Study of hydrogen dilation of membranes based on transition metals
Keywords:membrane, niobium, hydrogen permeability, Sieverts law, dilatation, thermal expansion coefficient, phase transition
Niobium absorbs hydrogen well, which is accompanied by structural and phase changes in the metal. To study the phenomenon of "hydrogen embrittlement" in niobium, the work presents studies of the dilatation of samples of pure niobium and palladium-coated niobium foil at different pressures in a gaseous medium. Hydrogen dilatation measurements were carried out on a setup developed based on a Shimadzu AG 100kNx electromechanical testing machine. A series of experiments to study the deformation of niobium membranes was carried out in two stages. At the first stage, pure niobium samples were studied; at the second stage, niobium samples palliated on both sides were studied. An oxide film on the surface of niobium significantly reduces the rate of diffusion of hydrogen atoms into the bulk of the sample, which leads to the development of slow dilatation in niobium in a hydrogen atmosphere. The deposition of a catalytic palladium film on the niobium surface provides a hundreds-fold increase in the flow rate of hydrogen atoms into the sample volume. It has been proved that it is advantageous for hydrogen to occupy tetrahedral positions in the niobium lattice. To study the strain rate and detect points of phase transitions, isobars for niobium and tantalum were plotted. Based on the isobar analysis, the linear thermal expansion coefficient of Nb and Ta was calculated. A rearrangement of the crystal lattice of the base metal in the region of high temperatures, accompanied by a change in the symmetry of the structure of the substance, has been found.
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