Optimising the dispersion on an alumina suspension using commercial polyvalent electrolyte dispersants

This paper describes the process optimisation of certain alumina ceramic aqueous suspensions by the use of three commercial and widely used dispersants. Three different commercially available dispersants - 'Darvan C' an ammonium poly(methacrylate), (R. T. Vanderbilt Company, Inc., USA), 'Aluminon' (aurintricarboxylic acid ammonium salt, Fluka Chemicals, UK) and 'Tiron' (4-5-dihydroxy-1, 3-benzenedisulfonic acid disodium salt, Fluka Chemicals, UK) have been employed as aqueous ceramic stabilising agents for a commercial alumina. It is shown that there is a critical concentration for each dispersant, which gives the lowest viscosity and other rheological parameters such as, the complex, storage and loss moduli. This critical concentration, which provides the lowest viscosity (called here the optimum concentration), was found as 1, 0.25 and 0.10 wt% for 'Darvan C', 'Aluminon' and 'Tiron', respectively, for the current alumina. The adsorption isotherm data show that, up to the optimum concentration, the dispersant molecules adsorb onto the alumina particles with a relatively high affinity. Beyond this concentration, the additive is virtually unadsorbed and then remains in the supernatant liquid and consequently interferes with the stabilising influence of the adsorbed species. Electrophoresis experiments have also been performed to measure the electrical potential of the alumina particles and to further establish a link to the origin of the concentration dependent stability of these suspensions. (C) 1998 Published by Elsevier Science Limited. All rights reserved.