Abstract: Carbon fiber reinforced carbon aerogel matrix (C/CA) composites have been considered as attractive can-didates for thermal protection system owing to their excellent thermal insulation and superior thermal stability. However, they still suffer from challenges with insufficient oxidation resistance in practical ap-plication. Herein, a series of novel SiBCN-modified C/CA are developed for the first time through ma-trix modification by introducing precursors with different molecular weights in order to control residual stress. Resultantly, the C/CA-SiBCN composites derived from a high molecular weight precursor show the large residual tensile stress even with the low ceramic contents of 10 % (mass fraction) due to the se-vere shrinkage mismatch during pyrolysis caused by the large SiBCN clusters and their inhomogeneous distribution, as well as the mismatched coefficients of thermal expansion. Comparatively, the composites derived from a low molecular weight precursor have the small carbon-ceramic particles with uniform dis-tribution even though the ceramic content is up to 30 %, thus resulting in the favorable residual compres-sive stress. Accordingly, the C/CA-SiBCN containing a 30 % ceramic content demonstrates the significantly enhanced performance with low residual compressive stress of 0.31 GPa, 52 % mechanical improvement and reduction in oxidation rate by 39.21 %-60.35 % at 80 0-110 0 °C compared to the original C/CA. This work offers a new avenue for enhancing oxidation resistance of C/CA applied as thermal insulators to cope with the harsh operating environments.

Key words: Carbon fiber reinforced carbon aerogel, composites, Matrix modification, Oxidation resistance, Residual stress, Thermal insulator