气凝胶复合材料各向异性导热系数实验研究

Experimental Study of Anisotropic Thermal Conductivity of Aerogel Composites

气凝胶复合材料具有孔隙率高、比表面积大和导热系数低等特点,为增强其力学性能,常在材料面内方向掺杂增强纤维,然而受测量方式和材料制备工艺的限制,目前研究多关注其厚度方向导热系数,对面内方向导热系数关注较少。本文采用基于稳态方法的“三明治”结构测试气凝胶复合材料厚度方向导热系数,采用基于瞬态平面热源法的Hot Disk热常数分析仪测试材料宏观等效导热系数,两者结合间接获得材料面内方向导热系数,并采用石英灯红外加热考核两类材料的高温隔热性能。测量结果表明其厚度方向和面内方向导热系数随温度上升而迅速增大,等效导热系数在对数坐标下随气压的增加呈现“S”变化规律,氧化铝气凝胶材料比氧化硅气凝胶材料高温隔热性能更优。

Aerogel composites have some unique properties, such as high porosity, large specific surface area and low thermal conductivity, etc. To enhance its mechanical property, the material is often doped with reinforced fibers in the in-plane direction. Due to the limitations of measurement method and material preparation process, most of the previous studies were focused on the out-ofplane thermal conductivity, and less attentions were paid on the in-plane thermal conductivity. In this paper, the out-of-plane thermal conductivity of aerogel composites is measured by a “sandwich”structure based on the steady-state method, the apparent effective thermal conductivity of aerogel composites is measured by the Hot Disk thermal constant analyzer based on the transient plane source(TPS) method, and the in-plane thermal conductivity is obtained indirectly from the above two values. In addition, the thermal insulation performance is also compared at high temperature by the infrared heating of quartz lamp. The results show that out-of-plane and in-plane thermal conductivity increases rapidly with the increment of temperature, and effective thermal conductivity in the Logarithmic coordinates shows an “S” variation with the increment of gas pressure, alumina aerogel composites has better high-temperature insulation performance than silica aerogel composites.