Sintering mechanism and properties of MgAl2O4-CaAl12O19 composites with ZnO addition

MgAl2O4-CaAl12O19 (MA-CA(6)) composites were prepared using Al2O3, MgO and CaCO3 powders as the raw materials by solid-state reaction sintering at 1200-1600 degrees C. The effects of ZnO addition on the physical and mechanical properties, microstructure, and phase composition were investigated. ZnO additive can significantly increase the amount of MA due to the formation of the (Mg1-xZnx)Al2O4 solid solution, which greatly improves the densification and the flexural strength of the composites after sintering at 1600 degrees C. Flexural strength reaches a maximum of 192.1 MPa and apparent porosity is 8.5 % when 2 wt% of ZnO is added. This is resulted by the close bonding between MA and CA(6) grains. However, further increasing the ZnO content results in a slight decrease in the strength of the composites due to the weakening of the plate-like CA(6) bridging effect and the concentration of Zn2+ at the MA grain boundary.