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 re inforced composite materials with ceramic matrix, in particular to inf iltrate carbon fibre woven structures with SiC. The infiltration has b een carried out at about 1000 degrees C under reduced pressure with a mixture of CH3SiCl3 (methyltrichlorosilane, MTS) and H-2 as the SiC pr ecursor. To investigate the gas reactions near the preform the emissiv ity has been measured by FTIR spectrometry. Several gaseous species co uld be detected including MTS, SiCl2, (SiCl3)(n=1,2), SiCl4, HSiCl3, C H4, CH3Cl and HCl, also possible indications for CH3 radicals and SiC clusters have been found. The interpretation of the multicomponent hig h temperature emission spectra has been supported by investigating ref erence spectra of individual components at working temperature. Band p rofile changes caused by both temperature and precursor decay have bee n detected. After radiation calibration, concentration changes and the degree of MTS decay could be roughly estimated. The spectroscopical r esults are evaluated in comparison with kinetic models of the MTS deca y.