Pek-Ing Au

Yield stress and microstructure of washed oxide suspensions at the isoelectric point: experimental and model fractal structure

The yield stress and microstructure of washed, relatively monodisperse spherical zirconia (ZrO2) and titania (TiO2) suspensions at the isoelectric point (pI) were characterised. The yield stress was found to be dependent upon the particle size. At a given solid concentration, the finer suspensions produced a larger yield stress due to the higher particle concentration and hence, a greater density of attractive interaction. At pI, only the van der Waals force is in play. Vitrified fractal microstructures of these suspensions at pI were captured by cryo-SEM. A power law relationship described the (maximum) yield stress–volume fraction data for both oxides which is consistent with the prediction of scaling theory. An exponent value of ∼3 was obtained for both oxides. The fractal dimension (Df) extracted from this exponent value of the scaling law for large aggregate cluster interaction in the slow flow regime was ∼2.3. The theoretical fractal structure with the same Df constructed from monodisperse spherical particles based on the off-lattice variable-Df model showed strong resemblance to the cryo-SEM imagery of the vitrified structure for both oxides.