Effects of applying different type SiO2 precursors on the structure of selected zirconia-silica gels

Abstract

Zirconia–silica materials are well known and studied for a long time. Application of the sol-gel method allows to expand their properties by introducing new type of components from the appropriate precursors used in the process. Simultaneously, facilitates fabrication materials, first of all because of the decrease the temperature of their synthesis. In this work, the main focus was put not on zirconia precursors (as in most articles), but on SiO2 introducing ones. Three different types of silica precursors were applied: TEOS – tetraethoxysilane, Si(OC2H5)4, DDS – dimethyldiethoxysilane, Si(OC2H5)2(CH3)2 and Aerosil™ (silica powder). As ZrO2 introducing component, zirconium (IV) propoxide, Zr(OC3H7)4 was exclusively applied. As methods of structural investigations, two complementary methods were selected: FTIR spectroscopy and X-Ray diffraction (XRD) in the standard configuration. To obtain additional data, thermal methods: thermogravimetry (TG) and differential scanning calorimetry (DSC) were applied. According to XRD studies, all the obtained samples remained amorphous after annealing up to 500 °C. At higher temperatures, t-ZrO2 and m-ZrO2 began to crystallize. The temperature of their formation depended on SiO2 precursor type and SiO2 concentration in the system. In the samples richer in ZrO2, crystallization of t-ZrO2 began only at 1000 °C but the tendency of its crystallization was much faster than in the samples richer in SiO2which was confirmed by comparison of mean crystallite sizes of t-ZrO2 in the samples synthesized with the use of different SiO2 precursors. FTIR spectra of the samples of higher silica concentration, despite the type of silica precursor, showed progressive formation of silica matrix, in which zirconium atoms were located.