A theoretical/experimental approach to the intrinsic oxidation reactivities of C/C composites and of their components

Abstract

The oxidation reactivities of two C/C composites and of their available components (fibers, bulk matrices) are determined by measurement of mass loss rate in a cylindrical oxidation reactor under dry air and at atmospheric pressure. In order to identify reactional and diffusional regimes, and to provide a safe method for the identification of the intrinsic heterogeneous reaction rates at high temperatures, a modeling approach has been developed. Diffusion of the oxidant is considered throughout the reactor for all the samples (global-scale modeling) in combination with convection and reactions. Fibers have been arranged in unidirectional bundles in which diffusion is also considered (local-scale modeling). The importance of the reaction rate relatively to global-scale and local-scale diffusion has been evaluated. When reaction is slow enough, diffusion effects can be neglected; in the converse case, the intrinsic reaction rates are extracted from the experimental data using the models. Incidentally, the comparison of the fiber and matrix intrinsic reactivities supports the idea that the composites feature a complex oxidation behavior mainly based on a weakest link process. This result is illustrated and discussed using SEM and TEM investigations.