Mechanically Robust Precursor‐Derived Si 3 N 4 Aerogel for Wave Transparency and Thermal Insulation

ABSTRACT 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.