Effects of ternary compound additives on densification and microstructure of alumina

The effects of ternary compound additives, MnO2–TiO2–CAS (CaO–Al2O3–SiO2 glass) and MgO–Y2O3–SiO2 on the densification and microstructure of alumina have been investigated, using simplex design and regression analysis. The results show that the enhanced densifications can be achieved by co-doping due to the combined effects of compound additives. With the addition of MnO2, TiO2, and CAS fixed at 0.6 wt% of the total weight of the ceramic and in the proportion of 2:3:1, the sample sintered at 1550 °C for 1 h reaches about 97% of theoretical density. Approximately 98% of theoretical density can be obtained for the sample incorporating the MgO–Y2O3–SiO2 additives, when the addition of MgO, Y2O3, and SiO2 was fixed at 6 wt% of total weight of the ceramic and in the proportion of 1:3:2. The influence of proportions of MnO2, TiO2, and CAS as well as MgO, Y2O3, and SiO2 on the anisotropic and abnormal grain growth, and grain size are also discussed.