Chapter 16. Overview of Dispersants and Ionic Strength Effects in Whiteware Suspensions

Summary

Dispersants and dissolved inorganic salts have an immense effect on the rheology of kaolinite-based whiteware suspensions. Five sodium dispersants — Na-polyacrylic acid, Na-polymethylacrylic acid, Na-silicate, Na-carbonate, and Na-hexametaphosphate — were evaluated. The amount ofdispersant addition was normalized to the specific surface area of the batch consistent with the concept of specific adsorption. The rheology of the suspensions was measured and the suspension pH was monitored (but not adjusted). To demonstrate the effect of ionic concentration on suspension rheology, six salts were used (NaCl, MgCl, CaCl₂, Na₂SO₄, MgSO₄, and CaSO₄) at three dispersant levels. The rheology results, supported by zeta-potential measurements, establish that anionic polyelectrolytes are responsible for dispersion (not Na⁺), and that the cations from salt additions are responsible for coagulation (not the anion, like sulfate).