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• An in situ extreme thermal-force coupled X-ray tomography testing system is described. • Temperature-induced failure mode transition is revealed by time-lapse X-ray tomography. • The role of thermal residual stresses and voids is analyzed via high-fidelity simulations. Carbon fiber reinforced silicon carbide matrix composites (C/SiC) have emerged as key materials for thermal protection systems owing to their high strength-to-weight ratio, high-temperature durability, resistance to oxidation, and outstanding reliability. However, manufacturing defects deteriorate the mechanical response of these composites under extreme thermal-force coupling conditions, prompting significant research attention. This study demonstrates a customized in situ loading device compatible with synchrotron radiation facilities, enabling high spatial and temporal resolution recording of internal material damage evolution and failure behavior under thermal-force coupling conditions. Infrared thermal radiation units in a confocal configuration were used to create ultra-high-temperature environments, offering advantages of compactness, rapid heating, and versatility. In situ tensile tests were conducted on C/SiC samples in a nitrogen atmosphere at both room temperature and 1200 °C. The high-resolution image data demonstrate various failure phenomena, such as matrix cracking and pore linkage. Image-based finite element simulations indicate that the temperature-dependent variation of the failure mechanism is attributable to thermal residual stresses and defect-induced stress concentrations. This work seamlessly integrates extreme mechanical testing methods with in situ observation techniques, providing a comprehensive solution for accurately quantifying crack initiation, pore connection, and failure behavior of C/SiC composites. [Display omitted] [ABSTRACT FROM AUTHOR]

• C f /(CrZrHfNbTa)C–SiC high-entropy ceramic matrix composites with excellent load-bearing, electromagnetic shielding and ablation resistance were designed and reported for the first time. • Single-phase (CrZrHfNbTa)C was successfully synthesized at 1700 ℃ with a small amount of Si as an additive, which is the lowest temperature for the synthesis of (CrZrHfNbTa)C via solid-phase route reported in literature. • C f /(CrZrHfNbTa)C–SiC composites were fabricated by a combined processing of SIL and PIP. • The total electromagnetic interference shielding efficiency of the composites are as high as 88.2 dB and 90 dB respectively in X-band and Ku-band. In this work, C f /(CrZrHfNbTa)C–SiC high-entropy ceramic matrix composites with good load-bearing, electromagnetic shielding and ablation resistance were designed and reported for the first time. The composites were fabricated by an efficient combined processing of slurry infiltration lamination (SIL) and precursor infiltration and pyrolysis (PIP). Density and porosity of the as-fabricated composites are 2.72 g/cm3 and 12.44 vol.%, respectively, and the flexural strength is 185 ± 13 MPa. Due to the carbon fiber reinforcement with high conductivity and strong reflection, and high-entropy (CrZrHfNbTa)C ceramic matrix with strong absorbability, the total Electromagnetic interference shielding efficiency (SE T) of the composites with a thickness of 3 mm are as high as 88.2 dB and 90 dB respectively in X-band and Ku-band. This means that higher than 99.999999 % electromagnetic shielding is achieved at 8–18 GHz, showing excellent electromagnetic shielding performance. The C f /(CrZrHfNbTa)C–SiC composites also present excellent ablation resistance, with the linear and mass ablation rates of 0.9 µm/s and 1.82 mg/s after ablation at the heat flux of 5 MW/m2 for 300 s (∼2450 °C). This work opens a new insight for the synergistic design of structural and functional integrated materials with load-bearing, electromagnetic shielding and ablation resistance, etc. [Display omitted] [ABSTRACT FROM AUTHOR]

