Evaluation of High Temperature Oxidation Characteristics of C/C Composite

Abstract

Oxidation kinetics of as-received and pre-heat-treated (PHT) C/C composites fabricated by the preformed yarn method were investigated. The weight loss due to gasification was measured as a function of oxidation time under various isothermal temperatures from 600 to 1100°C in air. In situ observation of microscopic morphological changes due to oxidation was conducted by a laser microscope during heating to 950°C in flowing air. Then, degraded inner and outer morphologies of C/C composites oxidized at various temperatures were examined through observation by a SEM and measurement of pore distribution by a mercury porosimeter. As a result, degraded morphologies due to oxidation were extremely different depending on the oxidation temperature. Inner structural changes became obvious, as the oxidation temperature decreased. Therefore, the rate-determining process of oxidation reaction was changed from the surface chemical reaction to reactive gas diffusion across the boundary layer of gaseous oxidation product as the oxidation temperature increased. Oxidation reactivity of as-received C/C was higher compared to that of PHT C/C due to metallic impurities such as Fe. Furthermore, it was considered that initial oxidation occurred preferentially in the matrix due to residual stress which was generated at the fiber and matrix interface by thermal expansion mismatch of each component at fabrication.