Electrochemical permeation experiments were performed on fully-annealed commercial-purity samples of 2 types. Type-I samples were plasma-cleaned and pre-sputtered, and type-II samples were not. The measurements were made at temperatures ranging from 25 to 80C. The diffusivity of H (table 37) could be described by:

D (cm2/s) = 7.93 x 10-4 exp[-7.340(kJ/mol)/RT]

When the diffusion activation energy was evaluated by using the time-lag model, the diffusion activation energy for type-II samples was 22.970kJ/mol. The energy barrier to desorption was lower in type-I samples than in type-II samples. The activation barrier to desorption for each of the two types of sample was higher than the activation energy for diffusion. The ratio of the drift velocities therefore increased with increasing temperature and made the time-lag method more appropriate at high temperatures.

Effects of Absorption and Desorption on Hydrogen Permeation - II. Experimental Measurements of Activation Energies. Y.P.Zheng, T.Y.Zhang: Acta Materialia, 1998, 46[14], 5035-43