Hydrogen sorption properties of V85Ni15

An alloy with nominal composition V85Ni15 was prepared in a vacuum induction melting apparatus. The chemical analysis of the sample showed a V (Ni) content of 82.63 (15.68) at and small contaminations by carbon and aluminum. XRD measurements confirmed that the bcc Ni-V solid solution phase is the main constituent of the sample. However, a minor impurity (approximately 6.5 wt%) due to the precipitation of the sigma NiV3-x phase is present in the sample. Hydrogen sorption measurements extending from 150 C up to 400 C in a wide pressure range (up to 90 bar) were performed. Upon hydrogenation below 250 C, one observes the subsequent presence of an a phase and of two hydride phases with different values of dehydrogenation enthalpy:DH dehydr ¼ 21 ± 1 kJ/mol for 0.15 H/M 0.30 and D H dehydr ¼ 26 ±2 kJ/mol for 0.53 H/M 0.59. Above 300 C, there is no evidence of the formation of hydrides and only an a phase is present up to the maximum measured composition, with a hydrogenation enthalpy D H hydr ¼ 10.0 ± 0.5 kJ/mol