Temperature Induced Bridge Flocculation of Aqueous Zirconia Suspensions in the Presence of Polyacrylic Acid.

Abstract

Temperature-induced bridge flocculation of aqueous zirconia suspensions in the presence of polyacrylic acid (PAA) has been studied. The viscosity (20 vol%) of zirconia suspensions with different concentrations of PAA as a function of temperature was measured. The results showed that the viscosity of the suspension in the absence of PAA suddenly increased with increasing temperature above 35°C due to the depletion of zirconium and yttrium cations. In contrast, heating the suspension over 45°C in the presence of PAA led to a sudden increase in viscosity, which can be rationalized by considering the increase in the ionic strength of the suspension as a result of leaching of both yttrium and zirconium cations and also the extent of adsorption of the PAA on the suspension particles. To confirm the bridge flocculation or gelation of the zirconia suspensions in the presence of PAA, viscoelastic measurements in terms of complex, storage and loss moduli (G* and G' and G, respectively) as a function of temperature were studied. Preliminary tests on temperature-induced bridge flocculation of high solid suspension (40 vol%) in the presence of PAA were also carried out. It was found that with increasing the temperature up to 85°C, the height stability of the samples reached to an optimum level and no deformation was detected. To reach the optimum stability for the samples at lower temperatures, the polymer dosage must be increased. G*, G' and G of high solid suspensions (40 vol%) were measured to evaluate the gel formation. The abrupt changes of G* and G' values from < 50 kPa to about 300 kPa, where G was approximately constant at <50 kPa at ∼55°C, can be taken to indicate the formation of gel-like stable solids.