SBIR-STTR Award

DOE needs to develop carbon-carbon composites to line the inside walls of future fusion devices. The carbon-carbons should have the highest possible resistance to fast neutrons while maintaining high thermal conductivity and good mechanical properties. This project will fabricate a new generation baseline carbon-carbon composite with very recently developed ultra high thermal conducting mesophase derived pitch fibers. These fibers will be used as a reinforcement in mesophase derived pitch carbon matrices. Processing will include densification with mesophase pitch and pyrolytic carbon and heat treatment above 2,500øC. The baseline materials will be further improved by growing fiber/whisker networks in the porosity of a preform after carbonization. The networks will be grown by chemical vapor deposition and/or by using a novel flow-through impregnation process. "VVhiskered" composites will be further densified and heat treated to complete their processing. The presence of the fiber/whisker networks will enhance through-the-thickness thermal conductivity and interlaminar shear and cross-plane tensile strengths. Additives will be identified that will reduce the surface erosion (chemical and physical sputtering) in a hydrogen plasma. Phase I is expected to show the superiority of the new generation of carbon-carbon composites over current state-of-the-art materials. Phase I will provide the data required to produce prototype composites for further physical, thermal, mechanical, and irradiation behavioral testing in Phase II.Anticipated Results/Potential Commercial Applications as described by the awardee:These carbon-carbons should make excellent material for first wall tiles and limiters in future fusion power reactors. This innovative research also will produce processing that may be applied in the short term to produce carbon-carbons for fusion devices, such as the Compact Ignition Tokamak (CIT). This technology may have application for missiles, electronic gear, solar energy converter satellites, space power satellites, heat exchanger pipes for the national aerospace plane engine, and commercial heat exchangers.

In Phase I, two-dimensional composites with in-plane thermal conductivities in the range 350 to 400 W/m K, tensile strengths in the range 58 to 60 Ksi, and moduli in the range 31 to 37 Msi were fabricated. A dense network of vapor-deposited fiber was grown catalytically in the "z" direction of 2D preforms consisting of 130 Msi modulus fiber in the "xy" plane. During Phase II, carbon-carbon composites will be fabricated with new mesophase pitch-derived carbon fibers that have moduli of 130 Msi and thermal conductivities up to 1180 W/mK. Two-dimensional composites will be tailored to provide optimum thermal conductivity and strength in the "xy" and "z" planes. Vapor-grown carbon fibers will be deposited with their axes in the "z" plane of 2D preforms consisting of high modulus fibers in the "xy" planes. Novel processing will be practiced to ease 3D weaving with the high modulus fibers and produce angle interlocked preforms for further processing into highly conducting and high strength composites. Additives will be incorporated into these composites to reduce surface erosion during plasma interactions in a Tokamak reactor. All of these composites will then be processed to promote a high degree of crystallinity in the fibers and matrix carbon to minimize damage under fast neutron irradiation at elevated temperatures. All composites will be characterized by measuring physical, thermal, electrical, and mechanical properties, and by irradiation in the High Flux Isotope Reactor at the Oak Ridge National Laboratory.Anticipated Results/Potential Commercial Applications as described by the awardee:This program should demonstrate the feasibility of fabricating highly graphitic 2D and 3D carbon-carbon composites with a high degree of resistance to fast neutron damage along with properties that will ease the design and maintenance and extend the life of first wall tile and limiters in fusion test reactors. These composites could also find uses as space radiators, electronic heat sinks, satellite structures, lightweight heat pipes, and engine components for the National Aerospace Plane.