Enhancing high-temperature antioxidation and ablation resistance of phenolic aerogel composites with Si-Zr ceramic-coated carbon fibers

Phenolic impregnated carbon ablator (PICA) is a lightweight ablative material extensively used in thermal protection systems. However, its performance is limited by the poor oxidation resistance of carbon fibers and the insufficient thermal stability of the phenolic matrix at elevated temperatures. To address these challenges, a Si–Zr binary-modified carbon fiber-reinforced phenolic aerogel composite (denoted as S a Z b -CF/PA) was fabricated via a two-step sol–gel process. A SiO 2 –ZrO 2 ceramic coating was formed in situ on the fiber surface, serving as an effective barrier against oxygen diffusion. The resulting composite exhibits a low density (∼0.70 g/cm 3 ), high compressive strength, and excellent oxidation and ablation resistance. After exposure to air at 1000 °C, S a Z b -CF/PA retained 47.5 wt% of its mass, whereas the unmodified composite retained only 2 wt%. Under oxyacetylene flame testing (2 MW/m 2 for 60 s), the composite demonstrated low linear and mass ablation rates of 0.0160 mm/s and 0.0048 g/s, respectively. Microstructural analysis revealed the formation of a dense and continuous SiO 2 –ZrO 2 -rich ceramic layer that effectively protects the underlying structure during ablation. These results indicate that fiber-level ceramic modification via sol–gel coating is a promising strategy for developing high-performance lightweight ablative composites for extreme thermal environments.