Silicon Oxycarbide Species

This mechanism accounts for the evolution of a gaseous SiO CO mixture, the growth of the SiC crystals and the deaease in the amounts of free cartxin and silicon oxycarbide. The relative amounts of CO and SiO which are formed and the composition of the final residue (i.e., SiC or SiC + C) depend upon the relative amounts of free caitton and silicon oxycarbide in the fiber. For the Nicalon fiber (NL 200), the main species in the gas phase is CO and the solid residue is SiC. There is therefore enough SiO formed by decomposition of the silicon oxycarbide phase (Equation 9) to consume all the free carbon by Equation 10 [73]. This mechanism also accounts for one of the processes used to produce oxygen-free nearly-stoichiomefric SiC fibers [38] [54]. Since CO and SiO diffuse and escape from the fiber, the decomposition starts near its surface and the decomposition front moves radially towards the fiber axis, yielding a skin/core microstructure [16]. 

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