Characterisation of spherical silicas obtained from sodium silicate and hydrochloric acid in emulsion medium using hexane as the organic phase

The process of silica formation in an emulsion medium with hexane as the organic phase has been studied. The precipitation reaction has been conducted with sodium silicate. The conditions of precipitation have been optimised and their effect on the physicochemical properties of the products obtained has been analysed. The products have been synthetic silicas of spherical particle shapes with a number of them revealing high activity. It has been established that by controlling the amount of non-ionic surfactants used as emulsifiers in the emulsions prepared, it is possible to obtain homogeneous silicas showing poor tendency towards agglomerate and aggregate formation. In particular, greater amounts of surf actants lead to changes in the diameter of the silica particles and increase their tendency to agglomerate formation evidenced by the particle size distributions (PSDs) or SEM and transmission electron microscope (TEM) evaluations. The silica agglomeration promotes sedimentation of their particles in water. The surface of the active silicas produced shows limited hydrophilic properties which is evidenced by the character of their wettability curves. Copyright (c) 2007 John Wiley & Sons, Ltd.