Influence of CaF2 on the Liquidus Temperature and Density of the Molten (СаСl2–КCl)–CaF2 System

Abstract

Influence of the CaF₂ additions on the liquidus temperature and density of the molten 75.3CaCl₂–24.7KCl (mol %) system has been studied. The system in question is a promising media for the innovation technology of electrolytic calcium production. The liquidus and solidus temperatures of the quasi-binary [75.3CaCl₂–24.7KCl]–CaF₂ system were determined within the CaF₂ concentrations range from 0 to 36 mol % using the thermal analysis. The eutectic point was found at 12.7 mol % CaF₂ and 903 K. The [75.3CaCl₂–24.7KCl]–CaF₂ system has a wide homogeneous area of the liquid state, which verifies the possibility of using it as an electrolyte in the electrochemical technologies, where CaF₂ concentration reaches 15–20 mol % at the temperatures of 920–940 K. Density of molten system [75.3CaCl₂–24.7KCl]–CaF₂ was measured by the hydrostatic weighing technique using the experimental installation located in the glove box with inert atmosphere; the CaF₂ concentration in the melt was not exceeding 36 mol % in the temperature range of 920–1090 K. Linear equations for the density temperature dependence were obtained. The dependence density–CaF₂ concentration in the melts containing different amount of CaF₂ as well as the dependence density–molar volume have a nonlinear character. The deviations from linearity are observed for the melts containing more than 12.7 mol % CaF₂ at 973 K, which may be associated with the changes in the melt structure at the increase in content of the fluorine ions, which have large ionic moment.