Shear thinning and shear thickening of concentrated ceramic suspensions

The steady shear properties of two important ceramic systems, Si3N4 powder, and the composite system SIC whiskers and Al2O3 particles, have been investigated. The concentrated, colloidally stable non-aqueous powder suspensions all displayed a shear thinning behaviour with an approach to a plateau at high shear rates which could be modelled by the high shear form of the Cross equation. The concentrated aqueous SiCw and composite suspensions showed a strong, sometimes discontinuous, shear thickening at some critical shear rate which was attributed to a possible hydrodynamic clustering. It was possible to fit the volume fraction dependence of the colloidally stable ceramic suspensions to a modified Krieger-Dougherty model which yields values of the maximum volume fraction Phi(m). Large differences in Phi(m) could be correlated to the differences in shape between the whiskers and powders. (C) 1998 Elsevier Science B.V.