The influence of solid solutions compound on the hydrogen permeable membranes characteristics from niobium and tantalum applied above films

Abstract

The paper presents the results of hydrogen permeability measuring and membranes dilatation from niobium and tantalum foils of 40 μm thickness, one side covered with a layer of NbMo, NbW and TaMo, TaW solid solution, respectively. The measurements are provided at the argon gas mixture contact with hydrogen of technical purity in 1/5 ratio at 500 kPa under cyclic temperature change conditions with a gradual decrease in its average value from 580-585 °C. NbMo, NbW, TaMo layers sputtering with a ~ 1 μm thickness is established to increase the maximum hydrogen permeability of membranes in comparison with the pure niobium and tantalum membranes. The most significant effect on this parameter is due to doping with tungsten niobium in an amount of 14 wt%. This effect can be explained as the more developed and pure from oxide films surface of deposited by films solid solutions, so the role of doping elements in dissociative absorption. The hydrogen permeability of membranes after reaching the maximum value is reduced. The reduction degree in hydrogen permeability is lower for membranes with a layer of a higher-doped solid solution, which is explained by their higher corrosion resistance. The dilatation and the operation period before the membranes destruction with a layer of solid solution is established to vary significantly in contrast to tantalum and niobium membranes, which is explained by the high influence of gas impurities in the argon composition which is used in magnetron sputtering. This is explained by the affinity of niobium and tantalum with such gases as oxygen and nitrogen, the presence of their small impurities in the films leads to a decrease in the hydrogen permeability of the membrane as a whole. Based on the provided studies, the possibility to use high-doped solid solutions of Nb-30 wt.% W, Nb-40 wt.% Mo and Ta-25 wt.% Mo as materials for depositing barrier layers on the surface of tantalum and niobium membranes for separation them from the palladium catalyst layer was crucially established.