查看更多>>摘要：Eutectic materials have been widely employed in many high-tech fields, and recently, eutectic high-entropy alloys (EHEAs) have become a research focus of eutectic materials; however, it is challenging to determine/ design the eutectic composition of alloys accurately, especially multi-component alloys and EHEAs. In this study, a new electromagnetic directional crystallization approach was proposed to determine/design eutectic alloy compositions. First, standard eutectic Al-Si, Al-Si-Fe, Al-Si-Ti, and Al-Si-Fe-Mn alloys were obtained by directly separating their respective melts using electromagnetic directional crystallization. Then their eutectic compositions were accurately determined by inductively coupled plasma-optical emission spectroscopy. Conflicting reports about the eutectic reactions and phase transformations occurring in the Al-Si-Ti system were also resolved. Thereafter, the application of electromagnetic directional crystallization was extended to EHEAs. The widely investigated AlCoCrFeNi2.1 EHEA was confirmed to have a eutectic composition, and a new EHEA Al16.8Co12.6Cr13.8Fe11.8Ni45.1 with a combination of high strength and high ductility was obtained in this study by separating the AlCoCrFeNi3 melt via electromagnetic directional crystallization. Therefore, in the absence of thermodynamic data, electromagnetic directional crystallization provides a promising approach for determining and designing the eutectic composition of alloys, especially EHEAs. This new approach is more direct, efficient, and simpler than the conventional thermodynamiccalculation approach because the application of the latter is significantly limited when thermodynamic data are not available.
查看更多>>摘要：The development of functionalized polymer-based filament enables the fused deposition modeling (FDM) 3D-printed materials or structures with a wide range of unique functions. This work explores the use of MAPbX(3) (MA = CH3NH3, X = Cl, Br, I or mixture of them) perovskite quantum dots (PQDs) by harnessing their unique optical properties for the development of fluorescent 3D printing filaments. Firstly, a one-pot strategy for scalable synthesis of MAPbX(3) PQDs-polycaprolactone (PCL) composite was proposed by in situ formation of PQDs in PCL matrix. To demonstrate the ability for the obtained PQDs-PCL composites to fabricate fluorescent filaments, the effects of filament functionalization on optical properties of PQDs, as well as thermal and mechanical properties of polymer matrix were then comprehensively studied. Owing to the good protective capability of PCL, the synthesized PQDs-PCL composites exhibit comparable PLQY and enhanced UV, water and thermal stability compared to that of pure PQDs. Moreover, high concentration of embedded PQDs in PQDs-PCL composites was obtained with decreasing amount of PCL. The aggregation of PQDs at high temperature combined with the poor interaction between PQDs and surrounding PCL matrix led to the decreased thermal transition temperature and reduced mechanical properties in PQDs-PCL composites relative to pure PCL. The glass transition temperature was found to decrease by 5.5 degrees C, while the mode of failure changed from plastic fracture for pure PCL to brittle fracture for the highest concentration of PQDs in PCL tested. Consequently, PQD-PCL composites were further processed into fluorescent filaments and further fluorescent objects or structures via 3D printing. Green LED and white LED devices were realized by the combination of UV LED chip with 3D printed MAPbBr(3) PQD-PCL thin-film, and blue LED chip with MAPbBr(3) PQD-PCL thin-film and K2SiF6:Mn4+ phosphor, respectively, demonstrating that the PQDs-functionalized 3D printing filaments have great potential in fields of optoelectronic application. (C) 2022 Published by Elsevier B.V.
查看更多>>摘要：One-dimensional (1D) hierarchical carbon nitrides nanorods (HCNNRs) mediated by cobalt was designed and synthesized using a template free hydrothermal approach for improving solar light assisted H(2 )evolution. The performance of 1D HCNNTs was significantly enhanced compared to bulk g-C(3)N4 due to larger active surface area, more visible light utilization and superior charge carrier along the unidirectional flow pathways. The 2% Co/HCNNRs (1D) exhibited excellent photocatalytic efficiency and optimal H-2 yield reached up to 620 mu mol g(-1), which is 11.27 and 17.71 folds more than it was attained with pure HCNNR and bulk g-C3N4, respectively. This reveals that 1D structure helps to accelerate charge transport, whereas, Co works as a mediator to trap electrons, thus improving photocatalytic performance. The crucial operating parameters such as sacrificial reagents, feed concentration and catalyst loading were further optimized based on highest H-2 evolution. Interestingly, mass transfer, charge transfer and amount of photoinduced charges were greatly dependent on the operating parameters. Higher methanol and lower TEOA concentration were beneficial to yield highest photoactivity and stability. This work provides new approach to construct template free 1D nanorods and would be beneficial to enhance performance in other solar energy related applications. (C) 2022 Elsevier B.V. All rights reserved.
