Tailoring Suspension Flow for the Gelcasting of Oxide and Nonoxide Ceramics

Abstract

ABSTRACTThe rheology of gelcasting slurries of concentrated (30 - 60 vol%) alumina, zirconia, silicon nitride, and sialon powders with isoelectric points varying between pH 5 and 9, was studied by measuring the viscosity and yield stress as functions of pH. Typically, the rheology is non-Newtonian. The lowest values of viscosity and yield stress that permit the highest solids loading were obtained at high and low pH values, where the powders are colloidally stable, far from the isoelectric points. This relationship applies whether or not a polymer dispersant is present. The acrylamide monomer which is used in gelcasting slurries, lowers these non-Newtonian properties permitting the preparation of more concentrated slurries. Fluid and pourable gelcasting slurries of each powder had apparent viscosities and yield stresses less than 2.0 Pa·s and 50 Pa, respectively.