Dispersion of ZrO₂ particles in aqueous suspensions by ammonium polyacrylate

Abstract

The effects of poly anionic-electrolyte (ammonium polyacrylate, PAA) as a dispersant on two kinds of ZrO₂ (monoclinic and yttria-doped tetragonal zirconia) aqueous suspensions were examined by the measurements ofζ-potential and viscosity, the sedimentation test and the determination of the wet point and flow point of the powders. Additions above 2.5 wt% PAA to zirconia gave a negative highζ-potential above −30 mV, and then −45 and −30 mV were obtained for monoclinic and tetragonal zirconia above 5 wt% PAA, respectively. A high negativeζ-potential above −30 mV was retained with 5 wt% PAA for a change in pH over a wider range (pH 6 to 10 for monoclinic ZrO₂, 7 to 9 for tetragonal ZrO₂) in comparison to that of ZrO₂ without dispersant. The increase of theζ-potential resulted in a decrease in the viscosity. The evaluation of dispersion by the sedimentation test was correlated well with the value ofζ-potential and the viscosity of the suspensions. The presence of native positive charge of monoclinic and tetragonal zirconia powders required an excess amount of PAA to attain dispersion of the suspension. There was a small difference in the least amount of PAA required to attain good dispersion between monoclinic and tetragonal ZrO₂. The difference was also indicated by changes of the flow point on PAA addition. Addition of 0.1% PAA to monoclinic ZrO₂ and 0.25 wt% to tetragonal ZrO₂ gave a maximum value of the flow point, whereas the positiveζ-potential fell to zero. Measurement of the flow point was a simple and useful technique for rapid evaluation of a required amount of dispersant for ZrO₂ suspensions.