The central role of interparticle forces in colloidal processing of ceramics

In this chapter, some literature examples will be considered to illustrate the application of such concepts to the control of interparticle interactions in ceramic suspensions. In most applications, the main reason for such a control is to avoid the formation of hard agglomerates, because these cause defects to be present in the sintered bodies, with consequent risk of cracking. Both water-based suspensions and suspensions in organic solvents will be considered in the following paragraphs. Although literature studies are available on both types of suspensions, full understanding of the basic mechanisms of colloidal stabilization is still lacking. Cases in point are the electrosteric stabilization of aqueous suspensions by polyelectrolytes and the stabilization of solvent-based suspensions by surfactants. In advanced shaping techniques like direct coagulation casting (DCC) or temperature-induced gelation (TIG), the creation of gels is a required processing step, in which case interparticle interactions are specifically driven toward the formation of three-dimensional structures by controlling either pH or temperature, respectively. One of the commonly used techniques to obtain indirect information about the degree of structuring of these complex systems is rotational rheometry, whose main features will be briefly described.