Synthesis of monodisperse spherical nano alumina by hydrothermal method and its mechanism study

Ultrafine alumina is widely used in advanced manufacturing industry, and its form, size and dispersion have important effects on its physicochemical properties and application characteristics. However, the superfine monodisperse spherical alumina is difficult to obtain in the actual synthesis process because the alumina precursor grain grows too fast and is easy to agglomerate. In this work, ammonium sulfate was added as the synthetic raw material to improve its dispersity. When the concentration reached 40 % of the aluminum source concentration, the isometric alumina precursor with a particle size of about 35 nm was obtained under the condition of rapid cooling. The influence of ammonium sulfate on the chemical structure of the precursor was determined by Fourier Transform Infrared spectrometer (FTIR) and X-ray photoelectron spectroscopy (XPS). The effects of reactant concentration and reaction temperature on the morphology, particle size and dispersion of the precursor as well as its mechanism were discussed in detail, and the optimal synthesis method of the nano alumina precursor was obtained. Finally, two kinds of precursors were calcined at different temperatures to obtain the equiaxed gamma-Al2O3 with a particle size of 20 nm and the monodisperse spherical alpha-Al2O3 with a particle size of 133 nm, respectively. In this study, nano alumina precursors were synthesized by a simple and reliable method, and monodisperse ultra-fine alumina with different particle size morphologies were obtained, which has great application prospects in precision polishing, special ceramic manufacturing, and 3D printing.