查看更多>>摘要：Ir3Z (Z = Ti, V, Zr, Nb, Hf and Ta) ultra-high temperature alloys, well known as their high melting point and excellent mechanical properties, are promising candidates for high temperature structural materials beyond nickel-based materials. Nevertheless, knowledge of their mechanical properties and the mechanism of tensile/shear deformation still remains poor. In this work, the fundamental mechanical properties and mechanical behavior under different tensile/shear loading directions of Ir3Z alloys were studied using DFT calculations. All Ir3Z alloys have very high mechanical moduli (404.7-561.3 GPa for Young's modulus). For both mechanical and tensile/shear strength, Ir3V, Ir3Nb and Ir3Ta are distinctly superior to Ir3Ti, Ir3Zr and Ir3Hf, in which Ir3V shows the most outstanding performance. Furthermore, these alloys exhibit similar tensile/shear stress-strain relationship and all of them show anisotropic mechanical behavior under strain, i.e., [100] direction shows the strongest resistance to tensile stress and (111)/[1(_)10] turns out to be the most likely slip system. Meanwhile, the results of average charge density as well as the density of states diagram suggest that the degree of interatomic bonding mainly determines the ideal strength of different structure and tensile/shear direction of Ir3Z alloys.
查看更多>>摘要：Silicon possesses high theoretical specific capacity but suffers from huge volume expansion and poor electrical conductivity during cycling, resulting in significantly reduced capacity and poor cycling stability. These issues could greatly be alleviated by the encapsulation of silicon nanoparticles in carbon materials. Therefore, a three-dimensional (3D) network Si@CTS precursor was prepared in this work through in-situ encapsulation of silicon nanoparticles in stable hydrogel formed by crosslinking chitosan with glutaraldehyde as a cross-linking agent. After freeze-drying followed by oxidation stabilization at 280 degrees C for 2 h under air and subsequent heat treatment at 800 degrees C for 2 h under Ar atmosphere, uniformly distributed 3D Si@C composites were obtained. The effects of added amounts of carbon nanotubes (CNTs) on the structures and electrochemical properties of the as-obtained composites were investigated. The results showed uniformly distributed silicon nanoparticles in the amorphous carbon layer owing to the freeze-drying and oxidation treatments conducive to maintaining the skeleton structure of the material. The amorphous carbon and appropriate CNTs effectively buffered the volume changes, as well as improved the ionic and electronic conductivity. Si@C/CNTs-10% showed better comprehensive electrochemical performances at CNTs added amount of about 10 wt%. The discharge specific capacities at 0.1 Amiddotg-1 after 150 cycles, as well as at 1.0 and 2.0 Amiddotg-1 after 1000 cycles were estimated to 943.1, 461.3, and 123.1 mAhmiddotg-1, respectively.(c) 2022 Elsevier B.V. All rights reserved.
查看更多>>摘要：Spark plasma sintering (SPS) is a promising method for producing high performance Cu-W composite with high copper and low tungsten content, which has wide application space in some occasions. Cu-20 wt%W composite with uniformly distributed ultrafine tungsten particles has been successfully fabricated under different spark plasma sintering temperatures. This paper deals with the impact of spark plasma sintering temperature on structure and performance characteristics of the composite. The intrinsic relationship between sintering temperature, microstructure and properties was studied. The results showed that the optimum SPS sintering temperature of Cu-20 wt%W composite powders produced by spray drying method is 950 degrees C. When the sintering temperature was increased, the content of copper-liquid would be increased, which could not only accelerate the rearrangement of tungsten particles but fill the holes to improve the performance of Cu-20 wt%W composite. However, a much higher temperature may lead to the sintering between tungsten particles, coarse copper net and the existence of copper vapor, ultimately resulting in the inhomogeneous distribution of tungsten and copper phases and the downward trajectory of the performance of the composite. The sintering mechanism was investigated and concluded with a detailed discussion. (c) 2022 Published by Elsevier B.V.
