Slip casting of alumina ceramics

Slip casting as a colloidal shaping method is one of the most common forming techniques, used in commercial production of different advanced ceramics. Colloidal shaping methods enable to achieve high microstructural homogeneity in green and sintered parts and offer near net shaping capabilities that reduce post-sintering machining and production costs. Slip casting is the process of filling a porous mold, usually a gypsum mold, with ceramic slurry. The first step in the slip casting process is the preparation of stable concentrated aqueous suspensions of the ceramic powders. At high solid loading, relatively low slip viscosity can only be achieved in the presence of an optimum dispersion state of particles. In this paper highly concentrated (70 wt. %) aqueous suspensions of alumina (Al2O3) were prepared with different amount of dispersant DOLAPIX CE 64. Stability of highly concentrated aqueous suspensions of alumina ceramics suitable for slip casting was monitored by rheological properties measurements (flow curves and rheological parameters). Recorded flow curves were fitted to the power law, Herschel-Bulkley and Bingham models. Minimal viscosity was determined for each prepared suspension, in order to determine optimal slip casting parameters. Power law, Herschel-Bulkley model and Bingham plastic model were used in order to explain, characterize and predict the flow and pseudo-plastic behavior of highly concentrated alumina suspensions.