Two commercial carbons (an activated carbon cloth and a rayon-derived carbon cloth) having vastly differing properties were used as substrates for the preparation of low- and high-temperature carbon/carbon composites by the liquid-phase impregnation/carbonization technique with two different pitches and one resin system as matrix precursors. The percentage of matrix in the composites was dependent on the surface area of the carbon cloth substrate. The oxidation behavior of the composites and their individual components was studied over the entire burn-off range (0-100%). The structure of the starting and partially reacted composites was investigated by X-ray diffraction, scanning electron microscopy and polarized-light optical microscopy. For the low-temperature composites, no synergism was found when thermoplastic matrices were used. When the thermosetting resin matrix was used, the oxidation behavior of the composites could not be predicted from that of their constituents. For the high-temperatures composites, synergistic effects were observed: composites obtained using high-surface-area activated carbon cloth showed improved oxidation resistance with respect to their individual components. In contrast, a simple additive effect was observed for the low-surface-area rayonbased composites.
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