Surface passivation of α-Al 2 O 3 powder using water vapor to achieve consistent slurry viscosity

Based on the significant viscosity variations in the aqueous α-Al 2 O 3 slurries depending on the powder pre-treatments and slurry retention, this study examined the surface chemistry of α-Al 2 O 3 to determine the factors affecting viscosity. An aqueous slurry prepared with the α-Al 2 O 3 powder exposed to air revealed a much higher viscosity than those prepared with heat treatment or exposure to moisture; the opposite trend was observed for a non-aqueous slurry. Surface analysis using Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy combined with viscosity measurements showed that the viscosity depended strongly on the amount of hydroxyl ions and carbonates adsorbed on the powder surface. Through surface passivation using water vapor at 750 °C for α-Al 2 O 3 powder, the viscosity of aqueous slurry decreased significantly with less variation, owing to the increased amount of firmly attached isolated hydroxyl ions on the α-Al 2 O 3 surface.