Effect of microsized ZrO2 on properties of reactive magnesia-bonded corundum-based castables

Reactive magnesia (RM) is a promising cement for preparing Al₂O₃-MgAl₂O₄ spinel (MAS) castables, but the pronounced volume expansion at elevated temperatures hinders the sintering and densification of castables, greatly restricting its practical application. To address this issue, this work systematically investigates the effect of microsized ZrO₂ on the phase composition, microstructural evolution, volume stability, and mechanical properties of RM-bonded corundum castables fired at temperatures ranging from 1200 °C to 1600 °C. The results indicate that the permanent linear change of the castables increases from 0.48 % to 0.65 % as the firing temperature increases from 1200 °C to 1400 °C, and further increases remarkably to 1.45 % after firing at 1600 °C. This trend demonstrates that the destructive volume expansion is not primarily caused by the formation of MAS, but rather by the substantial volume expansion of the castable constituents, coupled with the inherently sintering difficultly of MAS. With the addition of 0.5 wt% and 3 wt% ZrO₂, the volume expansion of the castables is significantly reduced to 0.47 % and 0.28 %, respectively. This improvement is attributed to the small in situ volume expansion of generated fine particles in matrix and the promoting sintering effect of ZrO 2 . Furthermore, the incorporation of ZrO₂ enhances the strength of the castables because of the decreased porosity and the superb bonding structure between the aggregates and the matrix. • The significant volume expansion in reactive magnesia-bonded castables primarily occurs above 1400 °C. • ZrO₂ favors the generation of ultra-fine MgAl₂O₄ spinel grains and the decrease of Al 2 O 3 particle size in castable matrix. • ZrO₂ greatly enhances the volume stability and accelerates the sintering and densification of castables. • Additional ZrO₂ improves the mechanical strength and thermal shock resistance of castables.