Synthesis of High Purity Silica Glass from Metal Alkoxide

Abstract

ABSTRACTHigh purity silica was synthesized by hydrolytic decomposition of tetramethylorthosilicate (TMOS), followed by polycondensation, supercritical drying and sintering. The key factors which govern the hydrolysis and polycondensation were systematically studied. Gas chromatography/mass spectrometry was used to monitor the hydrolysis rate. The hydrolysis of TMOS is the only reaction at ambient temperature in an acidic environment. The rate of polycondensation was also controlled by temperature as well as pH. The structural transformation from alkoxide to gel network and to glass was illustrated by FTIR. The structure of the TMOS derived supercritically dried gel sintered at 1000°C is identical to that of silica. The shrinkage kinetics and microstructural development of the gel heated at different temperatures was examined by dilatometry, B.E.T., TGA, and STEM. This combination of techniques showed that structural relaxation is not an important factor in the densification of these gels. Below 1000°C most shrinkage is due to condensation and water evolution. Above 1000°C, viscous sintering is the primary mechanism for shrinkage.