影响二氧化硅气凝胶隔热涂料热导率的因素

Effect of contents and sizes on the thermal conductivity of silica aerogel thermal insulation coatings

采用溶胶凝胶法及雾化技术制备了二氧化硅气凝胶微球,同时制备了二氧化硅气凝胶隔热涂料。利用扫描电镜(SEM)对涂料的微结构进行观测,采用激光粒度检测仪对二氧化硅气凝胶微球的尺寸进行检测,采用Hot Disk热导率仪测量了二氧化硅气凝胶隔热涂料的热导率。结果显示:根据SEM图像,气凝胶微球在涂料中形成明显团聚,且在气凝胶体积分数较高时,涂料中气孔增多。此外,小粒径气凝胶微球更容易形成团聚。由于气凝胶微球热阻极大,气凝胶隔热涂料的热导率随气凝胶微球含量的增加而下降。气凝胶微球的团聚相比均匀分散不利于热导率的降低,而孔隙的增多则有利于涂料热导率下降,因为空气的热阻高。小粒径微球的界面热阻比大粒径微球更大,导致小粒径微球制备的隔热涂料热导率低,混合粒径使气凝胶微球堆积密度增大,有利于降低涂料的热导率。

The silica aerogel microspheres were prepared by sol-gel method and atomization technology,and the silica aerogel thermal insulation coatings were also prepared. The microstructures were observed by scanning electron microscopy(SEM). The sizes of microspheres were tested by a laser particle detector. The thermal conductivity of the coating was measured by Hot Disk thermal content meter. The results show that significant aggregations of silica aerogel microspheres with a high volume fraction are generated in the coatings,the number of pores in the coating increases according to SEM diagrams. Additionally,the aggregations are easy to be formed by small size silica aerogel microspheres. The thermal conductivity of the coating decreases with the increase of volume fraction because of the high thermal resistance of the silica aerogel microspheres. Aggregations of the silica aerogel microspheres have a negative impact on the reduction of thermal conductivity compared with that evenly distributed,but the pores help reduce thermal conductivity because of the high thermal resistance of air. Meanwhile,the interfacial thermal resistance of silica aerogel microspheres of small sizes is bigger than that of big sizes. So the thermal conductivity of coatings with small size microspheres is lower than that of coating with big size microspheres. Hybrid sizes increase the stacking density of silica aerogel microspheres in coating which help reduce thermal conductivity.