New approach for measuring gelation rate during synthesis of ZnO/SiO2 gel

The synthesis of mixed ZnO/SiO2 oxides has been carried out using sol gel technique. Gelation time of the produced oxides gel has been measured experimentally by using turbidity change with time using Turbidimeter. In addition, gelation time was estimated visually. It is found that the gelation time is decreased by increasing the concentration of ZnO and SiO2. Correlations between gelation times and concentrations of products are also discussed. Surface energy between the formed gel and solution is calculated as 12.1 mJ/m2. The gelation rate is increased and the Gibbs free energy for the formation of critical nucleus is decreased by increasing the concentration product of ZnO · SiO2. The critical radius of the nucleus is decreased from 5.75 to 5.02 Å when the concentration product is increased from 6.42% to 15.72%. On the other hand, the number of molecules in the critical nucleus is decreased from 11 to 8 when the concentration product changed under the same conditions. This approach can be used as a model to discuss the effect of any additives on the enhancing or inhibition the gelation rate for any gel.