Development and evolution of a novel (Zr1-xSnx)O2 toughened alumina-mullite slip cast refractory: Effect of SnO2

Zr1-xSnxO2 reinforced alumina-mullite refractory was manufactured by slip cast methods using SnO2 as a sintering agent. SnO2 had considerable influence in the enhanced reaction kinetics of zircon dissociation and subsequent reaction sintering of alumina and zircon. Presence of pro-eutectic transient Al2O3-SnO2 liquid and SnO2-SiO2-ZrO2 amorphous phases, enhanced densification and mullitisation through liquid phase sintering and, mitigated SnO2 volatilisation by (Zr1-xSnx)O2 solid-solution formation. Based on their morphology and aspect ratios, three types of mullite crystals, MI, MII and MIII, were evolved across the matrix microstructure. Characterization of the evolved microstructure revealed coalescence and grain growth of matrix alumina grains including the presence of an acicular tertiary MIII mullite which acts as both a reinforcement and bridging network of matrix to aggregate grains. SnO2 had the effect of lowering the monoclinic – tetragonal phase transformation temperature. Hot flexural strength values remained nearly unchanged (±2%) compared with the AZS composition without SnO2 doping.