SILICON CARBONITRIDE DERIVED FROM AN ORGANOMETALLIC PRECURSOR - INFLUENCE OF THE MICROSTRUCTURE ON THE OXIDATION BEHAVIOR

The pyrolysis of the polymer issued from the octamethylcyclotetrasilazane (OMCTS) under nitrogen leads to amorphous silicon carbonitride residues containing high carbon levels. Their partial crystallization in alpha-Si3N4 depends on the experimental parameters (temperature, time). If the pyrolysis is carried out in a stream of ammonia (a reactive gas), the carbon content of the ceramics was drastically reduced (< 0.2% wt), the remainder being alpha-Si3N4. The study on the oxidation behaviour of these ceramic products investigated by TGA-MS allowed to point out the influence of pyrolysis conditions on the microstructure and, in particular, on the repartition of free carbon into the mineral residues. Oxidation of the partly crystallized SiCN products results from the preferential combustion of free carbon with CO and CO2 departure, followed by a degradation of the silicon carbonitride with the release of gas such as CO, CO2, NO, N2 and traces NO2. However, in the amorphous products, the carbon is oxidized with difficulty.