In-situ FTIR spectroscopic monitoring of a CVD controlled Si-N-O fibre growth process

High strength and high temperature composite materials such as CMCs represe nt a very promising family of future materials. A high temperature CVD-proc ess has been developed to produce a new type of high-performance amorphous silicon-oxynitride (Si-N-O) fibres. The fibres were grown on a SiC substrat e at 1450 degrees C exposing a stoichiometric precursor powder mixture of S iO2 + SiC, doped with 10 wt% Ti powder to flowing NI NH3. To improve CVD process control an in-situ FTIR monitoring system is in deve lopment. For application of a FTIR based monitoring to the fibre growth pro cess a specific optical adaptation has been designed onto the growth reacto r. The optical set-up allows an almost simultaneous in-situ measurement of the transmission and emission of the hot gas atmosphere just above the prec ursor powder mixture. In addition to the decomposition of NH3, different re action products have been identified, such as CO, HCN and CH4. Gaseous Si-O species could be detected which are responsible for the silicon transport in the gas phase from the solid SiO2 precursor powder to the fibre growth p osition. The assessment of the SiO bands has been supported by additional e xperiments which promote the formation of gaseous SiO.