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In this paper, SiC nanofibers (SiCNFs) as multifunctional interphase were prepared on carbon fibers via catalysis chemical vapor deposition (CCVD) in order to improve the microwave absorption for carbon fiber reinforced silicon nitride (CFs/Si 3 N 4 ) composites. Experimental results indicated that the chemical compatibility between CFs and Si 3 N 4 matrix under high temperature could be effectively improved by incorporating SiCNFs interphase. Additionally, the dielectric responses and microwave absorbing performance of CFs/Si 3 N 4 composites are significantly influenced by the mass fraction of SiCNFs on CFs. An optimal reflection loss (RL) of −14 dB and 96% absorbing bandwidth (BW) of X-band could be achieved in the CFs/Si 3 N 4 composites with 8 wt% of SiCNFs. Furthermore, experimental points of permittivity in Cole-Cole plane are inclined to distribute on distinguishing circular arcs, corresponding to three types of electric polarization modes. It is concluded that the hopping relaxation of electrons between SiCNFs plays more pronounced contribution to the superior microwave attenuation capability of CFs/Si 3 N 4 composites with SiCNFs interphase than the relaxation loss of free electrons inside short CFs. [ABSTRACT FROM AUTHOR]

Abstract Polycarbosilane-derived SiC (PCS-derived SiC) has been suggested as a promising candidate for particularly effective microwave absorption materials. To optimize the microwave absorption properties, while retaining the crystallinity of SiC, PCS-derived SiC ceramics were prepared by a combination of dehydrogenation, appropriate oxidation, and pyrolysis. This study investigated microstructures, dielectric properties, and microwave absorption properties of as-prepared PCS-derived SiC. Fourier-transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) results demonstrate that dehydrogenation effectively prevented the breakage of Si C bonds during the following oxidation. Furthermore, PCS-derived SiC with a similar core-shell structure was obtained after oxidation, the surface of which showed fewer SiC nanocrystals and shorter graphene-like carbon compared to the inner microstructure. Due to this unique microstructure, the oxidized PCS-derived SiC shows both better attenuation capability and impedance match than as-received PCS-derived SiC. Moreover, with extended oxidation time, the average ε ′ and ε ″ of PCS-derived SiC decreased from 13.0 to 5.2 to 10.5 and 4.4, respectively, which could be attributed to weakened polarization and decreased electrical conductivity. The minimum reflection loss of PCS-derived SiC could be significantly improved from −18 to −27 dB after oxidation, which indicates strong improvement in microwave absorption properties. Highlights • Microwave absorption properties of PCS-derived SiC were improved by oxidation. • Oxidized SiC particles with core-shell structure exhibits better impedance match. • The minimum RL for SiC is obviously decreased from −18 to −27 dB after oxidation. • The bandwidth below −10 dB extends to 3.4 GHz in X-band with a thickness of 2.3 mm. [ABSTRACT FROM AUTHOR]

Highlights • Ti 3 SiC 2 encapsulated by magnetic Ni 0.5 Zn 0.5 Fe 2 O 4 shell were successfully prepared. • Moderated complex permittivity for the Ni 0.5 Zn 0.5 Fe 2 O 4 /Ti 3 SiC 2 was achieved. • Desirable higher complex permeability for the Ni 0.5 Zn 0.5 Fe 2 O 4 /Ti 3 SiC 2 was realized. • The Ni 0.5 Zn 0.5 Fe 2 O 4 /Ti 3 SiC 2 coating with wide bandwidth (RL <-10 dB) of 5.3 GHz. Abstract Ti 3 SiC 2 particles encapsulated by Ni 0.5 Zn 0.5 Fe 2 O 4 shell were in-situ synthesized via a facile sol-gel method. Effects of Ni 0.5 Zn 0.5 Fe 2 O 4 shell on electromagnetic properties of Ti 3 SiC 2 were investigated in 2–18 GHz. Moderated complex permittivity and desirable higher complex permeability presented for the Ni 0.5 Zn 0.5 Fe 2 O 4 /Ti 3 SiC 2 composite, resulting in strong microwave attenuation ability and good impedance matching property. The measured effective absorbing bandwidth (RL < −10 dB) of 5.3 GHz and corresponding maximum RL of −38.6 dB were obtained for the Ni 0.5 Zn 0.5 Fe 2 O 4 /Ti 3 SiC 2 absorbing coating of 1.2 mm thickness. These results indicate that the Ni 0.5 Zn 0.5 Fe 2 O 4 /Ti 3 SiC 2 composite may become a new type of microwave absorbent. [ABSTRACT FROM AUTHOR]

