Equation of State for Calculating the Density of Halide Melts Taking into Account Charge–Dipole and Dipole–Dipole Interactions between Ions

With growing interest in the use of molten salts in industry, the development of an equation of state for quantitative prediction of the density of liquid electrolytes under various conditions has become one of the most important problems in physical chemistry. This equation should include not only the basic repulsive and Coulomb contributions to pressure, but also second-order corrections due to the charge–dipole and dipole–dipole interactions between ions. A new version of the equation of state is considered here, which includes both of these additional contributions to pressure based on the charged hard spheres (CHS) model. The proposed equation of state was used to calculate the packing coefficients of the whole subclass of molten alkali metal halides (AMHs) at their melting points. It was found that inclusion of both charge–dipole and dipole–dipole interactions in calculations leads to better agreement with experimental data by an average of ~5%. The dipole–dipole contribution is an order of magnitude smaller than the charge–dipole correction in this case. An analysis of these effects on the packing coefficient in the series of alkali metal halides showed that inclusion of both charge–dipole and dipole–dipole interactions leads to a more noticeable increase in density in the systems containing larger and polarizable cations and anions.