Rheological characterization and coagulation casting of Al2O3-Nano zirconia suspensions

The rheological behavior of electrosterically dispersed aqueous suspensions composed of submicrometer alumina and nano zirconia particles in different ratios and solids contents (from 34 to 40 vol%) has been studied during in situ coagulation casting. Glucono-delta-lactone was used as the coagulant to achieve destabilization of the ceramic suspensions by acidifying the suspension so that the pH became close to the isoelectric point for both powders. The effects of the lactone content (from 0.5 to 6.7 wt%) and the solids loading on the rheological parameters (dynamic and static measurements) during the coagulation process were studied. Dynamic measurements showed an increasing elastic modulus, G', with time and lactone content (viz. 180 and 340 kPa for 6.7 wt% lactone addition after 40 and 60 min, respectively, and 57.3 kPa for 0.5 wt% lactone after 60 min), suggesting the formation of stronger green bodies at higher additions and longer times. The conditions were optimized to yield homogeneous green samples with a uniform nanozirconia distribution and densities between 58% and 60% of the theoretical. These were subsequently sintered to yield composites with a final density up to 97%.