Silicon carbide (SiC) aerogels hold immense promise for extreme environment applications; however, conventional homogeneous architectures hinder their multifunctional integration. Herein, a sandwich-structured SiC nanowire aerogel with gradient porosity was engineered through a one-step in situ growth strategy, combining a dense sub-micropore (<1 μm) shell and a macroporous (10–360 μm) core. The nanoconfined pores of the shell suppress gas-phase thermal transport by limiting molecular collisions, while the air-entrapped macropores of the core minimize solid-phase conduction, synergistically yielding a low thermal conductivity of 0.05 W/(m·K), 33% lower than that of the homogeneous counterparts. The continuous gradient interface eliminates interfacial delamination and redistributes stress, achieving a strong mechanical resilience (11.2 kPa compressive strength) via shell-layer nanowire friction and elastic recovery (90% strain retention after 100 cycles) through core-layer dendritic flexibility. Single-crystal nanowires, stabilized by a self-passivating amorphous layer (~20 nm), ensure structural integrity at 1400 ℃ with negligible oxidation. Furthermore, the hierarchical architecture facilitates broadband microwave absorption via gradient impedance matching and multiscale reflections. By integrating template-guided polymer conversion and catalyst-directed nanowire assembly, this work pioneers a scalable paradigm for multifunctional aerogels that combine extreme thermal insulation, mechanical durability, and microwave absorption properties, providing a transformative solution for next-generation aerospace thermal protection systems.

Metal‒organic framework (MOF) derivatives employed as electromagnetic wave (EMW) absorption materials have gained considerable attention because of their plentiful coordination components and diverse nanomicrostructures. However, achieving broadband EMW absorption solely through nanoscale structural design remains challenging. Herein, a cross-scale structural engineering strategy is proposed to address this limitation. At the nanomicroscale, MOF-derived Co_xNi_y@C nanorods were fabricated via a solvothermal and pyrolysis process. Systematic manipulation of the built-in electric field (BIEF) heterointerface achieved through adjusting the Co/Ni atomic ratio significantly promotes electron-directed migration, alters the spatial charge distribution, and ultimately enhances the polarization relaxation and magnetic resonance effects, resulting in superior EMW absorption performance (the effective absorption bandwidth of Co₂Ni@C is 4.9 GHz at 1.75 mm). The geometric configuration of the electromagnetic metastructures was subsequently optimized via CST software. Through cross-scale structural design, the simulated gradient honeycomb structure metamaterial composed of Co₂Ni@C achieves multiband compatibility, and the EAB reaches 38 GHz (covering 2–40 GHz) with a total thickness of 15 mm. This research elucidates the BIEF loss mechanism of MOF-derived Co_xNi_y@C composites by rationally controlling the Co/Ni atomic ratio and provides novel insights into the structural design of electromagnetic nanomaterials.

To enhance the resistance of SiC_f/SiC to hydrothermal corrosion in the pressurized water reactor (PWR) environment, structurally tunable Ti₃SiC₂-based corrosion mitigation coatings for SiC_f/SiC were prepared using molten salt synthesis. The influence of various process parameters, such as Si/Ti molar ratio in raw materials, annealing time, and annealing temperature, on the phase composition and the structure of the coatings was explored. Through the process control, the fabricated coatings can be either Ti₃SiC₂ monolithic structure or TiC/Ti₃SiC₂ and TiC/Ti₃SiC₂/Ti₅Si₃C_x multi-layered structures. The coatings demonstrate strong bonding to the substrate due to in-situ reaction, exhibiting tensile and shear strength of at least 26.9 and 30.8 MPa, respectively. Incorporating TiC as a transition layer further enhances the tensile and shear strength to 41.3 and 51.4 MPa, respectively. Monolithic Ti₃SiC₂ coatings enhance the thermal conductivity of SiC_f/SiC by 10%–12%. Notably, Ti₃SiC₂ coatings effectively protect SiC_f/SiC from hydrothermal corrosion, demonstrating an 83% strength retention rate compared to 71% in the control group after corrosion. However, the Ti₅Si₃C_x layer exhibits unsatisfactory corrosion mitigation. The Ti₃SiC₂ monolithic coating has higher thermal conductivity, TiC/Ti₃SiC₂ multi-layered coating has higher bonding strength, and both have desirable resistance to the hydrothermal corrosion.

