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

A model, based on a simple axisymmetrical fiber/interphase/ matrix ass embly, is derived to depict the oxidation behavior of 1D-SiC/C/SiC com posites 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 th e geometry of the annular pore resulting from the consumption by oxida tion of the carbon interphase, (ii) the mass transfers by diffusion al ong the pore of the reactant and products, and (iii) the chemical reac tions with oxygen of both the pore walls (yielding silica) and the por e bottom (consisting of carbon). The model gives the gaseous species c oncentration and silica thickness profiles along the pore, the length of carbon consumed by oxidation, and the relative weight change. The m odel depicts in a satisfactory manner the features of the TGA curves r ecorded 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 b etter 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). U nder such conditions, the materials exhibit a self-healing behavior.