KINETICS AND MECHANISMS OF OXIDATION OF 2D WOVEN C/SIC COMPOSITES .2. THEORETICAL APPROACH

A model for the oxidation kinetics of SiC-coated 2D C/SiC composites is developed on the basis of mechanisms derived from TGA data (between 700-degrees and 1500-degrees-C in dry oxygen or air, P = 100 kPa). Carbon/oxygen reaction, gas phase diffusion through microcracks present in the external SiC coating, and silica growth are the main phenomena taken into account in the modeling. A morphological characterization of the microcracks network based on a compression test and SEM observations has been developed. The differential equations of the model are solved according to an iterative procedure. The mass variations of the composite during an oxidation test, as derived from the model, are in good agreement with the experimental data. The model is then used to predict the oxidation rate variations when (i) the oxygen partial pressure is decreased, and (ii) the state of damage of the external SiC coating is increased by mechanical loading.