Effect of in-situ generated MgAl2O4 spinel on thermal shock resistance of magnesia-zirconia refractories

This study aims to advance the application of magnesia-zirconia (MgO-ZrO2) refractories in non-ferrous metal smelting furnaces by enhancing their thermal shock resistance. To fabricate MgO-ZrO2-MgAl2O4 refractories, tabular corundum particles and activated alpha-Al2O3 powder are integrated into MgO-ZrO2 refractories. The analysis of thermal shock resistance, phase composition, and microstructure of the samples was conducted to gain insights into the toughening mechanisms. The results reveal a substantial enhancement in thermal shock resistance with the addition of 15 wt% tabular corundum (1-0.5 mm) and activated alpha-Al2O3. Compared to samples without these additives, a notable increase of over 50.0 % in the ratio of residual cold modulus of rupture is shown. The enhancement in thermal shock resistance is primarily attributed to the in-situ generated MgAl2O4 spinel. This process involves volume expansion and increased thermal expansion mismatch, which induce microcrack toughening. Additionally, larger tabular corundum particles form in-situ MgAl2O4 spinel, causing crack deflection and branching, thus extending the crack propagation pathway. Furthermore, the presence of micropores in the spinel zone absorbs the energy required for crack propagation, thereby improving toughness and thermal shock resistance. Consequently, the MgO-ZrO2-MgAl2O4 refractories containing in-situ MgAl2O4 spinel with micropores are promising candidate for chrome-free refractories used in non-ferrous metal smelting furnaces.