Thermal Conductivity of Silica Aerogel Thermal Insulation Coatings

In this study, silica aerogel microspheres were prepared through sol–gel method with tetraethyl orthosilicate as the silicon source. Thermal insulation coatings were prepared by mixing silica aerogel and acrylic emulsion. The relationships between the thermal conductivity and volume fractions, densities, sizes, and interfaces of silica aerogel microspheres were investigated through scanning electron microscopy and thermal conductivity analysis. The thermal insulation mechanism of composite coating was discussed in detail. Results showed that the aggregations prevented the decrease of thermal conductivity in the coating when the volume fraction of silica aerogel microspheres was lower than 30 %. However, the pores in the coating reduced the thermal conductivity when the volume fraction was higher than 30 %. The porosity of silica aerogel increased with the declining density, which improved the thermal insulation performance of silica aerogel and reduced the thermal conductivity of the coating. The thermal conductivity of the coating with large microspheres was lower than that with small microspheres at low volume fractions. However, the thermal conductivity of the coating with small silica aerogel microspheres was low because of their large interfacial thermal resistance at high volume fractions. Wetting agents were beneficial in improving the compatibility of hydrophobic aerogel microspheres and polymer, improving the volume fractions of silica aerogel microspheres in the coating, and reducing the thermal conductivity of the coating.