A New Class of Opacified Monolithic Aerogels of Ultralow High-Temperature Thermal Conductivities

The development of materials of ultralow high-temperature thermal conductivities for applications in high-temperature thermal insulations has become increasingly more important than ever in view of the ever worsening issues of fossil energy depletion and global warming that call for more demanding energy-saving practices. In this study, a new class of opacified monolithic aerogels of ultralow high-temperature thermal conductivities was developed for thermal insulation applications at high temperatures. Carbon nanofibers were successfully incorporated into the mesoporous network of silica aerogels at concentrations as high as 20 wt % through an accelerated-gelation sol−gel process to enhance the dimensional stability of the silica aerogels and to suppress the thermal radiations that become dominant at high temperatures, to achieve an ultralow thermal conductivity of 0.050 W/m-K at 500 °C, whereas maintaining a thermal stability above 500 °C (much better than the conventional high-temperature thermal insulation materials: 0.3 W/m-K at 500 °C for glass fibers, 0.1 W/m-K at 527 °C for alumina fused brick, and 1.7 W/m-K at 527 °C for sillimante).