A.G. Davydov, N.K. Tkachev.
ABSTRACT
A method to take into account polarization interactions between ions in binary molten salts with common cations and anions by means of thermodynamic perturbation theory based on the model of a mixture of charged hard spheres with different diameters is presented. On this basis, the melting points of simple sodium and cesium halide salts were calculated, as well as the liquidus in the phase diagrams of binary NaF–NaCl, CsF–CsCl, NaF–CsF and NaCl–CsCl mixtures of the eutectic type was computed. We have showed that the inclusion of ion-dipole interactions in the free energy of liquid phase leads to a decrease in the melting temperature of alkali-halide salts as compared with the reference system of charged hard spheres. The errors in determining the melting temperatures of sodium and cesium salts without fitting the parameters of pair potential don’t exceed ten percent. When describing the liquidus in considered binary systems, a shift in the position of the eutectic equilibrium towards the less infusible component by up to five percent is observed and a slight overestimation in the eutectic temperature as compared with the melting temperatures of pure components is showed.
KEY WORDS:
polarizability, charged hard spheres, thermodynamic perturbation theory, mean spherical approximation, sodium and cesium halides, fluoride-chloride mixtures, melting temperature, liquidus, phase diagrams, eutectic equilibrium.
DOI: 10.31857/S0235010620050035