Redispersion is an effective method for regeneration of sintered metal-supported catalysts. However, the ambiguous mechanistic understanding hinders the delicate controlling of active metals at the atomic level. Herein, the redispersion mechanism of atomically dispersed Pt on CeO2is revealed and manipulated by in situtechniques combining well-designed model catalysts. Pt nanoparticles (NPs) sintered on CeO2nano-octahedra under reduction and oxidation conditions, while redispersed on CeO2nanocubes above ∼500 °C in an oxidizing atmosphere. The dynamic shrinkage and disappearance of Pt NPs on CeO2(100) facets was directly visualized by in situTEM. The generated atomically dispersed Pt with the square-planar [PtO4]2+structure on CeO2(100) facets was also confirmed by combining Cs-corrected STEM and spectroscopy techniques. The redispersion and atomic control were ascribed to the high mobility of PtO2at high temperatures and its strong binding with square-planar O4sites over CeO2(100). These understandings are important for the regulation of atomically dispersed platinum catalysts.

The interface structure of supported catalysts plays a significant role in the strong metal–support interactions (SMSI). However, it remains limited on interpreting interface structures, thus affecting the understanding of SMSI origin and impact on catalytic performance. Herein, electronic energy loss spectroscopy was adopted to characterize the interface microstructures of Pt/TiO2materials. After high-temperature reduction processing, it was observed that the coating on the surface of the Pt metal particles was TiOx. Then, based on Gaussian function fitting, an effective and valid method was established for quantitative analysis on Ti L edge loss spectrum. This method allowed us to accurately determine the stoichiometric number of TiOxphases. In order to probe the classical phenomenon of strong metal–support interactions in more detail, we also discussed and analyzed the origin of TiOxand its effect on the electronic structure of the material using density functional theory calculations. The structure of surfaces and interfaces as well as the chemical evolution of supported catalysts on a microscale have been revealed, thereby providing a new analysis method and research perspectives for the future study of metal–support interactions.

• Fabricate an efficient 3D-rGO/BN/SiC EMWs absorber with a hierarchical structure. • The macro/microstructural of the hierarchical structures can be easily regulated. • The 3D-rGO skeleton endows strong multiple scattering of the incident EMWs. • The rGO/BN/SiC multi-interface structure optimizes the impedance matching. • The hierarchical structure introduces multiple loss mechanisms to attenuate EMWs. In this work, hierarchical hybrid composites consisting of porous three-dimensional reduced graphene oxide (3D-rGO) skeleton and lamellar boron nitride (BN)/silicon carbide (SiC) coatings are prepared by chemical vapor infiltration (CVI) process. The graphene framework prepared by 3D printing and frozen self-assembly exhibits a lightweight structure and a perforated conductive network, which extends the transmission path of incident microwaves. The introduced ceramic coatings can effectively tune the impedance matching degree and supply a lossy phase, and the hierarchical structure of the composites enhances the multiple scattering of the incident microwaves. As expected, the 3D-rGO/BN/SiC composites possess an excellent absorbing performance with a minimum reflection loss value of –37.8 dB, and the widest effective absorbing bandwidth (RL < –10 dB) of 5.90 GHz is obtained. The controllable fabrication of composites can provide a guideline for rational design and fabrication of high-performance electromagnetic waves absorbing materials in practical applications. [Display omitted] [ABSTRACT FROM AUTHOR]

Control of subsurface interstitial atoms in transition metals is an effective approach to modulate selectivity in hydrogenation reactions. In this study, nickel was alloyed with gallium to form Ni3Ga, thereby regulating the octahedral interstitial sites. Subsequently, carbon atoms were introduced into the Ni3Ga (forming Ni3GaC0.5) viathermal treatment in an acetylene atmosphere, leading to a significant enhancement in selectivity for acetylene hydrogenation reaction. The X-ray diffraction and transmission electron microscopy results demonstrate an increase in the lattice parameter due to the incorporation of carbon atoms and the uniform distribution of carbon in Ni3GaC0.5nanoparticles. The obtained Ni3GaC0.5/oCNT catalyst exhibits significantly improved selectivity in acetylene hydrogenation reaction, with approximately 82% ethylene selectivity at 98% conversion. Furthermore, it maintains good selectivity at various hydrogen-to-alkyne ratios and displays good stability during long-term operation. The introduction of carbon suppresses the formation of the subsurface hydrogen structure under reaction conditions. Additionally, the charge transfer between carbon and nickel results in the electron deficiency of nickel, effectively inhibiting the over-hydrogenation pathway and enhancing the selectivity. These results provide insights for the design of non-precious metal catalysts in selective hydrogenation reactions.

