Rigid–Flexible Coupled Si 3 N 4 Nanoribbon Aerogels With Carbon–Ceramic Hot‐Face Armor for Oxidation‐Resistant Thermal Protection Stable to 1600°C in Air

ABSTRACT Reconciling ultralight compliance with ultrahigh‐temperature oxidation resistance under one‐sided heating remains a key challenge for ceramic aerogels in extreme thermal protection systems (TPS). Here we report a spatially programmed rigid–flexible aerogel, locally impregnated ZrO 2 /SiO 2 /C–Si 3 N 4 nanoribbon aerogel (L‐ZSC‐SNRA), fabricated by bidirectional freeze‐casting and stepwise localized impregnation of polycarbosilane (PCS) and Zr‐containing PCS precursors followed by pyrolysis. The ≈30 mg cm −3 monolith is functionally graded, decoupling hot‐face protection from cold‐face compliance by integrating a multiphase ZrO 2 /SiO 2 /C hot‐face armor with a porous elastic Si 3 N 4 skeleton. Consequently, L‐ZSC‐SNRA achieves 98% recoverability at 60% strain with stable 1000‐cycle compression and retains ≈83% recoverability after single‐sided static oxidation in air at 1600°C. It exhibits low thermal conductivity from 25°C–1000°C (38.6–105.2 mW m −1 K −1 ) and strong flame shielding under a ≈1500°C torch, limiting the cold‐side temperature to 218.1°C for a 10‐mm slab after 10 min. Notably, the thermal‐conductivity increase at 1000°C after the 1600°C static oxidation is only 6.8%, evidencing robust high‐temperature thermal‐transport stability. This work overcomes the key trade‐off between ultralight compliance and ultrahigh‐temperature oxidation durability, demonstrating a scalable locally graded coating–architecture strategy for oxidizing extremes relevant to TPS.