Net-Shape Processing of Graphite via Powder Injection Molding of Mesophase Carbon with Tailored Binder Strength

摘要

Mesophase carbon powder is an excellent precursor material for the production of fine grained graphite parts with superior mechanical properties. To provide a net-shape technique for complex as well as thick-walled carbon parts, a powder injection molding process has been developed, making use of a water-based binder system. Since water can be removed by mere drying, the critical overlap of binder removal and pyrolysis / sintering of mesocarbon is avoided. This unique two component binder system (agar + water) also allows for an easy adjustment of the porosity of the dried green body by varying the water to agar ratio and adding gel strengthening additives. Modeling the shrinkage leads to a direct dependence of gel strength and green density of the dried part. A gel with higher strength provides a better force transmission between particles while the gel shrinks and in that way leads to less microcracking and a higher densification of the particles during the drying process. Thus, the porosity can be tailored to meet the requirements of the mesophase powder employed or the wall thickness aimed at. With higher gel strength a smaller amount of agar is necessary to provide the same green body stability and densification behavior during drying. As this reduces the elusion of gaseous products during thermal treatment a faster and more efficient debinding process respectively higher wall thicknesses can be achieved.