Thermodynamic assessment of the H–La–Ni system

The H–La–Ni system has been assessed according to the CALPHAD method. To this purpose, an assessment of the La–Ni binary system has been taken from the literature, while the H–Ni system has been partially reassessed with respect to the liquid phase, in order to be consistent with generally used lattice stability of liquid hydrogen. A first assessment of binary H–La system has been carried out in this work. The binary LaHx phase has been described with the sublattice model, in order to take into account a composition variations for 2 ≤ x ≤ 3 . Calculated p – c – T curves and Van’t Hoff plots agree well with experimental data. In the ternary system, hydrogen absorption data have been considered for the LaNi5 intermetallic compounds, leading to the LaNi5H7 hydride. Because the compound and the hydride have the same structure, the equilibrium between the two phases has been described as miscibility gap. Also in this case, calculated p – c – T curves and Van’t Hoff plots agree rather well with experimental data. The equilibrium phases have been calculated in the ternary system. The present thermodynamic description can be a useful tool for predicting the hydrogen absorption and desorption behaviour in commercial vessels based on the AB5 compounds.