Systems of univalent electrolytes

Alkali metal halides, mainly sodium and potassium fluorides and chlorides, are usually used as solvents for salts of multivalent metals, which are deposited on electrolysis at the cathode. Alkali metal halides improve the physico-chemical properties of the electrolyte and in many cases, it is the only possibility to deposit the desired metal altogether. 

Alkali metal halide melts are characterized by a quasi-crystalline structure originating by dilatation of the crystal structure and by the occurrence of different kinds of positional disordering. Cations and anions are preferably surrounded by ions of the opposite charge 

Alkali metal halides increase in general their volume at melting (Table 2.2), which is due to the lowering of atomic coordination and the formation of a free volume. 

Several attempts to calculate the properties of alkali metal halides on the basis of the equation of state can be found in the literature. Reiss et al. (1959, 1960) estimated the reversible work needed for creation of a spherical cavity in liquids of rigid spheres and derived the equation of state for these liquids 

Wertheim (1963) and Thiele (1963) showed that the equation of state derived by Reiss et al. (1959, 1960) is identical with the equation of state derived by Percus and Yevick (1958), who presented the exact solution of the integral equation for the radial distribution function. Lebowitz et al. (1965) generalized later the validity of this theory for the mixture of simple liquids. The same equation of state was derived by Stillinger (1961), who showed that Eq. (2.1) can be applied to fused salts also if we replace the fused salts by a rigid sphere fluid in which the particle diameter a equals the sum of the cation s and anion s radii. 

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