Permeation Techniques without Trapping

The permeation method has been widely used in studies of hydrogen diffusion, both with and without trapping considered in the analysis. It is based on the cell originally described by Devanathan and Stachurski. The metal or alloy of interest is 

The concentration gradient and therefore the hydrogen flux, J Xy t vary through the membrane with time and distance, so that the anodic current transient represents the variation in the flux at the output side, i = FJ(L, /), where L is the thickness of the membrane and F is the Faraday constant. The current eventually reaches a steady-state value (/qo) as the concentration gradient in the membrane becomes linear, with being a direct measure of the resulting flux, given by 

The dependence of l/J on L can therefore be used to evaluate from the intercept provided that the value of 6 is known independently. If k DIL, Eq. (10) simplifies to give J =ki 9, indicating that hydrogen permeation is controlled only by surface entry kinetics when the membranes are too thin with respect to the hydrogen dififusivity for the metal of interest. 

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