Preparation of extrudable alumina paste by coagulation of electrosterically stabilized aqueous slurries

The present work demonstrates the conversion of a low viscous concentrated (55 vol.%) alumina slurry into a thick extrudable paste by in situ coagulation. Highly concentrated (55 vol.%) electrosterically stabilized aqueous alumina slurry prepared using polyacrylate dispersant was coagulated by in situ generation of acetic acid. Acetic anhydride was used for acid generation and the miscibility of acetic anhydride in aqueous medium was increased by polyethylene glycol. Addition of acetic anhydride >0.16 mol/l converts the slurry in to a stiff paste, within 5 min. The paste exhibits extrudable consistency. Incorporation of 1% PVA in the slurry provides additional strength to the extruded tubes against deformation and development of drying cracks. The tubes sintered to 97% TD and the sintered samples showed a fine grained microstructure.