Hydrogen behavior in carbon-based materials and its neutron irradiation effect

Hydrogen retention in graphites and CFCs (carbon fiber/carbon composites) has been studied with the crystallographic data obtained by the X-ray diffraction (XRD) technique. The amounts of retained hydrogen vary substantially among the samples by a factor of up to 16. After neutron irradiation at 1.9 x 10(24) n/m(2)(similar to 0.2 dpa), the hydrogen retained becomes 20-50 times larger than that of unirradiated samples. A strong correlation is observed between the values of hydrogen retention and the lattice constant c(0). The size of crystallite also has a good correlation with the hydrogen retention. Hydrogen atoms will be trapped at dangling carbon bonds at edge surfaces of crystallite which are thermally stable even at high temperatures above 1000 degrees C. Differences among the desorbed amount of hydrogen gas from graphite materials can be also explained well by this model.