It was recalled that, when considering H permeation through a multi-layer membrane, it was usually assumed that the ratio of the H concentrations at the interface was equal to that of the H equilibrium solubilities in the materials. However, during diffusion permeation, the H concentrations at the interface were not the equilibrium values but were determined by the diffusion input D1/d1 and output D2/d2 rates and by the rate of passage through the interface; which was proportional to the ratio of the equilibrium solubilities S1 and S2 (where di and Di were the thickness of, and H diffusivity in, the ith-layer, respectively). Therefore the ratio of H concentrations at the interface could be characterized by the ratio, (S1D1/d1)/(S2D2/d2). By this approximation the analysis of H permeation through the duplex membrane in a diffusion-limited regime showed that the coating of the same materials could both decrease and increase the H permeability of the system depending on the ratio of these parameters. In this case it was possible to explain the contradictory results of experiments on H permeation through duplex membranes.

Hydrogen Permeation through Metal Membrane with Protective Coating in Contact with Atomic or Ionized Hydrogen. V.M.Sharapov: Journal of Nuclear Materials, 2002, 307-311[2], 1520-3