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

This paper describes the process optimisation of certain alumina ceramic aq ueous suspensions by the use of three commercial and widely used dispersant s. Three different commercially available dispersants - 'Darvan C' an ammon ium 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 disper sant, which gives the lowest viscosity and other rheological parameters suc h as, the complex, storage and loss moduli. This critical concentration, wh ich 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', r espectively, for the current alumina. The adsorption isotherm data show tha t, up to the optimum concentration, the dispersant molecules adsorb onto th e alumina particles with a relatively high affinity. Beyond this concentrat ion, the additive is virtually unadsorbed and then remains in the supernata nt 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 es tablish a link to the origin of the concentration dependent stability of th ese suspensions. (C) 1998 Published by Elsevier Science Limited. All rights reserved.