Preparation of Ultrafine α-Al_2O_3 Powder by Thermal Decomposition of AACH at Low Temperature

Ammonium aluminum carbonate hydroxide(AACH) was synthesized by the precipitation reaction of ammonium aluminum sulfate [NH4Al(SO4)2] and ammonium hydro-carbonate(NH4HCO3). By adding both seeds of a-Al2O3 and ammonium nitrate into this precursor, the transformation temperature from intermediate phase to a-Al2O3 was lowered from 1150oC to 950oC. It was found that the particles of the obtained a-Al2O3 powder with an average diameter of 90 nm by TEM are uniform in size, sphere morphology and little aggregation. The phase transformation sequence was found to be AACH→amorphous→g→g+a→a, and no q phase was detected in intermediate products.