Molecular hydrogen absorption into graphite was studied in order to obtain information on the 'true' hydrogen diffusion coefficient in graphite, oxygen effect and the mechanism of hydrogen trapping, which should be important issues on estimating hydrogen retention and recycling in plasma facing graphite and CFC. Hydrogen may permeate into a filler grain in the form of hydrogen molecules, diffuse through crystallite boundaries, and may finally be trapped as hydrogen atoms at the edge surface of a crystallite. The diffusivity could be described by:

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

when the trapping effect did not exist. A simulation with mass balance equations could reproduce the change in apparent diffusion coefficients.

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