Effects of Dispex A40 on rheology and filter pressing behaviours of concentrated alumina suspensions

Variation of plastic viscosity and extrapolated shear yield stress with the concentration of Dispex A40 for the concentrated Alcoa A16 alpha -Al2O3 su spensions at 0.27 powder volume fraction was investigated at 294 K. An opti mum level of Dispex A40 for full deflocculation is found to be at 0.18% mas s fraction of the powder, at which the rheological behaviour shows little d ifferent to that of adjusting the pH to 4 to obtain full deflocculation. It is demonstrated that the shear stress drop can roughly work as an index fo r the thixotropy in particular fixed conditions, and consequently an index for the deflocculation as the shear stress drop becomes larger when the lev el of the flocculation increases, and vice versa. It is also found that the addition of Dispex A40 can prevent the filter cakes from cracking, whereas the cakes at various pH values with polyvinyl alcohol as a sole polymer no rmally develop cracking during drying.