Thus, lowering the phase transformation temperatures is the target for preparing the nanoscale a-Al2O3. Currently, there are many reports about lowering the phase transformation temperatures of a-Al2O3. Li et al. [19] proposed that citrate polymeric precursor derived from aluminum nitrate and citric acid mixed solution promoted the g-Al2O3 transformed to
a-Al2O3 directly, which greatly reduced the transformation of a-Al2O3. Some studies [20–22] indicated that phase transformation temperature of u-Al2O3! can be influenced by some metal cations such as Fe2+,Cr3+and Ti4+. However, the addition of inorganic ion inevitably introduced impurities, which reduced the purity of a-Al2O3, therefor limits its application in some areas. The previous studies [23–25] have indicated that the a-Al2O3 seeding can provide the
nucleation sites in the process of the phase transition to reduce the activation energy and phase transformation temperature, besides, the a-Al2O3 seeding can prevent the formation of vermicular structure during sintering.