Stabilization of alumina polishing slurries using phosphonate dispersants

Stability of alumina slurry in high ionic concentrations was evaluated using the settling rate of alumina abrasives in various slurries. The zeta-potential was used to interpret the effect of electrostatic interaction. The presence of high ionic concentrations reduces the zeta-potential significantly by compressing the electric double layer. The addition of potassium phthalate does not change the zeta-potential at low concentrations (<2 wt %). However, the zeta-potential changes from positive to negative at high concentrations (>2.5 wt %) due to the adsorption of phthalate on the alumina surface. Citric acid decreases the zeta-potential and changes the sign at lower concentrations than that of potassium phthalate. Various phosphonate dispersants were evaluated in terms of the settling rate of alumina abrasives in the slurry. Their stabilization behavior is not well correlated to the surface charge on the alumina particle surface and may be related to the strength of adsorption and followed by the steric hindrance from the adsorbed dispersants.