Effect of carbon-coated Al2O3 powder on structure and properties of low-carbon MgO-C refractory composites

In this study, low-carbon MgO-C refractory composites with addition of uncoated (UA) and carbon-coated Al2O3 (CCA) powders were prepared. The effect of heat-treatment temperature on apparent porosity, cold modulus of rupture and thermal expansion was investigated. The results indicated that the CCA was present in the form of porous agglomerates of 400–800 µm in diameter in MgO-C matrix. The formation of spinel started at 1100 °C and 1250 °C in UA-MgO-C and CCA-MgO-C specimens, respectively. In the specimen CCA-MgOC, cyclic spinel was formed on the outer layer of CCA agglomerates, and the dense spinel layer hindered the diffusion of Mg(g) to the interior of the agglomerates, resulting in alumina residues at 1550 °C. The specimen CCA-MgO-C showed better mechanical properties and reduced porosity. Additionally, the average coefficient of thermal expansion of CCA-MgO-C was significantly lower than that of UA-MgO-C. Thus, CCA powder could improve the volume stability of the low-carbon MgO-C refractory composites