Hydrogen transport in plasma nitrided iron

Hydrogen permeation through membranes prepared from various parts of the nitrided iron specimens was investigated by an electrochemical technique. The membranes were charged with hydrogen by galvanostatic cathodic polarisation in 0.1 M NaOH. The successive partial decay and build-up transients were performed and analysed to determine the diffusivities of hydrogen in the outer compound layer, the inner diffusion zone, and the unmodified iron substrate. Hydrogen transport in the diffusion zone proved to be the most complex. It was found that hydrogen diffused mainly through the ferrite matrix and bypassed the nitride precipitates. Therefore, the real diffusion paths in the diffusion zone had various lengths and were longer than the membrane thickness.