Humic Acid as Dispersant of an Alumina Suspension and its Rheological Behaviour

The higher zeta potential for HA (-42 mV) was measured at pH 11 showing that an electrostatic repulsion might occur in the alumina/HA suspension. As a consequence of the long chain molecules of HA it was also expected a steric effect on deflocculation.

The best dispersion conditions for the alumina suspension (28 vol%) were found with 0.016 wt% HA, close to the viscosity achieved with a commercial sodium polyacrylate. The rheological characterisation showed results beneficial for the slip casting process, such as slightly thixotropy and pseudoplastic behaviour. The excellent colloidal stability at pH 11 as evidenced through rheological and sedimentation tests was attributed to the polyelectrolyte nature of the HA.