Abstract: 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.

Key words: silica, aerogel, thermal conductivity, particle size