Mechanical, Wave-Transparent, and Ablation Properties of Silicon Oxycarbide Aerogel Composites

Developing multifunctional lightweight thermal protection materials with reliable insulation, ablation resistance, and wave transparency is crucial for advanced thermal protection systems. Herein, SiOC aerogel-based composites were fabricated via a scalable polymer-derived route using organosilane aerogel precursors, which exhibit low densities of 0.35–0.65 g·cm–3, ultralow thermal conductivities of 0.046–0.058 W·m–1·K–1, and superior wave transparency with a transmittance >80% at 8–18 GHz. Such exceptional performance stems from the high-fidelity preservation of a nanoporous, low-carbon SiOC network during the polymer-to-ceramic transition. Under oxy-acetylene ablation at 1200–1600 °C, the SiOC composites demonstrated a 20–60% reduction in mass loss and 15–45% lower linear recession relative to polymeric precursors, attributed to the formation of a continuous, SiO2-rich passivating layer. Furthermore, the influence of four representative fibers on the dielectric and ablation properties was investigated, revealing a strong dependence on the fiber chemistry. The degradation pathways are categorized into surface densification or fiber oxidation- and melt-softening-dominated processes. This study elucidates the mechanisms of dielectric and thermochemical evolution from both nanoporous matrix and fiber perspectives, providing a reference for the design of multifunctional thermal protection materials.