Thermochemical optimization of the NaCl-MgCl2 system

The NaCl-MgCl₂ eutectic is one of the proposed heat transfer and fuel carrier salts for future molten chloride nuclear reactors. For this reason, an accurate and predictive thermodynamic model for this system is of interest for reactor operation, optimization, and regulatory activities. The system consists of two incongruently melting ternary compounds, namely, NaMgCl₃(s) and Na₂MgCl₄(s), which, despite numerous experimental efforts, there remain discrepancies with respect to their thermodynamic properties. To resolve the issue, the ternary compounds were experimentally investigated, by fabricating them by solid-state synthesis inside a low-oxygen glovebox, and then characterized by x-ray diffraction with elemental analysis performed by ICP-OES and oxygen contamination by fusion analysis. The melting points and molar heat capacity were measured using a Calvet DSC. Together with other information, revised thermodynamic values were generated, that allow the computation of accurate NaCl-MgCl₂ phase equilibria. The Gibbs energy functions will be included in the future versions of the Molten Salt Thermal Properties Database - Thermochemical (MSTDB-TC).