Hydrogen bulk retention in graphite and kinetics of diffusion

Molecular hydrogen absorption into graphite has been 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 diffusion coefficient can be given as D.(m(2)/s) 3.3 x 10(-10)(-1.3 eV/kT), when the trapping effect does not exist. The simulation with mass balance equations can reproduce change of apparent diffusion coefficients. (C) 2002 Elsevier Science B.V. All rights reserved.