Effect of Polyacrylic Acid on Flocculation and Dispersion Behavior of Fine α-Al₂O₃ Particles

Abstract

To clarify the flocculation and dispersion behavior of α-Al₂O₃ particles in aqueous solution, α-Al₂O₃ particles were added to various polyacrylic acid solutions differing in molecular weight, and added amount of polyacrylic acid, and pH. Median diameter, flow property, surface sedimentation rate, sedimentation volume, turbidity and zeta potential were measured for the α-Al₂O₃ particles in suspension. The effect of polyacrylic acid on the dispersion of α-Al₂O₃ particles and its mechanism were considered from the viewpoint of molecular length and dissolved state of the polyacrylic acid.
Physical properties such as median diameter, shear stress, surface sedimentation rate and turbidity are suitable for judgment of the flocculation and dispersion behavior of fine particles. The flocculation and dispersion vary with the molecular weight and added amount of polyacrylic acid. In the case of polyacrylic acid with molecular weight under 20,000, Al₂O₃ particles are flocculated at low concentrations of polyacrylic acid but dispersed in high concentrations. When polyacrylic acid with molecular weight of 450,000 is added to the Al₂O₃ suspensions, Al₂O₃ particles are flocculated over the whole range of polymer concentrations. The effects of pH on the dissolved state of polyacrylic acid and the flocculation/dispersion behavior of Al₂O₃ are also clarified.