CALORIMETRIC ENTHALPIES FOR SOLUTION OF HYDROGEN IN THE LANI5-H SYSTEM

Relative partial enthalpies for absorption (desorption) of H2 by LaNi5 have been determined at 298 K over the range of contents from H/LaNi5 ~ 0 to 6.4. The relative partial enthalpy of H2 solution decreases in exothermicity from H/LaNi5 — 0 to 0.23 and then is nearly constant with content to the lower phase boundary. The enthalpy corresponding to the formation of the hydride phase from the -saturated solid and gaseous hydrogen is —14.8 ± 0.5 kJ (molH)-1 and this value is within experimental error of the values of the partial enthalpies in single phase regions adjacent to the phase boundaries. The relative partial enthalpy for H2 solution in the hydride phase becomes increasingly exothermic with content. © by Akademische Verlagsgesellschaft