Ultralight, thermal insulating, and high-temperature-resistant mullite-based nanofibrous aerogels

The fabrication of insulation materials with ultralow thermal conductivity and excellent thermal stability at high temperatures (higher than 1200 degrees C) has remained an extremely challenging. In this study, we reported the manufacturing of mullite-based nanofibrous aerogels via the gel-casting and freeze drying methods using the electrospun nanofibers with different alumina/silica molar ratios (3:2, 3:1 and 3:0) as the matrix and silica sols as the high temperature binders. The formation process of the mullite-based fibrous aerogel and effect of aerogel composition on the sample physical and mechanical properties were investigated. All mullite-based nanofibrous aerogel show a similar multilevel pore structure. The minor pores were formed by the overlaps of nanofibers and were the fundamental porous structure of the aerogel, while the major pores was caused by the sublimation of the ice crystal. This unique multilevel pore structure make the mullite-based nanofibrous aerogels exhibit an ultralow density (34.64-48.89 mg/cm(3)) and low thermal conductivity (0.03274-0.04317Wm(-1) K-1) although the sintering temperature was as high as 1400 degrees C much higher than the service temperature of the traditional nanoparticle aerogel. In addition, besides controlling the fabrication parameters, the physical and mechanical properties could be also tuned by adjusting the composition of the nanofibers. The research of this work provides a new insight into the development of high efficient thermal insulation materials used at high temperatures.