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Although B4C-based composites exhibit excellent comprehensive mechanical properties, the microscopic strength and toughness mechanism are still unclear. In this paper, the B4C–ZrB2–SiC composites with excellent mechanical properties were prepared at 1900 °C and 45 MPa for 1 h using vacuum hot pressing assisted by reaction sintering (VHP-RS). They included the relative density of 95.97 ~ 99.25%, the Vickers hardness of 36.76 ~ 37.26 GPa, the flexural strength of 807.34 ~ 882.24 MPa, and the fracture toughness of 5.18 ~ 6.75 MPa·m1/2. Then, the strengthening and toughening mechanism of dislocation were systematically investigated by HRTEM, IFFT, EDS-mapping, etc. The classical "bow-out" process of dislocation line and lamellar dislocation ring was observed as the feature of the Orowan strengthening. Dislocation piling up at grain boundary inhibits the initiation of dislocation sources. The dislocations near twin boundaries are blocked by twin boundaries and stacking faults. Grain boundaries containing segregated silicon, boron and zirconium are easy to gather around the dislocation to nail the dislocation. The above reasons make the composites have excellent flexural strength. Meanwhile, dislocation slips in SiC and ZrB2 grains promote plastic deformation and improve the fracture toughness of the composites. The changes of the a relative density, Vickers hardness, and b flexural strength, fracture toughness of the B4C–ZrB2–SiC composites with the increase of component content. [ABSTRACT FROM AUTHOR]

TiO2/Au/BDD composites with a Z-scheme structure was prepared by orderly depositing gold (Au) and titanium dioxide (TiO2) on the surface of a boron-doped diamond (BDD) film using sputtering and electrophoretic deposition methods. It was found that the introduction of Au between TiO2 and the BDD, not only could reduce their contact resistance, to increase the carrier transport efficiency, but also could improve the surface Hall mobility of the BDD electrode. Meanwhile, the designed Z-scheme structure provided a fast channel for the electrons and holes combination, to promote the effective separation of the electrons and holes produced in TiO2 and the BDD under photoirradiation. The electrochemical characterization elucidated that these modifications of the structure obviously enhanced the electrocatalytic performance of the electrode, which was further verified by the simulated wastewater degradation experiments with reactive brilliant red X-3B. In addition, it was also found that the photoirradiation effectively enhanced the pollution degradation efficiency of the modified electrode, especially for the TiO2/Au/BDD-30 electrode. [ABSTRACT FROM AUTHOR]

Hot oscillatory pressing (HOP) has been shown to be a more effective technology for sintering various material systems than hot pressing sintering due to the use of oscillatory pressure. However, the effect of oscillatory pressure parameters on the sintering behavior is not clear. In this paper, the effect of pressure amplitude, frequency, and mean pressure of oscillatory pressure on the sintering behavior was studied by using sapphire whisker reinforced zirconia ceramic composite as a model material. The obtained results were discussed by considering grain boundary sliding as a viscoelastic process. The current work would provide scientific guidance for determining optimized HOP parameters. [ABSTRACT FROM AUTHOR]

CsPbX3 (X = Cl, Br, I) semiconductor nanocrystals (NCs) have excellent optical and photoelectric properties, and are potential core materials for various photoelectric devices. However, the toxicity of Pb and instability have been the key limitations to application of NCs. Herein, using MnBr2 and MnBr2·4H2O as manganese sources, heavy Mn-doped CsPbBr3 (Mn:CsPbBr3) NCs are synthesized by high-energy ball grinding, which avoids high temperature, a large number of polar solvents and atmosphere protection required in traditional liquid phase methods. However, when MnBr2·4H2O is used as the raw material, infinite solid solution doping can be achieved, and the synthesized Mn:CsPbBr3 NCs show smaller particle size, stronger PL intensity and stability. The reason is that presence of crystal water plays a similar role to wet milling in the ball milling process, and can promote the passivation effect of oleylamine (OAm) on nanocrystal defects and the connection between them. In addition, a simple, easy-operating and beneficial to commercial production method for the preparation of Mn:CsPbBr3 NCs/EVA flexible films is proposed, which can effectively improve the stability of Mn:CsPbBr3 NCs. This study is expected to provide an effective way for the synthesis and stability improvement of CsPbX3 NCs doped with different ions. [ABSTRACT FROM AUTHOR]

Ti3C2Tx MXene-based composites are attractive for use as electromagnetic wave absorption (EMA) materials due to their high conductivity and abundant dipoles on the surface. Nevertheless, the controlled synthesis of MXene foams with tailored dielectric properties for high-performance microwave absorption is still a challenge. Herein, the porous structure of MXene foams has been realized through a freeze–thaw assembly strategy in the presence of reduced graphene oxide (rGO). By adjusting the amounts of magnetic units of NiO particles, the complex permittivity and permeability of MXene/rGO can be tuned. The developed uniform cellular structure enables multiple reflections and scattering of electromagnetic waves among the microcellular network while the cooperation of NiO particles generated through calcination contributes to dielectric loss and magnetic loss. The obtained Ti3C2Tx/rGO/NiO composites achieve a minimal reflection loss of −62.98 dB at 7.5 GHz. This work provides a promising strategy for designing light weight and multifunctional MXene foam-based microwave absorbers. [ABSTRACT FROM AUTHOR]

