Radiolytic oxidation of single crystals of graphite by oxygen, carbon dioxide, and methane + carbon dioxide mixtures

Abstract

Oxidation of graphite by radiolyzed CO₂ or O₂ leads to the abstraction, by gaseous active species, of individual carbon atoms from basal planes producing vacancies. Vacancies and edges act as active centres for subsequent oxidation and expanding areas of carbon, 1 atom layer thick, are oxidized by a mechanism involving surface diffusion of oxygen-containing groups. The rate of vacancy formation is similar with O₂ or CO₂ implying that the same active species may be involved, but the rate of expansion is much higher with radiolyzed O₂, suggesting different species for this process. In the presence of 1 % CH₄, carbon dioxide is incapable of oxidizing graphite, and the graphite surface is modified in such a way that gold ceases to be mobile upon it at temperatures below 700°C.