Hydriding–dehydriding characteristics of aged Mg–10%Ni alloy hydride and water resistance of sol–gel encapsulated composite

Thermodynamic assessments of a 20-year-old Mg–10%Ni alloy hydride, which had been stored under a dry atmosphere, was carried out. More than 80 mol% of the magnesium in the aged sample was reactive to hydrogen. After a further two-year aging in an ambient atmosphere, formation of magnesium hydroxide proved to be significant. The hydrogen absorbing ability was diminished through consumption of magnesium, and the rate of deterioration was accelerated due to the increased surface area brought by decomposition of magnesium hydroxide on dehydriding at elevated temperatures. The presence of water would favor the formation of magnesium hydroxide. Encapsulation of the hydride with the siliceous shell prepared by the sol–gel method provided a water resistant composite which had fair hydriding–dehydriding characteristics.