Use of pure metals to analyse hydrogen electrochemical permeation in steels

The electrochemical permeation method is often used to study hydrogen diffusion and trapping in steels; unfortunately, there is great scatter in the experimental results. To identify the reason for this scattering, experiments were carried out using pure iron and pure palladium specimens. It is clearly shown that on the iron samples, surface phenomena are not controlled. In particular, the passive layer on the exit side induces variation of the hydrogen concentration on this side with time. On palladium samples, such phenomena can be controlled and stationary conditions as well as good reproducibility can be obtained. The use of a palladium coating on the exit side of ferrous samples can help to better control the surface phenomena during permeation experiments and so to obtain meaningful measurements.