The segregation of H and D to the (00•1) surface was studied by using nuclear reaction analysis, work function, secondary ion mass spectroscopy, and Auger electron spectroscopy. An apparent critical temperature of 194C was determined for H segregation and hydride precipitation in a sample with a bulk H content of 59ppm[at]. This was well below the solubility limit for bulk hydride precipitation. The apparent c-axis H diffusion coefficient (1.98 x 10-14m2/s at 150C) which was deduced from the segregation data was lower, than the bulk diffusion coefficient in polycrystalline material, by more than 2 orders of magnitude. The lower value of the diffusion coefficient indicated that H diffusion along grain boundaries was much faster than that within grains, or that precipitation controlled the observed kinetics. Auger data indicated that the segregated H was present as hydrides.

C.Zhang, B.J.Flinn, P.R.Norton: Journal of Nuclear Materials, 1993, 199[3], 231-6