Spherical alumina precursor powders were prepared by emulsification of aluminum-sec-butoxide(ASB) followed by hydrolysis of alkoxide emulsion droplets. The emulsification and hydrolysis reaction occurred by mixing a acetonitrile-$H_2O$ solution and an octanol-ASB solution. As ASB concentration increased, the average particle size and width of the particle size distribution increased. The increase of HPC concentration decreased the average particle size and the width of the particle size distribution. The increase of $H_2O$ concentration, the increase of reaction temperature, and the use of $HNO_3$(6.6×10^{-3}M) as a catalyst decreased the average particle size of alumina precursor powders. Experimental results were explained in terms of emulsion coagulation kinetics and hydrolysis kinetics, and are in good agreement with developed model equations. And in the present study, spherical, unagglomerated alumina powders with sub-micrometer size were prepared at high ASB concentrations (0.2M and 0.3M). Prepared powder was gelatious boehmite. It transformed to δ-alumina by heat treatment at 1000℃ for 60 minutes and to α-alumina at 1150℃ for 10 minutes.
In addition, spherical yttrium-aluminate precursor powders were prepared by emulsion-evaporation method. Emulsion was prepared by applying mechanical energy in the mixture of oil phase and water phase. Dried powder was gelatious and transformed to crystalline phases by heat treatment.