Electrical conductance in molten KCl, KI, TlI and KI–TlI

Abstract

Specific conductance, x, in the ionic melts KCl, KI, TlI and KI–TlI was measured by the a.c.-dispersion plateau method. The variation of x with temperature (T, °C) in the pure melts is given to ±0.1 % by empirical equations of the form: x=–a+bT–cT². Other equations can also be fitted to these and previously reported data, and it is concluded that it is unwise to attach theoretical significance to the parameters or to extrapolate measurements using temperature coefficients of x derived from such equations to seek a maximum in the curve.

The low frequency-dependence of x in TlI is accompanied by a low value of –d²x/dT², as is also the case for certain other heavy-metal halides. It is suggested that this rules out the possibility of electronic conduction and that the difference in the magnitude of dispersion in these halides and the halides of the alkali metals is attributable to ionic properties.

Isotherms of x in KI–TlI are remarkable in having two wells although no maxima could be detected in the liquidus by thermal analysis. This system, like KBr–TlBr, is therefore suspected of having strong ionic interactions that are peculiar to the liquid state. Re-examination of the x-isotherms of KBr–TlBr suggests that there may be incipient splitting into two wells as T increases.