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 addictive 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 trans-
formed 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 poly-
vinylpyrrolidone. 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.