Fabrication and synthesis of α-alumina nanopowders by thermal decomposition of ammonium aluminum carbonate hydroxide (AACH)

An alpha-Al2O3 nanopowder was prepared via the thermal decomposition of ammonium aluminum carbonate hydroxide (AACH). The AACH precursor, which had an average crystallite size of 5-8 nm, was fabricated at a reaction temperature of 8 degrees C with the pH of the aqueous ammonium hydrogen carbonate (AHC) precursor solution set to 10, which afforded the highest [NH4+][AlO(OH)(n)(SO4)(-)(3-n/2)]][HCO2-] ionic concentration. The AACH precursor was transformed to NH4Al(SO4)(2), rhombohedral (Al-2(SO4)(3)), amorphous-, theta-, and alpha-Al2O3 according to the heat-treatment temperature. A time-temperature-transformation (TTT) diagram for thermal decomposition in air was determined. The critical particle size of theta-Al2O3 in the theta -> alpha a phase transformation was similar to 30 nm. Homogeneous, spherical alpha-Al2O3 nanopowders with an average particle size of 70 nm were prepared by firing the precursor crystallites at 1150 degrees C for 3 h in air. (C) 2007 Elsevier B.V. All rights reserved.