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In this study, a chloride-assisted boro/carbothermal reduction method was employed to prepare HfB 2 whiskers, aiming to address the challenges associated with large-scale preparation of HfB 2 whiskers and the development of high-temperature resistant electromagnetic wave absorbing materials. When the precursors were mechanically stirred, the resulting mixture underwent calcination at 1450 °C for 3 h, leading to the formation of single-phase HfB 2 whiskers. The as-synthesized HfB 2 whiskers showed exceptional resistance to oxidation at temperatures up to 700 °C. The microwave absorption performance and mechanism of the HfB 2 whiskers/paraffin composite were also investigated. The results revealed that the composite achieved a minimum reflection loss of −41.29 dB when the HfB 2 whiskers content reached 80 wt%, while the widest effective absorption bandwidth of the composite reached 3.6 GHz when the HfB 2 whiskers content increased to 82.5 wt%. This work presents a novel candidate for high-temperature resistant materials used in absorbing electromagnetic wave. [ABSTRACT FROM AUTHOR]

In this study, a chloride-assisted boro/carbothermal reduction method was employed to prepare HfB 2 whiskers, aiming to address the challenges associated with large-scale preparation of HfB 2 whiskers and the development of high-temperature resistant electromagnetic wave absorbing materials. When the precursors were mechanically stirred, the resulting mixture underwent calcination at 1450 °C for 3 h, leading to the formation of single-phase HfB 2 whiskers. The as-synthesized HfB 2 whiskers showed exceptional resistance to oxidation at temperatures up to 700 °C. The microwave absorption performance and mechanism of the HfB 2 whiskers/paraffin composite were also investigated. The results revealed that the composite achieved a minimum reflection loss of −41.29 dB when the HfB 2 whiskers content reached 80 wt%, while the widest effective absorption bandwidth of the composite reached 3.6 GHz when the HfB 2 whiskers content increased to 82.5 wt%. This work presents a novel candidate for high-temperature resistant materials used in absorbing electromagnetic wave. [ABSTRACT FROM AUTHOR]

Nowadays, the increasingly severe electromagnetic (EM) wave pollution requires high-performance EM wave absorbing materials. Multi-principal-element materials are acknowledged as promising for broadening the applications owing to their tunable chemistries and structures in many fields, including as EM wave absorbers. Herein, we prepared a high-entropy MXene, (Mo 0.25 Cr 0.25 Ti 0.25 V 0.25) 3 C 2 T x. Furthermore, multi-principal-element (Mo 0.25 Cr 0.25 Ti 0.25 V 0.25) 3 C 2 T x /FeCoNi and (Mo 0.25 Cr 0.25 Ti 0.25 V 0.25) 3 C 2 T x /FeCoNiCu composites were synthesized via an in-situ hydrothermal process by combining high-entropy MXene with medium-entropy magnetic alloys. In contrast with the relatively narrow effective absorption bandwidth (EAB) of (Mo 0.25 Cr 0.25 Ti 0.25 V 0.25) 3 C 2 T x MXene (2.56 GHz), (Mo 0.25 Cr 0.25 Ti 0.25 V 0.25) 3 C 2 T x /FeCoNi composite with 50 wt% MXene can attain an optimum EAB of 4.88 GHz with the matching thickness of only 1.73 mm. As for (Mo 0.25 Cr 0.25 Ti 0.25 V 0.25) 3 C 2 T x /FeCoNiCu composites, both the absorption efficiency and absorption bandwidth are significantly enhanced. The combination of multi-principal-component strategy and composite construction endows the composites with synergistic dielectric and magnetic losses, optimized impedance matching as well as enhanced attenuation ability, thus improving EM wave absorption performances. In addition, radar cross section (RCS) simulation confirms that the prepared composites have broad application prospects as radar stealth materials. [ABSTRACT FROM AUTHOR]

In view of the lack of conformal, load‐bearing, light‐weight, and high temperature‐resistant integrated wave‐absorbing composites suitable for extremely complex conditions, the gel‐casting process was successfully applied to porous Si3N4 wave‐absorbing composites in this work. A universal low‐slurry for gel casting was prepared by using two dispersants acting together (tetramethylammonium hydroxide solution and sodium lauryl sulfate), which ensured the smooth completion of the gel casting process. Combining the thermogravimetric and differential thermal gravity curves of the composite green body, reasonable parameters of the rubber discharge process are given to avoid the problem of the green body swelling and cracking. The porous TiC/Si3N4 composites were successfully prepared by holding them at 1650°C for 3 h. The bending strength, density, minimum reflection loss, absorption bandwidth, and matched thickness in the P‐band of the composites with 30 wt.% TiC addition were 54.08 ± 3.02 MPa, 1.906 g/cm3, ‐37.75 dB, 1.9 GHz, and 4.1 mm, respectively. The electromagnetic wave loss mechanisms of the composites are a combination of conductivity loss, multiple reflections and scattering, interfacial polarization, and defect polarization. [ABSTRACT FROM AUTHOR]

The TiB 2 fibers were prepared by a chloride-assisted carbothermic method accompanied with the vapor-liquid-solid (VLS) mechanism. The influences of TiO 2 , B 2 O 3 , C 12 H 22 O 11 , and calcination temperature on the yield of TiB 2 fibers were investigated. In addition, the effects of TiB 2 fibers content on the electromagnetic (EM) parameters and microwave absorption (MA) properties of TiB 2 fibers/paraffin composite was studied in detail. The TiB 2 fibers/paraffin composite showed excellent microwave absorption performance, with an optimized reflection loss (RL) of −46.63 dB at 14 GHz and a thickness of 1.5 mm. Moreover, it exhibited a broad effective absorption bandwidth (EAB) (RL < −10 dB) of 3.9 GHz, ranging from 12 to 15.9 GHz. TiB 2 fibers exhibit promising potential as materials for high-temperature applications in the field of MA. [ABSTRACT FROM AUTHOR]

• High-entropy carbides powders were synthesized by carbothermal reduction method. • The solid-solution elements have a great influence on EMW absorption capability. • The intrinsic characteristics make the high-entropy carbides promising EMW absorbing materials. The electromagnetic wave absorption performance of high-entropy transition metal carbides, including (Ti 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ta 0.2)C, (Ti 0.2 Zr 0.2 Mo 0.2 Nb 0.2 Ta 0.2)C and (Ti 0.2 Zr 0.2 Cr 0.2 Nb 0.2 Ta 0.2)C, was investigated in the frequency from 2 GHz to 18 GHz. The electromagnetic parameter measurement and subsequent electromagnetic wave absorption evaluation showed that the high-entropy transition metal carbides possessed good electromagnetic wave absorbing properties, which had a great relation to the solid-solution elements. The (Ti 0.2 Zr 0.2 Mo 0.2 Nb 0.2 Ta 0.2)C with a 1.50 mm thickness displayed a minimal reflection loss of -32.1 dB, and the effective absorption bandwidth (<-10 dB) was in the frequency range of 13–18 GHz. Intriguingly, the minimum reflection loss reached -36.6 dB at the thickness of 2.50 mm. The electromagnetic wave absorption performance was mainly associated with conductivity loss and dipole polarization, which originated from intrinsic conductivity of the high-entropy carbides and lattice distortion resulting from solid solution of multiple elements, respectively. The experimental results show that the high-entropy transition metal carbides may be promising structural-functional integrated ceramics in wide applications. The single-phase high-entropy transition metal carbide powders without complex structure and multi phases design present excellent EMW absorption properties, including minute reflection loss and broad absorption bandwidth. [Display omitted] [ABSTRACT FROM AUTHOR]