and the results are re270’ increase linearly as a function of their simple ported in Table I.3 These and other systems are being ionic radius, while the observed mobilities of the alkali further investigated with relation to temperature, com(7) E‘. R. Duke and B. Owens, J . Electrochem. Soc., 105, 476 (1958). position, and effect of the supporting media on the mi(8) V. I. Malkin, S.F. Khokhlov, and L. A. Shvartsman, Intern. J . A p p l . gration. Rad. Isotopes, 2, 19 (1957): 1’. I. Malkin, Zh. Fiz. Khim., 35, 336 (1961). These preliminary results, together with previous (9) J Ketelaar and A. Dammers de Klerk, paper no. 88 presented a t the 13th C.I.T.C.E. Meeting, Rome, 1962. literature data on counter-current electromigration ex(10) R. W.Laity and C . T. Moynihan, ,J. Phys. Chem., 67, 723 (1963). periments in the systems SrBrz-BaBrz, CaBrz-KBr, and (11) In addition to the systems discussed by Laity and Moynihan, equalization of the ionic mobilities occurs also a t certain compositions and CaBr-LiBr, electrophoresis and electromigration extemperatures for the systems LiKOa-NaNOa, LiNOa-KNOa,’? LiBr-NaT%r, 6 periments of alkali and alkaline earth ions in LiBr-KBr,‘X and NaNOrKNOa.14 of metal ionic traces in KC1-LiC1,6 transport number (12) F. Lantelme and X. Chemla, J . chim. phys., 60, 250 (1963).
dry a t much higher temperatures. Very considerable dilution of the reaction solution before the heat treatment had only limited effect on the transformation. Table I gives some idea of the results obtained: the degree of magnetism was assessed empirically by measuring the force required to separate a standard magnet from a small receptacle filled with ferrite. Similar results were obtained from electrolytically produced mixed hydroxides. It has since been shown that the transformation to a spinel with magnetic properties can be carried out under the described conditions with wet precipitates yielding lFeFezO4, Xo.~Zno.4FeaO~, and Kio.45Zno.45M~.lFe~04. This work agrees with the comparable work of the Japanese scientists, but goes beyond it in its description of the much more poverful effects to be obtained by use of higher temperatures in an autoclave.
(1) F. Mdnes, G. Dman, and E. Roth, J . chzm. phys., 60, 245 (1963). (2) S.Forcheri and C. Monfrini, J . Phys. Chem , 67, 1566 (1963). (3) R. A. Bailey and A. Steger, J . Chromatog., :11, 122 (1963). (4) H. J. Arnikar, Compt. rend., 244, 2241 (1957). (5) H. J. Arnikar, Ann. p h y s . (Paris), 4, 1291 (1959). (6) G. Alberti, G. Grassini, and R. Trucco, J. Blectroanal. Chem., 3, 283 (1962)
(13) J. Perie, M. Chem!.a, and M. Gignoux, Bull. soc. chim. France, 1249 (1961). (14) F. Lantelme and M. Chemla, Bull. soe. chim. France, 2202 (1963). (15) R. W. Laity, J . Am. Chem. Soe., 79, 1849 (1957); R. W. Laity, in “Reference Electrodes: Theory and Practice,” ed. by D. J. G. Ives and G. J. Janz, Academic Presn, Xew York, N.Y., 1961, pp. 548 ff. (16) I. G. Murgulesou and D. I. Marchidan, Zh. Fiz. Khim., 34, 2534 (1960).
2506
COMMUNICATIONS TO THE EDITOR
Vol. 67
TABLE I Ion
Li( I )
Electrolyte composition
Temp., 'C.
NaKNOa eutectic
u x 104a +2.03 f 0.18
E,v./cm.
270 i 3
5
Remarks
Present work NaKNOa eutectic 270 i 3 5 f1.77 i .07 Present Na(I) work NaKN03 eutectic 270 f 3 5 f1.47 i .07 Present RbW work NaK&% eutectic 270 rt 3 5 $1.37 rt .04 Present CsU) work Ca( 11) NaKNOs eutectic 270 i 3 5 f 0 . 4 5 i .05 Present work NaKNOa eutectic 270 f 3 6 Sr(11) $0.55 i .08 Present work Ba(I1) NaKN03 eutectic 270 i 3 6 +0.79 It .06 Present work Cd(I1) LiNaKNOs eutecticd 200 7.5 +0.35 Present work Cd(I1) LiNaKNOa eutecticd 200 7.1 Present -0.44 0.8 M KCl work Cd(I1) LiKNOa eutectic 255 10 Ref. 3b f0.56 Cd(I1) KSCN 210 10 C Ref. 3b LiKXO2 eutectic 255 10 Cr(II1) Ref. ' 3 f0.42 Cr(II1) KSCN 210 10 -0.16 Ref. 3b a Ionic mobilities are given in cm.2v.-I set.-'; values for cathodic displacement and for anodic. Ionic Iriobilities were calculated from the displacement data given by the authora. c An insoluble precipitate was formed. 0.1 M Cd(NO& in melt investigated.
