The behavior of polysilicic acid. II. The rheology of silica suspensions

Abstract

The rheology of silica suspensions was investigated as a function of concentration, particle size, the polarity of organic solvents, and the pH and ionic strength of the aqueous phases. In addition the sedimentation volumes of quartz powder suspensions were measured in organic solvents and as a function of the pH and ionic strength of the aqueous phases. The sedimentation volumes of quartz powder suspensions were at a minimum with respect to pH at the maximum in the zeta potential-pH curve. The yield values and apparent viscosities begin to increase rapidly with pH at pH 9 in calcium hydroxide solutions and at pH 12 in sodium hydroxide solutions.

Ordinarily silica suspensions exhibit a Newtonian behavior. Einstein's equation for Newtonian systems of spherical particles in suspensions was apparently not obeyed in the case of dilute suspensions of silica sols until the deviations were accounted for by electroviscous effects and adsorbed layers of water. Non-Newtonian behaviors and large sedimentation volumes arise with nonpolar solvents and at higher pH values in aqueous media. Concentrated quartz powder suspensions exhibit a shear thickening behavior. Concentrated colloidal silica gels develop shear thinning properties.