Yield stress for particle suspensions within a clay dispersion

This article focuses on suspensions of coarse particles within a clay dispe rsion. The behavior of such suspensions is generally dictated by the colloi dal fine fraction, notably its yield stress. The dependence of this yield s tress on the solid concentration (in coarse particles) is examined. It has been experimentally shown that adding coarse particles usually induced an i ncreasingly marked enhancement of yield stress. However, in some cases, add ing a small amount of coarse particles led to a decrease in bulk yield stre ss. We propose two mechanisms responsible for variations in bulk yield stre ss. First, at low concentrations, depletion of clay particles may be suffic ient to induce an increase in the bulk yield stress. Two values for the dep letion layer thickness have been found depending on the coarse particle typ e. At large concentrations, the substantial increase in bulk yield stress h as been ascribed to the development of a coarse particle network within the dispersion. In this case, yielding results from the breakdown of indirect (lubricated) contacts between particles. (C) 2001 The Society of Rheology.