High-temperature oxidation of graphite

Abstract

Graphite is used in extreme environments, such as high-temperature gas-cooled reactors and anodes for high-temperature fuel cells, because of its outstanding irradiation performance and oxidation resistance. Its oxidation resistance at high temperature depends on the porosity, ash content, oxidizer concentration, burn-off degree and degree of graphitization. The rate of oxidation was determined for different graphite grades (GLM50, GLM and SPSS) at the isothermal temperature range from 773 to 1273 K in a controlled dry oxygen environment. The degree of graphitization was quantitatively measured using selected area electron diffraction patterns and Raman spectra and was shown to affect the oxidation resistance of the graphite grade. The lowest degree of graphitization (0.67) and a high average pore radius (15.4 nm) in GLM decrease the rate of oxidation due to limited active sites for oxidation. The pore radius and the high graphitic structure reduce the average activation energy of GLM50 (41.8 kJ/mol) compared to those of GLM (48.5 kJ/mol) and SPSS (58.5 kJ/mol) in the boundary-layer-controlled regime in the temperature range 1073-1273 K.