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Title:The precipitation of uniform silica particles through the controlled hydrolysis of silicon alkoxides
Author(s):Bogush, Gregory Harry
Doctoral Committee Chair(s):Zukoski, Charles F.
Department / Program:Chemical and Biomolecular Engineering
Discipline:Chemical Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Engineering, Chemical
Abstract:The formation of uniform silica particles by the alkoxide route has been investigated. Rates of chemical reactions involved in the precipitation are reported and linked to particle growth rates. Seeded growth experiments indicate that reactions between soluble species occur at rates that are independent of the size and number density of the seed particles. Estimates of hydrolyzed alkoxide concentrations based on solution conductivity suggest that the soluble silica concentration is above that required for nucleation until late in the reaction. These results are consistent with a particle growth mechanism whereby reactions occurring in solution proceed independently of the presence of particles, resulting in the formation of silica nuclei, which aggregate to form larger particles. This hypothesis has been further checked by carrying out precipitations at different electrolyte concentrations. While rates of hydrolysis and condensation are not substantially affected by NaCl concentrations up to 10$\sp{\rm -2}$ M, final particle size increases drastically.
An aggregative growth model has been developed and tested with rate and particle size distribution data gathered under various reaction conditions. Smoluchowski population balance equations with a source term were solved for conditions applicable to the precipitations studied. Size dependant aggregation rate constants were determined from estimates of particle properties. By assuming that particles grow solely by aggregation, the model provides good estimates of final particle size distribution parameters from measured reaction rates.
Issue Date:1990
Rights Information:Copyright 1990 Bogush, Gregory Harry
Date Available in IDEALS:2011-05-07
Identifier in Online Catalog:AAI9114178
OCLC Identifier:(UMI)AAI9114178

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