Thermodynamic re-optimization of the AClx-MgCl2 (A=Na, K, Rb, Cs and Ca, x=1 or 2) systems

Abstract

Thermodynamic evaluation of the AClx-MgCl2 (A = Na, K, Rb, Cs and Ca, x = 1 or 2) systems were carried out by the CALculation of PHAse Diagrams (CALPHAD) technique. Substitutional solution model (SSM) and associate solution model (ASM) were employed to describe the liquid phase. The eleven intermediate phases, i.e., Na2MgCl4, NaMgCl3, K2MgCl4, K3Mg2Cl7, KMgCl3, Rb2MgCl4, RbMgCl3, Cs3MgCl5, Cs2MgCl4, CsMgCl3 and CsMg3Cl7, were treated as stoichiometric compounds. The thermodynamic parameters for describing the AClx-MgCl2 (A = Na, K, Rb, Cs and Ca, x = 1 or 2) systems were optimized based on the available phase equilibria and thermochemistry data. A set of self-consistent thermodynamic parameters of these binary systems was obtained. The calculated phase equilibria, liquid mixing enthalpy and liquid activity are in good agreement with the experimental data. It indicates that the SSM and ASM are considered as effective models to describe the liquid phase with short-range ordering structure in the molten salt. This work not only enriches the thermodynamic database of the multicomponent molten salts, but also provides one more model choice for optimizing and designing the molten salt systems except modified quasi-chemical model.