TiB 2 –MgO microwave absorbing materials with TiB 2 as the absorber, MgO as the matrix are prepared by spark plasma sintering (SPS). The influences of commercial TiB 2 content and sintering temperature on dielectric and microwave absorption (MA) properties are studied. Besides, to optimize the MA performance, TiB 2 –MgO composite containing TiB 2 synthesized by the carbonthermal process is prepared. Meanwhile, its high-temperature dielectric and MA properties are investigated. Indeed, both the commercial TiB 2 content and sintering temperature play key roles in dielectric and MA properties, as they reaching 8 wt% and 1400 °C, the composite presents the optimal MA performance. For composite with synthetic TiB 2 as the absorber, the temperature has a positive effect on dielectric and MA properties. The enhanced high-temperature MA properties with minimum reflection loss (RL min) of −52.11 dB at 1.6 mm under 500 °C and effective absorption bandwidth (EAB, RL < −5 dB) of 4.2 GHz at 1.4–1.6 mm under 800 °C are obtained, which is mainly attributed to the temperature-dependent interfacial polarization compared to the temperature-insensitive conductivity. The excellent mechanical properties (flexural strength = 212.48 MPa), thin absorbing layer (d < 2 mm), enhanced thermal stability and high-temperature MA properties indicate that the TiB 2 –MgO composites can be considered as new candidates for high-temperature structure microwave absorbing materials. [ABSTRACT FROM AUTHOR]

Continuous fibers reinforced ceramic matrix composites (CFCMCs) are considered as key thermal structural materials for realizing components electromagnetic wave (EMW) stealth of future aircraft. As the main EMW absorber, design and manufacture fiber woven fabrics with high performance of EMW absorption for CFCMCs attract increasing global attentions. In this study, a thin, broadband-absorption multi-fibers mixed fabric structure was designed by using multi-fibers with different dielectric properties as design units. This as-designed structure can achieve effective absorption of < −10 dB throughout the whole X and Ku bands, while being insensitive to EMW angles. The absorption mechanism of multi-fibers hybrid fabric structure was investigated by numerical simulation. Reflected wave interference, multiple scattering and absorption of incident electromagnetic wave in the fiber fabric, and strong electromagnetic resonance absorption between adjacent fibers cooperation are key factors to realize broadband EMW absorption. [ABSTRACT FROM AUTHOR]

• This work proposed a new method for the synthesis of TiO 2 /C from Ti 3 C 2 T x. • Different morphologies of TiO 2 were obtained by adjusting the composition of the suspension. • The minimum reflection loss (RL) of −39.91 dB was obtained at 16.93 GHz with a thickness of only 1.4 mm. The layered structure with large specific area and moderate conductivity endow MXene with desired properties for microwave absorption. To date, oxidation of two dimensional (2D) Ti 3 C 2 T x to obtain composites including TiO 2 and C usually proceed under complex process, which impedes their further development. Herein, Ni/TiO 2 /C heterogeneous composites were synthesized in one pot reaction within a short time (10 min) by microwave irradiation of an aqueous mixture of nickel chloride and hexadecyltrimethylammonium bromide (CTAB) functionalized Ti 3 C 2 T x MXene. This simple one-pot microwave-assisted method is beneficial to obtain uniform TiO 2 nanoparticles with different morphologies (bipyramid and irregular) embedded in C layers, and the expanded interlayer originated from the intercalation of TiO 2 and Ni nanoparticles. In addition, the growth mechanism and different morphologies of TiO 2 from Ti 3 C 2 T x MXene are discussed. The elaborately designed laminar Ni/TiO 2 /C composites can be used as light and high efficient microwave absorption materials due to the synergistic effect of dielectric loss, magnetic loss and unique 2D heterogeneous nanostructure. The minimum reflection loss (RL) of −39.91 dB was obtained at 16.93 GHz with a thickness of only 1.4 mm. In addition, the dissipating heat ability of Ni/TiO 2 /C composites coated on lab-gown cloth was investigated via thermal infrared images. This work provides a simple and effective strategy for preparing other MXene-based heterogeneous composites. [ABSTRACT FROM AUTHOR]

