Effect of an excess of polyelectrolyte on viscoelastic properties of suspensions of alumina and zircon mixtures

Aqueous suspensions of alumina and zircon mixtures which are of practical interest in ceramics forming process were stabilized with an ammonium salt of a polycarboxilic acid as a dispersant (an anionic polyelectrolyte). Rheological properties of highly concentrated suspensions were determined by measuring shear viscosity and dynamic tests in the linear viscoelastic region. The effects of the degree of dispersion and solid volume fraction of the suspension phi between 0.45 and 0.57 on dynamic viscoelastic properties were studied. Flow behavior of the suspensions changed from predominantly viscous to more elastic at a critical solid content phi(c), which depends on the polyelectrolyte addition. If a high amount of non-adsorbed polyelectrolyte was in solution, the suspension flocculated and exhibited a relatively low phi(c) at which viscous to elastic transition occurred. The storage modulus reached a plateau in the high frequency region and gradually reduced at very low frequencies indicating a certain breakdown in the formed structure. The G' at the plateau increased significantly with increasing phi. Contrarily, heterocoagulated suspensions due to insufficient dispersant addition showed a predominant elastic behavior with viscoelastic parameters almost independent in the frequency region studied. Moreover, both moduli sharply increased with increasing phi and achieved a magnitude of several orders higher than that of the flocculated suspension. Changes in the storage G' and the loss G' moduli due to the different additions of polyelectrolyte provided information about modifications on the suspension structure. (C) 2007 Elsevier B.V. All rights reserved.