Formation of Uniform Submicron Particles Through Wet Precipitation Technologies

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Author Last Name: 
C F Zukoski
Report Type: 
Research Area: 
Particle Formation
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Publication Month: 
United States

Executive Summary

This IFPRI project investigates the formation mechanisms of uniform, submicron inorganic particles. Due to poor understanding of the physical chemistry governing particle nucleation and growth, this project has undertaken to determine if there are underlying physical or chemical themes that give rise to uniform precipitates. Previous work has focussed on spheres produced from the hydrolysis and condensation of silicon alkoxides. Here the necessity of achieving colloidal stability among the growing particles was hypothcsized as an essential step in the formation of process, Studies on the silicon alkoxide system indicated that particle growth occurred through the agglomeration of primary particles produced at a rate independent of the presence of larger particles and that unifomlity was the result of size dependent rates of aggregation.

In this annual report we review studies on a second alkoxide system. Here the formation of titanium hydrous oxide particles are discussed. The results of these studies demonstrate that a mechanism similar to that observed for silica is operable. In addition the necessity of maintaining colIoidal stability among the large particles is emphasized. This is demonstrated through experiments showing that early in precipitation reaction a constant number of colloidalIy stable particles is formed. If the particle surface potential is less than 12mV for the ionic conditions investigated, late in the reaction agglomerates are formed and become fused. If the surface potential is greater than 12mV and the reacting solution is not sheared, uniform particles are formed. However, a critical shear rate exists where for particles with surface potentials greater than 12mV, agglomerates are formed from uniform particles of a particular size. These results are interpreted in terms of particle interactions consisting of van der Waals, electrostatic and short range repulsive interactions, Agglomeration of uniform particles is hypothcsized to be the result of the combined action of the formation of a shallow minimum in pair interaction potential for particles of a partiuar size, and the continued precipitation of reactive material.