Investigation of high temperature thermal insulation performance of fiber-reinforced silica aerogel composites

Silica aerogel has been recognized as a promising material for thermal insulation applications in buildings, cryoengineering, and aerospace due to its ultralow thermal conductivity (0.014-0.020 W/(m.K)) and density (0.01-0.1 g/cm(3)). However, pure silica aerogel shows a high transmittance at the wavelength range of 2-8 ktm, resulting in an ultrahigh radiative thermal conductivity at high temperature (> 600 K). To block thermal radiation at high temperature and to increase the mechanical performance of silica aerogel, ceramic fibers (e.g., SiO2, and SiC) with a diameter comparable to the wavelength of incident thermal radiation are usually introduced into the pure silica aerogel. Here, we developed a theoretical model to investigate the thermal conductivity of fiber-reinforced aerogel composites at high temperature, which considers the inclination angle, diameter and mass fraction of the doped fibers. Our modelling results show that aligning the doped fibers in the direction perpendicular to the incident radiation is the most effective way to reduce the radiative thermal conductivity. The optimal fiber diameter decreases from similar to 5.0 mu m to similar to 2.5 mu m when the temperature increases from 600 K to 1400 K. Owing to the trade-off relationship between the conductive and radiative thermal conductivities, there exists an optimal mass fraction of doped fibers to achieve the minimized thermal conductivity. The work helps to understand heat transfer in aerogel composites and to guide the geometric design of thermal insulation materials for high-temperature applications.