Peculiar aspects related to the hydrogen permeation flux through a martensitic steel membrane before and after ion implantation

Abstract

We have observed peculiar hydrogen transient fluxes through stainless steel membranes which cannot be explained in terms of the linear permeation laws. In particular, before attaining the steady-state regime, the hydrogen flux may show a maximum, depending on the membrane temperature. Moreover, by repeating the measurement without changing the relevant parameters, the steady-state permeation rate may strongly differ from the first measurement. To clarify whether the observed anomalous behaviour is due to surface or bulk effects we have modified the membrane surface layers by implantation of a reactive (N +) or a non-reactive species (Ar +). The subsequent H-permeation experiments show that the implanted surface, when facing the high-pressure side, does not permit the flux peaks (independently of the implanted species). Moreover, permeation processes are reproducible in the sense that there is no difference between the steady rates of the first and second measurements, except at high temperature.