Thermolysis of Plastically Formed Ceramics: Modeling and Computer Simulation

Abstract

Several polymer processing techniques, such as extrusion, injection molding, vacuum forming, blow molding and film blowing can be used to mass produce complex shape components from engineering ceramic powders with a high degree of dimensional accuracy and good process control. In these processes the ceramic powder is dispersed in one or several additive(s), usually polymeric. These additives are only useful as the vehicle of the forming process and therefore have to be removed subsequently whilst retaining the architecture of the ceramic particle assembly which is densified by the conventional process of sintering. The removal of the additives, usually referred to as the debinding stage, is carried out usually by slow heating (thermolysis) to about 400°C. This is a crucial and a difficult stage as many unforgiving strength-limiting defects could appear during thermolysis. Defects which occur during thermolysis are difficult to prevent because these can be caused by several factors. Several variables, e.g. the section thickness, the geometry of the body, process control parameters such as the heating rate, development of porosity and numerous material properties (both of the additives and the ceramic powder) affect the process and influence the creation of defects. Therefore, trial and error experiments do not help in developing general criteria for the avoidance of defects which appear during debinding and there is no alternative but to model the process. Modeling combined with computer simulation seeks the variables which affect the creation of these defects. This leads to the identification of the critical variables which can be optimized and used in the design of additives and ceramic powders more suited for plastic forming.