Influence of additives on slag resistance of Al2O3-SiO2-SiC-C refractory bond phases under reducing atmosphere

The microstructures of Al2O3-SiO2-SiC-C refractory matrices with aluminum, silicon, Si3N4, BN, B2O3, and B4C additives are characterized before and af ter a crucible slag test, and the phases present are compared to those expe cted at thermodynamic equilibrium, The carbon content dominates the resista nce to CaO-MgO-Al2O3-SiO2 slag penetration, while the viscosity of liquid p hases present has a significant influence when the matrix carbon contents a re similar. Silicon and Si3N4 additives reduce slag penetration resistance because of indirect oxidation of carbon to form SiC. B4C, in particular, an d B2O3 also reduce slag penetration resistance because of formation of a mo re fluid boron-containing liquid, while aluminum and BN addition have no si gnificant effect. Carbon and BN hardly react with the slag, while SiC parti ally reacts with it, leading to deposition of carbon as a dense layer, Coru ndum present in the refractories also readily dissolves in the slag. Micros tructurally, slag penetration resistance is associated with the dense carbo n layer located at the slag-refractory interface.