| Monodispersely-sized micron-scale spherical colloids of metal oxides are important in many applications, including controlled fabrication of high quality ceramic materials, particulate coatings, chromatography, and catalysis. In sol-gel particle production, a metal alkoxide or salt is commonly hydrolyzed in water or in a water/alcohol mixture to produce monodisperse particles. It is often necessary to use a catalyst to force precipitation. Even though metal oxide particles are widely used in industry, the mechanism for particle formation and growth is yet to be understood.; In this thesis, we investigate the nucleation and growth mechanisms in different metal oxide systems. A good model system to study this is the "Stober process" where tetraethoxysilane (TEOS) is hydrolyzed in water/ethanol mixture with a base (commonly ammonia) catalyst to produce monodisperse silica spheres. In the Stober process, one can control the final particle size distribution by controlling reactor parameters such as water and ammonia concentrations and temperature. We use {dollar}sp{lcub}29{rcub}{dollar}Si nuclear magnetic resonance spectroscopy, conductimetry, scanning electron microscopy, and quasi-elastic light scattering measurement to verify the nucleation and aggregation mechanisms.; Our results suggest that precipitation of doubly-hydrolyzed monomer is responsible for nucleation. Our data from experiments and from simulations are consistent with an aggregation model in which small primary particles mature mainly by aggregation in the Stober process.; We also consider zirconia colloid synthesis where the zirconium oxy-chloride is hydrolyzed in aqueous solution upon heating under reflux. Using cryo-transmission electron microscopy and quasi-elastic light scattering techniques, we show that in zirconia colloid synthesis, both aggregation and recrystallization play an important role in particle maturation. |
