Further results on the erosion of carbon materials by hydrogen plasma

Abstract

The temperature dependence of the reactivity of graphite with an active hydrogen plasma is significantly different from that found in ion beam and afterglow studies. Reactivity maxima found on pyrolytic graphite in the basal plane orientation occur above 1000 K and their position on the temperature scale depend on the sample size. In contrast, no decrease of the reactivity of samples in the prism plane orientation was found. It is postulated that the surface chemistry in the active discharge is different from that in ion beam and afterglow experiments. The effect of radiation damage on the reactivity of several types of graphite was also investigated. It was found that after irradiation with 1–2 MeV He + ions the reactivity of the topmost surface layer of a thickness of about several thousand Å is the same within a factor of 3 for all materials, while the reactivity of the undamaged materials differs by an order of magnitude.