HYDROGEN PERMEABILITY OF MEMBRANES BASED ON NIOBIUM AND TANTALUM FOILS IN THE ATMOSPHERE OF TECHNICAL PURITY HYDROGEN

摘要

The paper presents the results of measuring the hydrogen permeability of membranes from niobium and tantalum foils with 40 urn of thickness. The measurements were carried out in a hydrogen atmosphere of technical purity with a smooth decrease in temperature followed by isothermal aging and under conditions of cyclic temperature variation. It is shown that the temperature and the magnitude of the excess pressure influence the hydrogen permeability of the niobium and tantalum membranes. A decrease in temperature causes a reduction in hydrogen permeability. The increase in hydrogen pressure shortens the period until the maximum of hydrogen permeability is reached. This indicates that an increase in the gas pressure loss accelerates the saturation of the membrane with hydrogen. The values of hydrogen permeability and the duration of the membrane before destruction are interrelated. The more hydrogen flow through the membrane, the faster it breaks down. When membranes function under cyclic temperature fluctuations, the period before their destruction is longer compared to that observed in membranes with a smooth temperature decrease followed by isothermal aging. This phenomenon is explained by a significant change in the solubility of hydrogen in niobium and tantalum in the range of 500-600 °C. Probably, a cyclic change in temperature leads to a decrease in the average concentration of hydrogen in niobium and tantalum and, as a result, increases their plasticity. Under conditions of cyclic temperature change, the optimal hydrogen permeability and the period before destruction of the niobium membrane show in the range of 535-555 °C at a pressure of 500 kPa, and membranes from tantalum in the range of 555-568 °C and 300-500 kPa. Investigation of the surface of membranes after contact with hydrogen showed that the main cause of their breakthrough are microcracks, which arise when crossing folds formed during membrane dilatation. It is assumed that the creation of^conditions to prevent the crossing of folds and their more orderly formation will significantly increase the service life of hydrogen permeable membranes. Upon contact with technical grade hydrogen, the surface of the membranes of tantalum and niobium is coated with a thin oxide film. This leads to a decrease in hydrogen permeability over time.