航天飞行器轻质纳米材料高温隔热性能

纳米隔热材料是一种新型航天飞行器热防护材料。本文使用自行研制的高速飞行器热试验系统，对Al₂O₃纳米材料的高温隔热性能进行试验研究及数值计算，为高速航天器热防护系统的安全可靠性设计提供重要依据。研究结果表明，厚度仅为10 mm的Al₂O₃纳米材料板，当前表面温度为1 200℃时（1 800 s），前后表面的温度差高达880.9℃，后表面温度降低了73.4%，且隔热性能稳定。另外与某空天飞行器轻质陶瓷材料进行了隔热性能的对比试验，结果显示轻质陶瓷材料板的背壁温度要比Al₂O₃纳米材料板高56%。说明Al₂O₃纳米材料的高温隔热性能非常优异，在航天器和高超声速飞行器热防护中具有重要的应用价值。由扫描电镜（SEM）图像知，当温度超过1 200℃后，Al₂O₃纳米材料颗粒快速聚集生长，颗粒间的空洞尺寸显著增大，材料内部纤维出现熔融现象，裂纹数量增多、深度及宽度显著增大，影响材料表观导热率。另外，当温度高于1 200℃时，纳米材料板边界出现了较大的收缩变形和弯曲变形。基于试验结果可知，Al₂O₃纳米隔热材料应该在小于1 200℃的热环境中使用。

High temperature thermal insulation performance of light nanomaterials for aerospace craft

The thermal insulation nanomaterial is a new thermal protection material with excellent thermal insulation performance for aerospace craft. Using the self-developed transient heating simulation system designed for high-speed aircraft, the high-temperature insulation performance of the Al₂O₃ nanomaterial is investigated with the experimental method and numerical simulation to provide important references for the thermal protection design of aerospace craft. The results show that for the Al₂O₃ nanomaterial plate with thickness of only 10 mm, when the front surface temperature was 1 200 ℃ (1 800 s), the temperature difference between the front and back surfaces was 880.9 ℃, the back surface temperature reduced by 73.4%, and the thermal insulation performance was stable. A comparison between the nanomaterial plate with the lightweight ceramic plate of a space vehicle shows that the temperature on the back surface of the ceramic plate was 56% higher than that of the nanomaterial plate. These results indicate that the Al₂O₃ nanomaterial has excellent thermal insulation performance, and is thus applicable in thermal protection of spacecraft and hypersonic vehicle. When the temperature was over 1 200 ℃, it was observed by Scanning Electron Microscope (SEM) that Al₂O₃ nanometric particles accreted rapidly, and the size of the cavities between particles increase significantly. The fibers inside the material were found melt, and the number, depth and width of cracks on the surface of the plate increased observably. These affected the thermal conductivity of the material surface. In addition, when the temperature was higher than 1 200 ℃, large deformation due to shrinkage and bending appeared on the edges of the nanomaterial plate. Experimental results demonstrate that the Al₂O₃ nanomaterial should be used at the temperature lower than 1 200 ℃.