Biomorphic Graphite/Copper Composites: Processing, Structure, and Properties.

摘要

Wood-derived ceramics and composites have garnered recent attention due to tailorable thermal and mechanical properties which arise from their unique, naturally-derived microstructure. Wood, possessing a biologic, anisotropic, open-porous microstructure, may be pyrolyzed to yield a porous carbon scaffold with a structure replicating that of the original wood. The wide variety of wood species available allows for microstructure customization based upon precursor selection.;The focus of this thesis is graphite/copper composites, which combine high thermal conductivity, mechanical robustness, and tailorable thermal expansion properties, making them attractive for use in thermal management applications. Factors such as pore volume, pore distribution, and composite structure strongly affect both thermal and mechanical properties. The production of wood-derived porous graphite and graphite/copper composites was explored and the thermal conductivity of resulting materials characterized.;The principle challenge encountered was that wood, like other cellulosic materials, yields an amorphous carbon upon pyrolysis that transforms to a non-ideal turbostratic carbon upon further heat treatment. A catalytic pyrolysis process was developed to promote carbon graphitization at temperatures as low as 1000°C while retaining the wood-derived scaffold microstructure for the addition of a copper second phase.;The wettability of copper on a carbon surface is notoriously poor. Copper alloys with high carbon wettability have poor thermal conductivity relative to pure copper and may react with the graphite scaffold to form a carbide phase, potentially further degrading the thermal properties of the composite. To introduce the copper second phase, an electrodeposition process was developed to deposit copper into the very high aspect ratio porosity of the wood-derived scaffold.;Porous carbon scaffolds and resulting graphite/copper composites were evaluated using thermal and microstructural characterization techniques. Finally, the impact of porosity on thermal conductivity was studied using finite element methods. Using original sample micrographs, the complex, natural porosity of wood was modeled to determine the true thermal conductivity of the solid phase. The thermal conductivity of composite structures was also predicted based on microstructural modeling and results were compared favorably to experimentally-determined values.