Abstract
Oxidation of MgO–C refractories containing 20 wt-%graphite was conducted by measuring the weight loss at regular intervals at various temperatures from 800 to 1600°C in air. The rate of decarburisation increased with rise in temperature from 800 to 1400°C and then remained more or less constant from 1400 to 1600°C. The oxidation kinetics were analysed in detail and reaction rate models derived for the temperature range 800–1400°C. The reaction rate was found to be controlled by diffusion of oxygen through the decarburised layer. At higher temperatures (>1400°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.
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