Layer-structured interphase, existing between reinforcing fiber and ceramics matrix, is an indispensable constituent for fiber-reinforced ceramic composites due to its determinant role in the mechanical behavior of the composites. However, the interphase may suffer high residual stress because of the mismatch of thermal expansion coefficients in the constituents, and this can exert significant influence on the mechanical behavior of the composites. Here, the residual stress in the boron nitride (BN) interphase of continuous SiC fiber-reinforced SiC composites was measured using a micro-Raman spectrometer. The effects of the residual stress on the mechanical behavior of the composites were investigated by correlating the residual stress with the mechanical properties of the composites. The results indicate that the residual stress increases from 26.5 to 82.6 MPa in tension as the fabrication temperature of the composites rises from 1500 to 1650 °C. Moreover, the increasing tensile residual stress leads to significant variation of tensile strain, tensile strength, and fiber/matrix debonding mode of the composites. The sublayer slipping of the interphase caused by the residual stress should be responsible for the transformation of the mechanical behavior. This work can offer important guidance for residual stress adjustment in fiber-reinforced ceramic composites.

The investigation of two-dimensional atomically thin superconductors—especially those hosting topological states—attracts growing interest in condensed-matter physics. Here we report the observation of spin–orbit–parity coupled superconducting state in centrosymmetric atomically thin 2M-WS2, a material that has been predicted to exhibit topological band inversions. Our magnetotransport measurements show that the in-plane upper critical field not only exceeds the Pauli paramagnetic limit but also exhibits a strongly anisotropic two-fold symmetry in response to the in-plane magnetic field direction. Furthermore, tunnelling spectroscopy measurements conducted under high in-plane magnetic fields reveal that the superconducting gap possesses an anisotropic magnetic response along different in-plane magnetic field directions, and it persists much above the Pauli limit. Self-consistent mean-field calculations show that this unusual behaviour originates from the strong spin–orbit–parity coupling arising from the topological band inversion in 2M-WS2, which effectively pins the spin of states near the topological band crossing and gives rise to an anisotropic renormalization of the effect of external Zeeman fields. Our results identify the unconventional superconductivity in atomically thin 2M-WS2, which serves as a promising platform for exploring the interplay between superconductivity, topology and strong spin–orbit–parity coupling.

Ultra-high temperature ceramics (UHTCs) are generally referred to the carbides, nitrides, and borides of the transition metals, with the Group IVB compounds (Zr & Hf) and TaC as the main focus. The UHTCs are endowed with ultra-high melting points, excellent mechanical properties, and ablation resistance at elevated temperatures. These unique combinations of properties make them promising materials for extremely environmental structural applications in rocket and hypersonic vehicles, particularly nozzles, leading edges, and engine components, etc. In addition to bulk UHTCs, UHTC coatings and fiber reinforced UHTC composites are extensively developed and applied to avoid the intrinsic brittleness and poor thermal shock resistance of bulk ceramics. Recently, highentropy UHTCs are developed rapidly and attract a lot of attention as an emerging direction for ultra-high temperature materials. This review presents the state of the art of processing approaches, microstructure design and properties of UHTCs from bulk materials to composites and coatings, as well as the future directions.

