Ion-Specific Strength of Attractive Particle Networks

The shear yield stress of alumina suspensions was measured by the vane tool technique, as a function of high concentration of various counterions. Slurries at pHs below the isoelectric point were coagulated with the sodium salts of IO 3 -, BrO 3 -, Cl -, NO 3 -, and ClO 4 - . Structure maker ions (IO 3 - and BrO 3 - ) produced the strongest particle networks, while structure breaker ions (ClO 4 -, NO 3 -, and Cl - ) produced weaker networks. Electrokinetic results (ζ potentials) suggest the structure makers adsorb inside the shear plane in greater quantities and are thus more efficient in collapsing the double layer. The high yield stresses in the case of IO 3 - cannot be fully explained by the concept of truncating the van der Waals attraction at a distance related to the size of the ion. When the possibility of either an additional attraction or a closer distance of approach is considered, the results can be adequately explained. Similar results were observed for zirconia.