Carbon-carbon composites
Background: At the University of Karlsruhe, the Deutsche Forschungsgemeinschaft (DFG) has been funding the special research project (Sonderforschungsbereich) SFB 551 called "Carbon from the gas phase: Elementary Reactions, Structures, Materials" since 1998. In a close collaboration of groups from the physics, chemistry, and materials science departments, the formation of carbon structures by chemical vapor deposition and infiltration are studied to develop carbon materials with extraordinary properties based on the knowledge of the elementary chemical and physical processes during the formation and correlations between elementary processes, structures, functions, and properties. The SFB was initiated and headed for six years by K.J. Hüttinger, who now as retired Professor still is actively consulting this research. Our group took over Hüttinger's project "D2: Chemical Vapor Infiltration of Pyrolytic Carbon and Synthesis of Carbon Fiber Reinforced Carbon" at the beginning of 2004. The scope of the project includes investigations concerning the Chemical Vapor Deposition (CVD) of and the Chemical Vapor Infiltration (CVI) with carbon as well as the manufacturing of carbon fibre reinforced carbon.
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Project: The goal of the project is a fundamental understanding of the processes based on knowledge of the molecular processes and, derived from this basis, the optimization of the overall process leading to desired physical properties such as density, texture, strength and fracture behavior of the resulting materials. The methods include experiments (synthesis and analyses), modeling (reaction mechanisms and transport phenomena) and, as a final goal, numeric simulation and mathematical optimization.
For the development of detailed models of the homogeneous and heterogeneous reactions (elementary reactions) occurring during CVI and of their interaction with transport phenomena it is important to analyze involved intermediates qualitatively as well as quantitatively. This goal exceeds the experimentally derived global models established previously and permits an optimization of the deposition process. Therefore, a new deposition reactor using an adequate analysis method (GC/MS- coupling) is set up.
In the past, the deposition of carbon was predominantly performed under steady state conditions using methane as a precursor gas. Future investigations will be increasingly performed using heavier hydrocarbons (ethane, ethene, ethine, propane, propene and benzene) as well as mixtures of these. Knowing the elementary processes occurring when using these precursors and using the results obtained in the collaborating projects investigating theoretical aspects of the deposition process and the physical and mechanical properties of the resulting carbon layers, the optimization finally will lead to an optimized time dependent variation of the composition of the gas phase, of the temperature and of the mass flow leading to an improved approximation towards desired physical properties of the product. Furthermore, we conduct the manufacturing of samples for other groups within the SFB.
Co-workers: S. Lichtenberg, K. Norinaga, G. Schoch
Collaboration: SFB 551
Funding: Deutsche Forschungsgemeinschaft
Further information:
W.G. Zhang, K.J. Hüttinger. Chemical vapor deposition of carbon from methane at various pressures, partial pressures and substrate area/reactor volume ratios. J. Mater. Sci. 36 (2001) 3503-3510