Behaviour of hydrogen in gas nitrided iron studied by electrochemical permeation and desorption techniques

Hydrogen permeation through and desorption from cathodically charged iron membranes with nitrides gamma', (epsilon + gamma') and epsilon layers have been studied. On the basis of the nonstationary permeation, the effective diffusion coefficients of hydrogen for the nitrided membranes, and hence the real diffusion coefficients in each nitride layer were evaluated. After cessation of charging, desorption rate of hydrogen was measured at both sides of the membrane. An analysis of the desorption rates enabled to distinguish the diffusible (mobile) hydrogen from the reversibly trapped one. Hydrogen trapping was enhanced by the gamma' precipitates and especially by the nitrided compound layers. (c) 2012 Elsevier Ltd. All rights reserved.