By using a time-lag technique, an investigation was made of H permeation through steel plates as a function of the H pressure (0.1 to 30atm) at the entry surface, the temperature (300 to 800C), and the membrane thickness (0.0252 to 0.2475cm). The permeabilities were strongly dependent upon the H pressure, and this was attributed to a resistance to flow at the membrane surface, rather than to a concentration-dependent diffusivity of H in the steel (table 58). Overall, the data could be described by:

D (cm2/s) = 0.44 exp[-12.5(kcal/mol)/RT]

J.R.Phillips, B.F.Dodge: American Institute of Chemical Engineers Journal, 1968, 14[3], 392-7