The rheology of alumina suspensions: influence of polysaccharides

We empirically correlated the rheology of aqueous suspensions of submicron alumina powder with the concentration, structure, and molecular weight of various polysaccharides that were added to these suspensions. We focus on the question of how to increase the alumina concentration to the highest level possible and still maintain a sufficient degree of plasticity to enable shape forming by plastic molding. We showed that, without polysaccharide, 30 vol.% alumina suspensions are thixotropic. These suspensions exhibited highly fluid, Bingham-plastic-like behavior upon the addition of maltodextrins and dextrans having low molecular weight. Branching of polysaccharide additives is not beneficial for the rheology of 30 vol.% alumina suspensions and 52-vol.%-alumina-filter-cakes. We observed that maltodextrins and potato dextrin (6.6 kDa) enabled filtration of plastic masses of alumina that were easily ram pressed. These materials dried into a strong, crack-free condition that could be handled without breaking.