In this work, carbon nanotube (CNT) based nanocomposites with high mass fraction are proposed by in-situ bridging carbon matrix into CNT paper through optimized chemical vapor infiltration (CVI). Nanoinfiltration behavior of CNTs is basically investigated under the CVI process. The contact between each CNT can be strengthened and the conductive pathways can be established, resulting in the better mechanical and electrical properties. Compared with the pristine CNT paper, the CNT/C composite after pyrolysis process confirms a remarkable advance in tensile strength (up to 310 ± 13 MPa) and Young's modulus (up to 2.4 ± 0.1 GPa). Besides, a notable feature of electrical conductivity also shows an improvement up to 8.5 S/cm, which can be attributed to the mass fraction of CNT (41 wt%) breaking the limits of percolation thresholds and the efficient densification of this sample to establish the conductive pathways. This study has a broad application in the development of the multi-functional electrical and engineering materials. [ABSTRACT FROM AUTHOR]

In this work, three-dimensional (3D) Cf/SiBCN composites were fabricated by polymer infiltration and pyrolysis (PIP) with poly(methylvinyl)borosilazane as SiBCN precursor. The 3D microstructure evolution process of the composites was investigated by an advanced X-ray computed tomography (XCT). The effect of dicumyl peroxide (DCP) initiator addition on the crosslinking process, microstructure evolution, and mechanical properties of the composites were uncovered. With the addition of a DCP initiator, the liquid precursor can cross-linking to solid-state at 120 °C. Moreover, DCP addition decreases the release of small molecule gas during pyrolysis, leading to an improved ceramic yield 4.67 times higher than that without DCP addition. After 7 PIP cycles, density and open porosity of the final Cf/SiBCN composite with DCP addition are 1.73 g·cm-3and ~10%, respectively, which are 143.0% higher and 30.3% lower compared with the composites without DCP addition. As a result, the flexural strength and elastic modulus of Cf/SiBCN composites with DCP addition (371 MPa and 31 GPa) are 1.74 and 1.60 times higher than that without DCP addition (213 MPa and 19.4 GPa), respectively.

Fiber damage and uniform interphase preparation are the main challenges in conventional short fiber reinforced ceramic matrix composites. In this work, we develop a novel processing route in fabrication of short carbon fiber reinforced ZrB2-SiC composites (Csf/ZrB2-SiC) overcoming the above two issues. At first, Csfpreforms with oriented designation and uniform PyC/SiC interphase are fabricated via direct ink writing (DIW) of short carbon fiber paste followed by chemical vapor infiltration. After that, ZrB2and SiC are introduced into the preforms by slurry impregnation and reactive melt infiltration, respectively. Microstructure evolution and optimization of the composites during fabrication are investigated in detail. The as-fabricated Csf/ZrB2-SiC composites have a bulk density of 2.47 g/cm3, with uniform weak interphase and without serious fiber damage. Consequently, non-brittle fracture occurs in the Csf/ZrB2-SiC composites with widespread toughening mechanisms such as crack deflection and bridging, interphase debonding, and fiber pull-out. This work provides a new opportunity to the material design and selection of short fiber reinforced composites.

In this work, the interconnected graphene scaffolds are prepared by three-dimensional (3D) printing for multifunctional gas detection with tunable sensitivity. The scaffolds with regularly aligned graphene conductive networks exhibit significant mechanical strength and high electrical stability to multi-direction deformation, which can be attributed to the typical core-shell structure of graphene and PVP. The resistance of the free-standing scaffolds can realize the real-time response to H 2 O and NO 2 , and the relative resistance change to 100 ppm H 2 O and 100 ppm NO 2 can reach 2% and 2.5 %, respectively. The charge doping of the oxidizing gases is considered to be the main reason for various response sensitivities of the scaffolds with different orthogonal layers, in which the interconnected conductive network can generate a large specific surface area and significantly improving the adsorption of the target gases and the transfer of charge. The controllable fabrication of regular structure has appropriately great potential for further optimizations and applications in gas detection. [ABSTRACT FROM AUTHOR]

