Preparation of spherical silica in emulsion systems using the co-precipitation technique

Silica powders with particles of spherical shape and a low tendency to agglomeration of primary particles have been prepared by precipitation from sodium metasilicate and hydrochloric acid via the emulsion technique. The organic phase of the emulsion system was cyclohexane while a non-ionic surfactant was applied as an emulsifier. In the course of silica precipitation three alternative ways of dispersion induction were applied: the top stirrer, homogenization and ultrasounds. The precipitation was performed at three temperatures (25 °C, 40 °C and 60 °C), using different variants of dosing schemes of the emulsion and the aqueous solutions of substrates. Homogenization of the reactive system yielded silica of spherical particles of the lowest mean particle diameter and the most uniform character. The only appropriate mode of dosing the reagents to the emulsion was the introduction of alkaline emulsion to acidic emulsion. A decreased tendency for silica particles agglomeration could be achieved by increasing the volume of the organic phase in the emulsions prepared. The optimum temperature for the precipitation reaction was 25 °C. The procedure permitted obtaining in SiO2 particles of the optimum diameter (<1 μm) and particles of spherical shape. Moreover, the silica adsorbents obtained manifested high activity. Their surface area reached values in the 340–390 m2 g−1 range.