Viscosity and Yield Stress of Alumina Slurries Containing Large Concentrations of Electrolyte

Viscosity and yield stress measurements of A1₂O₃ slurries containing high concentrations of electrolyte are reported. Contrary to what is expected from DLVO theory, the particles in coagulated slurries produced in this way are held together by weaker forces than particles in slurries brought to the isoelectric point by changing the pH. In both cases an attractive, connective particle network is present. However, the network at the isoelectric point is stronger, as indicated by its much higher yield stress and by its higher viscosity at stresses above the yield point. An additional short-range repulsive force that appears at low pH and high electrolyte concentrations is believed to be responsible. This force prevents the particles from reaching the primary minimum associated with particle contact. The effects of solids loading, electrolyte concentration and type, and particle size have been investigated.