Stabilization of alumina polishing slurries using phosphonate dispersants

Stability of alumina slurry in high ionic concentrations was evaluated usin g the settling rate of alumina abrasives in various slurries. The zeta-pote ntial was used to interpret the effect of electrostatic interaction. The pr esence of high ionic concentrations reduces the zeta-potential significantl y by compressing the electric double layer. The addition of potassium phtha late does not change the zeta-potential at low concentrations (<2 wt %). Ho wever, the zeta-potential changes from positive to negative at high concent rations (>2.5 wt %) due to the adsorption of phthalate on the alumina surfa ce. Citric acid decreases the zeta-potential and changes the sign at lower concentrations than that of potassium phthalate. Various phosphonate disper sants were evaluated in terms of the settling rate of alumina abrasives in the slurry. Their stabilization behavior is not well correlated to the surf ace charge on the alumina particle surface and may be related to the streng th of adsorption and followed by the steric hindrance from the adsorbed dis persants.