The Al2O3 from Al-3 had two kinds of particle size, which was caused by agglomeration and growth at high calcination temperature. While, a-Al2O3 powders with various amount of additives have uniform particle size, the average particle size was less than 50 nm. At the same temperature, the amount of seeds has no significant effect on the particle size of a-Al2O3 powders. The TEM micrographs of the a-Al2O3 particles in Fig. 11 shows that the a-Al2O3 prepared from
the precursor with seeds addictive had irregular sharp. Fig. 12 shows TEM micrographs of sample Al-4 and Al-7 calcined at 1000 C. From the result of XRD, we know that the pure a-Al2O3 can be obtained from sample Al-4 and Al-7. Comparing Fig. 12(a) with Fig. 12(b), we can find that polyvinylpyrrolidone had an important effect on reducing the particle growth and aggregation