It was pointed out that previous data on the diffusivity of H through this body-centered cubic material had been inconsistent. A statistical analysis of the data indicated that only those results which had been obtained by using electrochemical and H-gas equilibration methods involving ultra-high vacuum and Pd-coated membranes were reliable. It was concluded that, at temperatures between -40 and 80C, the most trustworthy expression for D was:

D (m2/s) = 7.23 x 10-8 exp[-5.69(kJ/mol)/RT]

At temperatures of between and 50 and 550C, the best expression was suggested to be based upon a pre-exponential factor of between 10-7 and 2.52 x 10-7m2/s and an activation energy of between 6.70 and 7.12kJ/mol. It was proposed that the differing diffusivities were the result of an increase, with increasing temperature, of the fraction of H atoms which hopped from octahedral, rather than from tetrahedral, sites. The diffusion of H in deformed Fe was analyzed by using a semi-quantitative model in which it was assumed that the retarding effect of trapping sites upon diffusion was partially compensated by pipe diffusion along dislocations.

K.Kiuchi, R.B.McLellan: Acta Metallurgica, 1983, 31[7], 961-84

Table 58

Rate of H Transport by Dislocations in Fe at a Strain Rate of 10-5/s