Preparation of spherical SnO₂ particles by W/O type emulsion method

Abstract

An attempt to prepare spherical particles was made using a W/O type emulsion as a reaction field. The effects of surfactant content, W/O ratio and stirring conditions for the preparation of emulsions, which determined the size of water drops in the emulsions, were investigated on the size and morphology of the obtained SnO₂ particles. The size and morphology of the obtained particles were largely influenced by a water/surfactant molar ratio (R-value) for the preparation of the emulsions. Particles having relatively high sphericity were obtained at an R-value below 1500. In order to obtain mono-sized SnO₂ particles with narrow distributions, R-value should be adjusted to the narrow range from 250 to 500. Spherical SnO₂ particles showing narrow particle size distributions were obtained at W/O ratio of 1/1 and surfactant content of 11.2 × 10⁻² mol/l or 22.4 × 10⁻² mol/l. Furthermore, the particle size and morphology of SnO₂ depended on the revolution rate of an emulsifier for emulsification. Mono-dispersed spherical particles having narrow size distributions formed at revolution rates of 3000 and 4000 rpm. At extremely low and high revolution rate of the emulsifier, particles showing high sphericity were not obtained, but agglomerates of un-spherical fine particles. The interfacial reaction time determined the internal structures of spherical particles. The reaction for short time yielded hollow spherical SnO₂ particles, and the internal structure of the particles became denser with increasing reaction time.