It was recalled that an effective diffusion coefficient for trap-controlled diffusion, like that of H in solid materials, was usually determined by considering the characteristics of trapping sites. However, it was possible that the initial conditions (H concentrations at normal and trapping sites) could also affect diffusion. In order to investigate this, a 2-dimensional analytical solution was derived for a diffusion equation with an arbitrary number of trapping terms. The model was checked by comparing it with experiments on H evolution from cylindrical specimens, for 2 different initial conditions. This comparison showed that the experimental results could be explained quite well by using the present solution. Effective diffusion coefficients were also calculated by varying the initial conditions for transient evolution from a cylindrical specimen, and it was shown that the coefficients were greatly affected by the initial conditions. This could not be explained by using the local equilibrium assumption. The effective diffusion coefficient which was determined by making the local equilibrium assumption was shown to be a sort of average of those calculated here.

Influence of Initial Conditions on Trap-Controlled Hydrogen Diffusion with Calculations of Effective Diffusion Coefficients. T.Kasuya, Y.Hashiba: Journal of Physics D, 1999, 32[20], 2674-82