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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]

In view of the lack of a conformal, load-bearing, lightweight, and high-temperature resistant integrated microwave-absorbing composites for applications under extremely complex conditions, this study successfully applies gel casting craft to porous Si 3 N 4 microwave-absorbing composites. The high-temperature decomposition reaction of Ti 3 SiC 2 powder was utilized to generate uniform Ti-C x -N 1−x grains in situ and to enhance the mechanical and microwave-absorption properties of porous Ti-C x -N 1−x /Si 3 N 4 composites. The bending strength, fracture toughness, density, maximum reflection loss value, absorption bandwidth and matched thickness in P-band of the composite with 30 wt% Ti 3 SiC 2 addition were 164.87 ± 7.56 MPa, 2.61 ± 0.13 MPa·m1/2, 2.077 g/cm3, 32.42 dB, 1.74 GHz and 4.2 mm, respectively. The fracture toughness and bending strength of the composite were increased by 71.71% and 58.13%, respectively, compared with monolithic porous Si 3 N 4. The electromagnetic wave loss mechanisms of the composites are proposed as a combination of conductivity loss, multiple reflections and scattering, interfacial polarization and defect polarization. [ABSTRACT FROM AUTHOR]

In this paper, BNNSs/Al 2 O 3 composite powder was prepared by in-situ reaction using borate nitridation method and BNNSs/Al 2 O 3 composite ceramics were prepared by hot-pressing sintering. This method achieves uniform mixing of BNNSs and Al 2 O 3 ceramic matrix and reduces the introduction of impurities in the processing process. The BNNSs/Al 2 O 3 composite ceramics have excellent bending strength (549.4 MPa), fracture toughness (5.18 MPa m1/2) and hardness (21.3 GPa). The high hardness of composite ceramics is attributed to high grain boundary strength and density. The reinforcing mechanisms of ceramics include BNNSs pull-out, BNNSs bridging, crack deflection as well as the transgranular fracture and intergranular fracture of Al 2 O 3 matrix. [ABSTRACT FROM AUTHOR]

In this study, Zn 8 B 3 H 3 O 14 nanosheets were synthesized through a one-step coprecipitation process and employed as both a boron source and substrate templates for the fabrication of boron nitride nanosheets (BNNSs), which were synthesized efficiently at low temperatures by the borate nitration method using ammonia as the nitrogen source. The thickness of the synthesized BNNSs ranged from 3 to 10 nm with a flake dimension of about 2.56 μm. The prepared BNNSs using this method realized 98.8% boron source utilization and single batch yields up to gram level. In addition, BNNSs/SiO 2 microwave-transparent composites were prepared to investigate the potential for large-scale applications of the BNNSs produced by using this method. The composites demonstrated a remarkable increase in bending strength and fracture toughness, reaching 122.02 MPa and 2.31 MPa·m1/2, respectively, with the addition of only 0.5 wt% BNNSs. Compared with SiO 2 without BNNSs, the fracture toughness of the composites is increased by 106%. A novel crack plugging strong toughening mechanism of BNNSs is proposed. Simultaneously, the composites exhibit exceptional microwave-transparent properties, with dielectric constants below 4 in the real part and below 0.03 in the imaginary part. Therefore, this study has successfully achieved the low-temperature and efficient synthesis of micron-scale BNNSs, laying the groundwork for their large-scale application. [Display omitted] • Zn 8 B 3 H 3 O 14 nanosheets were used as substrate templates for the synthesis of BNNSs. • BNNSs were synthesized with high efficiency at low temperatures (900 °C). • The single batch yield of BNNSs reached up to the gram level. • The BNNSs/SiO 2 wave-transparent composites with ultrahigh toughness were obtained. • A novel mechanism for strengthening and toughening (BNNSs plugging) is proposed. [ABSTRACT FROM AUTHOR]

Uniformly dispersed boron nitride nanosheets (BNNSs) reinforced silicon nitride (Si 3 N 4) composites were prepared by surface modification assisted flocculation combined with SPS sintering. In order to improve the dispersibility of the BNNSs in the composites, the liquid phase stripped BNNSs are surface functionalized by a two-step covalently modification. The amino-modified BNNSs (NH 2 -BNNSs) and Si 3 N 4 powders have opposite surface potential, mixed evenly by electrostatic interaction during flocculation. The results showed that mechanical properties of Si 3 N 4 composites were obviously enhanced by adding NH 2 -BNNSs. The fracture toughness and bending strength of Si 3 N 4 composites added 0.75 wt% NH 2 -BNNSs were increased by 34% and 28%, respectively, compared with monolithic Si 3 N 4. Toughening mechanisms are synergistic action of the torn, pull-out or bridging of BNNSs and crack deflection mechanisms with microstructural analyzes. The dielectric properties of the Si 3 N 4 ceramics are also improved after the addition of NH 2 -BNNSs. [ABSTRACT FROM AUTHOR]

