Novel PRSi/AlN aerogel composites enabled synergistic thermal insulation and microwave absorption by sealing enhancement strategy and spontaneous ceramization

The rapid advances in aerospace technology have intensified challenges related to extreme thermal and electromagnetic environments. The excellent thermal conductivity and low dielectric loss of AlN limit its use in applications requiring thermal insulation and microwave absorption. Herein, a sealing enhancement strategy (SES) was designed to fabricate silane-modified phenolic resin-reinforced AlN (PRSi/AlN) aerogel composites that combine high strength with spontaneous high-temperature ceramization. The directional pore channels of the AlN/C aerogel are filled with continuous silane-modified phenolic resin (PRSiO2) aerogels, forming a unique sealed structure. Impressively, the composites achieve a compressive strength 492 times that of the AlN/C skeleton, coupled with a low axial thermal conductivity of 0.0382 W·m− 1·K− 1. The oxidation of AlN is followed by spontaneous mullitization with SiO2 during thermal exposure, leading to the formation of a stable mullite phase. Under a short-duration oxyacetylene flame (1.2 MW·m− 2), the composites maintained a backside temperature between 53.4 °C and 68.4 °C, with a linear ablation rate of 0.071 mm·s− 1. Furthermore, the excellent microwave absorption results from synergistic effects within the carbonized layer, where interfacial polarization, dipole polarization, and conduction loss collectively enhance electromagnetic wave (EMW) dissipation. Both composites show excellent performance: PRSi1.0/AlN has a minimum reflection loss (RLmin) of -61.84 dB and an effective absorption bandwidth (EAB) of 5.83 GHz, while PRSi2.0/AlN achieves an even broader EAB of 7.06 GHz. This SES effectively strengthens PRSi/AlN composites by harnessing the advantages of both the reinforcement phase and skeleton, offering a novel paradigm for fabricating thermal protection composites.