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：At present, passivated emitter and rear cell (PERC) solar cells dominate the photovoltaic industry. However, light and elevated temperature-induced degradation (LeTID) is an important issue responsible for the reduction of PERC efficiency, which may lead to up to 16% relative performance losses in multicrystalline silicon solar cells, and this degradation occurs in almost all types of silicon wafers. Even in next-generation silicon solar cells like Tunnelling oxide passivated contact (TOPCon) and Heterojunction with Intrinsic Thinlayer (HJT) solar cells, LeTID can still cause an efficiency loss up to 1% relative. LeTID is a long process in terms of time during the whole cycle of degradation and regeneration, which will seriously affect the conversion efficiency and stability of solar modules, and hence increase the cost of electricity generated by solar cells. Furthermore, after years of research on LeTID, researchers are yet to determine the specific cause of LeTID. In this paper, we refer to specific literature, briefly describe the development history of LeTID, introduce the phenomena of LeTID in crystalline silicon solar cells, and describe its characteristics. In addition, we also analyzed the fundamental causes of LeTID, and found that the cause may be related to metal impurities or hydrogen contained in solar cells. At present, in view of the participation of hydrogen in LeTID and other existing related theories, this paper introduces several methods to inhibit LeTID in crystalline silicon. Finally, the content of this paper is summarized, and the development of solar cells in the future is prospected.
查看更多>>摘要：The flow behavior and dynamic transformation of near beta TC17 alloy with a bimodal structure were investigated by hot compression with the high strain rate range from 1 s-1 to 20 s-1 and in the temperature range from 840 degrees C to 900 degrees C in this study. The most evident discontinuous yielding and post strain hardening occur at 840 degrees C-20 s(-1 )due to its high alpha p volume fraction before compression and the subsequent strong work hardening effect. High strain rate can slightly promote dynamic transformation when alloy is compressed at 840 degrees C and 870 degrees C due to domination of the high flow stress and temperature raising. However, more dramatic dynamic transformation is obtained for 1 s(-1) at 900 degrees C because the deformation heating at higher temperature/lower strain rate is less evident, and the deformation time thus maters more greatly on the phase transformation. The fine alpha s shows an obvious phase transformation priority than the coarse alpha p under all conditions due to the enhanced alloy element (Al) diffusivity resulting from enlarged alpha/beta interface and higher dislocation (diffusion channel) density around it. The alpha p promotes the dynamic re crystallization of beta phase while this effect becomes weaker when dynamic transformation is progressed greatly, mainly due to the inevitable stored energy consumption and reduced alpha p volume fraction caused by phase transformation. (C) 2022 Elsevier B.V. All rights reserved.
查看更多>>摘要：The Zn3V3O8@N-graphene (ZnVO@NG) hybrid was successfully prepared by hydrothermal method as anode material for lithium-ion batteries (LIBs). The introduced N-graphene (NG) was used as a conductive carbonaceous matrix for encapsulating Zn3V3O8 (ZnVO) flowers due to good mechanical properties. The ZnVO@NG electrode has better rate performance and higher cyclic stability than most ZnxVyOz-based anode reported before. The reversible discharge capacity of the composite maintains 601 mAh g(-l) after 1200 cycles at the rate of 4 A g(-1). The enhanced performance owes to the fast lithium ion/electron transport kinetics, highly surface-controlled pseudocapacitive behavior, and improved interfacial storage of the composite. The density functional theory (DFT) calculations have demonstrated that the interfaces between the ZnVO and graphene sheets provide active sites for the adsorption of Li+ ions. In addition, charges redistribution occurring at the interface of the composite confirms the built-in electric field, which could accelerate Li+/electron diffusion. (C) 2022 Published by Elsevier B.V.
查看更多>>摘要：In this work, a gas atomized feedstock was used to fabricate an AlCoCrFeNi HEA coating using the high-velocity oxygen fuel (HVOF) process. The coating's resistance to room temperature surface degradation was evaluated using dry sliding wear and seawater corrosion testing. The coating retained the feedstock phase structure with negligible in-flight oxidation and was composed of a majority BCC phase with a minor B2 phase, resulting in a high micro-and nano-hardness of ~7 GPa. These observed phase compositions were consistent with thermodynamically calculated phase predictions using a CALPHAD model. Microstructure-mechanical property mapping revealed uniform microstructural characteristics. However, the multiscale wear resistance of the coating was critically affected by the presence of the hard BCC/B2 phase composition, which led to severe brittleness. Combinatorial assessment of the worn surface, wear debris and counter body indicated that wear was dictated by a combination of abrasive, surface fatigue, tribo-oxidation and adhesive wear. In addition, the coating exhibited superior general corrosion resistance compared with conventional SS316L, but the selective dissolution of the B2 phase preceded poor localized corrosion re-sistance, ultimately leading to pitting corrosion.(c) 2022 Published by Elsevier B.V.
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