Carbon nanotubes (CNTs) coated by extremely small FeCo-C core-shell nanoparticles (NPs) were synthesized by a facile method based on one-step metal-organic chemical vapor deposition (MOCVD). The CNTs have diameters of 10–50 nm, while the coated FeCo-C NPs have an extremely small average diameter of ∼5 nm and an average shell thickness of ∼1 nm. The as-synthesized nanotube-nanoparticle (CNT-NP) composite is stable in air up to ∼ 190 °C. When blended with 80 wt% paraffin wax, the CNT-NP composite exhibits a low optimal minimum reflection loss (RL min) value of −79.2 dB and a large effective microwave absorption bandwidth (BW eff) value of 6.3 GHz at a single thickness of 2.0 mm. Equivalent circuit modeling results reveal that CNTs can effectively regulate and optimize the dielectric loss properties of the as-synthesized CNT-NP composites. The outstanding microwave absorption performance of the composite can be attributed to the synergetic effects between the extremely small FeCo-C core-shell NPs and CNTs. This may provide a new strategy for the design of high-performance absorbers. The facile MOCVD-based method developed in this work is expected to be a universal route for the large-scale fabrication of CNT-NP composites. A facile approach is put forward to large-scalely synthesize of extremely small FeCo-C core-shell nanoparticles coated CNTs with outstanding microwave absorption. Image 1 [ABSTRACT FROM AUTHOR]

Carbon-rich SiC powders with high dielectric loss were prepared via pyrolysis of polycarbosilane (PCS). The effects of pyrolysis temperature on microstructures, dielectric response and microwave absorption properties in X-band (8.2–12.4 GHz) of PCS-derived SiC powders were investigated. The PCS-derived SiC powders are mainly composed of SiC nanocrystal, turbostratic carbon and amorphous phase (SiC and/or C). The size of SiC nanocrystals and the graphitization degree of carbon both increase with the elevation of pyrolysis temperature. Furthermore, the residual carbon is transformed from amorphous into turbostratic structure with a phenomenon of regional enrichment. Moreover, the relative complex permittivity increases notably with the higher pyrolysis temperature. Meanwhile, the dielectric loss tangent increases from 0.19 to 0.57, while the microwave impedance decreases from 73.20 to 53.58. The optimal reflection loss of −35 dB for PCS-derived SiC powders is obtained when the pyrolysis temperature is 1500 °C, which exhibits a great application prospect in microwave absorbing materials. [ABSTRACT FROM AUTHOR]

