Analysis of geometrical and surface effects on experimental data extracted from a hydrogen permeation test: Consequences of an oxide layer

摘要

To understand a metal susceptibility to Hydrogen Embrittlement (HE), it is important to quantify the diffusion of hydrogen through a metallic membrane. Electrochemical permeation tests are the most common methods for experimentally determining the diffusion coefficient of a metal. However the parameters directly accessible from experiments are the time required for a stream to be observed and the flux saturation corresponding to a steady state. The literature offers different models to obtain the diffusion coefficient from these curves. But this diffusion coefficient is not that of the membrane alone because it also takes into account the surface state and the kinetics of trapping. For some thicknesses of membrane and surface coatings (oxide) this approximation cannot be considered fair. We propose to simulate numerically the influence of the oxide thickness on the effective diffusion coefficient taking into account the trapped hydrogen. This study should enable us to correct the experimental data to provide value of lattice diffusion and hydrogen solubility.