of fiber modulus. The constants C,, and Cs6 show difference between composites containing carbonized fibers and those containing graphitized fibers; these differences are not related to fiber Young's modulus or preferred orientation.
44. Carbon-fiber thermal insulation
Z. L. Ardary and C. W. Reynolds (Union Carbide Corporation, Nuclear Division, Oak Ridge, Tennessee). A carbon fiber composite material was developed for use as thermal insulation. Rayon fibers and various starches serve as the precursors for the carbon fibers and binders. A vacuum-filtration process is used in the fabrication of insulators. From a dilute water slurry containing carbon fibers and insoluble starch, a filter cake is vacuum-molded on a perforated mandrel of the desired shape. After forming, the molding, which consists of starch particles dispersed in a fibrous mat with residual water, is processed through curing, drying, and furnacing operations to effect a rigid, carbon-bonded fibrous structure. Machining to reasonably close tolerances can be readily performed with single-point tooling. In an inert environment or in vacuum, the insulation can be used to temperatures of 4500ยฐF. The material has both a low density and low coefficient of thermal conductivity. In an argon environment, the thermal conductivity of a 12 pcf density insulator is about 0.8 BTU-in./hr-"F-f? at 1000ยฐF and increases to 4.0-55 BTU-in./hr-OF at 4000ยฐF. The insulation has usually been prepared with densities in the 7-16 pcf range. Over this density interval, the room temperature compressive strength increases from near 20 to 250 psi (at 10 per cent deflection).