Rheological Characteristics of Aqueous Alumina Slurry for Tape Casting

Dispersibility and fluidity of aqueous alumina slurry containing 3.75wt% polyacrylic acid (binder), 3.75wt% polyetylene glycol (plasticizer), and 1wt% polyacylic ammonium (dispersant) were studied for controlling density and microstructure of green sheet and sintered body by tape casting. At pH 1, the slurry behaved as Newtonian liquid with low viscosity and formed green sheet with 57.8% of theoretical density. The green sheet was densified to 99.2% of theoretical density by sintering at 1600°C for 1h. In the slurry at pH 1.8 to 4.8, the apparent viscosity decreased with increasing shear rate (shear thinning behavior). The slurry at the isoelectric point (pH 2.4) showed the highest viscosity and yield stress because of the formation of particle agglomerates. The green sheet with 52.5% of theoretical density resulted in non-uniform structure of 98.6% of theoretical density by sintering at 1600°C for 1h. On the other hand, the low-viscosity slurry showing Newtonian flow at pH>5.8 led to green sheet of 55.7% theoretical density and sintered body of 99.8% of theoretical density with uniform structure at 1604°C for 1h.