Influence of Gaseous Activation on Hydrogen Sorption Properties of TiNi and Ti₂Ni Alloys

Ti-Ni-type alloy powders were prepared through mechanical alloying and annealing at 1382 K for 0.5 h of pure Ti and Ni elements. Samples were activated n-times (n is a number between 0 and 3) in two-stage process. The samples were initially heated for 12 h at 673 K in vacuum to remove impurities. In second step, materials were hydrogenated at a pressure of 3 MPa for 3 h. Phase components, microstructure, particle size, and hydrogen sorption properties of materials were investigated. X-ray diffraction analyses revealed the formation of TiNiH and Ti₂NiH_2.5 phases after hydrogenation. It was observed that cyclic hydrogenation process increased cell volume, resulting in fracturing of the powders. This effect was beneficial for hydrogen storage capacity due to creation of fresh reaction surfaces. Hydrogen activation of Ti-Ni-type alloys caused significant increase in concentration of absorbed hydrogen and improvement of hydrogen sorption kinetics.