The 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.