Oxidation mechanism of MgO-C in air at various temperatures

Oxidation of MgO-C refractories containing 20 wt-% graphite was conducted by measuring the weight loss at regular intervals at various temperatures fi om 800 to 1600 degrees C in ail. The rate of decarburisation increased with rise in temperature from 800 to 1400 degrees C and then remained more ol less constant from 1400 to 1600 degrees C. The oxidation kinetics were analysed in detail and reaction rate models derived for the temperature range 800-1400 degrees C. The reaction rate was found to be controlled by diffusion of oxygen through the decarburised layer. At higher temperatures (>1400 degrees C), oxidation of graphite also takes place indirectly by the reaction MgO(s)+C(s)-->Mg(g)+CO(g). The magnesium vapour thus produced is reoxidised at the outer surface and redeposited as MgO. This leads to a reduction in porosity in the decarburised outer shell and, consequently, a reduction in the rate of oxidation. (C) 2000 IoM Communications Ltd.