Structure of ZrO2SiO2 gels

xZrO(2)(1 - x)SiO2 gels have been prepared by hydrolytic polycondensation of tetraethylorthosilicate and zirconium n-propoxide in alcohol solution (x = 0.1-0.5). The formation of the gels has been investigated in situ by conventional small-angle X-ray scattering. (SAXS) experiments. Primary particles of size 1-2 nm have been found in all hydrogels at the first stage of the gelation process. With further progress of the gelation, the primary particles have been found to aggregate into secondary clusters with fractal characteristics. It has also been observed that the higher the Zr concentration in the sol the faster the rate of aggregation of the primary particles. Anomalous small-angle X-ray scattering (ASAXS) and wide-angle X-ray scattering (WAXS) experiments have also been carried out on samples of ZrO2-SiO2 xerogels that have been dried only and samples that have been further heat-treated at various temperatures. The ASAXS experiments have shown that the xerogels obtained without manipulating the aggregation rate do not exhibit microinhomogeneities even when heated up to 800 K. Reverse Monte Carlo simulations based on the experimental wide-angle diffraction data have also been carried out. In line with the findings of the ASAXS experiments, the simulations have suggested that Zr and Si atomic species in the ZrO2-SiO2 xerogels investigated are homogeneously distributed at the atomic scale. The first traces of a phase segregation into Si-and Zr-rich phases, as demonstrated by the emergence of tetragonal ZrO2, were detected only after prolonged heat treatment at 1100 K.