Design of hollow glass fiber/silica aerogel composites for high-temperature thermal insulation applications

Pure silica aerogels are not suitable for high-temperature (500 ∼ 2000 K) thermal insulation applications due to their transparency to infrared thermal radiation. The addition of solid glass/ceramic fibers, such as aluminum oxide and silicon oxide, into the silica aerogel matrix can remarkably suppress the radiative heat transfer. However, the introduced solid fibers increase the structural density and enhance heat conduction in silica aerogel composites. Herein, we propose adopting hollow fibers (HFs) to simultaneously minimize thermal radiation and heat conduction through silica aerogels in a high-temperature environment. The results show that increasing fiber hollowness improves the short-wavelength (<5 µm) extinction efficiency, indicating that using HFs is an effective way to lower the thermal conductivity (TC) at high temperatures of silica aerogels. To achieve minimal radiative TC, the fiber hollowness needs to increase with the external diameter of the fiber at a specific temperature, for example, at 1500 K. This study contributes to the understanding of heat transfer mechanisms in porous materials, particularly those with hollow structures, and offers valuable insights for the strategic design of thermal insulation structures effective at high temperatures.