Residual stress originated from thermal expansion mismatch determines the mechanical properties of ceramic matrix composites (CMCs). Here, continuous SiC fiber reinforced SiC matrix (SiCf/SiC) composites were fabricated by nano-infiltration and transient eutectic-phase (NITE) method, and the residual stress of the composites was investigated using high-temperature Raman spectrometer. With temperature increasing from room temperature to 1400 °C, the residual stresses of the matrix and the fiber decrease from 1.29 to 0.62 GPa and from 0.84 to 0.55 GPa in compression respectively, while that of the interphase decreases from 0.16 to 0.10 GPa in tension. The variation of residual stress shows little effect on the tensile strength of the composites, while causes a slight decrease in the tensile strain. The suppression of fiber/matrix debonding and fiber pulling-out caused by the residual stress reduction in the interphase is responsible for the decreasing tensile strain. This work can open up new alternatives for residual stress analysis in CMCs.

Graphene has attracted increasing attention for strain sensing due to its unique electrical and mechanical properties by tailoring and assembling functional macrostructures with a well-defined configuration. Here a novel graphene-based planar network (GPN) with highly stretchable strain sensing is developed by direct ink writing. The integrated and regulated structure of GPN indicates an excellent response sensitivity and cyclic stability to various strain modes compared with the traditional graphene-based woven fabric (GWF) structure. An equivalent resistance network is introduced to analyze the resistance change mechanism and fracture failure mode of the network structures, in which the difference can be mainly attributed to the interfacial resistance at the crosspoints of the crossed ribbons. The tunable and interconnected GPN shows a significant difference in the response sensitivity under stretching strain in different directions, and the relative resistance change is up to 20 and 3 in horizontal and vertical directions after 1000 cycles for a 20% stretching strain, respectively, which can be explained by the transformation of the stretching mode from macro-structural stretching to micromaterial stretching. The controllable fabrication of GPN can be utilized not only for the detection of full-range human activities but monitoring external stress distribution in real-time by integration.

A thin BN interphase is applied on BNNTs surface to tailor the interfacial bonding between BNNTs and SiC matrix in hierarchical SiCf/SiC composites. The thickness of BN interphase ranging from 10 to 70 nm can be optimized by chemical vapor deposition after BNNTs are in situ grown on SiC fiber surface. Without BN interphase, the fracture toughness of hierarchical SiCf/SiC composites can be impaired by 13.6% due to strong interfacial bonding. As long as BN interphase with 30–45 nm thickness is applied, the interfacial bonding can be optimized and fracture toughness of hierarchical composites can be improved by 27.3%. It implies that tailoring BNNTs/matrix interface by depositing a layer of BN interphase is in favor of activating energy dissipation mechanisms at nanoscale induced by BNNTs.

Reactive melt infiltration (RMI) is an effective method for fabrication of highly dense carbon fiber reinforced ultra-high temperature ceramic matrix composites (Cf/UHTCs). In this work, Cf/SiC-ZrC-ZrB2composites were fabricated by infiltrating ZrSi2melt into porous Cf/B4C-C preforms, where the physical and chemical reactions involved during the RMI process were identified and analyzed. Inhomogeneous infiltration between the inter- and intra-bundle pores was revealed, and was found to be strongly related to the pore structures of the Cf/B4C-C preform. It is indicated that the inhomogeneous infiltration can be mitigated remarkably with increasing porosity and pore size of the preform. The effect of pore size on the RMI process was also investigated by a quantitative model, which agrees very well with the experiment results. It further indicates that the inhomogeneous infiltration can also be relieved at elevated RMI temperature. However, excessive infiltration at elevated temperature or more porous preform may cause serious erosion on interphase and fibers, leading to mechanical properties deterioration of the final composites.

