The diffusion and permeation of H through pure Fe membranes was investigated by using a time-lag method. The existence of 2 diffusion regimes was confirmed, and the results were consistent with an effective barrier to diffusion of 0.20cm; as compared with the value of 0.05cm which had previously been obtained for Pd-plated Fe. The true value of the H diffusivity at 25C was deduced to be equal to 4.5 x 10-5cm2/s. It was also found that the H permeation and apparent diffusivity were functions of the current density and over-potential, and reached a maximum at 30 to 40mA/cm2. The diffusion and permeation effects were attributed to changes at the membrane surface rather than to a critical H concentration for cavity formation within the metal.

The Diffusion and Permeation of H through Pure Fe Membranes. S.Wach, A.P.Miodownik: Corrosion Science, 1968, 8[4], 271-9

Table 40

Parameters for Diffusion and Permeation of H in Fe and Fe-1.5%Ni

a: kcal/mol, b: cm mm/s atm½,