Stabilisation of lead zirconate titanate aqueous suspensions with lignosulphonate

The stabilisation of aqueous suspensions of lead zirconate titanate (PZT) powder with a lignosulphonate polyelectrolyte was studied as a function of pH and lignosulphonate dosage. Suspension stability (as indicated by sedimentation behaviour, zeta potential magnitude, and apparent viscosity) increased with increasing pH. At each pH examined, maximal suspension stability was achieved using an optimal amount of lignosulphonate that corresponded to monolayer adsorption onto the PZT particles. The optimal amount decreased with increasing pH as a result of the expanding conformation and increasing degree of dissociation of the lignosulphonate molecules. Although the zeta potential of PZT particles in lignosulphonate-free suspensions was reasonably large at pH 9.2, there was insufficient electrostatic repulsion for stabilisation of suspensions. The adsorption of lignosulphonate at this pH marginally increased the zeta potential magnitude but markedly increased the suspension stability, indicating that the stabilisation mechanism was a combination of electrostatic and steric stabilisation. Stable suspensions of the PZT powder suitable for ceramic wet forming processes were achieved under conditions of high pH with an optimal lignosulphonate dosage of ∼0.2-0.3 wt%.