Author:

Abstract:

We have previously shown that capillary suspensions can be used as stable precursors to create porous ceramics with a high open porosity. Capillary suspensions are three-phase systems with a small amount (< 5 vol%) of an immiscible secondary phase added to a suspension. The secondary phase creates a strong particle network due to capillary forces, which changes the material strength from fluid-like or weakly elastic to strong gel-like behavior. The particle network connected through capillary bridges is much stronger than the corresponding network created only by attractive van der Waals forces; it does not collapse during debinding or sintering, and therefore can serve as precursor for sintered materials with high open porosity. We combine this approach with an extrusion process to achieve green bodies for highly porous ceramics with complex shapes. Capillary suspensions designed for this process are based on ceramic powder as solid phase and molten wax as bulk phase. We show an increased mechanical and thermal stability of the extruded green bodies by adding a secondary phase (glycerol). The capillary suspensions allow for the processing of more complex extrusion bodies with a higher accuracy during debinding in comparison to pure suspensions. We succeeded in forming the capillary suspensions through a suitable twin-screw apparatus from the raw components without any difference from premixed capillary suspensions. The effect on pore size distribution and pore size is preserved through the extrusion process and is similar to mold casting.