Dispersion of kaolin powders in silica sols

The dispersion properties of kaolin powders in silica sols were investigated by electrokinetic, viscosity and rheological measurements. Silica sol improved the dispersion of kaolin powders by increasing the negative charges on kaolinite particles. Electrophoretic mobility and viscosity of the kaolin particles in silica sol changed significantly in comparison with dispersions in deionized water. The kaolinite particles in silica sol showed a maximum of the electrophoretic mobility and a minimum in viscosity around pH 11.5. The viscosity of the dispersion reached a minimum when the silica sol concentration was 5 mass%. The flow behavior was non-Newtonian showing shear-thinning. When the solid content exceeded 45 mass%, the dispersion showed pronounced thixotropic behavior.