Boron nitride nanosheets (BNNSs)/magnesium oxide (MgO) composites were prepared via hot pressing. Mechanical properties of MgO ceramics were improved obviously in virtue of adding BNNSs. The bending strength of the 1 wt% BNNSs/MgO composite increased by about 85% than that of the monolithic MgO. The fracture toughness increased by 34% with the addition of 1.5 wt% BNNSs. Microstructural analyzes have shown that the toughening mechanisms are combinations of the pull-out and bridging of BNNSs, crack deflection, and crack bypassing mechanisms. The addition of a small amount of BNNSs don't destroy the excellent dielectric properties of composites. The dielectric constant of the sample doped with 1 wt% BNNSs was about 9.5 in the whole X-band and the vast majority of P-band, and the loss tangent was less than 5 × 10−3 in 10–15.8 GHz. [ABSTRACT FROM AUTHOR]

The aim of achieving integration of lightweight, high strength, high‐temperature resistant, and satisfactory electromagnetic (EM) wave absorption was successfully accomplished in the present study by synthesizing TiC–TiB2 fibers reinforced Si3N4 composites, which were pressureless sintered at 1650°C for 2 h. The preparation of TiC–TiB2 fibers was conducted through a chloride‐assisted carbothermic method. This work focused on investigating the effects of incorporating TiC–TiB2 fibers on the mechanical properties and EM wave absorption characteristics of the composites. The 30 wt% TiC–TiB2/Si3N4 composite displayed the bulk density of 1.89 g/cm3, bending strength of 93.11 ± 3.91 MPa, fracture toughness of 1.81 ± 0.10 MPa m1/2, minimum reflection loss of −38.87 dB, and effective absorption bandwidth of 1.43 GHz in the Ku‐band, respectively. The as‐synthesized TiC–TiB2/Si3N4 composites are promising candidates for EM wave absorbing load‐bearing materials due to their outstanding mechanical properties and microwave absorption properties. [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]

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]

• The Zn 8 B 3 H 3 O 14 nanosheets were discovered and efficiently synthesized by the one-step coprecipitate method. • This method is simple, high yield and low cost to prepare Zn 8 B 3 H 3 O 14 nanosheets. • The nanosheets have good thermal stability, and their decomposition temperature reaches 414 °C. With the rapid development of two-dimensional materials, the exploration of new two-dimensional materials has become a research hotspot. In this work, novel Zn 8 B 3 H 3 O 14 nanosheets were efficiently synthesized by the one-step coprecipitate method using the water bath reaction at 70 °C for 24 h. The preparation of Zn 8 B 3 H 3 O 14 nanosheets by this method has the advantages of a simple preparation process, low cost, low equipment requirements, and mass production. The microstructure and morphology of nanosheets were characterized in detail. In addition, the nanosheets have good thermal stability properties, and their decomposition temperature reaches 414 °C. This allows the nanosheets to adopt higher processing and service temperatures when applied to polymer materials. [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]

The boron nitride nanosheets (BNNSs)/aluminum nitride (AlN) composites were prepared by hot press sintering at 1600°C. The microstructure, mechanical properties, and thermal conductivity of the samples were measured, and the effect of adding BNNSs to AlN ceramics on the properties was studied. It is found that the addition of BNNSs can effectively improve the mechanical properties of AlN. When the additional amount is 1 wt%, the bending strength of the sample reaches the maximum value of 456.6 MPa, which is 23.1% higher than that of the AlN sample without BNNSs. The fracture toughness of the sample is 4.47 MPa m1/2, a 68.7% improvement over the sample without BNNSs. The composites obtained in the experiment have brilliant mechanical properties. [ABSTRACT FROM AUTHOR]

Compared with common monoanionic high entropy ceramics, polyanionic high entropy ceramics, with better performance, are more difficult to prepare. Since transition metal carbides have high hardness and transition metal nitrides have good toughness, it is hoped that high entropy carbonitride ceramics can combine the advantages of the two. In this paper, a series of novel (Ti 0.25 Nb 0.25 Hf 0.25 Ta 0.25)C x N 1–x (x = 0.3, 0.4, 0.5, 0.6, and 0.7) high entropy ceramics were successfully synthesized for the first time using spark plasma sintering at 1850 °C with metal carbides and metal nitrides as raw materials. The phase evolution, microstructure, hardness and fracture toughness of high carbonitride entropy ceramics were investigated. X-ray diffraction indicates the ceramics with the single-phase face-centered cubic structure were successfully prepared. It was found that the high entropy ceramics sintered at 1850 °C with four cationic components have excellent performance on fracture toughness (KIC = 7.1746 MPa m1/2). With the increase of carbide proportion, the hardness of the ceramics increased, but the fracture toughness and bending strength decreased slightly. And it was found that the differences of grain size and porosity content were the main reasons for the mechanical properties difference. The excellent hardness properties, good bending strength and outstanding fracture toughness of the high entropy ceramics provide the possibility for the application of high entropy ceramics in aerospace and other applications requiring high performance. [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]

