Investigation of Hydrolytic Polycondensation in Systems Based on Tetraethoxysilane by DK-Spectrophotometry Method

摘要

The research of the hydrolytic polycondensation kinetics of tetraethoxysilane (TEOS) is required in order to understand the sol-gel synthesis processes and identify the factors determining the direction of these processes. An extensive analysis of these problems permits us to predict appropriate ways for the synthesis of new substances with the predetermined properties. Studying the kinetics of the polycondensation of TEOS above the gel point will allow solving problems of the gels' strength and the gels' degree of structuring and thus optimizing the conditions of the further processing materials for the production of the final synthesis products. In this paper the results of the research on the structuring kinetics of the silica in the modeled aqueous-alcoholic solutions of TEOS, including boron-containing solutions, before and after the gel point at various molar ratios of H2O : SiO2 and pH values of 2.0 and 6.0 by the differential kinetic spectrophotometry are presented. The kinetic scheme developed by the authors and the mathematical tool allow determining the degree of the direction of the process of silica polycondensation. The data obtained on the model systems were applied to the description of the silica structuring process in the acid solutions resulting from the treatment of the single-phased sodium borosilicate glass. The obtained results will form the base for the interpretation of the experimental data on the kinetics of the silica structuring contained in the unstable phase of the two-phased alkali-borosilicate glass during the leaching process; i.e., it will allow predicting the dissolution rate, forms of existance, gelation time, strata formation time and, as a consequence, the formation of some porous structure of the resulting porous glass.