SOL-GEL TRANSITION IN SILICA ALKALINE-SOLUTIONS - A NMR-STUDY

We carried on the NMR study of alkaline silica solutions and of their precipitates obtained under CaCl2 action. The mean degree of connectiv ity of the ionic precursors in solution is dependent on the silica and alkali concentrations. By CaCl2 action, two kinds of precipitates are obtained, the mean degree of connectivity of which may be related to their chemical analysis and to the molar ratio Rm(s)=SiO2/K2O (or Na2O ) of the mother solution. The effect of washing the precipitates with water was studied also.