Investigation into the structure and quality of carbon/carbon-SiC composites

In this work, pyrolytical carbon and C-SixCy-SiC coatings were deposited by chemical vapour deposition (CVD) in a "Cold Wall" reactor. The C/C samples from "Schunk Kohlenstofftechnik GmbH", Germany were used as substrates. The pyrolytical carbon coatings were obtained by CH4 cracking at 1200-1300 C. SixCy and SiC coatings were deposited from SiCl4/H-2 mixtures by varying the H-2/SiCl4 ratio (alpha). Micro-Raman spectroscopy and X-ray diffraction have been used to determine the order grade for pyrolytical carbon coatings and to investigate the structure and composition of SiC coatings depending on the deposition conditions. In particular, the analysis of Raman spectra of carbon films in the region of 1200-1800 cm(-1) allowed the determination of crystal size in a film, which varied from 2.6 to 8.5 nm depending on a. The presence of a strong narrow band at 2712 cm(-1) in the second order Raman spectra region (2300-3400 cm(-1)) indicated a high degree of perfection of the crystalline lattice and an onion like structure in some of the carbon films. XRD investigation of the SiC-peak showed a shift in frequency and a reduction in intensity when compared to the substrate. The peak shift corresponds to a crystal-geometric grading of the coating.