Further Studies of the Isothmns of LaNi 5 _ , Snx –

Complete hydrogen isotherms have been measured using highly stoichiometric, activated LaNi5 over a wide temperature range, 373 K to 228 K. Van’t Hoff plots for hydride formation and decomposition have been constructed using the isotherms in the low temperature range from 228 K to 298 K. The following thermodynamic results have been obtained from these plots: IAHP1., I = 15.4 kJ/ mol ~H2 and lASpIa~l = 54.4 J/K rnol ~Hz. These should be regarded as reliable in view of the nearly stoichiometric LaNi5 employed and the wide and low temperature range because the latter avoids degradation of the alloy which can be a factor at higher temperatures due to the inherent instability of the H-containing alloy. It has been observed previously in the LaNi5 – H system that the absorption plateau measured with virgin alloys, i.e., before activation, is significantly higher than the subsequent values. This phenomenon was investigated in this research using the LaNi5– XSnX alloys with x=(), 0.05, 0.lO1 0.20, 0,25 and 0.32. Isotherms for the virgin and