• Magnetic CoNi-wrapped Ti 3 SiC 2 composites were successfully prepared. • Obvious regulated electromagnetic parameters for the composites can be realized. • The EAB of 4.88 GHz and optimal RL value of −41.41 dB were achieved. The magnetic–dielectric composites with synergetic magnetic and dielectric losses have exhibited great potential in the practical applications of microwave absorbing material. This paper reports a simple low-temperature in situ hydrothermal approach for synthesizing novel composites composed of the dielectric Ti 3 SiC 2 wrapped with magnetic CoNi nanoparticles. The microstructure, morphology, electromagnetic properties, and microwave absorption performance of as-synthesized samples were investigated. By adjusting the content of formed magnetic CoNi nanoparticles on the surface of Ti 3 SiC 2 , obvious regulated frequency-dependence of electromagnetic parameters for the proposed CoNi/Ti 3 SiC 2 composites can be realized. Consequently, the effective absorption bandwidth (RL < −10 dB) and optimal reflection loss value of CoNi/Ti 3 SiC 2 -40 composites under thinner thickness of 1.55 mm can reach up to 4.88 GHz and −41.41 dB, respectively. Exceptional microwave absorption performance of the CoNi/Ti 3 SiC 2 composites is attributed to its simultaneously improved attenuation characteristics and optimized impedance matching, and thus can be undoubtedly identified as high-efficiency microwave absorbing material. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) transition metal carbides (MXenes) exhibit great potential application in the microwave absorption (MA) field due to their layered structure, excellent dielectric loss and adjustable layer spacing. Herein, Nb 2 O 5 with different morphologies (columnar and irregular granular) was successfully synthesized in situ and implanted between the layers of a Nb 2 CT x MXene through a rapid microwave-assisted hydrothermal method. Newly formed Nb 2 O 5 and Nb 2 CT x from an incomplete reaction composed the Nb 2 O 5 /Nb 2 CT x hybrids. Compared with that for the pure Nb 2 CT x , the Nb 2 O 5 /Nb 2 CT x composites showed enhanced MA performance, especially the Nb 2 O 5 /Nb 2 CT x composites with columnar Nb 2 O 5 (c-Nb 2 O 5 /Nb 2 CT x). The minimum reflection loss (RL) value reached −44.1 dB at 2.8 GHz with a thickness of 5 mm, indicating that approximately 99.99% of the incident microwaves were absorbed. The special morphology of the columnar Nb 2 O 5 , the increased lamellar spacing of the Nb 2 CT x , and the optimized impedance matching characteristic are all important factors that contributed to the enhanced MA performance. • Controllable morphology regulation of Nb 2 O 5 was achieved through oxidation of Nb 2 CT x. • Nb 2 O 5 with a columnar structure could supply expanded spacing between Nb 2 CT x layers. • Impedance matching and multiple scattering were enhanced for Nb 2 O 5 /Nb 2 CT x composites. [ABSTRACT FROM AUTHOR]

A facile approach is proposed to obtain ultra-small FeNi-C core-shell nanoparticles with tunable Fe/Ni ratio and excellent microwave absorption performance. • Ultra-small FeNi-C is fabricated via facile one-step metal-organic chemical vapor deposition on a large scale. • Microwave absorption properties of the FeNi-C can be tuned Fe/Ni ratio of nanocores. • FeNi-C exhibits a low optimal RL of -63.7 dB and a great effective bandwidth of 6.5 GHz at a thickness of 2.2 mm. • This work offers a facile method for the synthesis of ultra-small FeNi-C core-shell NPs for microwave absorption. A facile and scalable metal-organic chemical vapor deposition method is proposed for the fabrication of ultra-small FeNi-C core-shell nanoparticles. As-synthesized nanoparticles are composed of ultra-small FeNi nanocores of an average diameter of ∼ 6.2 nm and thin shells of 1–3 nm in thickness, which are stable in air atmosphere up to 210 °C. The ratio of Fe/Ni in the nanocores was tuned by varying the reaction temperature, suggesting a simple route to tailor the magnetic and microwave absorption properties of the synthesised nanostructures. These core-shell nanoparticles with a filler loading of 16.7% in paraffin wax exhibited a low minimum reflection loss (R L m i n) of -63.7 dB, together with a great effective bandwidth (B W e f f) of 6.5 GHz at a thickness of 2.2 mm, attributing to their ultra-small size and unique magnetic-dielectric core-shell nanostructure. Such core-shell nanoparticles should be a strong candidate as a light-weighted absorber with tunable microwave absorption performance. [ABSTRACT FROM AUTHOR]