+
+
-
'
ions in the NaNO3-KNO3 eutectic a t 270' decrease linearly with the increase in the ionic radius. The behavior of the mobilities of the alkaline earth ions is contrary to Stokes' law on mobilities according to which the mobilities should decrease as the radius increases. I t is likely that the smaller ions have a greater tendency toward the formation of "complexes" or toward aggregation. Increasing the temperature will have the tendency to dissociate these species. The mobility of the smaller cation should therefore have a larger activation energy leading to an eventual reversal of the mobilities. Measurements are actively pursued on this point at present.17 Acknowledgment.-The authors wish to acknowledge helpful discussions with Dr. M. Chemla and G. Dirian. They also want to thank Dr. Chemla for having made available a preprint of the paper on the mobilities in the system NaN03-KN03.
Both the specific and molar conductance of these salts, when plotted against temperature, pass through a maximum 125-250' above their melting points. Positive temperature coefficients of conductance ( 1 / ~ dK/dT) are typical of most fused salts but negative coefficients have been found in fused HgL, Inch, and InBr3.' However, the bismuth halides are the only pure fused salts in which both positive and negative temperature coefficients have been observed. Even though this behavior was unexpected, it is possible that this "anomaly" may be observed in other molten salts if the electrical conductivity is measured a t sufficiently high temperatures. The preparation of reagents and the apparatus used in this work have been described elsewhere.3~4 The conductivity cells were constructed of heavy walled (>2 mm.) quartz tubing. The specific conductivities of BiCIS, BiBs, and BiI3 as a function of temperature are shown in Fig. 1. Maxima in the specific conductances (17) Some indication of a similar effect has been found in the LiNaKNOa ternary eutectic containing 1 M KCl. In eleotromigration experiments on were observed at 425" for both BiCla and BiBra and powder alumina strips a t low temperature (100°), two ill-defined bands of a t 525' for Bi13. The corresponding molar conducanionio migration are observed for C1- (Cl*a). These are most probably due tivity maxima are found a t 460' and a t 610'. The t o free C1- and t o a n ionic association containing C1. As the temperature increases, this second band disappears, and a t 240' we are left with only one sharpness of the maximum decreased with increasing band corresponding t o the normal migration of C1-. molecular weight of the halide. (18) Author to whom correepondence should be addressed. The factors contributing to the maxima observed A. BERLIN'^ SERVICESDES ISOTOPES STABLES in fused bismuth halides may be similar to those reF. MBNBs CENTRED'ETUDES NUCL~AIRES DE SACLAY sponsible for the maxima observed in many solutions FRANCE near the critical temperature. It was found that the DIPARTIMENTO MATERIALI S. FORCHERI conductivities of many solutions of electrolytes disCHIMICAALTE TEMPERATURE C. MONFRINI solved in aqueous or nonaqueous solvents reached a C.C.R. EURATOM maximum a t about 100" below the critical temperature ISPRA-VARESE, ITALY of the solvent and then continued to decrease with RECEIVED AUGUST22, 1963 temperature until the critical temperature was reached.6 ANOMALOUS BEHAVIOR OF T H E (1) This work was supported by the U. S. Atomic Energy Commission. (2) I. K. Delimarskii and B. F. Markov, "Electrochemiatry of Fused ELECTRICAL CONDUCTIVITY OF MOLTEN Salts,"Sigma Press, Washington, D. C., 1951,pp. 12.15. BISMUTH H A L I D E S (3) (a) L. F. Grantham and S. J. Yosim, J . Chem. Phys., S8, 1071 (1903); (b) 8. J. Yosim, L. D. Ransom, R. A. Sallaoh, and L. E. Topol, J . Phus.
Sir:
Chem., 66,28 (1962).
We wish to call attention to the seemingly anomalous electrical conductivity of molten BiIs, BiBr3, and BE&.
63, 230 (1959).
(4)
S. J. Yosim, A. J. Darnell, W. G. Gehman, and 8. W. Mayer, ibid.,
(5) C.A. Kraus, Phys. Rev., 18,40,89 (1904).
