In order to determine the diffusivity of H in material which was free of trapping by dislocations and impurities, electrochemical permeation measurements were performed by using various grades of Fe at temperatures of between 278 and 318K. Although these specimens, in which the dislocation densities were between 6 x 1010 and 4.4 x 1011/m2, had been annealed at temperatures of between 973 and 1223K, the measured diffusion coefficients were affected by the trapping action of dislocations. Therefore, the diffusion coefficients for no dislocation trapping and for no dislocation or impurity trapping were deduced, from the measured coefficients, on the basis of trapping theory. In 4N-purity specimens, the various measured and calculated values indicated that the diffusivity in this case was little affected by impurity atoms. The temperature dependence of H diffusivity in the absence of dislocation and impurity trapping effects was found to be described by:

D (m2/s) = 5.8 x 10-8exp[-4.5(kJ/mol)/RT].

Diffusion Coefficient of Hydrogen in Iron without Trapping by Dislocations and Impurities. H.Hagi: Materials Transactions, 1994, 35[2], 112-7