Silica nanowires-reinforced silica aerogels with outstanding thermal insulation, thermal stability and mechanical properties

Silica aerogels possess extremely low thermal conductivity, low density and high porosity, which can be regarded as candidates for new thermal insulation materials. However, silica aerogels suffer from low strength, brittleness, modeling difficulties and high moisture absorption. In this work, compatible inorganic silica nanowires are introduced as one-dimensional reinforcing materials, and silica nanowires-reinforced silica aerogels (SiO2NWsMSAs) are synthesized using a two-step acid-base catalytic in-situ sol-gel method combined with atmospheric pressure drying, aiming to improve the comprehensive performances of the composite aerogels. The composite aerogels exhibit good mechanical properties, and the composite aerogel has a compressive strength of 1.379 MPa at a strain of 60 % when the doping amount of silica nanowires is 11 %. The volumetric shrinkage of the composite aerogels varies between 11.58 and 12.81 % and the density ranges from 0.11 to 0.13 g cm-3. SiO2NWs-MSA2 has a low thermal conductivity and good high-temperature insulation properties with thermal conductivity of 0.039 W m-1 K-1 at 25 degrees C and 0.046 W m-1 K-1 at 150 degrees C. The thermal stability of the composite aerogels is improved, and the thermal decomposition temperature reaches 500 degrees C. Meanwhile, the water contact angles of the composite aerogels all exceed 140 degrees. In addition, the composite aerogels can maintain the amorphous state at 1200 degrees C, and the microstructure remains basically unchanged at 1000 degrees C, showing excellent hightemperature resistance.