Synthesis of Si-C-N coatings by thermal Plasmajet chemical vapour deposition applying liquid precursors

• Published in: Applied organometallic chemistry Vol. 15; no. 10; pp. 841 - 857
• Main Authors: Wilden, Johannes, Wank, Andreas, Asmann, Marcus, Heberlein, Joachim V. R., Boulos, Maher I., Gitzhofer, Francois
• Format: Journal Article
• Language: English
• Published: Chichester, UK John Wiley & Sons, Ltd 01.10.2001; Wiley
• Subjects: Applied sciences; Building materials. Ceramics. Glasses; Ceramic industries; Chemical industry and chemicals; DC Plasmajet CVD; Exact sciences and technology; HF plasma; high rate synthesis; liquid precursor; Miscellaneous; plasma diagnostics; Si3N4; SiC; supersonic; Technical ceramics; thermal plasma; TPCVD; Coating material; Organic siloxane; Silicon Carbides nitrides; Manufacturing; Experimental study; Organic silazane; Chemical vapor deposition; Thermal plasma; Precursor; Non oxide ceramics
• ISSN: 0268-2605; 1099-0739
• DOI: 10.1002/aoc.239

Materials in the system Si–C–N feature excellent properties for wear protection applications, even at elevated temperatures, and an excellent thermal shock resistance. As these materials have no melting point, coatings have to be manufactured via a synthesis. Conventional chemical vapour deposition (CVD) processes have the disadvantage of low deposition rates. Thermal Plasmajet CVD processes with liquid feedstock feature the highest deposition rates among the gas‐phase synthesis processes. Single and triple DC torches and HF torches with supersonic nozzles have successfully been applied to produce Si–C(–N) coatings on different steel, aluminium, titanium and copper alloys, as well as on graphite. Besides chlorosilanes, hexamethyldisiloxane, tetramethyldisiloxane and hexamethyldisilazane have been used as liquid single precursors. Deposition rates up to 1500 μm h−1 have been achieved. The coatings show cauliflower, columnar or dense morphology and an amorphous or nanocrystalline structure. The formation of both α‐ and β‐Si3N4 has been verified by X‐ray diffraction. The application of chlorosilanes always results in chlorine‐containing coatings. The chlorine causes severe corrosion in the interface to mild carbon steel substrates. The processes are compared taking into account their characteristics concerning the injection modes, gas temperature and velocity profiles determined by enthalpy probe measurements. The process conditions are correlated to the coating microstructure and the adhesion to the substrates and guidelines for the optimum production of ­Si–C–N coatings by Plasmajet CVD are deduced. Emission spectroscopy is used to determine the mechanisms of the coating formation. Full dissociation of the liquid feedstock in the plasma jet has been verified. Copyright © 2001 John Wiley & Sons, Ltd.