查看更多>>摘要：Flame vapor deposition (FVD) is a powerful method to prepare rapidly and economically the nanostructured thin film with high purity and high crystallinity. One-dimensional (1-D) nanostructured tungsten oxide (WO3) thin film has high potential for various applications as photocatalytic material and, in this study, was prepared from tungsten wire as a precursor by FVD process. The nucleation and growth rates in FVD process could be controlled by changing the precursor supply rate in flame instantaneously by installing additional wire traverse feeder and the nanotree structured WO(3 )thin film was prepared successfully. The concentration of nano-branches at nanotree structured WO3 thin films could be controlled by adjusting wire traversing speed. The proper wire traverse feeding speed could increase surface area and allow more light absorption by additional growth of nano-branches, but too low wire traverse feeding speed could make random and dense growth of nano-branches to reduce the electrical properties and total surface area. The proper growth of nano-branches could increase the photoelectrochemical (PEC) performance of WO3/BiVO4 heterojunction thin film by providing the larger interfacial contact area for heterojunction, but too much growth of nano-branches could reduce the PEC performance because of non-uniform loading of BiVO(4 )in WO3 thin film during spin-coating process. This study can be a basis to prepare by FVD process not only the nanotree structured WO3 thin film for its PEC application but also many nanostructured thin films of various materials for their suitable applications. (C)& nbsp;2022 Elsevier B.V. All rights reserved.
查看更多>>摘要：Recently, Metal-Organic Frameworks-derived carbide catalysts draw lots of attention because of their low price, abundant reserves and superior stability. However, the metal element tends to form particles at a high temperature still a challenge to achieving high Oxygen Reduction Reaction (ORR) activity. Herein, a kind of Zeolitic imidazolate frameworks (ZIFs) based carbon nanosphere with well-dispersed Co-N-x active sites (Co and N co-doped holey Hollow Carbon nanospheres, hHCS) are prepared by using Polyvinylpyrrolidone as the surfactant to realize the well dispersion of Cobalt. Then KOH activation is used to enlarge specific surfaces area (SSA). In an alkaline medium, the obtained sample shows excellent ORR catalytic performance with a half-ware potential of 0.80 V and a limiting current density of 6.53 mA cm(-2), which are even comparable with that of commercial Pt/C. Further, the simple also exhibits remarkable stability during long-term working and better tolerance of methanol. According to the Density Functional Theory (DFT), the outstanding ORR activity can be ascribed to the favorable dispersed Co-N-x. It can be also attributed to the high SSA, hierarchically pore structure and N-base active sites. (C)& nbsp;2022 Elsevier B.V. All rights reserved.
查看更多>>摘要：In this study, trivalent dysprosium (Dy3+) activators were doped into barium tellurooxyphosphate Ba2TeP2O9 (BTP) by a solid-state sintering procedure, where alkali metal (A = Li, Na, and K) ions co-doped as charge compensator were aimed at improving the luminescent performance. To investigate optical absorption behavior, the electronic structure of the BTP host was realized via the density functional theory (DFT) method. The BTP:Dy3+ phosphor excited by 349 nm shows bright yellow emission. When the concentration of the Dy3+ activator is greater than 0.03 mol, concentration quenching occurs owing to dipole-dipole interaction. After doping 0.03 mol A+ ions into the BTP:0.03Dy3+ phosphor, the emission intensity of BTP:0.03Dy3(+)enhances by 1.18 (Li+), 1.43 (Na+), and 2.32 times (K+). Additionally, the BTP:0.03Dy3+,0.03 K+ phosphor exhibits satisfactory thermal stability. A white light-emitting diode (w-LED) was successfully fabricated from the BTP:0.03Dy3+,0.03 K+ and commercial blue phosphors with a 365 nm LED chip. The study reveals that the BTP:0.03Dy3+,0.03 K+ phosphor is a prospective yellow-emitting candidate for w-LED.(C) 2022 Elsevier B.V. All rights reserved.
