Preparation of Al₂O₃ Microsheres by Ultrasonical Spray Pyrolysis

Abstract

Al₂O₃ microsphreres have been successfully fabricated by ultrasonic spraying of 0.5 M Al(NO₃)₃ aqueous solution, followed by instantaneous thermal decomposition and calcination at 1300^oC. The crystal phase of as-prepared microspheres was δ-Al₂O₃, but turned into α-Al₂O₃ after post-calcination at 1300^oC for 2 h. In addition, some microspheres were changed from solid to hollow structure by the post-calcination. The fraction of hollow microspheres in the resultant products was less than 30% and the mean diameter of these microspheres was 0.7 μm under these preparation conditions. However, the fraction could be increased up to 80% by the addition of a small amount of a surfactant to the precursor solution.