Effect of calcination temperature on the electrokinetic properties of colloidal zirconia

The zeta potentials of three different zirconia samples which had been calcined at 450, 650 and 850°C, in aqueous KNO₃ solutions at 25°C were measured using the technique of microelectrophoresis. The effects of pH and electrolyte concentration on the electrokinetic properties of the zirconia colloids were investigated. An Atomic Force Microscope (AFM) was used to measure the forces of interaction, as a function of the distance of separation, for a colloidal sphere of zirconia (calcined at 850°C) with a polished, flat, zirconia plate. These measurements were performed across a range of pH values at three different electrolyte concentrations. The experimental data were seen to fall between the best fits to the DLVO theory at the limits of constant surface charge and constant surface potential although, typically, they tended towards the higher constant charge limit. Potentials obtained from these best fits to the AFM data were compared with the zeta potentials derived from the electrophoresis experiments. The force-distance data obtained with the AFM at the isoelectric point were seen to be well fitted with an attractive van der Waals interaction curve having a Hamaker constant of 6 × 10^-20 J.