Molecular H absorption onto graphite was studied in order to obtain information on the true H diffusion coefficient in graphite, on the O effect and on the mechanism of H trapping. The H could permeate into a filler grain in the form of H molecules, diffuse through crystallite boundaries, and finally be trapped as H atoms at the edge surface of a crystallite. The diffusion coefficient could be described by:

D (m2/s) = 3.3 x 10-10 exp[-1.3(eV)/kT]

when the trapping effect did not exist. Simulations based upon mass-balance equations could reproduce changes in the apparent diffusion coefficients.

Hydrogen Bulk Retention in Graphite and Kinetics of Diffusion. H.Atsumi: Journal of Nuclear Materials, 2002, 307-311[2], 1466-70