Structure-stabilized SiO2 packed beds based on sawdust-doped for high-temperature thermal insulation

Abstract

The utilization of nanoparticles for thermal insulation has attracted many interests. However, due to their low melting point at high temperatures, the volume shrinkage of the materials leads to a significant increase in thermal conductivity. In this work, sawdust was employed as an additive to constrain the thermal shrinkage of SiO2-based thermal insulation materials. In the sintering treatment, sawdust will be converted into carbon, while the structure will become more porous. Due to the large thermal contact resistance between carbonized sawdust and SiO2, as well as the abundant pores, which could further reduce thermal conductivity. Results show that adding 20 % of sawdust in SiO2 nanoparticles could lead to a significant decrease of 15 % in density and a substantial reduction of 22 % in thermal conductivity. Simultaneously, adding sawdust could improve the volume shrinkage resistance. Besides, the addition of 20 % sawdust is the optimal choice because of the lowest thermal conductivity of 0.037 W/(mK). Excessive addition of sawdust could lead to an increase in water adsorption, compromising the thermal insulation performance. The thermal cycle stability of 20 % carbonized-sawdust/SiO2 nanoparticle bed under high humidity conditions was also investigated, and the bed shows a stable thermal conductivity of 0.04 W/(mK). This work provides a facile method to inhibit the structural shrinkage of thermal insulation materials, which is of great significance for the application in high-temperature.