Role of dispersion conditions on grindability of yttria stabilized zirconia (YSZ) powders

A precursor for zirconia - 8 mole% yttria (YSZ-ZrO₂-8 m% Y₂O₃) powder was prepared by coprecipitation and the calcination temperature was fixed as 900°C from TG-DTA and XRD studies. The calcined powder could be dry ground only to a mean particle size (D₅₀) of 6 Μm containing substantial amount of coarse agglomerates in the size range 10–100 Μm. The dispersion conditions for its wet grinding were evaluated through zeta-potential and viscosity studies. The zeta-potential variation with pH of the aqueous suspensions of the powder exhibited maximum numerical values at 3 and 11 pH, exhibiting the ideal pHs for dispersion stability through electrostatic columbic repulsion mechanism. Slurries of dry ground powders with solid concentration in the range 15–30 vol.% exhibited pseudo-plastic flow characteristics, indicating presence of flocculates. With progress of grinding, the increase in viscosity of the slurries became less significant with decreasing solid concentration. Even though the particle size of the ground slurries decreased with decreasing solid content, there was little change in it for slurries with solid content < 20 vol.%. Grinding conditions for formation of sinter-active powders of YSZ with sub-micron size (D ₅₀ ∼ 0.7 Μm free of agglomerates of size > 5 Μm) were established. Compacts from this powder could be sintered at 1400°C to translucent bodies with 99% theoretical density.