Silica from hydrolysis and condensation of sodium metasilicate in bicontinuous microemulsions

Abstract

Colloidal silica particles ranging from about 10 to 20 nm in diameter were synthesized by the controlled hydrolysis and polymerization of sodium metasilicate (Na2SiO3) in bicontinuous microemulsions at room temperature. The bicontinuous microemulsion system consisted of mixed non-ionic surfactants of NP-5/NP-9, petroleum ether (b.p. 60-80 °C) and an aqueous solution of sodium metasilicate. The system could tolerate as high as 0.2 M sodium metasilicate solution at various pH (4-11). The specific surface area of the silica powders with higher sodium residues of about 2 to 7 wt.% were very low (< 100 m2 g-1) when they were prepared at higher pH (9-11). However, this increased to about 500 m2 g-1 for those samples with less than 0.5 wt.% sodium residue as they were prepared at pH 4. On the contrary, the treatment of some calcined silica powders with hexadecyltrimethylammonium hydroxide also increased their specific surface areas rather significantly.