KINETICS OF HYDROLYSIS AND PRECIPITATION IN AQUEOUS-ORGANIC SYSTEMS .1. ANALYSIS OF HOMOGENEOUS NUCLEATION AND AGGLOMERATION

Hydrolysis and precipitation from mixed aqueous-organic systems is a promising method for synthesizing oxide ceramic powders for use in high-performance applications. Examples include the precipitation of silica, alumina, etc., from alkoxide solutions and the precipitation of oxides from carboxylate solutions by hydrolytic stripping. In order to prepare powders with specific particle characteristics it is necessary to control all stages of precipitation: nucleation, agglomeration and growth. These processes have been analyzed by applying two different theoretical models. This paper analyzes homogeneous nucleation and agglomeration using a population balance model, assuming that there is negligible growth. The model gives good predictions of the precipitation kinetics and particle size of silica precipitated by hydrolysis of tetraethylortho silicate. The model was also fitted to kinetic data for the homogeneous precipitation of nickel ferrite by hydrolytic stripping of iron-nickel carboxylate solutions at 170 degrees C, allowing key parameters appearing in the rate equations to be identified.