Effect of surfactant adsorption on aggregate structure and yield strength of zirconia-wax suspensions

The suspension structure and strength of the particle network in a flocculated zirconia-wax system have been investigated through capillary extrusion at a temperature above the melting temperature of the wax. Submicrometer zirconia particles were first coated with various amounts of stearic acid for providing steric stabilization of differing degrees before being blended with the wax of a fixed solids fraction (50 vol%). When the acid coverage was ∼20% of the nominal particle surface, an apparent particle network in a form of connected “dimples” together with isolated wax ligaments was found after shearing. As the acid coverage was raised further, a collection of discrete flocs rather than the particulate network was seen after deformation. The agglomerate flocs reduced their size as the acid adsorption was increased. Yield stress of the suspension, which is a macroscopic property, exhibited a linear dependence with the surface coating. A reduction over 90% in the yield value was found as the surface adsorption increased from 20 to 100% at the working temperature employed.