Materials World Network: Ceramic Composites from Natural and Synthetic Scaffolds

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Nature has provided some sophisticated examples of complex, but effective materials design for mechanical strength, toughness, thermal insulation and fluid conduction. These designs can be replicated to produce ceramic materials using wood as a template. "Biomorphic" SiC ceramics can be formed through the controlled pyrolysis of wood to provide a carbon scaffold for infiltration by a silicon-containing liquid or gas. The silicon reacts with the carbon to form SiC with a complex cellular microstructure reminiscent of the wood. The porous SiC structure, with its open channels, provides a useful scaffold for further infiltration by metals resulting in a new class of composite materials for enhanced mechanical robustness, electrical or thermal conductivity. It is the goal of this work to establish new directions in composite materials produced with naturally derived scaffolds. Because silicon carbide and its precursor carbon are extremely versatile materials in which properties can range from insulting to highly conductive, and from hard to lubricious, studies focus on the use of silicon carbide and carbon scaffolds for composite design. Biomorphic composite materials are compared to synthetically derived structures in their thermal, electrical and mechanical response. The objectives of this work are three-fold: (1) To identify optimal alloy systems, based on thermodynamic considerations, and develop processing methodologies for SiC/Si and C/Cu biomorphic composites, (2) To characterize the thermal, electrical and mechanical properties of biomorphic-based composite materials and contrast them with synthetically derived composites, and (3) To use microstructural-based finite element analysis to predict optimal composite microstructures and to understand the behavior of complex composite microstructures in their thermal, electrical and mechanical response. The project is done in conjunction with Universidad de Sevilla (processing and microstructural characterization) and Universidad Politcnica de Madrid (mechanical properties and modeling) in Spain and the Ioffe Physico-Technical Institute (electrical, thermal, and elastic properties) in St. Petersburg. Northwestern focuses on C/Cu materials, their mechanical and thermal properties, and modeling.The collaboration among Northwestern University, Universidad de Seville, Universidad Politcnica de Madrid, and the Ioffe Physico-Technical Institute offers significant inter-university training of students. Since porous ceramic materials play such an important role in applications from sensors to fuel cells to insulation, a joint effort among collaborators to create a course on porous materials is planned. Course materials will be developed and distributed via the web to augment dissemination. This award is co-funded with the Office of International Science and Engineering.