CARBON-CHEMISTRY DUE TO COMBINED H+ AND O+ IRRADIATION

An investigation of carbon chemistry due to simultaneous H+ and O+ imp act of pyrolytic graphite is presented. As an introduction, an overvie w is given of previous results related to the chemical erosion process es of graphite due to single-species impact by hydrogen and oxygen. So me limited previous synergistic results of various multispecies impact studies of graphite are also presented. In the present investigation, pyrolytic graphite (Union Carbide HPG99) was exposed to 5 keV O+ and 1 keV H+, resulting in a 10-20% reduction of CO and CO2 erosion yields (in comparison with the O+-only case) for flux ratios of phi(O+)/phi( H+)similar to 6-27%. Maximum CO and CO2 reduction was observed at simi lar to 800 K graphite temperature. In addition, water production was o bserved with a maximum of similar to 0.15 H2O/O+ at similar to 800 K. Only a small reduction (similar to 5-10%) in the methane yield (CH4/H) was seen. (C) 1997 Elsevier Science B.V.