Inhibited radiation transmittance and enhanced thermal stability of silica aerogels under very-high temperature

Silica aerogels are applied extensively in thermal insulation due to their extra-low density and thermal conductivity. However, this can be heavily undermined under high temperature, especially beyond 700–800 °C, due to not only a high transparency for radiation heat transfer, but also an instability caused by nanoparticle collapse. The present study demonstrated a solution to this problem by two steps. Firstly, the size effect of nanoparticles is explored by experimentally preparing unconventional samples composed of large-diameter particles (larger than 20 nm). The prepared sample microstructures and radiative characteristics are investigated by SEM apparatus and FTIR measurements, respectively. Additionally, based on the fractal structures reconstructed using the Diffusion-Limited Colloid Aggregation (DLCA) method, the effects of particle size on thermal stability of silica aerogels are theoretically investigated and the light shielding performance is numerically analyzed by the Generalized Multiparticle Mie-solution (GMM) method. The simulation and experimental results indicate that the enhanced size of nanoparticles can improve the radiative inhibition and thermal stability property under high temperature significantly. However, the ideal above should be refined as it brings an increasing contribution of conduction heat transfer. Thus, a novel structure of core-mantle nanoparticle is proposed to retain the excellent resistance in radiation but avoid an increased thermal conduction. The present work may pave a new direction for developing aerogels under extreme temperature conditions, compared with the widely-used opacifier addition.