Kinetic anisotropy in the oxidation of graphite

Abstract

Abstract Determinations of the rate of oxidation of graphite do not generally permit a distinction to be made between rates along specified crystallographic directions. A simple interferometric technique enables the depths of etch pits produced on graphite single crystals by oxygen and by nitric oxide to be measured. This information leads directly to R( a c ) , the ratio of oxidation rates along and perpendicular to the basal plane: this ratio is an index of the kinetic anisotropy. By combining the value of the ratio with previously determined values for the rate of oxidation along , estimates of the absolute rate of reaction in the c-direction can be made. For the temperature range studied (800° to 910°), the kinetic anisotropy does not alter significantly with temperature. The value of R( a c ) at 800° C, in oxygen, is twenty six, which means that, at the etch pits, the rate of oxidation per cm2 of basal surface is about 2×10−6 g/sec.