Thermodynamics of the MgCl2-MgSO4 and CaCl2-CaSO4 systems

Thermodynamic properties of MgCl₂-MgSO₄ and CaCl₂-CaSO₄ binary systems hold significant importance in the exploration of potential phase change materials for thermal energy storage applications. This study aims to elucidate the phase diagrams and thermodynamic properties of the eutectic mixtures within these systems, employing experimental techniques such as Differential Thermal Analysis (DTA) and Differential Scanning Calorimetry (DSC). Through comprehensive experimental investigations, the phase diagrams of the MgCl₂-MgSO₄ and CaCl₂-CaSO₄ systems were meticulously delineated, revealing the eutectic compositions and transition temperatures. Specifically, the eutectic composition for MgCl₂-MgSO₄ was proposed to be 28.0 mol% MgSO₄ with a melting temperature of 663 ± 5 °C, while for the CaCl₂-CaSO₄ system it was found to be at 14.0 mol% CaSO₄ and 722 ± 5 °C. Additionally, the enthalpy of fusion of these eutectic mixtures was for the first time determined, providing crucial insights into their thermal behaviour. They are 38.2 ± 1.0 kJ/mol for the Mg-containing system and 30.2 ± 0.4 kJ/mol for the Ca-containing system, respectively. The experimental data obtained in this study served as the foundation for the development of a new Gibbs energy dataset, which is essential for conducting thermodynamic calculations. The utilisation of this dataset enables accurate predictions of thermodynamic properties across the entire composition and temperature ranges of the systems under investigation.