High temperature performance of micro-plasma sprayed CNTs/Al₂O₃-TiO₂ composite coating

5wt% CNTs/Al₂O₃-TiO₂ coatings were prepared by micro-plasma spraying. Microstructure and high temperature properties of CNTs/Al₂O₃-TiO₂ composite coatings were studied. Its microstructure was dense and the porosity was low. CNTs were dispersed uniformly in CNTs/Al₂O₃-TiO₂ composite coating. In the thermal oxidation process from 20°C to 700°C, the initial weight loss temperature of CNTs was 471.29°C. The initial weight loss temperature of CNTs/Al₂O₃-TiO₂ composite coating was raised to 507.8°C. The plasma heating process improved the graphite phase transformation of CNTs, which was helpful for the improvement of initial weight loss temperature of CNTs/Al₂O₃-TiO₂ composite coating. When CNTs/Al₂O₃-TiO₂ composite coating was heated to 300°C, and the high temperature reflectivity was measured at 2-18 GHz, the minimum reflection loss was -7.86 dB at 25°C. With increasing temperature, the reflectivity peak continuously decreased and the resonant frequency moved to the low frequency. The experimental reflectivity peak was -12.88 dB, and the frequency bandwidth for less than -5 dB was 4.48 GHz at 300°C. The results suggests that CNTs/Al₂O₃-TiO₂ coating is a good candidate for high-temperature microwave-absorbing material.