SAXS investigations of structure of formation in alcoholic ZrO2---SiO2 solutions

Small-angle X-ray scattering was used to examine in situ formation of ZrO₂---SiO₂ structures in alcoholic solution of tetraethoxysilan (TEOS) as a function of the ratio of ZrO₂ to SiO₂. For the moment of the first measurement (15 min after the preparation) primary particles with R_g ≈ 1.5 nm exist in all investigated mixed gels. These particles aggregated to secondary clusters. The resulting clusters can be described by means of fractal theory, where the determining mechanism of formation is cluster-cluster aggregation (diffusion or chemical limited). The time of gelation is a function of the ZrO₂ concentration. The higher the ZrO₂ concentration in the solution, the faster is the aggregation to secondary clusters. Gelation times were between 170 and 970 h.     

The Structure Formation of Zirconium Oxide Gels in Alcoholic Solution

Zirconium oxide gels were prepared by controlled hydrolysis and condensation of zirconium-n-propoxide in alcoholic solution. After completion of the gelation the aging and drying of the alcogel was observed in situ by Small and Wide Angle X-ray Scattering experiments at room temperature. The xerogels obtained have been annealed at different temperatures to crystallization. The structural changes were observed by using SAXS and WAXS. Structural models reproducing the experimental WAXS data have been simulated by the reverse Monte Carlo method. A comparison between zirconium oxide xerogels obtained under different thermal treatments was made and evidence was found that thermal treatment at higher temperatures and preparation conditions affect the atomic arrangement of these amorphous gels.