In order to obtain the H diffusion coefficients in material which was free from dislocation and impurity trapping, electrochemical permeation measurements were performed on high-purity Fe (99.99wt%), pure Fe (99.99wt%, high substitutional and low interstitial impurity content), pure Fe (99.94wt%) and commercially pure Fe (99.83wt%), at 278 to 318K. These specimens, in which the dislocation densities were between 6 x 1010 and 4.4 x 1011/m2, were annealed at 973 to 1223K. The diffusion coefficients were affected by the trapping effect of dislocations. Therefore, coefficients which were free of dislocation and impurity trapping were calculated from the measured diffusivity on the basis of trapping theory. In 4N-purity specimens, the diffusivities which were corrected for dislocation and impurity trapping were almost equal to the diffusivities which were corrected for dislocation trapping. This indicated that the former value, for 4N-purity specimens, was little affected by impurity atoms. After correcting for dislocation and impurity trapping, the data could be described by:

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

H.Hagi: Journal of the Japan Institute of Metals, 1993, 57[7], 742-8