Low-Interfacial-Defect Carbon Aerogel/Carbon Fiber Composites with In situ Repair–Induced Ultrahigh Compressive Strength for High-Temperature Insulation and Structural Applications

Although carbon aerogel/carbon fiber composites (CACFs) exhibit excellent thermal stability and high-temperature insulating capacity, their compressive strength remains limited because of interfacial defects arising from mismatched carbonization-induced shrinkage between fibers and matrix. Herein, we developed robust CACFs (RCACFs) with ultralow interfacial defects using an in situ repair route to simultaneously meet the demands of high-temperature insulation and structural integrity. X-ray micro computed tomography (micro-CT) revealed that the repair process reduced the interfacial defects (>9.73 μm3) from 22.4 to 4.6%. The repaired composite (0.75 g·cm-3) achieved a compressive strength of 14.3 MPa at a 5% strain, a 180.4% improvement over that of untreated CACFs (5.1 MPa, 0.73 g·cm-3). During high-temperature tensile testing at 1200 °C, in situ micro-CT confirmed the excellent thermal mechanical stability of RCACFs, which retained stable small voids (<0.5 × 102 mm3) and effectively suppressed defect expansion during loading. The as-prepared RCACFs maintained a low thermal conductivity of 0.173 W·m-1·K-1 at 25 °C and 0.901 W·m-1·K-1 at 1200 °C, exhibited negligible volumetric shrinkage at 1600 °C, and demonstrated superior ablation resistance with a linear ablation rate of 1.3 μm·s-1 under an oxyacetylene flame at 1800 °C. These results position RCACFs as promising materials for high-temperature insulation and load-bearing applications in extreme environments.