The Binding of Monovalent Electrolyte Ions on α-Alumina. II. The Shear Yield Stress of Concentrated Suspensions

Abstract

The shear yield stress properties of α-alumina suspensions have been investigated as a function of pH and different monovalent electrolyte types and concentrations. The results have then been compared with complementary electrokinetic studies of α-alumina under analogous suspension conditions. Over the entire pH range at an electrolyte concentration of 1.0 mol dm-3, the shear yield stress is shown to decrease in the sequence Li+ > Na+ > K+ > Cs+, showing that the strength of the interparticle network decreases in the same order. In addition, use of the shear yield stress model of Scales et al. indicates that the interparticle separation in the presence of these species decreases in the sequence Cs+ > K+ > Na+ > Li+. These findings are consistent with the water “structure making−structure breaking” model of Gierst et al. and Bérubé and de Bruyn, which predicts that an entropic attraction will exist between ions and surfaces that promote similar ordering effects in their local aqueous environments. By contrast, almost identical shear yield stress versus pH results are obtained in the presence of Br-, Cl-, I-, and NO3 - over the entire range of electrolyte concentrations investigated. The interparticle separation is similarly found to be the same in those cases. These results cannot be predicted using the water “structure making−structure breaking” model, and do not allow the mechanism of anion−surface association to be conclusively resolved.

Dynamic Features of Short-Range Interaction Force and Adhesion in Solutions

“…There are the other reports claiming that the repulsive force between silica surfaces is explained by the hydration of surfaces rather than by a gel layer (8,9). The existence of a thick structured layer is also suggested by coagulation experiments with silica dispersions (24) and rheological studies on silica and aluminum slurries (25)(26)(27).…”

Electrolyte Anion Affinity and Its Effect on Oxyanion Adsorption on Goethite

“…The PZC is assigned to the common intersection point in NaNO 3 , assuming identical ion pair formation constants for Na + and NO ion adsorption in NaNO 3 . New experimental techniques (29,41,42), like the novel acoustic electrophoreses, may in the future lead to additional information at the high electrolyte levels (shift of isoelectric point) enabling a full differentiation of individual ion pair formation constants.…”

Plastic flow of saturated alumina powder compacts: Pair potential and strain rate

“…With the exception of bodies formulated at pH 6, this figure shows that the increase in salt concentration increases the relaxed yield stress. By comparing Figure 5a to 5b, one can see that a greater fraction of the stress is relaxed for 1996; Leong et al, 1993;Scales et al, 1998;Johnson et al, . 1999 , the rheological data presented here suggests that the depth of the attractive minimum is controlled by pH and salt concentration.…”

“…In addition, the attractive network formulated by adding salt to an initially dispersed slurry is usually not as strong as the network formulated at the isoelectric point. More recently, it has been shown that the strength of the weaker network is also governed by the particular type of counterion (Colic et al, 1997;Johnson et al, 1999).…”