Novel In-situ Coagulation Casting of Ceramic Suspensions

Abstract

In this chapter, direct coagulation casting of ceramics via controlled release of high valence counter-ions and novel in-situ coagulation casting of ceramic suspensions via dispersion removal are discussed systematically. Direct coagulation casting of ceramics via high valance counter-ions (DCC–HVCI), as a new direct coagulation casting method, is proposed based on the strong coagulation ability of high valance counter-ions (HVCI) on ceramic suspension. The influence of types and addition content of dispersant, pH value, and solid loading on zeta potential and viscosity of ceramic suspensions has been systematically investigated. Several new methods for controlled release of HVCI have been proposed, such as using temperature as the leading controlling factor, chemical reaction and pH value as assisting controlling means, the increase of solubility of calcium iodate, calcium phosphate reacting with hydrochloric acid and decomposition of citric acid salt, and so on. It has been proved from both experimental and theoretical calculation results that the suspension of DCC–HVCI is coagulated at the primary minimum. This avoids the problems such as cracks formation and inner stress resulted from monovalence ions coagulation method which has been proved to coagulate at the second minimum. The results of this chapter are the basis for the deep research and applications of DCC. Based on the stabilization mechanism of ceramic suspension, we systemically investigate another new ceramic colloidal forming method, namely, dispersion removal coagulation casting (DRCC). Dispersant reaction, hydrolysis, crosslink, and separation have been used to control the dispersion removed processing. In the second part, the coagulation mechanisms of different ceramic suspension systems with different stabilization mechanisms are systematically investigated and the idea of the dispersion removal has been proposed. Different kinds of oxide and non-oxide ceramics and green bodies with excellent performance have been successfully prepared by dispersion removal method. The results are the basis for the further research and applications of ceramic colloidal forming. It provides a new idea and new method for the further study of the colloidal processing of advanced ceramics and also provides a new way for the industrialization of advanced ceramics with complex shapes.