Hydrogen behavior in graphite at elevated temperatures

We have examined deuterium retention in the graphite exposed to deuterium atoms (D0) at elevated temperatures by means of reemission and thermal desorption techniques. The total retention increases with exposure times showing a t1/2 dependence without any saturation behavior, which is interpreted as diffusion-limited formation and growth of a modified layer. On the other hand, desorption spectra obey second order desorption kinetics and their peak structure is hardly dependent on exposure time. The deuterium retention under D0 exposure and succeeding thermal desorption are well interpreted by deuterium diffusion in the saturated layer and recombinational release in the saturated layer, respectively, and both the second order desorption rate and diffusion coefficient of deuterium in the saturated layer are determined. (orig.)