Effect of annealing heat treatment on an atomized AB₂ hydrogen storage alloy

The hydrogenation and electrochemical properties of atomized powders of a Ti-Zr based hydrogen storage alloy have been studied. The atomization process deteriorated the capability of hydrogenation in the P-C-I measurements, while its effect on the electrochemical discharge capacity was limited. Once the atomized powder was broken under pressure to create microcracks, the hydrogenation capacity was found to improve significantly. This indicates that the surface layer characteristics of the powder were responsible for the retardation of the hydrogenation reaction. A reason for this was the presence of a partially amorphous phase of the powder, which has low hydrogen diffusivity. Annealing heat treatment increased the degree of crystallization of the atomized powder, and the discharge capacity was markedly enhanced after annealing at 850°C for 4 h.