All‐inorganic perovskite nanocrystals (NCs) have been widely used in many fields due to their excellent photoelectric properties. However, the instability of their structure and the high lead content need to be solved. Herein, the concept of "High‐entropy" is introduced into NCs to prepare High‐entropy perovskite Cs(Pb1/3Mn1/3Ni1/3)Br3 NCs by high‐energy ball milling method. The effects of milling time and doping ratio of B‐site elements on the structure and performance of perovskite NCs are studied. It is found that Mn2+ and Ni2+ successfully enter the lattice of Pb2+ to form "High‐entropy" perovskite NCs. In addition, compared with Cs(Pb0.72Mn0.14Ni0.14)Br3 NCs, Cs(Pb1/3Mn1/3Ni1/3)Br3 NCs have greater luminous intensity and stability, which because of the enhancement of band gap and valence bonds. Furthermore, photoluminescence intensity at 515 nm increase obviously when Cs(Pb1/3Mn1/3Ni1/3)Br3 NCs are heated at 120 °C. This is due to the lattice distortion effect brought about by ion doping. This study is expected to provide an effective way for synthesis and stability of all‐inorganic perovskite NCs doped with more kinds of different ions. Moreover, it also lays the foundation for the introduction of "High‐entropy" into perovskite functional ceramics. [ABSTRACT FROM AUTHOR]

Due to their special appearance, spherical α‐Al2O3 nanoparticles play an important role for obtaining high‐performance structural and functional ceramics. However, there are still problems such as easily agglomerates to form worm‐like structures at high temperatures and difficult availability of spherical nanoparticles. In this study, spherical α‐Al2O3 nanoparticles with high dispersion were prepared by a combination of a microwave hydrothermal method and an addition of nano‐Al particles as seeds. First, spherical amorphous alumina precursors were synthesized by the microwave hydrothermal method at 100°C for 30 min using Al2(SO4)3·18H2O, Al(NO3)3·9H2O, and urea, as raw materials, and then spherical α‐Al2O3 nanoparticles with a diameter of about 66 nm were acquired after calcined the precursor at 1050°C for 90 min by adding nano‐Al seeds, which reduced the calcination temperature by 50°C and holding time by 30 min compared to that without seeds. Kinetic analysis shows that 5 wt.% nano‐Al seeds can reduce the activation energy of crystalline transition of γ‐Al2O3 to α‐Al2O3 from 516.51 to 474.37 kJ/mol. Moreover, the microscopic mechanism of nano‐Al particles as seeds was investigated. The characterizations of sintering properties show that spherical α‐Al2O3 nanoparticles facilitate the acquisition of uniform microstructure for resulting ceramic and the fracture modes include both intergranular and transgranular fractures. [ABSTRACT FROM AUTHOR]

The fabrication of ultra‐high performance absorbers with low thickness, light weight, hierarchical structure, and strong microwave absorption (MA) capability in a wide frequency range is a critical objective of the scientific community. The unique two‐dimensional lamellar and sandwich‐like structure of MoS2 (S‐Mo‐S) in combination with Ti3C2Tx offers exceptional metallic features, an enriched surface area and a hierarchical structure; hence, it is an appealing alternative to high‐efficiency microwave absorbers. Herein, two‐dimensional C/MoS2‐functionalized Ti3C2Tx hierarchical structures with superior attenuation capabilities (dielectric losses) are creatively designed and fabricated, and a minimal reflection loss (RLmin) of −42.7 dB is achieved at a thickness of only 1.5 mm. These excellent microwave absorption properties are attributed to better impedance matching, which is due to the tunable complex permittivity; intensive interfacial polarization, which stems from the numerous interfaces of multiple components; multiple scattering, which originates from the presence of plentiful two‐dimensional nanosheets; and ohmic loss, which arises from the formation of conductivity networks. The interconnected sandwich‐like and layered structure is proven to be an effective strategy for enriched microwave absorption by functionalized Ti3C2Tx nanocomposites. [ABSTRACT FROM AUTHOR]

Facing the fast development of telecommunication technology, traditional electromagnetic wave absorbing materials are unable to meet the microwave shielding requirements in practical applications. Herein, a Ti3C2Tx MXene/rGO composite aerogel was synthesized by facile hydrothermal and freeze-drying treatment. The prepared aerogel shows a unique porous three-dimensional network structure, which is of great advantage in improving its microwave absorption capability. Mixing Ti3C2Tx and rGO adjusts the impedance match in the absorption process. When the weight ratio of Ti3C2Tx to rGO is 1 : 6, the minimum reflection value (RLm) reaches −53.49 dB at 17.0 GHz (thickness = 2.2 mm), and the corresponding effective absorption bandwidth is 4.4 GHz (from 13.6 GHz to 18.0 GHz). rGO nanosheets of large size could retard the oxidation of Ti3C2Tx to some extent. With its excellent microwave absorption performance, broad effective bandwidth, outstanding thermal resistance, and heat insulating properties, the composite aerogel has a great practical potential. [ABSTRACT FROM AUTHOR]