Rate of reactions between carbon dioxide and graphite

Solid graphite rods have been oxidized at temperatures between 1020 and 1510 °C using CO 2 containing gases. The activation energy was found to be 270 kJ/mol in the temperature range from 1020 to 1170 °C where the reaction is chemically controlled. At higher temperatures the reaction is controlled by external mass transfer of CO 2 with an activation energy of 86 kJ/mol. The shift from chemical to mass transfer control depends on the CO 2 pressure and the gas flow behaviour. Since per mol of carbon consumed one net mol of gas is produced, there is a net gas flow away from the graphite surface. This makes the transport of CO 2 to the surface more difficult, retarding the rate at high temperatures.