Calorimetric investigation of interactions in the LaNi4.75Al0.25-H-2 and LaNi4.8Sn0.2-H-2 systems

The interaction of hydrogen with intermetalic compounds LaNi4.75Al0.25 and LaNi4.8Sn0.2 has been studied in the temperature range 308-353 K by the cal orimetry titration method. The mechanism of hydrogenation was investigated. It was shown that, as the temperature increases, the initial concentration of hydrogen in the metal lattice needed for P-hydride formation decreases. It was assumed that this effect is related to the concentration of Hdelta atoms, which "oxidize" the metallic matrix according to the scheme Hdelta + M-0 --> Hdelta- + M+. The enthalpy and entropy of hydrogenation for the LaNi4.75Al0.25-H-2 system were calculated from the p-C-T curves and the cal orimetry results. The thermodynamic parameters of the LaNi4.8Sn0.2-H-2 syst em were obtained for the first time.