The relationship between the chemical elements of high-entropy boride (HEB) ceramics and their hardness is important for the prediction of high-hardness HEB ceramics. In this work, by designing four HEB ceramics with different chemical elements, the effect of lattice parameter difference factor (δ, represents the difference-degree in lattice parameters among the five individual constitute diborides) on phase composition and lattice-distortion, and the effect of rule of mixture (ROM) average hardness and lattice-distortion on HEB ceramics hardness were studied. The results indicated that, as δ value increases, more severe lattice-distortion occurs inside the HEB ceramics, and a single solid-solution is difficult to be formed. Furthermore, lattice-distortion and the ROM average hardness codetermine the HEB ceramics hardness. The greater lattice-distortion brings about significantly higher hardness for HEB ceramics than their ROM average hardness. Among the four HEBs, (Hf 0.2 Zr 0.2 Ta 0.2 V 0.2 Nb 0.2)B 2 exhibits the high hardness of 26 GPa measured using a load of 9.8 N. [ABSTRACT FROM AUTHOR]

A sol-gel method was employed for the synthesis of new High-entropy boride (HEB) powders, (Hf 0.2 Nb 0.2 Cr 0.2 Ta 0.2 Mo 0.2)B 2 , with nanoscale. The as-synthesized powders were obtained at a relatively low temperature of 1650 °C, and had small average particle size of 62.09 nm. X-ray diffraction confirmed that the (Hf 0.2 Nb 0.2 Cr 0.2 Ta 0.2 Mo 0.2)B 2 powders were hexagonal single-phase without any oxide impurities. In particular, electrochemical performance of the (Hf 0.2 Nb 0.2 Cr 0.2 Ta 0.2 Mo 0.2)B 2 powders with multiphase and high-entropy single phase were investigated using a three-electrode system. The improved electrochemical performance of the HEB powders is realized, with 27% higher in specific capacitance compared to the powders with multiphase. The HEB powders electrode exhibits a high capacitance retention of 97.03% after 5000 cycles. [ABSTRACT FROM AUTHOR]

BNNSs were prepared efficiently by magnesium borate nitridation. BNNSs/eutectic-composition Al 2 O 3 /YAG/YSZ ceramics were prepared by hot pressing sintering. The addition of BNNSs did not change the phase composition of BNNSs/eutectic-composition Al 2 O 3 /YAG/YSZ ceramics. The bending strength and fracture toughness of 1.5wt%BNNSs/ eutectic-composition Al 2 O 3 /YAG/YSZ ceramic were increased by 19.0% and 18.9% respectively. Doped BNNSs exist at the grain boundary between two or more different grains. The toughening mechanism of BNNSs contains mainly crack deflection, BNNSs pullout and BNNSs bridging. • BNNSs/eutectic-composition Al 2 O 3 /YAG/YSZ ceramics were originally prepared with excellent mechanical properties. • The toughening mechanism of BNNSs was discussed. • The effects of temperature and BNNSs doping amount on the mechanical properties of ceramics were explored. [ABSTRACT FROM AUTHOR]

The fracture toughness and oxidation resistance are crucial factors affecting the practical applications of high-entropy diboride ceramics (HEBs). In this study, silicon carbide whiskers (SiC w) were introduced as a reinforcement for HEBs for the first time. To achieve a uniform dispersion of SiC w within the HEB powders, a combination of simultaneous ultrasonic dispersion, mechanical agitation, and freeze-drying technology was employed. Consequently, a series of composites, (Hf 0.2 Zr 0.2 Ta 0.2 V 0.2 Nb 0.2)B 2 -nSiC w (n = 0–20 vol%), were densified by spark plasma sintering. The effect of SiC w on the microstructure and mechanical properties of the HEBs were studied, as well as the toughening mechanism involved. The results revealed that the introduction of SiC w led to grain-size refinement in (Hf 0.2 Zr 0.2 Ta 0.2 V 0.2 Nb 0.2)B 2 , along with significant improvements in relative density, hardness, fracture toughness, and oxidation resistance. The relative density, hardness and fracture-toughness of (Hf 0.2 Zr 0.2 Ta 0.2 V 0.2 Nb 0.2)B 2 -SiC w composites exhibited an initial increase followed by a decrease with increasing SiC w content. Specifically, the (Hf 0.2 Zr 0.2 Ta 0.2 V 0.2 Nb 0.2)B 2 –15 vol% SiC w composite simultaneously obtained the highest hardness of 25.6 GPa and fracture-toughness of 4.8 MPa·m1/2, representing a 26% improvement compared to (Hf 0.2 Zr 0.2 Ta 0.2 V 0.2 Nb 0.2)B 2 ceramics. • The effect of SiC w on microstructure, mechanical properties and oxidation resistance of HEBs were studied for the first time. • The K Ic of (Hf 0.2 Zr 0.2 Ta 0.2 V 0.2 Nb 0.2)B 2 ceramic was increased by 26% without loss of hardness by introducing SiC w. • The oxidation resistance of HEBs was greatly enhanced due to the addition of SiC whiskers. [ABSTRACT FROM AUTHOR]