Coagulation Kinetics and Mechanical Behavior of Wet Alumina Green Bodies Produced via DCC

Ceramic green bodies can be produced by enzyme-catalyzed reactions from suspensions with high solids loading. There are two ways of destabilizing an electrostatically stabilized suspension: shifting the pH to the isoelectric point (IEP) or increasing the ionic strength. Both can be done via the urease-catalyzed decomposition of urea. The properties of wet green bodies produced by these two methods were compared using compressive strength measurements. Ionic-strength samples needed 24 h or more to achieve sufficient strength because the high urea concentrations required for these slurries inhibit the enzyme. Due to the long coagulation time and to the weak attractive forces formed, the particles can rearrange. This causes the wet green strength and the Young's modulus of these bodies to be considerably higher than those of the pH shift bodies. For the latter, coagulation needs only about one hour, and the interparticle attractive forces are strong. pH shift bodies are more or less insensitive to vibration, whereas ionic-strength bodies tend to flow under oscillatory stress. Copyright 1999 Academic Press.