Microtexture, microstructure evolution, and thermal insulation properties of Si3N4/silica aerogel composites at high temperatures

Abstract

Insights into the micro-texture, micro-morphology, and pore structure of Si₃N₄/SiO₂ aerogel composites at high temperatures are presented. At high heat treatment temperatures, the silica aerogel inside the composite material gradually crystallised, and the fusion of micropores caused the decrease of pores and the increase of pore size. Compared with the pure SiO₂ aerogel, Si₃N₄ particles embedded in the nano-network structure provided effective support and hindered the aerogel crystallisation at high temperatures. To reduce the radiative thermal conductivity, Si₃N₄/silica aerogel composites were doped with the opacifier TiO₂. At higher TiO₂ content, the thermal diffusivity and thermal conductivity of the composites decreased more slowly below 800 °C, and substantially above 1000 °C. For TiO₂ 20 wt%, the measured dielectric constant was 2.85, and the thermal conductivity of the composite decreased by approximately 35% (at 1300 °C). The results show that an appropriate TiO₂ content improved the thermal insulation performance of the composite, but damaged the wave permeability, whereas high contents were unfavourable. This study provides theoretical and technical support for the preparation and application of high temperature wave permeable insulation materials.