A sol to gel transition reaction of three metal alkoxides with water in the preparation of gel in the K20-AleO 3-SiO 2 system was investigated using in situ viscosity measurements and the Raman scattering technique. The viscosity measurements reveal that the viscosity of the solution and the dependence of the reduced viscosity on polymer concentrations change abruptly near the gelation point. The Raman scattering results suggested that the hydrolysis of the TMOS was the rate-limiting step of the overall reaction. It was also found that a basic solution with excess amounts of water was needed to synthesize a transparent crack-free gel.

The structural evolution during a sol to gel transition reaction in the K20-AI203-SiO2 system was investigated by using in situ small angle X-ray scattering (SAXS) technique. The results are interpreted as evidence of the presence of at least two different gel phases. The analysis shows that the primary phase is composed of small particles with characteristic size of ,-,3.0 nm, and considerable size and shape variation. The primary phase is identified as a random phase in the Debye sense. The primary particles aggregate into larger formations with spherical symmetry. The size of larger aggregates (second phase) increases continuously in the course of gelation and levels off after reaching ~ 15.0 nm. The volume fraction of the second phase keeps increasing until the end of the measurement which is far after the gelation (3-fold of the gelation time)~