• Magnetic CoFe 2 O 4 -decorated Ti 3 C 2 MXene were successfully prepared. • Tunable electromagnetic properties were observed in the CoFe 2 O 4 -Ti 3 C 2 MXene. • A broad effective bandwidth of 8.5 GHz was achieved. Ti 3 C 2 MXene has demonstrated to be a potential microwave absorber if some difficulties, e.g., poor impedance matching and lack of magnetic loss, can be well-solved. In this paper, laminated Ti 3 C 2 MXene was synthesized using the HF etching method. CoFe 2 O 4 nanoparticles-decorated Ti 3 C 2 MXene (CoFe 2 O 4 -Ti 3 C 2) composites were then fabricated via a novel in-situ solvothermal process. The incorporation of CoFe 2 O 4 nanoparticles on the electromagnetic (EM) and microwave absorption properties of Ti 3 C 2 MXene were systematically studied over 2–18 GHz. Interestingly, increased percolation threshold and controlled complex permittivity were well-observed in the CoFe 2 O 4 -Ti 3 C 2 composites. Furthermore, additional magnetic loss due to the existence of magnetic CoFe 2 O 4 was easily obtained. Benefiting from tunable electromagnetic properties, the minimum reflection loss (RL) value of the CoFe 2 O 4 -Ti 3 C 2 -filled absorbing coating achieved −30.9 dB with a matching thickness of only 1.5 mm. A wide effective absorption bandwidth (RL < −10 dB) of 8.5 GHz was correspondingly realized. These results demonstrated that the CoFe 2 O 4 -Ti 3 C 2 composites are favorable as a broadband microwave absorbent. [ABSTRACT FROM AUTHOR]

An optically transparent metamaterial absorber (MMA) operated in the C-band (4–8 GHz) is optimally designed based on the second-order cross fractal structure. The experimental results show that the reflection loss of the proposed MMA is lower than −10 dB from 3.98 GHz to 8.68 GHz. Two overlapped resonances located at 4.77 GHz and 7.33 GHz, respectively, are caused by the second-order cross fractal structure. Distributions of surface current, electromagnetic field and power loss density are investigated to illustrate the absorptive characteristics and electromagnetic loss mechanisms of the proposed MMA. Moreover, the average optical transmittance of the MMA is close to 75% from 390 nm to 780 nm. The MMA possesses simultaneously strong absorptive capacity in the C-band and high transmittance in the visible light range, showing potential application in special environment. • The designed metamaterial absorber with second-order cross structure shows strong microwave absorption and good optical transmittance. • The reflection loss is lower than -10dB in 3.98~8.68 GHz range. • The average optical transmittance is about 75% in 390~780 nm range. [ABSTRACT FROM AUTHOR]

The dynamic behaviors of 2A12 aluminum alloy under dynamic impact and its energy absorption mechanisms under dynamic penetration at wide temperature ranges and large angles were examined using experiments, simulations and theoretical model predictions; a mathematical dynamic energy absorption model was established based on the results of these experiments and simulations. The results indicate that, at impact temperatures lower than 150 °C, the strain rate hardening of the material prevailed; at impact temperatures higher than 250 °C, the strain rate hardening of the material appeared to be regionalized. At different penetration angles, the bullet displayed different degrees of deflection and the bullet hole also appeared in different forms: At penetration angles lower than 20°, the bullet was inversely deflected and the bullet hole was V-shaped; at penetration angles higher than 40°, the bullet hole looked like a convex or concave thumb. Errors between the simulated and numerically calculated energy absorption efficiencies were within the permissible limit of error in all cases, and were all smaller than 10% when the penetration angle was higher than 30°. This suggests that our mathematical dynamic energy absorption model is more accurate in predicting larger penetration angles. • Dynamic energy absorption characteristics of wide temperature range are investigated. • Large Angle dynamic shock behavior was investigated. • Dynamic impact damage evolution mechanism was revealed. [ABSTRACT FROM AUTHOR]