Oxidation behavior and property degradation of nuclear-grade C/C composites oxidized in air

Oxidation behavior and property change after oxidation of several nuclear-grade C/C composites were evaluated. A chemical reaction appeared to control the oxidation rate of C/C composites below 650-700 degrees C through thermo-gravimetric oxidation analyses. The activation energy of the oxidation reaction in the chemical-reaction controlled oxidation regime was 196.6 kJ/mol and 165.4 kJ/mol for 1501YR and CX-270G composites, respectively, which were within a similar range as nuclear graphites. The properties of C/C composites such as flexural strength, inter-laminar shear strength and thermal diffusivity were largely degraded even at the oxidative weight loss of 1-3%. A preferential oxidation at the inter-bundle and fiber/matrix interfaces more sensitively affected the inter-laminar shear strength and the transverse thermal diffusivity than the flexural strength and the in-plane thermal diffusivity.