2506
COMMUNICATIONS TO THE EDITOR
Vol. 67
TABLE I Ion
Li( I )
Electrolyte composition
Temp., 'C.
NaKNOa eutectic
E,v./cm.
270 i 3
5
u x 104a +2.03 f 0.18
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 at 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 at 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 at 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 THE (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 HALIDES (3) (a) L. F. Grantham and S. J. Yosim, J . Chem. Phys., S8, 1071 (1903);
Sir: We wish to call attention to the seemingly anomalous electrical conductivity of molten BiIs, BiBr3, and BE&.
(b) 8. J. Yosim, L. D. Ransom, R. A. Sallaoh, and L. E. Topol, J . Phus. Chem., 66,28 (1962). (4)
S. J. Yosim, A. J. Darnell, W. G. Gehman, and 8. W. Mayer, ibid.,
63, 230 (1959).
(5) C.A. Kraus, Phys. Rev., 18,40,89 (1904).
COMMUNICATIONS TO THE EDITOR
Nov., 1963
Some solid semiconductor systems such as arsenicdoped germanium also exhibit maxima in the electrical conductivity as a function of temperat~re.~Two opposing effects are responsible for these observations. As the temperature increases the number of carriiers increases but the mobility of each carrier decreases. Eventually, a temperature is reached at which the latter effect overshadows the former; hence the conductivity passes through a maximum and then decreases with increasing temperature. A slight decomposition of BiIg occurs at high temperaturles; these decomposition products may act as dopants. However, it is questionable whether doped fused salts should be compared with solid semiconductors due to the many orders of magnitude difference in dopant concentration. This apparently anomalous behavior in the electrical conductivity of molten bismuth halides may not be an unusual phenomenon ; the electrical conductivity of other molten salts should be measured over a wider range of temperature and pressure to see if this behavior is unique to bismuth halide systems.
055
-I
0.50
E Y
E 0.45 r 0
v
>-
F
5
040
F
0 3
n 0.35
0 LL ~
a
2507
0.30
v)
0.25
(9) P. P.Debye and E. A t . Conwell, Phv/s. Rev.,93, 693 (1954).
ATOMICSINTERNATIONAL A DIVISION OF NORTH AMERICAN
0.20 200
300
400
500
600
TEMPERATURE
700
800
900
PC).
AVIATION, INC. CANOGA PARK,CALIFORNIA RECEIVED AUGVST27, 1963 -
Figure 1.
This decrease in conductivity is associated with the decrease in density and dielectric constant of the solutions as the temperature is increased. It is reasonable to expect the conductivity of fused salts to reach a maximuni as the critical temperature is approached, since the ions present would tend to associate to form nonconducting species at sufficiently decreased densities. (In the limiting case of an ionic gas at low pressures, the ions are known to be completely associated.) However, the temperature of the maxima observed in these measurements is still relatively low compared to the critical temperature of the salt (-900” for BiC13 and BiBr3).E Recently,‘ negative temperature coefficients were found in the electrical conductivities of nonaqueous solutions containing cupric perchlorate dihydrate as the temperature was3 varied from 15 to 40”. This unusual behavior was explained on the basis of Falkenhagen’s8treatment of the Onsager conductivity equation. Differentiation of this equation with respect to temperature show4 that the equivalent conductivity is the differenceof two terms. The first term, which is a function of the fluidity, increases with temperature; the second term, which is a function of the concentration and of the inverse of the solvent dielectric constant, also increases with temperature. For solutions having a high concenlration of electrolyte in a low dielectric medium, the second term may become larger than the first as the temperature is increased; hence the conductivity would pass through a maximum. However, this approach assumes a nonionic solvent and is probably not applicable to fused salts. (6) D. Cubiociotti and J. IT.Johnson, private communication. (7) P. T. Armitage and C. Ivl. French, J . Chem. Soc., 743 (1963). (8) H. Falkenhagen, “Electrolytes,” Clarendon Press, Oxford, 1934, p. 201.
L. F. GRANTHAM S. J. YOSIM
SPECTROPHOTOMETRIC STUDY OF MOLTEN LITHIUM. METAL-LITHIUM CHLORIDE SOLETIOATS
Sir: Spectrophotometric and visual observations of lithium metal-lithium chloride systems have recently been made both above and below the melting point of lithium chloride. This exceedingly corrosive solution1 was contained for these studies in newly developed captive liquid cells2made from molybdenum. These cylindrical all-metal windowless cells are designed to permit transmission of light through a portion of a liquid contained therein. Molybdenum was chosen as the material of construction for these cells because of its compatibility with lithium3 over the temperature range of interest. Similar preliminary results were obtained with the use of copper captive liquid cells, which are not, however, inert to lithium.3 Purified LiCl and lithium metal (approximately 1.5 mole %) were placed in the cell in an inert-atmosphe,re box and the samples were transferred to a high-temperature cell assembly4 without exposure to the atmosphere for subsequent melting. All spectrophotometric measurements were made with a Cary recording spectrophotometer, nhdel 14M. At the end of an experimental observation the sample was cooled and transferred, again without any known exposure to the atmosphere, to a vacuum-tight apparatus6 where it was treated with water in vacuo and any liberated gas was collected. (1) A. S. Dworkin, H. R. Bronstein, and M. A. Bredig, J . Phva. Chena., 66, 572 (1962). ( 2 ) J. P. Young, Anal. Chem., in press. (3) R. N. Lyon, “Liquid Metals Handbook,” 2nd Ed., U. S. Government Printing Office, Washington, D. C., 1952, pp. 158-161. (4) J. P. Young and J. C. White, Anal. Chern., 81, 1892 (1959). (6) G. Goldberg, to be submitted for publication.
