SiBCN ceramic aerogels have emerged as a new generation of integrated thermal insulation and microwave absorption materials but face great challenges in terms of mechanical properties, high-temperature stability, and absorption bandwidth in practical applications. Herein, SiBCN/SiOC composite ceramic aerogels were prepared by solvent thermal crosslinking, freeze-drying, and pyrolysis of precursors. Polyhydromethylsiloxane (PHMS) was introduced in situ by the hydrosilane addition reaction during the solvothermal process, which endowed the precursor aerogel with a complex and robust three-dimensional network structure and further resulted in a 260% improvement in the compressive strength of the SiBCN/SiOC composite aerogel compared with that of the pure SiBCN aerogel. Additional investigations revealed that the SiBCN/SiOC composite aerogel enjoyed a low thermal conductivity (0.044–0.051 W·m⁻¹·K⁻¹) and a light weight (0.13–0.16 g·cm⁻³), which was favorable for thermal barrier material. Notably, the SiBCN/SiOC composite aerogel exhibited excellent microwave absorption performance with an effective absorption bandwidth of 6.7 GHz and a reflection loss of −43.89 dB at a thickness of 2.5 mm due to improved impedance matching, multiple reflections, and enhanced interfacial polarization. Furthermore, the introduction of SiOC significantly inhibited the crystallization of SiBCN at high temperatures. After heat treatment at 1600 °С, the composite aerogel retained its amorphous nanoparticle pearl-chain-like structure, with thermal conductivity remaining as low as 0.052 W·m⁻¹·K⁻¹. The in situ introduction of PHMS provided novel insight and a promising strategy for enhancing the overall performance of SiBCN ceramic aerogels, expanding their application in high-temperature environments.

C/SiC composites have been identified as significant potential thermal protection materials for aerospace. However, the widespread application of most C/SiC composites is generally limited by their poor balance between rapid, efficient fabrication and superior material performance. Here, we propose a scalable combined process that integrates multistep slurry impregnation (MSI) with a polymer infiltration and pyrolysis (PIP). The MSI process developed in this work enabled the consistent infusion and tight packing of a substantial SiC powder content (34 vol%) within the fiber fabric, leading to a green body with a relative density reaching 64.7 vol%. This densely packed structure was subsequently infiltrated and consolidated by a pyrolytic SiC phase through a rapid PIP cycle, resulting in a composite characterized by high bulk density (2.24 g/cm³) and very low open porosity (2.90%). Notably, the pore size of these C/SiC composites is one to two orders of magnitude smaller than that of those fabricated via conventional PIP methods. The resulting composites display excellent mechanical properties, including a flexural strength of 421±31 MPa and a fracture toughness of 16.33±1.70 MPa·m^1/2. Under exposure to an oxyacetylene flame at 1600–2000 °C, they exhibit exceptionally low mass loss and linear ablation rates, attributed to their minimal porosity and the thermal stability of the integrated matrix at high temperatures. This integrated MSI-PIP technique represents a rapid, efficient, and scalable method for producing high-performance C/SiC composites and is well suited for advanced aerospace applications.

Finding the optimum balance between strength and toughness, as well as acquiring reliable thermal shock resistance and oxidation resistance, has always been the most concerned topic in the discussion of ultra-high temperature ceramic composites. Herein, PyC modified 3D carbon fiber is used to reinforce ultra-high temperature ceramic (UHTC). The macroscopic block composite with large size is successfully fabricated through low temperature sintering at 1300 ℃ without pressure. The prepared PyC modified 3D C_f/ZrC-SiC composites simultaneously possess excellent physical and chemical stability under the synergistic effect of PyC interface layer and low temperature sintering without pressure. The fracture toughness is increased in magnitude to 13.05 ± 1.72 MPa·m^1/2 accompanied by reliable flexural strength of 251 ± 27 MPa. After rapid thermal shock spanning from room temperature (RT) to 1200 ℃, there are no visible surface penetrating cracks, spalling, or structural fragmentation. The maximum critical temperature difference reaches 875 ℃, which is nearly three times higher than that of traditional monolithic ceramics. The haunting puzzle of intrinsic brittleness and low damage tolerance are resolved fundamentally. Under the protection of PyC interface layer, the carbon fibers around oxide layer and matrix remain structure intact after static oxidation at 1500 ℃ for 30 min. The oxide layer has reliable physical and chemical stability and resists the erosion from fierce oxidizing atmosphere, ensuring the excellent oxidation resistance of the composites. In a sense, the present work provides promising universality in designability and achievement of 3D carbon fiber reinforced ceramic composites.