Counter-diffusion and counter-permeation of deuterium and hydrogen through palladium

Experiments for counter-diffusion and counter-permeation of deuterium and hydrogen through a palladium membrane (25 μm thick) were performed. Deuterium permeation rates as a function of upstream D2 pressure were measured under condition where hydrogen permeated in the opposite direction by supplying H2 gas at the 'other' side (downstream, corresponding to D permeation) of the membrane. It was found that significant deuterium permeation occurred even when the deuterium upstream pressure was much smaller than the hydrogen downstream pressure. The deuterium permeation rate was gradually reduced by increasing the downstream H2 pressure and the corresponding counter H permeation. The deuterium permeation rate under counter H permeation can be represented reasonably well by a simple model in which the ratio of the deuterium permeation rates with and without counter H permeation are assumed to be proportional to the fractional concentration of deuterium in the bulk. However, as the hydrogen counter flow increases, the deuterium permeation rate deviates from the model. This implies that adsorption (absorption) of D2 from the gas phase may be inhibited, and also surface recombination of deuterium may be blocked by hydrogen. (orig.)