Alloying effects on the stability of vanadium hydrides, V2H, VH and VH2

The phase stability has been investigated systematically for vanadium hydrides formed in a variety of binary and ternary vanadium alloys. The PCT curves are measured for the beta phase (V2H or VH) at low hydrogen pressures using an electrochemical method devised newly for this investigation, and for the gamma phase (VH2) at high hydrogen pressures using a Sieverts-type apparatus. It is found that the phase stability of vanadium hydrides is affected largely by the presence of a small amount of elements in the alloy. Also, the alloying effects on the hydride stability are different between the gamma phase and the beta phase. For example, the gamma phase becomes most unstable when the 8 group elements, Fe, Ru and Os, are added into vanadium metal. On the other hand, the stability of the beta phase changes monotonously following the order of elements, M, in the periodic table. In addition, it is shown that the plateau pressure of the y phase changes almost linearly with the amount of alloying element added into vanadium. Using this linear relation, the plateau pressures can be estimated in the wide compositional range of ternary V-Ti-Ru and V-Ti-Cr alloys.