The binding of monovalent electrolyte ions on α-alumina.: II.: The shear yield stress of concentrated suspensions

The shear yield stress properties of a-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 alpha-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. (1) 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.(2) and Berube and de Bruyn,(3) 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.