Hydrogen solubility in V85Ni15 alloy

The membranes made from a relatively inexpensive V85Ni15 alloy can be used to purify hydrogen in compact devices. We carefully studied the solubility of hydrogen in this material using a Sieverts type apparatus in the range of temperatures 100-500 °C and pressures 0.1-1000 Torr. The alloy was produced in a vacuum arc furnace in an argon atmosphere using high purity materials, re-melted several times and finished with homogenizing annealing. The shape of the family of isotherms was found to be typical for temperatures above critical. For low hydrogen concentrations linear sections of the isotherms were isolated and approximated that allowed obtaining the dependence of the equilibrium solubility on temperature. On this basis possible operating temperature and pressure ranges for the membranes made of the investigated alloy were estimated. The approximation of isotherms with van der Waals model was carried out and the critical temperature - another parameter of interest for applications - was evaluated to be T = −13 °C. The experimental verification by cooling of the saturated samples in a hydrogen atmosphere and recording XRD spectra showed the presence of V2H hydride phase, which indicates that the critical temperature is actually higher than room temperature.