INJECTION-MOLDING OF SUBMICROMETER ZIRCONIA - BLEND FORMULATION AND RHEOLOGY

The formulation and rheological properties of feedstocks containing a submicron-sized zirconia powder were studied. The major components of the binder phase were polystyrene and corn oil, present in a ratio of 2:3 by volume. It was shown that cold blending of the constituents followed by mixing with a twin-screw extruder produced more suitable feedstocks than those for which the blending step was performed at 220-degrees-C. The hot-blended feedstocks had higher viscosities, were inhomogeneous and exhibited binder separation under an applied shear stress. Stearic acid additions were effective at reducing the viscosities of the feedstocks but this effect decreased with increasing temperature and was not a significant factor at 200-degrees-C. Feedstocks containing 57 vol% zirconia were found to have a viscosity greater than 1000 Pa s at 200-degrees-C and exhibited a higher sensitivity to changes in temperature than feedstocks containing lower concentrations of zirconia. For the binder system being used, a feedstock containing 53 vol% zirconia appeared most suitable for injection molding in terms of maximizing the solids loading while maintaining an acceptable rheological performance.