Oxidation Phenomena in Carbon containing Refractories and their Protection

Abstract

This paper highlights the various mechanisms of oxidation reaction of the carbon-bearing refractories in different atmospheres with special emphasis to IMO-C and A1203-C refractory composites. Kinetics of oxidation of the graphite phase in alumina-carbon refractdries have been discussed in detail along with various models. In case of IVIgO-C refractories: besides oxidation reaction, reduction of MgO by carbon present in the composite and the effect of various atmospheres/gases thereupon have also been discussed. This paper also discusses the effects of pore-structure, service-temperature, graphite-content, flake-size and purity of graphite and binders used (tar, pitch, resin etc.) on the oxidation behaviour of alumina-carbon and magnesia-carbon refractories. The reaction kinetics at lower temperatures are controlled largely by chemical rate and partly by pore diffusion, while at higher temp-erature the reaction kineticis controlled by diffusion of oxidising gases; initially through the stationary surface gas film and then throtigh the pore-structure of the de-carbonized layer. The protective measures to be taken to reduce the oxidation of carbon-bearing refractory composites in different atmospheres have also been dealt with. The addition of silicon, magnesium, aluminium, sili-con-aluminium alloy, silicon carbide, boron carbide etc. has been found to increase the oxidation resistance and thus resulting in longer lining lives. The paper thus contributes to the understanding of the effects of vari-ous parameters on the oxidation reaction in carbon containing refractories and also the remedial measures to be taken to enhance the oxidation resistance.