The Electrical Conductivity of Solutions of Alkali Metals in their Molten Halides1

Abstract

The electrical conductivity of alkali metal solutions in their molten halides has been measured by means of a synthetic sapphire conductance cell. The specific conductance increases with increasing metal concentration. The equivalent conductance of K, A K, in both KCl and KBr also increases, namely, from 2800 ohm/sup -1/ cm/sup 2/ (K--KCl, 820 deg ), 6100 (K--KBr, 760 deg ), and 6500 (K--KBr, 870 deg ) at infinite dilution, to 38,000, 83,000, and 71,000 ohm/ sup -1/ cm/sup 2/ at 19, 23, and 20 mole% K, respectively, the maximum concentrations measured. However, LAMBDA /sub Na/, for Na in NaBr at 895 deg decreases from 12,500 to a minimum of 7300 ohm/sup -1/ cm/sup 2/ at ca. 9 mole% metal. At 805 deg /sub Na/ in NaBr decreases from ca. 12,000 at infinite dilution, i.e., approximately the same value as at 895 deg , to less than 5000, and in NaCl at both 845 and 890 deg from ca. 6000 to less than 3000 ohm/sup -1/ cm/sup 2/. These values are the equivalent conductances at 5, 4 and 3 mole% Na, respectively, representing the metal solubility limits which are too low to permit the equivalent conductance minima to be realized. Themore » different behavior of sodium and potassium may be related to the liquid phase equilibria and to the dissociation energies known for the diatomic gaseous metal molecules, both of which reflect a greater tendency to associate for Na than for K at the test temperatures. Such association, which increases with metal concentration, decreases the number of metal particles per equivalent of metal on which the electronic fraction of the conductance is thought to depend. The effect of the association, not strong enough in the K systems to produce a minimum in equivalent conductance, is, in the Na systems, surpassed, at the minimum, by the effect of the gradual establishment of the metallic conductance band through overlap of the orbitals of the metal pelymers. The differences in equivalent conductance at infinite dilution for the various systems may be taken to reflect the influence of the different degrees of polarization of the anions by the cations on electron mobility. (auth)« less