查看更多>>摘要：Microstructure evolution of a eutectic VNbTiSi medium entropy alloy (MEA) was systematically investigated during annealing heat treatment. Polymorphic transformation from beta-(Nb, X)(5)Si-3, a high-temperature metastable phase, to '-or gamma-(Nb, X)(5)Si(3 )is revealed and is demonstrated to be closely related to element diffusion. There was mutual diffusion between V and Si, forming a diffusion transition, and the Ti diffusion promoted the formation of gamma-(Nb, X)(5)Si-3 mainly distributed at the grain boundary because of the Ti su-persaturation in the BCC phase during solidification. Strong elemental diffusion promotes the formation of a thermal groove at the three junctions of sub-grain boundaries, contributing to the fast spheroidization of (Nb, X)(5)Si-3, while the termination migration dominates the subsequent coarsening stage. Polymorphic transformation of silicides brings in sub-grain boundaries or low angle grain boundaries (LAGBs), con-tributing to silicide refinement. As a result, the compressive strength at elevated temperatures is greatly improved due to the increasing volume fraction of (Nb, X)(5)Si-3 after heat treatment. (C) 2022 Elsevier B.V. All rights reserved.
查看更多>>摘要：The application of supercapacitor is often restricted by unsatisfactory performance of negative electrodes and limited voltage window. Herein, the CuS/Fe2O3 nano-heterojunction with O and S vacancies is constructed by calcination and selective sulfurization, and applied as negative electrode for asymmetric supercapacitor devices. Compared with bare Fe2O3 and CuS, the heterojunction and defect endow the hybrid with improved conductivity, exposed full electrochemical active sites and enhanced charge transfer. Density functional theory (DFT) calculations suggest that the electronic interface reconstruction between CuS and Fe2O3 optimizes the electronic structure and accelerates the electron transport. Therefore, the heterostructured CuS/Fe2O3 exhibits superior supercapacitor negative performance with high capacitance (921 F g1 at 1 A g-1) and good rate capability. After assembling an asymmetric solid-state supercapacitor (CuS/ Fe2O3//MnO2 ASC) in a PVA/KOH gel, the device shows a high energy density of 56.6 Wh kg-1 at the power density of 900 W kg-1. In addition, employing polyvinyl alcohol/sodium alginate (PVA/SA/KOH) gel as the electrolyte, a flexible solid-state supercapacitor (CuS/Fe2O3//MnO2 SSC) provides 27.8 Wh kg-1 at 900 W kg1. This work designs and fabricates defect-rich heterojunction between metal sulfide and oxide and provides insights into developing high-performance electrode materials for supercapacitors. (c) 2022 Elsevier B.V. All rights reserved.
Trang, Ton Nu QuynhDoanh, Tieu TuTrinh, Nguyen Thi PhuongThu, Vu Thi Hanh...
14页
查看更多>>摘要：Semiconductor/metal hybrid nanostructures-based finely tuning the charge transfer as a promising approach has been identified for photocatalytic activity recently towards renewable hydrogen (H2) evolution reaction (HER) and environmental remediation. Engineering surface-active facets of the metal cocatalyst on the surface of 3-dimensional (3D) structured photocatalysts not only efficiently promotes charge separation and transfer but also serves as reaction active sites for the further development of advanced photocatalysts. Herein, taking 3D SrTiO3 (STO) as a model, we introduce a plasmonic photocatalyst involving the adjusted loading of well-defined Ag active components as a cocatalyst deposited on the surface of 3D STO nanocubes to form the binary Ag/STO nanostructures for photocatalytic behavior driven by light at wavelengths of 365 nm and 420 nm. After the incorporation of the functional cocatalyst, the photocurrent response of STO was substantially increased, while its photoluminescence emission significantly declined, which could be due to the Schottky channel and enrichment of surface reactants: (i) the enhancement of the interfacial separation and inhibition of the recombination process of the photogenerated electron-hole pairs; and (ii) the Ag arrangement on the 3D structure could not only promote the enhanced light absorption but also provide a large surface area with highly active sites for the photocatalytic reaction. The as-synthesized hybrid photocatalyst with a loading content of 1 wt% Ag displays a high photocatalytic H2 evolution and RhB degradation reaching 30 mu mol g-1 h-1 (H2 gas) and a rate constant (k) of 0.027 min-1 (RhB dye), which was 2.5, and 3.4 times higher than that of the pristine STO specimen (12.5 mu mol g-1 h-1 and k = 0.008 min-1, respectively, at 385 nm). Under a wavelength of 420 nm, the binary Ag/STO structures exhibited excellent performance for the H2 production (17.5 mu mol g-1 h-1) and RhB degradation (k = 0.0134 min-1) in comparison with the pristine STO specimen. They also demonstrated remarkable stability for H2 evolution and dye degradation performance in continuous cycles. Based on the experimental outcomes, an energy band outline and a plausible mechanism have been proposed to describe the charge transfer and separation process for enhanced HER activity and RhB degradation.
