IN-SITU FTIR EMISSION-SPECTROSCOPY IN A TECHNOLOGICAL ENVIRONMENT - CHEMICAL-VAPOR INFILTRATION (CVI) OF SIC COMPOSITES

A method has been established to detect transient species inside a hot wall technological reactor. The CVI plant is used to produce fibre reinforced composite materials with ceramic matrix, in particular to infiltrate carbon fibre woven structures with SiC. The infiltration has been carried out at about 1000 degrees C under reduced pressure with a mixture of CH3SiCl3 (methyltrichlorosilane, MTS) and H-2 as the SiC precursor. To investigate the gas reactions near the preform the emissivity has been measured by FTIR spectrometry. Several gaseous species could be detected including MTS, SiCl2, (SiCl3)(n=1,2), SiCl4, HSiCl3, CH4, CH3Cl and HCl, also possible indications for CH3 radicals and SiC clusters have been found. The interpretation of the multicomponent high temperature emission spectra has been supported by investigating reference spectra of individual components at working temperature. Band profile changes caused by both temperature and precursor decay have been detected. After radiation calibration, concentration changes and the degree of MTS decay could be roughly estimated. The spectroscopical results are evaluated in comparison with kinetic models of the MTS decay.