Determining critical ceramic powder volume concentration from viscosity measurements

This paper presents a method to determine the critical powder volume concentration (CPVC) of ceramic slurry from viscosity measurements. It was found that the CPVC determined in this manner could be successfully applied as a criterion of low bound to the extrusion process. Our experience indicated that only slurry with solid contents higher than CPVC could be successfully extruded. The slurries consist of dispersed alumina and kaolin particles in deionized water with additives such as sodium salt of polyacrylic acid (PAA), carboxymethyl cellulose (CMC), stearic acid and glycerol. The viscosity data from Brookfield rheometer were satisfactorily fitted with an empirical equation modified from Brodnyan equation: η=η0exp2.5φ+0.399φ0.001p−11.481−bγ̇kφ. The CPVC was then calculated from the best-fit k value as 1/k=CPVC, which is equivalent to the maximum particle packing fraction. Reasonable correlation was also found between best-fit p and k values. Effects of formulation and shear rate on CPVC were also discussed.