Preparation of silica dispersion and its phase stability in the presence of salts

In the present study, the phase stability of spherical silica particle disp ersion was investigated experimentally. The silica particles were synthesiz ed by the sol-gel method and stabilized by electrostatic and steric stabili zation. For a given pH, the silica particles were coagulated at a certain c ritical salt concentration, which depended on the chemical nature of the ad ded salts. The critical coagulation concentration showed that the particle zeta-potential in the presence of electrolytes, such as NaCl, NaBr,and KCl, had no appreciable influence on the stability of silica dispersion. The ag gregate sizes measured by dynamic light scattering gave useful information on the coagulation process in the presence of the electrolytes. The critica l coagulation concentration of a salt containing sodium decreased monotonic ally as pH increased. Meanwhile, the phase stability in the presence of Kions was the worst at the pH 8.5. In addition, the zeta-potential that show ed a strong dependence on pH in the presence of Na+ ions was a very weak fu nction of pH in the presence of K+ ions.