QUANTIFICATION OF HIGHER SIC FIBER OXIDATION RATES IN PRESENCE OF B2O3 UNDER AIR

Ceramic Matrix Composites, such as SiC/SiC, exhibit excellent thermomechanical properties. To enhance the lifetime of these composites, a self-healing matrix with boron bearing species has been developed in order to resist in a large range of temperatures under oxidant atmosphere. The chemical and thermal stabilities of the generated B2O3 are enhanced through the formation of borosilicate by dissolving SiO2. However, the dissolving process should be avoided as soon as it acts over the silica protective layer on the SiC fiber surface: the oxidation of SiC fiber may be highly enhanced. A quantification of the silica dissolution rate is done, through the development of a simple global modelling taking into account a. competition between the silica formation rate by oxidation and its disappearance by dissolution in B2O3. This scenario is checked by many experiments in oxidizing environment with various oxygen partial pressures at different temperatures ranging from 600 degrees C to 900 degrees C.