Structural Improvement of High Thermal Conductivity Carbon Foam for Ballistic

Ceramic Composites Inc. has increased the elastic modulus of high thermal conductivity carbon foam heat exchanger material, making it possible to consider the material for improving sub-system thermal management. The material already provides significantpotential for weight and volume reduction, but has inherent issues in strength, friability and dustiness. The strength enhancement was accomplished by taking commercially available high thermal conductivity carbon foam material supplied by POCO ThermalMaterials, processing the open cell foam with Starfirer, a polymeric silicon carbide precursor, and pyrolyzing the structure to form an amorphous silicon carbide coating upon the ligament structure of the foam. The friability, dustiness, and erosionsusceptibility of the foam was also decreased. The use of a silicon carbide coating will allow the use of conventional epoxies and brazes to bond heat sources and containment shells to the foam, and improve the oxidation resistance. Under this proposedstudy, we will evaluate Starfirer and KionT International VL20 silicon carbide precursors, optimize their processing conditions, and establish the relationship between the infiltrant/processing parameters and the resultant material property enhancement ofthe carbon foam. Based upon requirements inputs from contractors, CCI will focus on tailoring the Enhanced Carbon Foam properties for specific allocations in the latter stages of Phase I. Prototype testing and optimization will occur Phase II with thesupport of The Boeing Company and others. Carbon foam heat exchangers offer: -Significant weight reduction-Volume efficiency improvement.- Structural support- Complex forming capabilitThe composite material is expected to possess such favorable properties as:-Greater flexural strength-Greater compressive strength-Greater thermal conductivity-Greater oxidation resistance-High electrical resistivity-Higher strength-to-weight ratio- Good Fire resistance- Reduced friability- Reduced dustiness- Increased ability to be brazed- Reduced erosion in fluid heat exchangersThe composite material can be incorporated into a wide range of heat exchanger and structural applications such as:- Electronics cooling- Heat exchangers (solid/gas, solid/liquid, solid/solid, liquid/gas, liquid/liquid, gas/gas, and gas/liquid)- Heat dissipation-Engine cooling-Catalyst supports- Heat Pipes- Fuel CellsThe innovation is broadly applicable. The process of using a liquid precursor to form a silicon carbide coating is appropriate to any open celled carbon foam structure and would augment the benefits of a structurally tailored foam structure. The polymericsilicon carbide precursors are available from multiple sources. The viscosity of the precursor, the number of infiltration steps and the number of pyrolysis steps present a variety of tailorable coating properties. The process is scalable usingcommercially available equipment and technologies. Replacement of existing heat exchangers has been demonstrated with graphite foams and the SiC coating is expected to enhance the foam's performance for multiple applications.