INTERFACIAL CHARACTERISTICS AND COLLOIDAL STABILITY OF CORDIERITE DISPERSION

Abstract

Natural cordierite [2MgO.2Al2O3.5SiO2] dispersion is characterized by three distinct points of the zeta potential reversal 9PZR). PZR1, which occurs at pH approximately 2, corresponds to the inherent isoelectric point (IEP) of an aqueous cordierite suspension. The anomalous increase in the zeta potential above the IEP (PZR1) leads to a second zeta potential reversal (PZR2) at a higher pH value. It is attributed to the readsorption of dissolved aluminum hydroxy species via the surface-induced hydrolysis. As the pH of the suspension further increases, the zeta potential decreases again, revealing another point of zeta potential reversal at the PZR3. Analysis of the data indicates that the surface-induced adsorption of the molecular Al(OH)2 and the subsequent formation of the hydroxylated aluminum surface sites are responsible for the PZR3. The stability ratio (W) of cordierite dispersion exhibits two local minima which are in accord with PZR2 and PZR3 in the electrophoretic mobility-pH diagram. Analysis of the packing density of the cordierite sediments derived from aqueous suspensions shows that the stability ratio should be larger than a certain critical value (W(C)) for a green body with high density.