SHEAR INDUCED AGGREGATION DURING THE PRECIPITATION OF TITANIUM ALKOXIDES

Studies are presented on shear induced agglomeration during the homogeneous nucleation and growth of particles formed through the hydrolysis and condensation of tetraethylortho-titanate in aqueous ethanol solutions. In the absence of shear, the reaction results in the formation of uniform spherical particles if the growing particles have surface potentials, ψ0, greater than 12 mV. For ψ0 > 12 mV in the presence of shear, particles initially grow as discrete units. However, above a critical shear rate the particles grow to a size at which they aggregate and the final precipitate is composed of agglomerates consisting of fused particles. Variations in critical shear rate with surface potential and ionic strength are explored. Shear aggregation is found to be consistent with a model of pair potentials composed of van der Waals, electrostatic, and short range repulsive interactions. © 1992.