OXIDATION MECHANISMS AND KINETICS OF 1D-SIC/C/SIC COMPOSITE-MATERIALS .2. MODELING

A model, based on a simple axisymmetrical fiber/interphase/ matrix assembly, is derived to depict the oxidation behavior of 1D-SiC/C/SiC composites within the temperature range 900-1300 degrees C and for 10 < P-O2 < 100 kPa. It takes into account (i) the changes versus time of the geometry of the annular pore resulting from the consumption by oxidation of the carbon interphase, (ii) the mass transfers by diffusion along the pore of the reactant and products, and (iii) the chemical reactions with oxygen of both the pore walls (yielding silica) and the pore bottom (consisting of carbon). The model gives the gaseous species concentration and silica thickness profiles along the pore, the length of carbon consumed by oxidation, and the relative weight change. The model depicts in a satisfactory manner the features of the TGA curves recorded on actual composites and it is in excellent agreement with the measurements of the carbon interphase lengths consumed by oxidation. It shows that the oxidation resistance of 1D-SiC/C/SiC composites is better at high temperatures (T equal to or greater than 1100 degrees C) and for thin carbon interphases (e equal to or less than 0.1 mu m). Under such conditions, the materials exhibit a self-healing behavior.