Carbon-Carbon For Improved Environmental Quality

Carbon-carbon (C-C) composites have properties that make them attractive for increasing the efficiency of a variety of commercial and industrial combustion systems and heat-utilization processes. Increased efficiency will lower the emission of harmful products for direct improvements in environmental quality. A major barrier to commercial and industrial uses of C-C composites is high cost. A rough analysis performed for this proposal indicates that over 50% of the cost of some C-C composites is associated with conventional densification that requires processing at high temperatures in nonoxidizing environments. As a result, simplifying and increasing the efficiency of the densification could result in as much as a 33% reduction in the final cost of simple high-production C-C components. An effective approach for lowering the densification cost of C-C composites would be to minimize or tally eliminate the need for nonoxidizing high-temperature processing. In this vein, the approach proposed here is based on impregnating carbon fiber preforms with sugars of appropriate characteristics and paralyzing these at low temperatures in air to form the carbon matrix. Preliminary work at MSNW has proven that sugar densification by multiple cycles of melt impregnation and low-temperature pyrolysis in air is effective to a significant degree. However, the process is compromised by foaming of the sugar during pyrolysis. The purpose of the proposed program is to identify methods to suppress foaming and to demonstrate the fabrication of C-C composites of acceptably high density and tensile strength. The proposed 6 month program would be conducted in two sequential 3 month tasks. Task 1 would be used to evaluate sugar polymerization and low-temperature pressure pyrolysis as methods for eliminating or greatly reducing pyrolysis foaming. C-C composite samples would be fabricated in Task 2 for characterization and tensile testing. An optional Task 3 is proposed in which five 4 in. x 4 in. x 0.125 in. C-C panels would be fabricated by the preferred method identified in Tasks 1 and 2 for delivery to the sponsor.