Influence of surfactant addition sequence on the suspension properties and electrophoretic deposition behaviour of alumina and zirconia

A well-known polyelectrolyte salt, ammonium polymethacrylate (Darvan-C) is used to stabilise ethanol-based Al2O3 and Ce-ZrO2 suspensions with butylamine addition. The sequence in which n-butylamine and Darvan-C are added to the suspension greatly affects the properties of the wet deposit obtained by electrophoretic deposition. To investigate this effect, electrical conductivity of the suspension and the shear rate dependence of its viscosity are investigated. When n-butylamine is added first, the equilibrium in the suspension is almost immediately reached and a plastically deformable wet deposit is obtained over a large n-butylamine/Darvan-C ratio. The suspension has a shear-thinning viscosity and the deformable deposit is characterised by a high solvent content, which allows the rearrangement of particles during drying. When Darvan-C is added before the n-butylamine, the wet deposit is smooth and rigid. The suspension has a lower viscosity and a near-Newtonian behaviour is observed. A similar behaviour is observed for Al2O3 and Ce-ZrO2 suspensions. The green density of the dried deposits is not influenced by the addition sequence and higher green densities are obtained for Al2O3 when compared to Ce-ZrO2.