Investigation Of The Thermal Radiation Properties Of C/SiC Composites

Thermostructure parts of C/SiC composites have the advantages of small density, excellent resist-washing out, lower cost, simple stucture and better anti-oxidation capabilities than C/C composites.The thermal radiation properties of C/SiC composites is very important reference date to use and key parameter to design the thermal protect systems. It will severely influence the working efficiency and using life of C/SiC composites thermostrcture parts. In this thesis, the effect of character of C/SiC surface, coating thickness, heat treatment and oxidation in high temperature on 2D and 3D C/SiC composites were studied. The main contents and results are as follows:(1) The effect of preform on the thermal radiation properties of C/SiC composites was studied. The results indicated that the total hemisphere emissivity of 3D C/SiC is higher than 2D C/SiC. And the emissivity of 2D and 3D C/SiC is 0.78 and 0.82, respectively. It was shown that the thermal radiation properties of 3D C/SiC is better than 2D C/SiC. The main reason is that the normal spectral reflectance of 2D C/SiC is higher than 3D C/SiC(among infrared 2.5μm~25μm).(2) The effect of coating thickness on the thermal radiation properties of C/SiC composites was investigated. With the increasing thickness of SiC coating, both the emissivity of 2D and 3D C/SiC composites reduced first and raised then, and the difference of the emissivity of 2D and 3D C/SiC composites is little gradually. When the thickness of SiC coating is about 70μm, the lowest emissivity of 2D C/SiC and 3D C/SiC is 0.45 and 0.83, respectively. When the thickness of SiC coating inceases to 140μm, the emissivity of 2D and 3D C/SiC composites attains 0.82 and 0.83.(3) The effect of character of surface on the thermal radiation properties of C/SiC composition was researched. The results indicated that the emissivity of 2D and 3D SiC-C/SiC remarkably declined after polishing.(4) After 1h heating treatment in vacuum at 1600℃, the total hemisphere emissivity of C/SiC composites declined, but SiC-C/SiC and polishing SiC-C/SiC increased remarkably.(5) After 5h oxidation treatment in air at 1600℃, C/SiC, SiC-C/SiC and polishing SiC-C/SiC were all oxidated with different degree. SiO2 film appeared. And the total emissivity of the samples with three character surface all increased.