Electrochemical measurements were made of H permeation through Pd/Nb multilayers on Pd substrates. A marked retardation of the permeation was observed at low H contents. The experimentally applied boundary condition, of a vanishing current at the output side, yielded an expression for the time-lag which was quite complicated. Considerable simplification of the mathematics was achieved by applying a zero-concentration boundary condition at the output side. The permeation behavior was modelled on the basis of the bulk properties of the pure metals. This model was able to explain the retardation as arising from the differing free energies of H dissolution in the metals. At higher H contents, a more complicated permeation behavior was observed, and was not yet entirely understood.

Diffusion of Hydrogen through Metallic Multilayers. G.Schmitz, P.Kesten, R.Kirchheim, Q.M.Yang: Physical Review B, 1998, 58[11], 7333-9