Experimental study of the chemical vapor deposition from CH3SiHCl2/H2: Application to the synthesis of monolithic SiC tubes

Abstract

International audienceThe aim of the present work is to synthesize high strength monolithic SiC tubes to improve the imperviousness of a SiC/SiC composite structure. A few hundred micrometers-thick tubular coatings were produced by chemical vapor deposition (CVD) at atmospheric pressure, from CH 3 SiHCl 2 /Ar/H 2 mixtures. The CVD-SiC tubes were obtained by deposition on the inner walls of a SiO 2-tube substrate, previously coated with a pyrocarbon interfacial layer to promote delamination. A continuous deposition process was developed to allow the realization of relatively long CVD-SiC tubes, by sliding the heating system along the substrate. The chemical composition and the microstructure of the tubes were studied by electron probe microanalysis, Raman spectroscopy and scanning electron microscopy. The deposition rate, composition and microstructure of the CVD-SiC coatings were investigated as a function of the substrate temperature and the gas flow rates. A Fourier transformed infrared (FTIR) spectroscopy analysis was carried out at the reactor outlet to characterize the gas phase reactions. The FTIR analysis of pure species from the Si-C-Cl-H system as well ab initio calculations at the density functional theory (DFT) level allowed the assignment of the main IR features in the experimental spectra and th

Synthesis and characterization of monolithic CVD-SiC tubes

“…The SiC coatings were deposited by APCVD at 1200 • C inside a vitreous silica tube (L = 500 mm, ∅ int = 8 mm) serving as a template substrate in a reactor, as described in our previous work [11]. A thin layer of pyrolytic carbon (PyC) was deposited on the inner wall of the silica tube prior to SiC deposition.…”

“…Propene was used as an additional source of carbon to adjust the final sample composition [10]. When used without PZ, the addition of propene was found to promote the production of solid particles condensing at the silica tube outlet, in cool parts of the main CVD reactor [11]. Long SiC tubes could not be obtained in these conditions because of the clogging up with the condensates.…”

“…The PZ consisted of a baffled graphite reactor brought to a temperature of 800 • C by an additional electrical resistor furnace. The resident time of the gases at 800 • C was approximately 3 s. The initial purpose of the PZ was to deplete the effective gas mixture reaching the substrate of the highly reactive silicon-containing species formed at the initial stage of the MDCS decomposition [11]. The influence of the PZ on the composition of the coating was found to be limited, but a side effect -actually the main advantage -was to prevent the production of solid particles.…”

“…On the basis of the CVD-SiC filament processing experience, CVD-SiC tubes were prepared by atmospheric pressure CVD (APCVD) using dichloromethylsilane (DCMS, CH 3 SiHCl 2 ) diluted in hydrogen as the SiC precursor [11]. CVD-SiC tubes could be obtained in both static and continuous configuration.…”

“…CVD-SiC tubes could be obtained in both static and continuous configuration. This APCVD process was thoroughly investigated through both gas and solid analyses using the former option, while the synthesis of a few decimeters long specimens was demonstrated in the latter configuration [11]. As a follow-up, the objective of the present study is to characterize in details the CVD-SiC tube specimens obtained through the continuous APCVD process in terms of composition, structure and thermomechanical properties.…”