THERMODYNAMIC AND DEGRADATION STUDIES OF LANI5 (CLOSELY STOICHIOMETRIC)-H AND LANI5-XMNX-H WITH X = 0.5-2.0

Plateau pressures and reaction calorimetric enthalpies have been measured for activated (3 x) LaNi5-xMnx-H for x = 0.5, 1.0, 1.5, 2.0 and for LaNi5 of rather exact stoichiometry. The calorimetric enthalpies for hydride formation increase in exothermicity and the plateau pressures decrease with x. There are extended regions of hydrogen solubility in the hydride phase where \DELTAH(H)\ falls linearly with H content for intermetallics with larger values of x. Degradation of the x = 1.5 alloy does not occur appreciably during cycling at 573 or 623 K but does occur significantly when it is allowed to remain at these temperatures at large hydrogen contents.