Rheological Monitoring of Gelation Kinetics of Siuca Sols

Abstract

ABSTRACTDynamic oscillatory measurements at low strains are used to monitor the gelation kinetics of particulate aqueous sols composed of alkoxide-derived silica powders. The dynamic storage modulus is sensitive to the sizes of the growing clusters below the gel point. A transition in the modulus is observed and large normal forces are measured at the gel point. These tests do not disrupt gel structure (in contrast to shear viscosity measurements) and therefore the measurement process does not alter the gelation kinetics. To facilitate gelation of sols composed of low-surface area silica particulates, silica powders doped with F ions were added to the undoped powder in various concentrations (10, 15 and 20 wt.%). These additions allowed a change in gelation time from 80 min. (for 10% of the F containing powder) to 17 min. (for 20%).