SURFACE-CHEMISTRY AND RHEOLOGICAL PROPERTIES OF ZIRCONIA SUSPENSIONS

The pH and nature of anions were found to have a very significant effect on the rheological properties of zirconia suspensions. The variation in rheological properties with pH and anion type correlated well with the change in surface properties of zirconia. Zirconia suspensions with maximum yield stress and viscosity occurred at and near the isoelectric point (IEP). At a pH where the magnitude of the electrophoretic mobility of the zirconia is high, a low viscosity dispersed suspension was obtained. The zirconia suspensions were dispersed with potassium hydroxide at high pH while hydrochloric acid or nitric acid was used for dispersion at low pH. Sulfuric acid however did not disperse the suspensions at low pH because of significant sulfate adsorption on the zirconia particle. Polycarboxylate additives (polyacrylate) shifted the pH of maximum yield stress of zirconia to a lower pH. The degree of pH shift increased with increasing concentration of polycarboxylate; an effect attributed to the adsorption of polycarboxylate on the zirconia particle and to the degree of adsorption which increased with increasing concentration of polycarboxylate.