Effect of ultrasonication on colloidal dispersion of Al₂O₃ and ZrO₂ powders in pH controlled suspension

Colloidal processing is well known to be an effective method to avoid the agglomeration of particles in powder processing. In this method, particles are dispersed by the electrostatic repulsion arising from their surface charge which can be controlled by the pH-value of the suspension. Since fine particles tend to agglomerate, however, additional redispersion treatment is necessary to obtain dispersed suspension of submicrometer-sized particles. In this study was used ultrasonication such as additional re-dispersion treatment for the dispersion of fine powders. Al₂O₃ and ZrO₂ used in this study were high-purity fine powders and their particle sizes were 0.2 and 0.07 μm, respectively. Three types of suspensions were prepared under different conditions of mixing with ultrasonication for various treatment periods. With increasing degree of ultrasonication, the apparent viscosity of suspension decreased, the dispersion of the particles in the suspensions was promoted and the relative densities of the compacts and the sintered specimens increased, because of a decrease in both total pore volume and the pore size. The microstructure of the sintered specimen prepared from the sufficiently ultrasonicated suspension was very fine, which resulted in high superplasticity.