查看更多>>摘要：The SiBCN composite fibers with strong electromagnetic wave (EMW) absorption performance were successfully prepared via polymer-derived ceramics (PDCs) and electrospinning methods at relatively lower preparation temperature. The results showed that the in-situ generated free carbon which existed in the matrix in the form of simple substance and was characterized by low crystallinity. The graphite carbon improved the dielectric loss and properties of SiBCN composite fibers. In particular for the SiBCN composite fibers pyrolyzed at 1300 degrees C, the in-situ generated nano beta-SiC crystallization increased the EMW absorption performance significantly. The minimum reflection loss (RLmin) of the SiBCN-3 reached - 54.91 dB at 2.35 mm and the effective absorption band (EAB, RL <= -10 dB) reached 4.72 GHz (13.28-18 GHz, 1.75 mm). Hence, the SiBCN fibers prepared at relatively lower temperature give good absorption performance and predict a broader application prospect in the field of EMW absorption materials.(c) 2022 Elsevier B.V. All rights reserved.
查看更多>>摘要：The development of fine-tuned non-platinum group metals and their derivatives, which are high-performance, economical, and stable electrocatalysts used for the oxygen reduction reaction (ORR), is critical for the large-scale deployment of fuel cells and metal-air batteries. This study presents a novel strategy that uses vitamin B12 (VB) as a bioinspired resource for the ORR; VB was modified using metal and non-metal incorporation to boost the efficiency of the ORR. The chemical structure of VB on a graphene substrate was tailored by synergistically incorporating both iron and sulfur upon pyrolysis, yielding various active sites based on Fe-(N,S)-C and Co-(N,S)-C. The resultant catalysts, termed Fe-SVB/GR, exhibit prominent electrocatalytic performance for the ORR via a favorable 4e(- )reaction pathway. The onset and half-wave potentials of the optimized electrocatalyst were 0.90 and 0.74 V vs. reversible hydrogen electrode, respectively, which are comparable or better than those previously reported for non-platinum group catalysts. The Fe-SVB/GR electrocatalyst developed in this study outperformed a commercial Pt/C catalyst in terms of its durability and methanol tolerance. Therefore, this study introduced a novel strategy to produce bio-derived materials as non-platinum group electrocatalysts used as efficient cathode materials in energy-conversion devices. (C)& nbsp;2022 Elsevier B.V. All rights reserved.
查看更多>>摘要：Pure and Al-doped ZnO nanoparticles are synthesized by hydrothermal technique. The structural and phase analysis of the prepared powder is attained by X-rays diffraction and concluded that Al doping increases the crystallite size and causes compressive stress formation in the material network. Fourier transforms infrared spectroscopy reveals the formation of the aluminum oxide phase but with a tiny size that XRD cannot detect. The impact of different ratios of Al doping influence on powder morphology is carried out using transmission electron microscopy, and the optical bandgap of all synthesized products with the doping ratio is investigated by UV-visible reflectance. The electronic defects localized in the material band-gap are studied via photoluminescence spectroscopy and inferred that Al doping alters significantly the electronic defects nature present in the band-gap. In this study, the intrinsic oxygen vacancies are removed by replacing Zn when Al atoms are introduced into the material network. (C) 2022 Elsevier B.V. All rights reserved.
查看更多>>摘要：Hydrogenation properties of Mg2-xPrxNi4 (x = 1.0, 1.2 and 1.4) and their structural degradation (amorphization) upon hydrogenation have been investigated using in-situ X-ray diffraction. In Mg1.0Pr1.0Ni4, the crystalline phase was stable up to a temperature of 573 K under 3 MPa of hydrogen pressure and amorphization did not take place. Mg0.6Pr1.4Ni4 was directly transformed to an amorphous hydride, Mg0.6Pr1.4Ni4H~7.2, while Mg0.8Pr1.2Ni4 transformed to amorphous Mg0.8Pr1.2Ni4H~6 through the formation of Mg0.8Pr1.2Ni4H~4 having an orthorhombic structure. While reversible hydrogen absorption and desorption was observed in the first plateau region between Mg0.8Pr1.2Ni4 and Mg0.8Pr1.2Ni4H~4. First principles calculation indicate that the elastic modulus and bulk modulus decreased with increase of the Pr content and hydrogen content in Mg2-xPrxNi4 suggesting that decrease of bulk modulus induce amorphization upon hydrogen absorption. These results clearly indicate that the hydrogenation properties, the stability of crystalline hydride and amorphization behavior strongly depend on the chemical composition of Mg2-xPrxNi4 and their hydrogen content. (C)& nbsp;2022 Elsevier B.V. All rights reserved.
NSTL
Elsevier