Ultrafine ceramic powder injection moulding: The role of dispersants

It is shown that chemically derived ultrafine zirconia powders (mean particle size less than or equal to 100 nm) can be processed at up to 60 vol% in a wax-based organic vehicle by the selection of suitable dispersants and addition levels. These suspensions have been injection molded, and the resulting components sintered. This article describes the effects of two dispersants on the rheological behavior of suspensions. For the more effective dispersant, a high apparent maximum packing fraction correlates with a low yield stress, the appearance of a Newtonian plateau at low shear rate and volume fraction, and a high flow behavior index. Conversely, a less effective dispersant provides a higher yield stress, lower maximum packing fraction, and lower flow behavior index. In identical compositions of fluid, a coarse powder displays the same effects and also, when well-stabilized, presents a dilatant transition which is ceramic volume fraction dependent. These behaviors are consistent with current interpretations of suspension rheology based on particle interactions. (C) 1996 Society of Rheology.