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Rheological Behaviour of Silicic Acid Sol in Relation to Interaction with Certain Cations

Rheological behaviour of silicic acid sols with and without different cations (e.g., Pb2+, Zn2+, Al3+ and Zr4+) was studied by steady shear and oscillatory flow measurements at different ageing periods. From the steady shear flow curves, the changes in viscosity, area of hysteresis of the flow curves and the yield stress were measured with ageing time of the sols. A sharp change of the above parameters (e.g., viscosity, area of hysteresis of the flow curves and yield stress) occurred after a certain time of ageing. It indicated qualitatively the point of gelation of the sols. The gel point of the sols could be quantitatively measured from their oscillatory flow measurement. From the above results it was observed that gel point (the time of gelation) increased in the order of Pb2+<Zn2+<AI3+<Zr4+ for Pb2+-, Zn2+-, AI3+- and Zr4+- containing silicic acid sols respectively. Gelling time of pure silicic acid sol (without added cations) was in between Pb2+-, Zn2+- and AI3+-, Zr4+- containing silicic acid sols.