Synthesis and Formation Mechanism of Ultrafine Spherical Al<SUB>2</SUB>O<SUB>3</SUB> Powders by Ultrasonic Spray Pyrolysis

Abstract

Synthesis of high-purity submicrometer spherical particles of α-alumina is performed by ultrasonic spray pyrolysis. As precursors, 0.5 M water solutions of both AlCl3·6H2O and Al(NO3)3·9H2O have been used. The influence of aerosol droplet genesis on the particle size distribution of α-alumina is regarded as a main control parameter. In the case of very fine droplets (smaller than 0.3 μm), regardless of the precursor, the precipitation of dissolved compound inside the droplet occurs by the volume precipitation mechanism. Morphology of the particles corresponds to that of the realized aerosol droplets. An increased activity of produced powders enables the phase transformation of γ- to α-alumina in the temperature range 1073∼1173 K, while at 1273 K the transformation process is complete.