Study on ultrasound-assisted preparation of sphere-like high-purity alumina

Spherical alumina with a purity greater than 99.999% is calcined by the precursor obtained from the reaction of high-purity aluminum with ultrapure water, which is of great interest for grinding in semiconductor processing and other fields. In this study, tetramethylammonium hydroxide is introduced to the aluminum-water (Al-H2O) reaction, and the crystal growth of the HPA precursor is adjusted by ultrasonication. The ultrasound can break the gas barrier film at the early stage of the reaction, then increase the reaction potential energy on the aluminum surface, accelerate the reaction rate, and inhibit the preferential growth of Al(OH)3 crystals along (110), (111), (131), and (202) faces. It increases the dissociation rate of crystals in the corresponding crystal faces and promotes the formation of the Al-O bond in Al(OH)3 and Al2O3 to obtain fine HPA precursors with uniform size distribution. Then, the ultrafine and sphere-like α-Al2O3 powders with a particle size D50 of 370 nm are prepared after calcination at 1250 °C. •High-purity alumina (99.999%) is prepared from Al-H2O reaction by ultrasonication.•The alumina is sphere-like shape with an average particle size of 370 nm.•The mechanism of the Al-H2O reaction by ultrasonication has been studied.•The ultrasound inhibits the preferential growth of Al(OH)3 crystal faces.