Evaluation of High-Temperature Oxidation Characteristics of Two Directionally Laminated C/C Composite Fabricated by the Preformed Yarn Method

Oxidation kinetics of as-received and preheat-treated C/C composites fabricated by the preformed yarn method were investigated. The weight loss due to gasification was measured with oxidation time. In situ observation of microscopic morphological change due to oxidation was conducted using a laser microscope during heating in flowing air. Then, degraded inner and outer morphologies of C/C composites oxidized at various temperatures were examined through observation by SEM and measurement of pore distribution using a mercury porosimeter. As a result, degraded morphologies due to oxidation were extremely different depending on the oxidation temperature range. The inner structural changes became obvious as the oxidation temperature decreased. Therefore, the rate-determining process of the oxidation was changed from the surface chemical reaction to reactive gas diffusion across the boundary layer of a gaseous oxidation product as the oxidation temperature increased. The oxidation reactivity of C/C composites was related to metallic impurities such as iron and residual stress generated during fabrication.