- freely available
Coatings 2017, 7(7), 101; https://doi.org/10.3390/coatings7070101
Aim and Objectives
2.1. CVD Process Setup
2.1.1. Chlorination Reactor
2.1.2. CVD Reactor
2.1.3. Mixing Manifold
2.2. CVD Procedure
2.3. Characterization and Morphology
2.4. Ablation Test Using Lene Flame
3. Results and Discussion
3.1. Coatings on Tubular Graphite Substrates
3.2. XRD and XPS Analysis of the As-Deposited Coating
3.3. Characterization after Thermal Shock and Ablation
3.4. Morphology and Phase Analysis of the Ablated Specimens
- Chlorination of tantalum chips at ≈550 °C has resulted in the in situ synthesis of TaCl5. Based on TaCl5-CH4-Ar and CH3SiCl3-H2-Ar reactive systems, the crack-free multilayer coating of TaC and SiC is successfully developed on a graphite tube by CVD at 1050–1150 °C and 50–100 mbar. XRD and XPS studies confirm the formation of TaC and SiC.
- By depositing SiC as transition layers between the graphite and TaC, the stress concentration could be released and crack-free coating could be obtained. The coating remained intact even after the ablation test under oxyacetylene flame. At 1150 °C the thickness of the coating was about 600 μm, while at 1050 °C it was about 400 μm for the same duration and flow conditions.
- The oxyacetylene flame ablation of the TaC coating is mainly an oxidation process where surface TaC is oxidized to TaO2 and Ta2O2, while SiC oxided SiO2 and acted as protective liquid film to prevent further oxidation of the graphite underneath.
- The uniform deposition of TaC on the cylindrical graphite tube has established the process for generating a CVD coating of TaC on similar geometrical featured propulsion systems such as graphite throat inserts, as well as the chambers and nozzles of rocket motors.
Conflicts of Interest
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