TABLE OF CONTENTS The requirements for mono-dispersed solid particles in the range of micrometer or sub-micrometer are becoming more and more recognized. Recording devices, for example, require magnetic an-isometric particles; high quality inorganic pigments require uniform particle size distribution. In some cases, spherical particles allow theoretical calculation for predicting a material's characteristics and properties.
There are many techniques to separate metal ions from a salt solution. Chemical co-precipitation is the most popular technique that is used in industrial applications because of its cheap raw materials, ease of handling and large-scale production. Hydrolysis is attractive because it can produce fine, spherical particles with improved chemical purity, better chemical homogeneity and controlled particle size.
Most of the homogeneous precipitation processes involve ionic solutions. Mono-dispersive particles can be prepared by carefully controlling the kinetics of the precipitation. Once the solution reaches a critical super-saturation of the particle-forming species, only one burst of nulcei occurs. A continuous diffusion of solutes onto the existing nuclei leads to the growth of the particles. Care must be taken to avoid secondary nucleation to narrow the size distribution.
The easiest way to prepare uniform colloidal metal (hydrous) oxides is based on forced hydrolysis of metal salt solutions (Matijevic, 1983). It is well known that most polyvalent cations easily hydrolyze, and that deprotonation of coordinated water molecules is greatly accelerated with increasing temperature. Because hydrolysis products are intermediates to precipitation of metal (hydrous) oxides, these complexes can...
