Chemical Vapor Deposition of TaC/SiC on Graphite Tube and Its Ablation and Microstructure Studies

Tantalum carbide (TaC) and silicon carbide (SiC) layers were deposited on a graphite tube using a chemical vapor deposition process. Tantalum chloride (TaCl5) was synthesized in situ by reacting tantalum chips with chlorine at 550 °C. TaC was deposited by reacting TaCl5 with CH4 in the presence of H2 at 1050–1150 °C and 50–100 mbar. SiC was deposited at 1000 °C using methyl-tri-chloro-silane as a precursor at 50 mbar. At 1150 °C; the coating thickness was found to be about 600 μm, while at 1050 °C it was about 400 μm for the cumulative deposition time of 10 h. X-ray diffraction (XRD) and X-ray Photo-Electron Spectroscopy (XPS) studies confirmed the deposition of TaC and SiC and their phases. Ablation studies of the coated specimens were carried out under oxyacetylene flame up to 120 s. The coating was found to be intact without surface cracks and with negligible erosion. The oxide phase of TaC (TaO2 and Ta2O5) and the oxide phase of SiC (SiO2) were also found on the surface, which may have protected the substrate underneath from further oxidation.