Using liquid poly(methylvinyl)borosilazanes (PMVBSZ) as precursor, carbon fiber reinforced SiBCN matrix composites (Cf/SiBCN) were fabricated by a modified polymer infiltration and pyrolysis (PIP) process. With dicumyl peroxide added as cross-linking agent, the PMVBSZ could be solidified at a low temperature of 120 °C, leading to a high ceramic yield of ~70%. The cross-linking mechanism and ceramization processes of the precursor were investigated in detail. Moreover, a modified infiltration technology was developed, which improved the efficiency and protected the precursor against moist air during PIP. Consequently, the obtained Cf/SiBCN composites had an oxygen content of around 1.22 wt%. Benefiting from the high ceramic yield and high efficiency of the modified PIP, Cf/SiBCN composites with an open porosity of ~10% and uniform microstructure were obtained after only 7 cycles of PIP. The flexural strength and fracture toughness of the derived Cf/SiBCN composites were 371 MPa and 12.9 MPa·m1/2, respectively. This work provides a potential route for the fabrication of high performance Cf/SiBCN composites.

ZrB2–ZrC–SiC ternary coatings on C/C composites are investigated by reactive melt infiltration of ZrSi2alloy into pre-coatings. Two different pre-coating structures, including porous B4C–C and dense C/B, are designed by slurry dip and chemical vapor deposition (CVD) process respectively. The coating prepared by reactive melt infiltration (RMI) into B4C–C presents a flat and smooth surface with a three-layer cross-sectional structure, namely interior SiC transition layer, gradient ZrB2–ZrC–SiC layer, and ZrB2–ZrC exterior layer. In comparison, the coating prepared by RMI into C/B shows a more granular surface with a different three-layer cross-sectional structure, interior unreacted B–C pre-coating layer, middle SiC layer, and exterior ZrB2–ZrC–ZrSi2layer. The forming mechanisms of the specific microstructures in two coatings are also investigated and discussed in detail.

Boron carbide (B4C)/graphite (C) ceramic pellets containing 25 wt% B4C as an ideal structural component in Chinese 10 MW high temperature gas-cooled test reactor (HTR-10) were successfully prepared by a two-stage operation method at low temperature. Initially, the samples were pressurelessly sintered at 1373 K and subsequently infiltrated with phenolic resin, pyrolysed at 1473 K, then coated with carbon by chemical vapour deposition at 1273 K. Morphology and structure of the samples were analysed by SEM and X-ray diffraction. The mechanical properties of the sintered bodies were also investigated. Superior properties were obtained due to the formation of pyrolytic carbon during the two-stage operation process. Density and compression strength of the samples were 1.94 g.cm–3and 620 N, respectively. In addition, the rate of abrasion and moisture resistance were near zero for the samples.

Here a free-standing and high-performance electromagnetic wave (EMW) absorber is developed by the in-situ growth of SiC into 3D-printed carbon-based scaffolds by chemical vapor deposition (CVD). The porous and interconnected network of graphene nanoplatelets (GNPs)/carbon nanotubes (CNTs) is oriented constructed and Fe-based magnetic nanoparticles are uniformly dispersed. Accompanied by the optimization of SiC to the mechanical properties of composites, the impedance matching behavior and attenuation capacity can be regulated by reducing the electrical conductivity of the carbon-based nanonetwork. Therefore, the as-prepared composites present a minimum reflection loss (RL) value of −48.7 dB, and a 2 mm-thick absorber whose reflection loss is better than −10 dB in 11.5–15.8 GHz is also achieved. Besides, the absorbing properties of the material remained consistent after annealing at 400 °C for 4 h. The controllable fabrication of composites shows appropriately promising potential as absorbers in a high-temperature environment with considerable EMW absorption performance.

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A new strategy for elaborate regulation of microstructure was successfully introduced by the ice template‑assisted 3D printing and chemical vapor deposition strategy, including graphene nanoplate/silicon carbide nanowires hierarchical porous structure and graphene nanoplate/boron nitride composite heterogeneous interface.The composite exhibits excellent electromagnetic wave absorption performance with an RLminof -37.8 dB and an EABmaxof 9.2 GHz (from 8.8 to 18.0 GHz) at 2.5 mm. And the high-temperature absorption stability makes it a promising absorber candidate under high temperature and oxidizing atmosphere.