Multifunctional integrated CNTs/Si-Zr hybrid phenolic aerogel composites with excellent thermal protection and microwave absorbing properties

Designing multifunctional integrated materials for thermal protection and microwave absorption in extreme environments is significantly challenging. In this work, surface-hydroxylated multiwalled carbon nanotubes (OH-MWCNTs) were incorporated into silicon-zirconium (CNTs/Si-Zr) hybrid phenolic aerogel to fabricate lightweight composites having a density of 0.42 g/cm 3 and thermal conductivity of 0.130 W/(m·K). The OH-MWCNTs enhanced the graphitization of pyrolytic carbon and promoted in situ formation of ZrO 2 /SiC multiphase ceramic layers during ablation, demonstrating an ultralow linear ablation rate of 0.034 mm/s under oxyacetylene flame at 2.0 MW/m 2 . The hierarchical porous structure of the hybrid aerogel composites, combined with the encapsulation mosaic architecture of OH-MWCNTs and ceramic-enriched matrices, facilitated multiple electromagnetic wave scattering and interfacial polarization. Consequently, the OH-MWCNTs incorporated CNTs/Si-Zr aerogel composites exhibited broadband microwave absorption, covering 100 % of the Ku-band and 50 % of the X-band. This work demonstrates a synergistic ceramic-forming strategy to integrate thermal protection and microwave absorption in a single material, advancing the development of multifunctional aerogel-based composites for extreme environment applications.