Preparation of Fine Powder Silica from Polysilicic Acid Esters

Abstract

Silicic acid was extracted with tetrahydrofuran from an aqueous sodium metasilicate solution neutralized with hydrochloric acid. Polysilicic acid esters (PSAE) with various degrees of esterification (DE) were prepared by esterification of silicic acid with methyl, ethyl, n-propyl and n-butyl alcohols. An attempt was made to prepare fine silica powders by adding an alcohol solution of PSAE to the solvent with a low solubility of PSAE. Fine silica particles were obtained when PSAE's with DE 40-59% (Me), 30-50% (Et), 15-30% (n-Pr) and 20-30% (n-Bu) were added to water, chloroform, benzene and hexane, respectively. Silica may be formed by the condensation of PSAE when and after it was precipitated. Scanning electron microscopy showed that silica is obtained in the form of secondary particles with a size of several ten μm formed by condensation or aggregation of primary particles less than 0.1μm in diameter.