Effect of ionic strength on rheological properties of binary Al2O3/ZrO2 suspensions

The role of ionic strength in determining rheological properties of suspensions containing oppositely charged, polyacrylate-coated ceramic particles was investigated. It was found that the dispersion stability was strongly dependent on both the composition of solids and polymer concentration in the presence of electrolyte. When there was a low coverage of polymer on particle surface for binary systems with 1:1 number ratio of Al2O3 to ZrO2, the electrostatic attractive interaction between dissimilar particles prevailed because the positively charged and negatively charged colloids were equivalent. The stability of mixed suspensions was enhanced with increasing ionic strength, exactly opposite the behavior of 1:1 (v/v) Al2O3/ZrO2 suspensions, where electrostatic repulsion was more pronounced between particles because one type of colloids was in excess and its charge prevailed. Whereas when polymer concentration was high enough to obtain Newtonian behavior for 1:1 (by number) Al2O3/ZrO2 suspensions, the salt addition resulted in destabilizing effect due to screened electrosteric barrier by counter ions, consistent with the behavior of 1:1 (v/v) Al2O3/ZrO2 suspensions.