Low temperature synthesis of ultrafine α-Al2O3 powder by a simple aqueous sol–gel process

Ultrafine α-Al2O3 was synthesized by a simple aqueous sol–gel method using a citrate polymeric precursor derived from aluminum nitrate and citric acid mixed solution. The thermal decomposition of the precursor and subsequent formation of α-Al2O3 was investigated by X-ray diffractometer (XRD), field emission transmission electron microscope (FETEM), thermogravimetry-differential scanning calorimetry (TG–DSC)–mass spectra (MS) and Fourier transform infrared spectra (FTIR). The molar ratio of citric acid to metal nitrate (C/N), which played an important role in phase transition and morphology controlling of alumina, was also investigated. A single-phase α-Al2O3 powder resulted after heat treatment at ∼1000 °C. The increasing molar ratio of C/N was found to be in favor of γ- to α-Al2O3 phase transition, whereas the precursor with C/N = 1 yielded a relatively well dispersed ultrafine α-Al2O3 powder with particle size of ∼200 nm.