As shown in Fig. 5, When the temperature was lower than 900 C, weak diffraction peaks of a-Al2O3 can be found, which
could attributed to the additive of a-Al2O3 seed. Diffraction peaks of g-Al2O3 could be found when the calcination temperature reached to 800 C, which was as same as Fig. 4. Indicating that the a-Al2O3 seed have no impact on phase transformation of g-Al2O3. Compared to Fig. 4, a-Al2O3 seed promoted the g-Al2O3 transformed to a-Al2O3. The thermal decomposition and phase transition of the precursor (Al-7) have been further studied by TG-DSC analysis. The TG-DSC curves are shown in Fig. 6, There are three stages of weight loss, the first stage ranges from 20 C to 130 C was caused by the evaporation of the absorbed water and residual solvent, the second stage ranges from 130 C to 230 C referred to the removal of the structural water existing in the precursor. The third stage ranges from 230 C to 510 C with a relatively sharp and intense exothermic peak around 341.7 C can be attributed to the decomposition of the glucose and polyvinylpyrrolidone. The small endothermic peak at 652.4 C was associated with the amorphous aluminum hydroxide decomposed to g-Al2O3. The small exothermic peak at 870 Ccorresponded to the transformation of g-Al2O3 to a-Al2O3. Which was consistent with the XRD results. From the results of XRD and TG-DSC, we can conclude that the multi-step process involves the following chemical transformation.