The effect of bulk hydrogen inventory on the chemical erosion of graphite

Methane formation due to sub-eV H0 impact on pyrolytic graphite is characterized by an initial transient effect, followed by a steady state behaviour. The nature of the transient is strongly affected by the pre-exposure history of the sample, viz, sample bakeout temperature during preparation, preheating of sample before H0 exposure and previous exposure of sample to H0 fluxes. Preheating of the sample at ≥ 2200K for several minutes results in the elimination of the transient. By contrast, the steady state CH4 production does not appear to be sensitive to previous sample history for samples initially baked at ≥ 1700K