Extraction of Binders with Supercritical Carbon Dioxide

Plastic forming methods such as injection and extrusion-molding require the use of large amounts of organic compounds which must be removed prior to sintering. Thermal debinding remains one of the most critical steps of ceramic processing. An original method of extraction of organic additives, by a supercritical fluid, is presented. Two mechanisms occur during supercritical debinding: solubility and diffusion of solubilized molecules. Solubility of the binder is experimentally determined and a model is developed. Kinetics of binder extraction by supercritical CO sub 2 can be satisfactorily represented by a diffusion-based model. Finally, better mechanical properties (flexural strength, Weibull modulus) are obtained after a short time (3 h) of supercritical treatment ( sigma =277 MPa, m=13.7) than after 18 h of thermal pyrolysis ( sigma =253 MPa, m=12.4). The major factors causing defects in the pyrolytic binder removal, such as binder redistribution in the liquid phase and the outward diffusion of degradation products, do not take place in the supercritical debinding method. (Example material: alumina.)