Mechanically Robust Precursor-Derived Si3N4 Aerogel for Wave Transparency and Thermal Insulation

Structure-function integrated ceramic aerogels that offer mechanical strength, high-temperature stability, wave transparency, and thermal insulation are vital for aerospace radomes and protective systems. Herein, Si 3 N 4 ceramic aerogels were prepared by a carbothermal reduction−nitridation of pre-densified resorcinol–formaldehyde/silica hybrid aerogel powder. Benefiting from an interconnected skeleton and optimized crystallization, the Si 3 N 4 aerogel exhibits a high compressive strength of 48 MPa with a density of 1.02·g cm −3 . Meanwhile, it achieves a low dielectric constant of 2.19–2.36 with ultralow dielectric loss (5.4×10 −3 –9.6×10 −3 ) in the range of 2–18 GHz and a low thermal conductivity (0.0344 Wm −1 ·K −1 at 25°C), ensuring excellent electromagnetic wave transparency and thermal insulation. Ablation tests confirm improved oxidation resistance and structural integrity. This unique combination of properties highlights Si 3 N 4 aerogels as promising candidates for next-generation aerospace radomes and multifunctional components operating in harsh environments.