Phase Transition Process of Different Al₂O₃ Precursors

α-Al₂O₃ is widely used in the fields of machinery, chemical industry, electronics and other fields due to its excellent properties such as high hardness, ultra-high wear resistance, and chemical resistance. At present, most of the methods for preparing α-Al₂O₃ powders use different precursors calcinated at a certain temperature. In this study, α-Al₂O₃ was synthesized by using γ-AlOOH and γ-Al₂O₃ as precursor materials and using MgO as a doped additive. The phase transition process was characterized by SEM, XRD and particle size distribution. The results show that both γ-Al₂O₃ and γ-AlOOH undergo α phase transition process of γ-Al₂O₃→ θ-Al₂O₃→α-Al₂O₃ during calcinations and pure α-Al₂O₃ phases could be obtained at 1200 °C and 1100 °C, respectively. The temperature for pure α-Al₂O₃ phase is affected by the particle size distribution of γ-Al₂O₃ formed during its calcination, and MgO doping additive can promote the α-Al₂O₃ phase transition process. The promotion effect is most obvious when the doping amount is appropriate and it would be weakened when the doping amount is too high or too low. When the MgO doping amount (mass fraction) is 0.5%, the temperature at which γ-Al₂O₃ completes the α phase transformation is 1050 °C, which is 150 °C lower than that without MgO. When γ-AlOOH is doped with 0.3% and 0.5% MgO, the temperature for complete transition to α-Al₂O₃ is 1075 °C, which is 25 °C lower than that without MgO. The promotion effect of MgO on the phase transition of different precursors is affected by the size of the primary particles of the powder.