Exploitation of interparticle forces in the processing of colloidal ceramic materials

Abstract

Wet colloidal processing techniques such as milling, spray drying, slip casting, pressure filtration and centrifugal casting may be employed to produce ceramics of improved reliability. Each of these processes requires specific rheological behaviour which is governed by the type and nature of interparticle forces in the suspensions. This paper illustrates the use of various surface chemistry controls such as pH, ionic strength and adsorbing additives to obtain the different interparticle forces. These include the electrostatic, van der Waals, steric, bridging and ‘hydrophobic’ forces. Steric, bridging and ‘hydrophobic’ forces arise only in the presence of an adsorbing additive. The type of interaction force is determined by the nature of the adsorbing additives. Small hydrophilic additives such as low Mw polyacrylic acid give rise to mainly steric interaction. High Mw polyacrylic acids cause both steric and bridging interactions. Surfactants such as sodium dodecyl sulphate produce ‘hydrophobic’ interactions. All these forces greatly affect the yield stress of the ZrO 2 suspensions. Steric interaction improves the consolidation of suspension in compression while the bridging interaction has the opposite effect.