Hydrogen absorption and desorption properties of amorphous TiNi and HfNi alloys

Abstract

Hydrogen absorption and desorption properties of amorphous TiNi and HfNi alloys, prepared by the melt spinning technique, were investigated by X-ray diffraction and the volumetric method. These amorphous alloys absorb hydrogen in the amorphous state at low temperature and pressure-composition-temperature curves of the hydrogenated amorphous alloys do not show pressure plateaux. Solution of hydrogen in the amorphous phase obeys Sieverts' law in the low hydrogen concentration region, but shows a positive deviation with increasing hydrogen concentration. Although the hydrogen absorption capacity of the amorphous alloys increases with inceasing titanium or hafnium content in the alloy, which is lower than that of the corresponding amorphous ZrNi alloys, approximately two hydrogen atoms are absorbed per titanium or hafnium atom. At higher temperatures, the amorphous TiNi alloys crystallize to TiNi 2 + TiH 2, while the HfNi alloys transform to HfH 2 + Hf 7Ni 10H x , HfNiH 3 and Hf 2Ni 5 + Hf 7Ni 10H x depending on the alloy composition.