研究目的
Fabrication of highly oriented thick 3C-SiC coatings on the inner surface of a graphite tube via HHH-CVD at a high deposition rate using a SiCl4/CH4/H2 system, and investigation of the deposition rate, microstructure, and preferred orientation of the coating.
研究成果
A highly oriented and crystalline 3C-SiC coating with a thickness of 615 μm and deposition rate of 300 μm/h was successfully fabricated on the inner surface of a graphite tube using HHH-CVD. The coating's properties, including orientation and microstructure, are influenced by temperature distribution along the tube axis, making it suitable for nuclear reactor applications such as free-standing SiC tubes. Future work could focus on improving uniformity and scaling up the process.
研究不足
The study is limited to specific precursor flow rates and deposition conditions; variations might affect results. The coating properties vary along the tube axis due to temperature gradients, which could be optimized for uniformity. The method may not be directly scalable for industrial applications without further refinement.
1：Experimental Design and Method Selection:
A high-frequency induction-heated halide CVD (HHH-CVD) system was established for depositing 3C-SiC coatings on the inner surface of a graphite tube using SiCl4, CH4, and H2 as precursors. The method was chosen to achieve high deposition rates and good crystallinity.
2：Sample Selection and Data Sources:
A monolithic graphite tube (L = 500 mm, Φint = 40 mm, Φout = 50 mm) was used as the substrate. Samples were cut into 10 mm pieces along the tube axis for analysis.
3：List of Experimental Equipment and Materials:
Equipment includes a cylindrical quartz tube, alumina insulation layer, graphite tube, high-frequency induction coil, mass flow controllers (MFC, Sevenstar), W/Re thermocouple, X-ray diffractometer (XRD, Ultima III, Rigaku), field-emission scanning electron microscope (Quanta-250, FEI), and Raman spectrometer (LabRAM HR Evolution, Horiba). Materials include SiCl4 (
4：5% purity, Aladdin), CH4 (999% purity, Xiangyun Industry), and H2 gas. Experimental Procedures and Operational Workflow:
The graphite tube was heated by induction, precursors were mixed and fed into the tube, deposition occurred at 10 kPa pressure for 120 minutes, with the tube moved at 1 mm/min to achieve uniform coating. Temperature was profiled, and samples were analyzed using XRD, SEM, and Raman spectroscopy.
5：Data Analysis Methods:
XRD for phase identification and texture coefficient calculation, SEM for microstructure and thickness observation, Raman spectroscopy for composition and defect analysis.
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