Thermal expansion of alkali and alkaline earth halides in solid and molten states

Abstract

Thermophysical properties of the alkali and alkaline earth halides, widely used in numerous electrochemical technological processes, are necessary for the design and operation of various devices in a wide temperature range. This review discusses the thermal expansion coefficients of solid and molten salts of the alkali and alkaline earth fluorides and chlorides, the regularities of their change depending on the nature, molar volume and temperature. The thermal expansion of the solid alkali and alkaline earth halides in the range from room temperature to the melting point does not obey a linear law. When salts melt, the thermal expansion coefficient increases, and the increase is greater the larger the cation size. In the liquid state, the temperature dependence of the volumetric thermal expansion coefficient is linear and changes slightly with temperature. The dependence of the thermal expansion of all molten alkali halides on the molar volume can be described by a linear function, which indicates the uniformity of interparticle interactions in these salts and the ionic nature of the bond. For fluorides and chlorides of alkaline earth metals, such a dependence is more complex