The flow of H through the stainless steel was markedly affected by surface reactions. Pressure-modulation methods indicated that the diffusivity could be described by:

D (m2/s) = 1.22 x 10-6 exp[-6600/T(K)]

and that the permeability could be described by:

P (mol/s m Pa½) = 4.8 x 10-7 exp[-7990/T(K)]

The surface reaction was deduced to be of the form: H2 (gas) → 2H(solid). The reactions were fastest on in situ H ion beam-cleaned surfaces. Those surfaces which had been chemically cleaned and annealed in H, or had been ion-beam cleaned and slightly oxidized, exhibited progressively lower rates of surface reaction.

Hydrogen in 304 Steel: Diffusion, Permeation and Surface Reaction. D.M.Grant, D.L.Cummings, D.A.Blackburn: Journal of Nuclear Materials, 1987, 149, 180-91