ULTRAFINE CERAMIC POWDER INJECTION-MOLDING - THE ROLE OF DISPERSANTS

It is shown that chemically derived ultrafine zirconia powders (mean p article size less than or equal to 100 nm) can be processed at up to 6 0 vol% in a wax-based organic vehicle by the selection of suitable dis persants and addition levels. These suspensions have been injection mo lded, and the resulting components sintered. This article describes th e effects of two dispersants on the rheological behavior of suspension s. For the more effective dispersant, a high apparent maximum packing fraction correlates with a low yield stress, the appearance of a Newto nian plateau at low shear rate and volume fraction, and a high flow be havior index. Conversely, a less effective dispersant provides a highe r yield stress, lower maximum packing fraction, and lower flow behavio r index. In identical compositions of fluid, a coarse powder displays the same effects and also, when well-stabilized, presents a dilatant t ransition which is ceramic volume fraction dependent. These behaviors are consistent with current interpretations of suspension rheology bas ed on particle interactions. (C) 1996 Society of Rheology.