REACTION-MECHANISM OF THE PYROLYSIS OF POLYCARBOSILANE AND POLYCARBOSILAZANE AS CERAMIC PRECURSORS

The pyrolytic processes of polycarbosilane (PCS) to silicon carbide and of polycarbosilazane (PCSZ) to silicon carbonitride were studied by gas analysis, electron spin resonance (ESR), and X-ray diffraction. On the progress of conversion from organic polymers to ceramics above 800 K, decomposition gases like CH4 and H-2 evolved, and free radicals as the intermediate active species in the chemical reactions were detected during the pyrolysis. The gas yield and the radical concentration profile against pyrolysis temperature indicated that there were several steps in the pyrolysis of PCS and PCSZ. At the last step in the pyrolysis of PCS, the microcrystals of beta-SiC began to precipitate, while the microcrystals of beta-SiC and Si3N4 precipitated in the pyrolysis of PCSZ.