Thermodynamic Assessment of the Mn-H and Mg-Mn-H Systems

Abstract

Mn-H and Mg-Mn-H are two important sub-systems in the Mg-Mn-Ni-H system, which is considered as a very promising hydrogen storage system. In this work, the available phase diagram and thermodynamic data of the Mn-H and Mg-Mn-H systems were critically reviewed and the thermodynamic assessments of the two systems were carried out using the CALPHAD method. In the thermodynamic modeling, the liquid phase was described by a substitutional solution model, the solid solution phases and binary ε hydride were described by the two-sublattice model, and the two ternary hydrides (Mg₃MnH₇ and Mg₃MnH₆) were treated as stoichiometric phases. Using the obtained thermodynamic parameters for the Mn-H and Mg-Mn-H systems, the phase diagrams of the two systems at different pressure were calculated. Comparisons between the calculated and experimental results showed that the reliable experimental data can be reasonably described by the present thermodynamic description. Some predictions of the two systems were also presented according to the obtained thermodynamic parameters.