The permeation of hydrogen through the passivating films on iron and nickel

Hydrogen permeation transients for passivated iron and nickel were measured at room temperature as a function of applied anodic potential and electrolyte composition. The permeation of hydrogen through the passivated metals is controlled chiefly by the kinetic processes in the passivating films. A model describing the diffusion of hydrogen in the metal coupled with an activated jump of protons across a kinetic barrier is developed. The kinetics of hydrogen transport through passive films on iron and nickel are qualitatively discussed in terms of the specific rate parameter derived from the coupled diffusion-activated jump model fitted to the experimental curves. However, the nickel/oxide system shows inconsistencies with the model. A coupled diffusion-diffusion/migration model is proposed as an improved approach.