ZrO2/SiO2/C nanofiber aerogels with enhanced mechanical and thermal insulation properties fabricated by freeze casting

Abstract

Because of the inherent high-temperature resistance, the application of ZrO2 nanofiber aerogels in thermal insulation is promising. However, the contradiction between mechanical and thermal insulation properties has limited its applications. In the present work, nanofiber aerogels of ZrO2/SiO2/C with enhanced thermal insulation and compressive strength were successfully prepared by freeze-casting using tetraethoxysilane (TEOS) as a binder. The effect of TEOS content on the microstructure, compressive and thermal insulation properties was investigated. The porosity of the fabricated aerogels is higher than 97.3 %. The pore structure exhibits hierarchical characteristics, with honeycomb pores on the micro-scale and mesopores on the nano-scale. Part of the SiO2 phases generated by TEOS hydrolysis bond ZrO2 nanofiber to form fiber junctions, while the others cover the surface of ZrO2 nanofibers forming core-shell structure. With the increase of TEOS content, ZrO2/SiO2/C nanofiber aerogels showed a slightly decrease in thermal conductivity to a lower value of 0.032 W m−1 K−1 and an increase in compressive stress to 11.9 KPa. The thermal insulation mechanism and deformation mode during compression of aerogels were analyzed. This study not only provide ZrO2/SiO2/C nanofiber aerogels with both enhanced mechanical and thermal insulation properties, but also can guide the design and fabrication of other ceramic aerogels with excellent properties.