Colloidal processing, surface characterization, and sintering of nano ZrO₂ powders

Colloidally stable suspensions are required to fabricate dense samples with uniform microstructure by colloidal processing methods, which necessitate dispersion of ceramic powders in a liquid medium. Aqueous nano ZrO₂ suspensions were prepared using polyethylenimine (PEI) as a dispersant. PEI adsorption on nano ZrO₂ surfaces was promoted with increasing initial PEI content and suspension pH. Isoelectric point was shifted from pH 7 at 0 wt% PEI to pH 10.4 at 3 wt% PEI. Stable suspensions had mean particle sizes in the range of 100 to 150 nm and sedimentation rates less than0.4 mm/h, as compared to 2–5.5 μm and 10–50 mm/h for unstable suspensions. Samples with 98% relative density were fabricated after sintering at 1300 °C for 4 h from colloidally stable suspensions.