Research of Silica Extracted from the Hydrothermal Solutions

Abstract

Silica sols and powders extracted from hydrothermal solutions have been investigated. Hydrothermal solutions contain the colloidal silica forming as a result of polycondensation of the molecules of orthosilicic acid. Via ultrafiltration membrane concentration of hydrothermal solutions, silica sols with SiO2 contents up to 940 g/dm3 (62.2 wt %) and particle radii of 29-135 nm are obtained. The silica powders with the specific surface of 50-500 m2/g, average pore diameter of 3-12 nm, and pore volume of 0.2-0.3 cm3/g are obtained via cryochemical vacuum-sublimation drying of sols with the use of liquid nitrogen. Silica sols and powders were used as additivities for rising concrete compressive strength.