The accelerated diffusion of H was observed at room temperature, in polycrystalline samples, by using an electrochemical permeation technique. It was found that a higher H flux was measured in annealed samples with a 25 grain size, whereas faster H diffusion was observed in the early stages of permeation in samples with a grain size of 150. The large flux in small-grained material was attributed to the contribution that was made, by grain boundaries (table 156), to the total H flux. The effect of grain boundaries was limited to the near-ambient temperature range, as shown by comparing permeation data which had been obtained at 293 and 373K. It was suggested that the influence of short-circuit diffusion was minimized by trapping effects.

A.M.Brass, A.Chanfreau: Acta Materialia, 1996, 44[9], 3823-31

Table 157

Room-Temperature H Diffusivities in Ni