Resilient Si ₃ N ₄ Nanobelt Aerogel as Fire-Resistant and Electromagnetic Wave-Transparent Thermal Insulator

With the prevailing energy challenges and the rapid development of aerospace engineering, high-performance thermal insulators with various functions are attracting more and more attention. Ceramic aerogels are promising candidates for thermal insulators to be applied in harsh environments because of their low thermal conductivity and simultaneously excellent thermal and chemical stabilities. In general, the effective properties of this class of materials depend on both their microstructures and the intrinsic properties of their building blocks. Herein, to enrich the family and broaden the application fields of this class of materials, we prepared ultralight α-Si ₃ N ₄ nanobelt aerogels (NBAs) with tunable densities ranging from 1.8 to 9.6 mg cm ^-3 . The α-Si ₃ N ₄ NBA realized resilient compressibility (with a recoverable strain of 40-80%), fire resistance (1200 °C butane blow torch), thermal insulation (0.029 W m ^-1 K ^-1 ), and electronic wave transparency (a dielectric constant of 1-1.04 and a dielectric loss of 0.001-0.004) in one material, which makes it a promising candidate for mechanical energy dissipative, fire-resistant, and electronic wave-transparent thermal insulator to be applied in extreme conditions. The successful preparation of such resilient and multifunctional α-Si ₃ N ₄ NBAs will open up a new world for the development and widespread applications of ceramic aerogels.