Characterization of silicas precipitated from solution of sodium metasilicate and hydrochloric acid in emulsion medium

Investigations were performed on silica precipitation from sodium metasilicate solution, using hydrochloric acid. Optimum composition of the emulsion and optimum parameters of precipitation were undertaken. Nonionic surfactants, polydisperse mono(4-nonylphenyl)polyoxyethylene glycol ethers, were used as emulsifiers. Basic physicochemical properties of the silicas were tested, including their zeta potential, particle shape and morphology, particle size and polydispersity. Moreover, specific surface area (BET) and pore volume were estimated. The obtained silicas demonstrated low bulk density (60 to 100 g/dm(3)) and high paraffin oil absorbing capacity (750 to 1100 cm(3)/100 g). Depending upon the techniques applied in the course of precipitation (high rate stirring, homogenization, ultrasounds), the obtained silicas manifested an ideally spherical shape of particles mainly when such surfactants as Rokafenols n-5 and n-6 were applied. When homogenizer was used, the spherical particles proved to be highly uniform in size and they practically showed no tendency to form agglomerates. Moreover, the obtained silicas demonstrated a relatively high specific surface area, ranging between 120 and 260 m(2)/g. (C) 2002 Elsevier Science B.V. All rights reserved.