Thermal Conductivity of Oriented Fibrous Carbon Insulation from 300 to 1300°K in Nitrogen and Argon at One Atmosphere

Abstract

The thermal conductivity, λ, of three samples of oriented fibrous carbon insulation of possible interest to fusion reactors was measured from 300 to 1300°K in a radial heat-flow apparatus. Samples of 0.18 g/cm³ density were prepared by a vacuum filtration process from carbon fibers and powdered phenolic resin and were characterized after carbonization. The λ of these low-density composites depended on both the heat treatment temperature and the fiber orientation. For samples heat treated at 1575°K, the room-temperature λ perpendicular to the planes of fibers was ∼0.5 mW/(cm °K) and was three times as high in the direction parallel to the planes. At 1000°K, the λ in both directions had doubled, primarily because of the positive dλ/dT of the amorphous carbon fibers. Material heat treated at 2775°K had a significantly higher room-temperature λ and a negative dλ/dT, indicating that a slight degree of ordering or graphiti-zation had occurred in the fibers during heat treatment. At high temperatures, the λ of all three samples increased markedly because of radiative heat transport.