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 i s 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). Car bon/oxygen reaction, gas phase diffusion through microcracks present i n the external SiC coating, and silica growth are the main phenomena t aken into account in the modeling. A morphological characterization of the microcracks network based on a compression test and SEM observati ons has been developed. The differential equations of the model are so lved according to an iterative procedure. The mass variations of the c omposite during an oxidation test, as derived from the model, are in g ood agreement with the experimental data. The model is then used to pr edict the oxidation rate variations when (i) the oxygen partial pressu re is decreased, and (ii) the state of damage of the external SiC coat ing is increased by mechanical loading.