Ceramics-Silikáty 48, (1) 6 - 13 (2004)

The basic assumptions of suspension rheology (existence of a unique viscosity and dependence of the effective viscosity on the solids volume fraction) are discussed from the viewpoint of rational mechanics and micromechanics. The most important effective viscosity formulae are presented in a new way, which clarifies the status of these formulae and makes a clear distinction between exponential (Mooney-type) relations and power-law (Krieger-type) relations. Based on a functional equation approach, a tentative explanation is given why the latter are more successful. The Frankel-Acrivos relation is modified to exhibit correct behavior in the dilute limit.