Preparation of Hollow Alumina Microspheres by Mechanofusion and Ultrasonic Spray Pyrolysis

摘要

Hollow alumina microspheres with various diameters were prepared by using mechano-fusion and ultrasonic spray pyrolysis followed by calcination in air. Core/shell-type hybrid particles, polymethylmethacryrate (PMMA) microspheres (diameter (d): 10 μm) coated with a layer of a-Al_2O_3 powders (d: ca. 0.2 μm) containing 5 wt% SiO_2 fine powders (d: ca. 0.011 μm), were easily prepared by utilizing the mechanofusion system. Hollow α-Al_2O_3 microspheres of 10-60 μm in diameter were obtained by calcination of the core/shell microparticles at 1600℃ for 3 h. On the other hand, hollow alumina microspheres of 0.1-5.0 μm in diameter could be prepared by ultrasonic spray pyrolysis (frequency: 1.6 MHz) of an aqueous Al(NO_3)_3 solution by adjusting the flow rate of air as a carrier gas and the concentration of Al(NC_3)_3. The hollow alumina microspheres as-obtained were metastable α-Al_2O_3, but the post-calcination at 1300℃ for 1 h in air transformed the product into δ-Al_2O_3. These two methods are promising for preparation of hollow ceramic microspheres.