Hydrogen permeation through metal membrane with protective coating in contact with atomic or ionized hydrogen

The use of protective coatings is one of the most common methods to reduce the hydrogen permeation through structural materials. Considering the hydrogen permeation through such multilayer membrane it is usually suggested that the ratio of hydrogen concentrations at the interface is equal to that of the hydrogen equilibrium solubilities in these materials. However, during diffusion permeation the hydrogen concentrations at the interface are not equilibrium values but they are determined by diffusion input D1/d1 and output D2/d2 rates and by passage rate through interface which is proportional to the ratio of equilibrium solubilities S1 and S2 (di, Di – thickness of and hydrogen diffusivity in i-layer, respectively). Therefore the ratio of hydrogen concentrations at the interface can be adopted by the ratio (S1D1/d1)/(S2D2/d2). By this approximation the analysis of hydrogen permeation through the duplex membrane in a diffusion-limited regime showed that the coating of the same materials can both decrease and increase the hydrogen permeability of the system depending on the ratio of these parameters. In this case it is possible to explain the contradictory results of experiments on hydrogen permeation through duplex membranes.