Preparation of a SiC/Cristobalite-AlPO₄ Multi-layer Protective Coating on Carbon/Carbon Composites and Resultant Oxidation Kinetics and Mechanism

Jianfeng Huang 1),Wendong Yang 1,2) and Liyun Cao 1) 1) Key Laboratory of Auxiliary Chemistry & Technology for Chemical Industry,Ministry of Education,Shaanxi University of Science & Technology,Xi an 710021,China 2) Laboratory of Opto-Functional Materials and Photochemistry,Technical Institute of Physics and Chemistry,Chinese Academy of Sciences,Beijing 100190,China

摘 要：In order to improve the oxidation resistance of carbon/carbon （C/C） composites,a SiC/C-AlPO4 multi-layer coating was fabricated on the C/C composites by a simple and low-cost method.The internal SiC bonding layer was prepared by a two-step pack cementation process and the external C-AlPO4 coating was deposited by hydrothermal electrophoretic deposition process.Phase compositions and microstructures of the as-prepared multi-layer coating were characterized by X-ray diffraction （XRD）,scaning electron microspocy （SEM） and energy dispersive spectrometer （EDS）.Anti-oxidation properties,oxidation behavior and the failure behavior of the coated composites were investigated.The results indicate that the multi-layer coating exhibits obviously two-layer structure.The inner layer is composed of β-SiC,α-SiC phase with a scale of silicon phase.The outer layer is composed of cristobalite aluminum phosphate （C-AlPO4） crystallites.The SEM observation shows the good bonding between the inner and outer layers.The multi-layer coating displays an excellent oxidation resistance in air in the temperature range from 1573 to 1773 K,and the corresponding oxidation activation energy of the coated C/C composites is calculated to be 117.2 kJ/mol.The oxidation process is predominantly controlled by the diffusion of O2 through the C-AlPO 4 coating.The failure of the multi-layer coating results from the generation of the microholes that may be left by the escape of the oxidation gases.

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