Cf. Chan et al., Influence of additives on slag resistance of Al2O3-SiO2-SiC-C refractory bond phases under reducing atmosphere, J AM CERAM, 81(12), 1998, pp. 3177-3188
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.