Abstract: Due to excellent thermal insulation performance at room temperature and ultralow density, silica aerogels are candidates for thermal insulation. However, at high temperatures, the thermal insulation property of silica aerogels decreased greatly caused by transparency to heat radiation. Opacifiers introduced into silica sol can block heat radiation yet destroy the uniformity of aerogels. Herein, we designed and prepared a silica aerogel composite with oriented and layered silica fibers (SFs), SiC nanowires (SiC_NWs), and silica aerogels, which were prepared by papermaking, chemical vapor infiltration (CVI), and sol-gel respectively. Firstly, oriented and layered SFs made still air a wall to block heat transfer by the solid phase. Secondly, SiC_NWs were grown in situ on the surface of SFs evenly to weave into the network, and the network reduced the gaseous thermal conductivity by dividing cracks in SFs/SiC_NWs/SA. Thirdly, SiC_NWs weakened the heat transfer by radiation at high temperatures. Therefore, SFs/SiC_NWs/SA presented remarkable thermal insulation (0.017 W (m K)^-1 at 25 °C, 0.0287 W (m K)^-1 at 500 °C, and 0.094 W (m K)^-1 at 1000 °C). Besides, SFs/SiC_NWs/SA exhibited remarkable thermal stability (no size transform after being heat treated at 1000 °C for 1800 s) and tensile strength (0.75 MPa). These integrated properties made SFs/SiC_NWs/SA a promising candidate for highly efficient thermal insulators.

Key words: Silica aerogel, Thermal insulation, SiC nanowires, Layered structure