The role of organic dispersants in aqueous alumina suspensions

Several groups of organic compounds were investigated as potential dispersants for aqueous suspensions of micrometric aluminum oxide powder. They were compounds dissociating into bulky cations and small anions (tetralkylammonium chlorides and hydroxides, Methylene Blue), into bulky anions and small cations (phenols, mono- and poly-carboxylic acids, and fluorescein sodium salt), organic acids, and bases (tetralkylammonium hydroxides), and bulky, non-dissociating, polar compounds (Malachite Green and maltodextrin). We selected these compounds in order to contribute to the knowledge of how electrostatic interactions, the size and structure of the additive, and surface sorption onto alumina influence the rheological properties of colloidal alumina suspensions. We focused on low molecular weight additives, of different shape to influence interparticle electrostatic interactions as the most essential in reducing the shear stress at a given strain rate. The size and structure effects of these low molecular weight additives may be overshadowed by interparticle electrostatic interactions. In the case of non-dissociating macromolecules (e.g., maltodextrin), electrostatic interparticle interactions are minimal, and sorption is a principal factor influencing rheology.