The effects of MoSi2 on the oxidation behavior of carbon/carbon composites

PAN-based carbon fibers impregnated with phenolic resin used as a precursor of carbonized matrix were modified by addition of molybdenum disilicide (MoSi2) in different concentrations i.e., 0, 4, 12 and 20% by weight for improving anti-oxidation properties of the composites. In this work, the oxidation behavior of carbon-carbon composites made with MoSi2 as an oxidation inhibitor in flowing air, has been studied in the temperature range of 600-1000 degreesC. The results showed that the oxidation behavior of the composites made without MoSi2 differs from those of the composites made with MoSi2 and involves a degradation mechanism of its own, resulting in the highest oxidation rate during the initial phase of the oxidation. And the composites made with MoSi2 led to a significantly improved oxidation resistance owing to both the reduction of the crack in composites and the formation of a mobile diffusion barrier for oxygen when compared to those made without MoSi2. Hence, carbon active sites were blocked and oxidation of carbon was limited. This is probably due to the effect of the inherent MoSi2 properties, resulted from a formation of the protective layer against oxygen attack, in the above of 800 degreesC. (C) 2001 Published by Elsevier Science Ltd.