Sol-emulsion-gel synthesis of alumina nanospheroids

Alumina nanospheroids (10–50 nm) were synthesized by the solemulsion-gel method under simultaneous mechanical agitation (750–1500 rpm) and sonication (26 kHz). An aqueous alumina sol (“water phase” of high dielectric constant) was emulsified with an organic solvent (“oil phase” of low dielectric constant) for obtaining an water-in-oil (w/o) type emulsion. 1,1,1-trichloroethane (TCE) was used as the “oil phase”. The high interfacial tension between the “water phase” and the “oil phase” was reduced (i.e., stabilization of the sol droplets) by the addition of an amphiphilic non-ionic surface active agent (Span 80). Two vol% of Span 80 was used in all the experiments. The stabilized sol droplets were subjected to gel formation by increasing the basicity of the emulsion system with an organic amine (triethylamine, TEA). The crystallization of phase-pure α-Al2O3 occurred at a relatively low temperature (800°C, 60 h). Differential thermal analysis (DTA) indicated the crystallization of γ-Al2O3at 378°C as the first phase. Transmission electron microscopy (TEM) revealed that the nanospheroids were generally in chain-like agglomerates. Particle size analysis as also BET specific surface area measurements showed the calcined powders to be composed of large agglomerates with low surface area, indicative of nanosized primary particles as the building units