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 A1203 particles, has been investigated. The concentrated, colloidally stable powder suspensions displayed a shear thinning behaviour with an approach to a plateau at high shear rates. 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 order-disorder transition of the suspension structure. 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; Φm. Large differences in Φm could be correlated to the differences in shape between the whiskers and powders. The viscosity of the composite suspensions were sucessfully predicted from the Farris theory using the rheological data for the separate components.

Nyckelord

Ceramic

colloid

rheology

particle

suspension

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