The diffusion coefficients of hydrogen and deuterium in commercially pure iron deformed and annealed under various conditions have been measured at temperatures between 283 and 318 K by an electrochemical permeation method. The temperature dependence of the diffusion coefficients of hydrogen (DH) and deuterium (DD) is discussed on the basis of the trapping theory by Oriani. Two trapping parameters, the binding energy of hydrogen or deuterium with trapping sites and the trap site density are determined by fitting the diffusion coefficient calculated from the trapping theory to the experimental results. The ratio of the diffusion coefficient of hydrogen to that of deuterium, DH/DD, has been found to be dependent on temperature, but not on the trap site density. This indicates that the trap site density and the binding energy are, within an experimental error, the same for hydrogen and deuterium, although the activation energy of diffusion in a normal lattice is found to be mass dependent. The binding energies with trapping sites (dislocations) for both hydrogen and deuterium are determined as about 27 kJ/mol, which shows a good agreement with those reported by Gibala, Oriani and others.
trolyte. Tritium and hydrogen were introduced from one side of a specimen by cathodic polarization with a constant current density, while at the other side of the specimen the permeated tritium and hydrogen were extracted by potentiostatical ionization. Nearly all of the potentiostatic current of the extraction side stands for the ionization of hydrogen, because the concentration of tritium in the cathodic electrolyte is very small. The amount of permeated hydrogen was obtained by integrating the anodic current, and that of tritium was determined by measuring the radioactivity of the electrolyte sampled from the extraction side. The separation factor for permeation obtained under steady state conditions (the ratio of permeation rates of hydrogen to tritium divided by the ratio of the concentration of hydrogen to tritium in the charging electrolyte) is 12 at 288K. This value is independent of cathodic current density. Diffusion coefficients of tritium (DT) and hydrogen (DH) in iron were determined from the time lag of
The diffusion coefficient of hydrogen in iron with various interstitial impurity (C, N) contents has been measured at 298 K by an electrochemical permeation method. The diffusivity of hydrogen is significantly reduced by cold-working. In commercially pure iron specimens (high C, N specimens), the diffusivity of hydrogen is slightly restored by aging at room temperature after cold-working. In decarburized-denitrided specimens (low C, N specimens), however, this change by aging is not observed. Annihilation of dislocations by heat treatments causes recovery of the diffusion coefficient. That is, dislocations serve as trapping sites for hydrogen, and the formation of atmosphere of interstitial impurities (C, N) around dislocations weakens the trapping effect of dislocations. The diffusion coefficient of hydrogen has been analyzed on the basis of the trapping theory, and the trap density (i.e., the ratio of the number of the trapping sites to that of total lattice sites) has been calculated. The trap density before the formation of the C, N atmosphere around dislocations is, within experimental error, proportional to the dislocation density.
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