Rheological properties of Al2O3-SiC whisker composite suspensions

The rheological properties of both aqueous and non-aqueous composite suspensions were investigated together with a characterization of the colloidal stability of the separate components. The colloidally stable, concentrated aqueous SiC_w and Al₂O₃-SiC_w composite suspensions displayed strong shear thinning followed by a severe, sometimes discontinuous, shear thickening at a critical shear rate. The non-aqueous composite suspensions, containing weakly flocculated SiC_w, only showed a continuous shear thinning behaviour. The variations in the steady shear behaviour were related to the differences in the colloidal stability and possible shear induced effects on the suspension structure. It was possible to fit the volume fraction dependence of both the SiC_w and the Al₂O₃ suspensions to a modified Krieger-Dougherty model which yields values of the maximum volume fraction; _m(Al₂O₃)=0.61, _m(SiC_w)=0.28. The viscosity of the composite suspensions were successfully predicted from the Farris theory using the rheological data for the separate components.