Mass transfer and kinetics of the chemical vapor deposition of SiC onto fibers

Abstract

An internally consistent set of data was generated for the chemical vapor deposition (CVD) of SiC from methyltrichlorosilane (MTS) and H2 at atmospheric pressure. A moving fiber tow was used as the substrate. Coating rates between 0.3 and 3.7 µm/min and deposition efficiencies between 24 and 48% were obtained for MTS and H2 flow rates in the range 30 to 200 cm3/min and 300 to 2000 cm3/min, respectively. The data were analyzed and found to be best fit under a mass transfer regime. Based on this fit, a value of the constant in the Chilton–Colburn j factor expression for a moving fiber tow was estimated to be 2.74 × 10−6 with a standard deviation of 3.2 × 10−7. The efficiency of the reaction was found to decrease with increases in the total flow rate, indicating that the effect of the decreased residence time of reagents in the reactor was larger than the increase in the mass transfer coefficient. Finally, a comparison between the efficiencies for a stationary and a moving tow revealed that the moving tow had a higher efficiency, possibly due to a disruption of the boundary layer by the tow motion or due to the decrease in the canning of the moving tow.

Computational thermodynamic study of SiC chemical vapor deposition from MTS‐H2*

“…12,14,[24][25][26][27][28]33,34,[39][40][41][42][43][44][45] Additionally, as shown in Table 1 and Figure 9B, the calculated deposit purity is in good agreement with available experimental data. 24,39,44 These results inspire us to understand the discrepancy between thermodynamic calculations 46,48,51 and experimental observations 25,28,40,42,44 at the H 2 /MTS ratios of 10 or lower from the perspective of deposit purity. In the context that (1) the crystal structure of the deposit was mainly characterized by X-ray powder diffraction (XRD) in previous experiments 25,28,40,42,44 and the uncertainty of such measurement is generally ~1 wt.%; (2) carbon is a poor scatterer, which likely results in higher uncertainty in measured deposit composition; and (3) if the graphite within the deposit is small in crystallite size in the deposit, the XRD peaks of graphite will be broad and could be overlooked.…”

“…Conditions allowing the fabrication of pure SiC in the MTS-H 2 system by CVD/CVI vary with regards to deposition temperatures, pressure, input gas composition, and gas flow rate, but they are commonly in the temperature range of 1000 to 1400°C, at pressures below 26 664 Pa (200 Torr), and H 2 /MTS ratios below 100. 12,14,[24][25][26][27][28]33,34,[39][40][41][42][43][44][45] Although extensive experimental investigations have been performed on SiC deposition from the MTS-H 2 system, the full range of deposition conditions has not yet been covered as such studies are time-consuming and cost-prohibitive. Several attempts have been made to explore this system by computational thermodynamics instead.…”

Thermodynamics, Kinetics, and Microstructure of Laser Chemical Vapor Deposition of SiC

“…Results from past attempts to determine the kinetics of the CVD of SiC from MTS and H 2 ranged widely, with apparent activation energies between 40 and 400 KJ/mol and reaction orders between 0 and 2.5 depending on the experimental parameters 12,13 . Experimentally, Sone et al 14 .…”

“…The byproduct HCl generated from the deposition of SiC from MTS has been shown to suppress the deposition rate at temperatures below 1200°C 16 . Lackey et al 13 . examined the process of depositing SiC onto carbon fiber substrates in a cold‐wall reactor and found that a mass transfer model explained the deposition rate data much better than a kinetic expression, i.e., the process was operating within the diffusion limited regime.…”

Modeling and Development of a Microwave Heated Pilot Plant for the Production of SiC-Based Ceramic Matrix Composites

“…Methyltrichlorosilane (MTS, Sigma-Aldrich, 99% of purity)) was used as the precursor material for SiC deposition (Lackey et al, 1998). The MTS gas (boiling point: 66°C) was produced by the vaporization of MTS liquid in a suitable temperature controlled vessel.…”