It was shown that that the diffusivity was different when measured during or after cathodic charging. The diffusivities at 25C were equal to 3 x 10-6cm2/s during charging and 3.4 x 10-7cm2/s after charging. The overall results could be described by:

during charging:     D (cm2/s) = 1.48 x 10-4 exp[-0.1(eV)/kT]

after charging:     D (cm2/s) = 3.11 x 10-4 exp[-0.175(eV)/kT]

They were explained in terms of 2 different types of H trapping; one type being reversible (during charging) and the other being irreversible (de-gassing after charging).

H.Veysseyre: Métaux: Corrosion Industrie, 1966, 495, 405-24