Capillary flow behaviour of microcrystalline wax and silicon carbide suspension

Suspensions of ceramic particles in low or high molecular weight polymers a re shaped into various three-dimensional parts using various moulding and e xtrusion technologies. Such bodies are subsequently fired-up and sintered t o remove the binder. The utilities of such three-dimensional ceramic bodies depend on the restrictions related to the shapeability of the ceramic susp ension, hence to the flow and deformation behaviour of the suspension. In t his study, factors affecting the flow and deformation behaviour of a 50% by volume of silicon carbide in a wax binder was investigated. Consistent wit h the previously observed behaviour of other highly filled materials, the c eramic suspension exhibited viscoplasticity, plug flow and wall slip. Furth ermore, flow instabilities associated with the axial migration of the low v iscosity binder under the imposed pressure gradient were observed. These re sults pinpoint to the various difficulties associated with the collection o f rheological data and emphasize the relevance of various flow mechanisms, including wall slip and mat formation and filtration based flow instabiliti es, which would also occur in processing/shaping flows of such ceramic susp ensions including extrusion and moulding. (C) 1998 Kluwer Academic Publishe rs.