The self-catalytic role of zirconium n-propoxide in sol–gel syntheses of ZrO2–SiO2 mixed oxides

Abstract

The self-catalytic role of zirconium n-propoxide (ZP) has been investigated with respect to the synthetic parameters of ZrO ₂ –SiO ₂ binary gels. It is found that gelation time can be shortened with a high concentration of tetraethoxysilane (TEOS) in the presence of a small amount of ZP. There are two different gelation regions depending on the amount of water added. When ZP is prehydrolyzed, the gelation time is prolonged, resulting in a more transparent gel. Based on the amount of water consumed, it is known that the hydrolysis is a relatively fast process for the ZP–TEOS sols. The mixing level of calcined binary metal oxides has been investigated by FTIR. A linear correlation between the mixing level and metal content holds up to 50 mol% of ZrO ₂ under the studied conditions. For a low Zr content system, the mixing level of the metal oxides is almost independent of water concentration, whereas for a higher Zr content system, high water concentration is beneficial to the formation of Zr–O–Si hetero-linkages. On the basis of the synthetic data, a mechanism for the ZP-catalytic reactions has been proposed. Condensation rates of hydrolyzed products are addressed and their effect on the gel homogeneity and oxide mixing level are also discussed.