HYDROGEN BEHAVIOR IN CARBON-BASED MATERIALS AND ITS NEUTRON-IRRADIATION EFFECT

Hydrogen retention in graphites and CFCs (carbon fiber/carbon composit es) 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 neutro n 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 rete ntion 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 whic h are thermally stable even at high temperatures above 1000 degrees C. Differences among the desorbed amount of hydrogen gas from graphite m aterials can be also explained well by this model.