Dual-Layer Oxidation-Protective Plasma-Sprayed SiC-ZrB2/Al2O3-Carbon Nanotube Coating on Graphite
Graphite is used in high-temperature gas-cooled reactors because of its outstanding irradiation performance and corrosion resistance. To restrict its high-temperature (>873 K) oxidation, atmospheric-plasma-sprayed SiC-ZrB2-Al2O3-carbon nanotube (CNT) dual-layer coating was deposited on graphite substrate in this work. The effect of each layer was isolated by processing each component of the coating via spark plasma sintering followed by isothermal kinetic studies. Based on isothermal analysis and the presence of high residual thermal stress in the oxide scale, degradation appeared to be more severe in composites reinforced with CNTs. To avoid the complexity of analysis of composites, the high-temperature activation energy for oxidation was calculated for the single-phase materials only, yielding values of 11.8, 20.5, 43.5, and 4.5 kJ/mol for graphite, SiC, ZrB2, and CNT, respectively, with increased thermal stability for ZrB2 and SiC. These results were then used to evaluate the oxidation rate for the composites analytically. This study has broad implications for wider use of dual-layer (SiC-ZrB2/Al2O3) coatings for protecting graphite crucibles even at temperatures above 1073 K.
Keywordsoxidation plasma spraying SiC sintering ZrB2
- 10.J.N. Ness and T.F. Page, The Structure and Properties of Interfaces in Reaction-Bonded Silicon Carbides, Tailoring Multiph. Composite Ceram., 1986, p 347-356Google Scholar
- 16.K. Balani, A. Agarwal, and T. McKechnie, Near Net Shape Fabrication Via Vacuum Plasma Spray Forming, Trans. Indian Inst. Met., 2006, 2(59), p 237-244Google Scholar
- 31.A. Nisar, S. Ariharan, T. Venkateswaran, N. Sreenivas, and K. Balani, Oxidation Studies on TaC Based Ultra-High Temperature Ceramic Composites Under Plasma Arc Jet Exposure, Corros. Sci., 2016Google Scholar