1993 Volume 57 Issue 7 Pages 742-748
In order to obtain the diffusion coefficients of hydrogen in iron free from dislocation and impurity trapping, electrochemical permeation measurements have been done using high purity iron (99.99 mass%Fe), pure iron (99.99 mass%Fe, high substitutional and low interstitial impurity contents), pure iron (99.94 mass%Fe), and commercially pure iron (99.83 mass%Fe) between 278 and 318 K. Though these specimens, in which dislocation densities are (0.6∼4.4)×1011 m−2, have been annealed at high temperatures (973∼1223 K), the diffusion coefficients measured (Da) are influenced by the trapping effect of dislocations.Therefore, the diffusion coefficients free from dislocation trapping (Ddf), and free from dislocation and impurity trapping (DH) have been calculated from Da on the basis of the trapping theory. In the iron specimens of 99.99 mass% purity, the values of DH are nearly equal to those of Ddf. This indicates that Da obtained in the 99.99 mass% purity iron specimens is little influenced by the impurity atoms. The temperature dependence of DH has been determined as follows:
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