Synthesis of Nanocrystalline α-Al_2O_3 using a 2-step Calcination Method

摘要

Nanocrystalline α-Al_2O_3 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-Al_2O_3 powder resulted after calcinations above 1150℃, but during heat treatment α-Al_2O_3 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℃ and second calcinations were done in oxidizing atmosphere at the relatively low temperature of 1000℃. 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-Al_2O_3 particles obtained by this 2-step calcinations method had an average specific surface area of > 170m~2/g, with an average particle size between 40 and 60nm.