The effect of SnO2 additive on the densification, microstructure and mechanical properties of MgAl2O4–CaAl12O19 composites

The self-toughening property of platelet calcium hexaluminate (CaAl12O19, or CA6) grains causes great interest in the in-situ CA6 in engineering ceramics. MgAl2O4–CaAl12O19 (MA-CA6) composites with SnO2 additive by solid-state reaction sintering at 1200–1600 °C were prepared. The physical and mechanical properties, microstructure, and phase composition were investigated. The results showed that the addition of SnO2 could accelerate the formation of MA and CA6 due to the appearance of the (Mg1-2xSnx)Al2O4 solid solution in the composites. The composites, with the addition of 1 wt% SnO2 and sintered at 1600 °C, presented denser microstructures, and accordingly, the flexural strength reached a maximum of 179 MPa. This was a result of the close bonding between MA and CA6 grains. However, increasing the SnO2 content further resulted in a decrease in the densification of the composites due to the bridging effect of plate-shaped CA6 and the lamellar growth of CA6. Therefore, adding the appropriate amount of SnO2 is important in improving the properties of MA-CA6 composites.