查看更多>>摘要：A partially recrystallized sample of the Ni-based superalloy AD730 was taken from an intermediate stage of the ingot to billet conversion process and isothermally forged in a single stroke compression test at a subsolvus temperature (1080 degrees C). The as-received material had a heterogeneous microstructure, containing a mixture of coarse and much finer recrystallized grains as well as unrecrystallized ones, and also heterogeneous gamma ' precipitation. The recrystallization mechanisms occurring dynamically in the different grain populations were investigated via electron backscatter diffraction (EBSD). It was found that local microstructure could affect the operative recrystallization mechanism, with different mechanisms seen in the deformed and recrystallized regions, owing to their different precipitate distributions. Within a single deformed grain, three apparently distinct dynamic recrystallization (DRX) mechanisms were identified. The interaction of recrystallization with precipitates plays a central role in DRX. In certain cases precipitates may stimulate discontinuous DRX by providing recrystallization nuclei, alternatively they may impede and limit the growth of recrystallized grains, or in other cases still they promote continuous recrystallization.(c) 2022 The Author(s). Published by Elsevier B.V. CC_BY_4.0
查看更多>>摘要：With excellent compressive mechanical properties, FeNiCrAl medium entropy alloys with multi-principal components have attracted extensive attention in recent years. However, the limited tensile ductility of FeNiCrAl medium entropy alloys is the bottleneck for their industrial applications. In this work, dual phases of FCC + B2 and BCC + B2 were modulated in FeNiCrAl medium entropy alloys for excellent tensile behaviors. In the as-cast state, the tensile yield strength and ultimate tensile strength are 1140 MPa and 1423 MPa, respectively, with a uniform elongation of 6.0%. (c) 2022 Elsevier B.V. All rights reserved.
查看更多>>摘要：The microstructural evolution of K4750 nickel-based superalloy with different hafnium (Hf) contents was investigated by thermodynamic calculations (TC) and experiments. According to TC, with the increases of Hf content from 0 wt% to 1.5 wt%, the redissolving temperature of MC carbide first decreased rapidly and then tended to be relatively stable, the precipitated temperature of M23C6 carbide decreased gradually, while the gamma ' weight fraction increased first and then stabilized. Three alloys containing 0 wt%, 0.11 wt%, and 0.28 wt% Hf were then prepared to further study the evolution of the microstructure. The experimental results showed that the increase of Hf content changed the morphology of MC carbide from long strip to rodlike and blocky, which is caused by the decrease of Ti and Nb contents and the increase of Hf content in MC carbides. The addition of Hf also changed the morphology of M23C6 carbide from continuous to granular due to the different MC distribution at grain boundaries (GBs). In addition, a small amount of Hf segregated into the gamma ' phase, reducing the Al and Nb contents of the gamma ' phase, resulting in an increased gamma/gamma ' lattice mismatch. As the Hf content increased from 0 wt% to 0.11 wt% and 0.28 wt%, the mean stress rupture life at 750 degrees C and 430 MPa increased from 99.54 h to 105.73 h and 170.96 h, which was closely related to the evolution of MC, M23C6 and gamma ' precipitates. Therefore, the relationship between microstructure and stress rupture properties was discussed in detail.
查看更多>>摘要：Vanadium-based oxides are one of the most promising cathode materials, but pure vanadium-based oxides have poor cycle performance and are prone to structural collapse. Hence, many cumbersome synthesis methods have been used to synthesize vanadium-based compounds. Here, we used a very simple one-step hydrothermal method to fabricate disordered V12O26/V2O5 composites with different microstructure, indicating that layered structure is beneficial to improve electrochemical performance of V12O26/V2O5 composites. After assembling the battery, the specific capacity is 374 mAh g(-1) at 0.5 A g(-1), and the capacity remains 211.5 mAh g(-1) after 2500 cycles at 5 A g(-1). (C) 2022 Elsevier B.V.All rights reserved.
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