High temperature interaction of hydrogen with intermetallic compound CaNi<inf>5</inf>

The intermetallic compound CaNi5 disproportionates rapidly into CaH2 and Ni when treated with hydrogen above 350° C. The kinetics of this reaction in the initial stages follows the nucleation and growth mechanism. The pressure-composition-temperature isotherms for hydrogen interaction with CaNi5 in the temperature range 640°C to 725°C have been determined and the ΔHf for CaNi5 is calculated to be 12.9 kcal/mol. Differential thermal analysis confirms the scheme proposed for the CaNi5-H2 reaction. Even a 5% disproportionation of the alloy drastically affects the kinetics of hydrogen Sorption at room temperature. © 1988.