Three strategies were proposed to prolong the service life of continuous fiber-reinforced silicon carbide ceramic matrix composite (CMC-SiC), which served as thermal-structure components of aeroengine at thermo-mechanical-oxygenic coupling environment. As for some thermal-structure components with low working stress, improving the degree of densification was crucial to prolong the service life, and the related process approaches were recited. If the thermal-structure components worked under moderate stress, the matrix cracking stress (σ_mc) should be improved as far as possible. The fiber preform architecture, interface shear strength, residual thermal stress, and matrix strengthening were associated with σ_mc in this review. Introducing self-healing components was quite significant with the appearance of matrix microcracks when CMC-SiC worked at more severe environment for hundreds of hours. The damage can be sealed by glass phase originating from the reaction between self-healing components and oxygen. The effective self-healing temperature range of different self-healing components was first summarized and distinguished. The structure, composition, and preparation process of CMC-SiC should be systematically designed and optimized to achieve long duration target.

The microstructure of polymer-derived ceramics (PDCs) was closely related to processing. This study demonstrated that SiCN matrix prepared by polymer infiltration and pyrolysis (PIP) at 900 ℃ inside a Si₃N₄ whisker (Si₃N_4w) preform with submicro-sized pores differed from its powder- consolidated analogue in both the content and structure of free carbon. Chemical analysis showed that PIP process had a higher free carbon yield. Raman spectroscopy and transmission electron microscopy (TEM) observation discovered a higher graphitization degree of free carbon and the existence of nanocrystalline graphite in SiCN matrix. Dielectric properties of Si₃N_4w/SiCN composites were greatly enhanced when volume fraction of SiCN matrix reached 24.5% due to dielectric percolation caused by highly-lossy free carbon. Reconsolidation of hydrocarbon released during pyrolysis by gas-state carbonization in Si₃N₄ whisker preform was supposed to account for the high yield and graphitization degree of free carbon in PIP process.

The SiBCN matrix via chemical vapor infiltration (CVI) or/and polymer infiltration pyrolysis (PIP) technologies was orderly introduced to SiC_f/SiC composites to optimize the mechanical property and electromagnetic (EM) shielding effectiveness simultaneously. The BN interface with the thickness of 350 nm was designed to obtain a little stronger interface bonding. The flexural strength of SiC_f/SiC-SiBCN composites reached 545.45±29.59 MPa thanks to the crack deflection between the CVI SiC and CVI SiBCN, as well as CVI SiBCN and PIP SiBCN matrix because of the modulus difference between them. The fracture toughness (K_IC) with the value of 16.02±0.94 MPa·m^1/2 was obtained owing to the extension of crack propagation path. The adverse effect of stronger interface bonding was eliminated by the design of matrix microstructure for SiC_f/SiC-SiBCN composites. The thermal conductivity in the thickness direction was 7.64 W·(m·K)^-1 at 1200 ℃ and the electric resistivity decreased to 1.53×10³ Ω·m. The tunable dielectric property was obtained with the coordination of wave-absorption CVI SiBCN matrix and impedance matching PIP SiBCN matrix, and the total shielding effectiveness (SE_T) attained 30.01 dB. It indicates that the SiC_f/SiC-SiBCN composites have great potential to be applied as structural and functional materials.

Porous Si₃N₄-Si₃N₄ composite ceramics were fabricated by 3D printing combined with low-pressure chemical vapor infiltration (CVI). This technique could effectively improve the designability of porous Si₃N₄ ceramics and optimize the mechanical and dielectric properties. The effects of process parameters including the deposition time and heat treatment on the microstructure and properties of porous Si₃N₄-Si₃N₄ composite ceramics were studied. The study highlights following: When CVI processing time was increased from 0 to 12 h, the porosity decreased from 68.65% to 26.07% and the density increased from 0.99 to 2.02 g/cm³. At the same time, the dielectric constant gradually increased from 1.72 to 3.60; however, the dielectric loss always remained less than 0.01, indicating the excellent electromagnetic (EM) wave-transparent performance of porous Si₃N₄-Si₃N₄ composite ceramics. The maximum flexural strength of 47±2 MPa was achieved when the deposition time attained 6 h. After heat treatment, the porosity increased from 26.07% to 36.02% and the dielectric constant got a slight increase from 3.60 to 3.70 with the dielectric loss still maintaining lower than 0.01. It has been demonstrated that the porous Si₃N₄-Si₃N₄ composite ceramics are a promising structural and EM wave-transparent material suitable for high temperature service.