Synthesis of Nanocrystalline α-Al2O3 Using a 2-Step Calcination Method
Nanocrystalline α-Al2O3 powders have been prepared by the pyrolysis of a resin compound of aluminum with polyester by a two-step calcination process. A polymeric precursor was prepared using a complexing agent to keep the metal ions in homogeneous solution, which gives sufficient flexibility for the system to exist homogeneously throughout the reaction without undergoing precipitation. The metal-ion-polyester resin forms the precursor material on complete polymerization reaction of aluminum nitrate, citric acid and ethylene glycol. A single-phase α-Al2O3 powder resulted after calcinations above 1150°C, but during heat treatment α-Al2O3 particles grow very fast by coalescence. So 2-step calcination was used, where the first step was done in a reducing atmosphere at above 1150°C and second calcinations were done in oxidizing atmosphere at the relatively low temperature of 1000°C. The precursors and the heat-treated final powders have been characterized by X-ray diffractometry, thermogravimetry , transmission electron microscopy(TEM), and BET surface area analysis. The nanocrystalline α-Al2O3 particles obtained by this 2-step calcinations method had an average specific surface area of >170m2/g, with an average particle size between 40 and 60nm.
T. Ohji, T. Sekino and K. Niihara
M.J. Cho, S. H. Youn, J. J. Kim, K. H. Hwang, B.S. Jun, S. Y. Yoon, J. K. Lee, "Synthesis of Nanocrystalline α-Al2O3 Using a 2-Step Calcination Method", Key Engineering Materials, Vols. 317-318, pp. 199-202, 2006