Study on particle dispersion changes over time in aqueous Al2O3 slurries containing ammonium polyacrylate

Abstract In this study, we investigated the effects of additive amounts of polyelectrolyte and the amounts of unadsorbed polyelectrolyte on the long-term changes in the amount of polyelectrolyte adsorbed and the particle dispersion state of aqueous alumina slurries containing polyacrylic acid. Slurries were evaluated on the basis of viscosity, amount of adsorbed polymer, and elution amount of Mg and Al ions. At 80 days after the preparation of the sample slurry, the amounts of ammonium polycarboxylic acid adsorbed in the slurries had stabilized. The slurries were classified into two types: one in which particles agglomerate as the adsorption increases, and one in which dispersion occurs instead with increasing adsorption. In a slurry in which the amount of polymer electrolyte added is less than the saturated adsorption amount of the polymer electrolyte, polyvalent metal ions eluted from the powder bind the adsorption layers on the particle surface to each other, and the particles aggregate over time. In a slurry in which the amount of polymer electrolyte added is larger than the saturated adsorption amount of the polymer electrolyte, the eluted polyvalent metal ions bind to the unadsorbed polymer electrolyte; hence, the particles do not aggregate with each other and disperse with increase in the amount of polymer electrolyte adsorbed. Thus, when adding a polymer electrolyte to a slurry in which polyvalent metal ions are eluted, the amount of added polymer electrolyte should be greater than the amount of saturated polymer electrolyte adsorbed on the particles to maintain the dispersed state for a long period.