Sol to gel reaction in the K2O---Al2O3---SiO2 system

A sol to gel transition reaction of three metal alkoxides with water in the preparation of gel in the K2O---Al2O3---SiO2 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.