Hydrogen absorption in plasma-nitrided iron

Hydrogen absorption by membranes prepared from various parts of plasma-nitrided iron specimens was studied using electrochemical techniques. The membranes were charged with hydrogen by galvanostatic cathodic polarisation in 0.1 M NaOH. After cessation of hydrogen charging, the desorption rate of hydrogen was measured at both sides of the membrane. An analysis of the desorption rates enabled to one distinguish the amounts (concentrations) of the diffusible and the reversibly trapped hydrogen in the nitrided compound layer, the diffusion zone and the unnitrided iron substrate. Trapped hydrogen accounted for the majority of the total absorbed hydrogen. Hydrogen trapping was enhanced by nitride precipitate-iron matrix interfaces, and especially by the nitrided compound layer.