查看更多>>摘要：Valence electron concentration (VEC) was treated as a useful parameter to predict the stability of solid solution phases. However, the available experimental data to support this criterion is far from enough. In the current study, the high-throughput ab initio modeling is applied to investigate the relative stability of FCC and BCC single crystals of the Al-Co-Cr-Fe-Ni high entropy alloys (HEAs) by using the special quasi-random structure (SQS) approach. The predictions start with pure elements of the Al-Co-Cr-Fe-Ni system and are continued with binaries, ternaries, and quaternary compositions, which come up with 180 com-positions (360 structures). After that, the reliability of the VEC criterion is testified. The results show that the VEC criterion not only works for the stable structure but also works effectively for metastable structure when both FCC and BCC are not thermodynamic stable. However, it is found that the old VEC criterion proposed by Guo et al. fails to work effectively for compositions containing high concentrations of light-weight metals such as Al at VEC < 5. To solve this problem, the present work proposed a new VEC rule to define the stability of FCC and BCC structures at the ground state. With the implementation of the new VEC rule, the effectiveness of the VEC rule (EVEC) of both FCC and BCC structures is enhanced, especially for pure elements and binary compositions, indicating that this rule does not only work effectively for multi-component systems but also works for low-order systems.(c) 2022 Published by Elsevier B.V.
查看更多>>摘要：With the rapid development of the miniaturization and high-integration of electronic devices, conventional thermal conductive materials cannot ensure the safety and reliability of the high-power devices in working environments. It is urgent to develop thermal management materials with excellent thermo-physical and mechanical properties. In this work, the tungsten-coated graphite flakes (GFs(W)) were prepared by the immersion reduction, and the GFs(W) reinforced copper matrix composites (GFs(W)/Cu composites) were prepared by the vacuum hot-pressing sintering. Based on the microstructure and surface analysis, the W coating obtained at 900 & DEG;C and 200 g/L AMT appears the excellent surface structure and interfacial adhesion, which transfer the interfacial bonding from mechanical combination to mechanical-metallurgical synergy between the GFs and Cu. In addition, the volume fraction of W coating has a threshold to improve properties of the GFs(W)/Cu composites, in which the GFs(6 W)/Cu composites show the outstanding comprehensive performance: the in-plane thermal conductivity and flexural strength are 879.0 & PLUSMN; 10.0 Wm(-1)K(-1) and 166.9 & PLUSMN; 3.4 MPa respectively, which are improved by 22.3% and 356.0%, and the lowest coefficient of thermal expansion is 4.3 & PLUSMN; 0.5 ppmK(-1). To sum up, it provides an effective way to develop novel structural and functional integrated graphite/copper composites for thermal management. (c) 2022 Published by Elsevier B.V.
查看更多>>摘要：Dynamic mechanical relaxation processes (i.e., beta relaxation and alpha relaxation) are closely connected with the mechanical and physical properties of metallic glasses. In the current work, the beta relaxation of La60Ni15Al25 metallic glass was studied in sequential heating and cooling experiments by dynamic mechanical analysis. The values of the loss modulus peak were found to reach a relatively stable state during the progress of the heating-cooling cycles. The evolution of the flow unit distribution during thermal cycling was revealed by stress relaxation tests. The experimental results of stress relaxation were well described by a generalized Maxwell model, allowing the analysis of the underlying relaxation time and activation energy distributions. We also show here a suppressed relaxation behavior observed under repeated loading cycles, which is attributed to the annihilation of flow units and the modification of the relaxation time spectrum obtained in the framework of the generalized Maxwell model. (C) 2022 Elsevier B.V. All rights reserved.
查看更多>>摘要：Power generation from ethanol by solid oxide fuel cells (SOFCs) can be a clean and green way to utilize renewable fuel. In this study, the performance of the reduced La0.4Sr0.6Co0.2Fe0.7Nb0.1O3-delta (LSCFN) with anchored Co-Fe nanoparticles is investigated as the electrode in low concentration ethanol for the first time. The cell with the LSCFN as the symmetrical electrodes demonstrates considerable peak power density (0.32 W cm-2) and excellent durability (160 h) at 800 C. Moreover, the reduced LSCFN is further applied as a catalyst layer to prevent the Ni-YSZ anode-supported cell from coking in ethanol fuel. Interestingly, both cells modified with or without this LSCFN layer demonstrate similar output performance in H-2. While in ethanol, the catalyst layer modified cell exhibits better coking resistance and stability than the conventional cell, showing 0.97 W cm-2 at 800 C, as well as excellent durability for 210 h. The results suggest that combining the Ni-YSZ anode-supported cells with the excellent carbon tolerance of the LSCFN can clean and stable directly generate power from ethanol. (C) 2022 Published by Elsevier B.V.
查看更多>>摘要：Laves type AB(2) intermetallics belong to the most abundant group of intermetallic compounds containing over 1000 compounds. A large variety of the chemical nature of A (Mg, Ca, Ti, Zr, Rare Earth Metals) and B (V, Cr, Mn, Fe, Co, Ni, Al) metals together with the existence of the extended solid solutions formed by mixing various selected components on both A and B sites dramatically extends the list the known binary and ternary individual compounds. A vast majority of the Laves type intermetallics crystallises with C15 / FCC MgCu2 and C14 / hexagonal MgZn2 types of structures, both formed for a large range of ratios between the atomic radii of the A and B components outside the ideal ratio r(A)/r(B)= 1.225. Their hydrogenation per-formance is defined by the chemical composition and structure of the alloys and proceeds according to the following alternative / parallel mechanisms: (a) Formation of the insertion type interstitial hydrides con-taining up to 6-7 at. H/f.u.AB(2); (b) Amorphisation of the alloys on hydrogenation; (c) Disproportionation with the formation of a binary hydride of the A metal and depleted by A metal B-components based alloys/ hydrides. Equilibrium pressures of hydrogen desorption from the AB(2)-type hydrides span a huge range of ten orders of magnitude and thus Laves type-based intermetallics satisfy the requirements for various applications including getters of hydrogen gas, volume-and mass-efficient hydrogen storage materials operating at ambient conditions, materials for the efficient thermally driven compression of hydrogen gas with an output pressure of several hundred bar and high capacity and high rate anode materials for the metal hydride batteries operating in a challenging temperature range -at subzero temperatures and also above 60 degrees C. The paper contains references to 245 publications and will guide the future work in the areas of fundamental research and also in advancing the applications of the hydrides of the Laves type inter-metallics. (C) 2022 The Author(s). Published by Elsevier B.V.
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：Due to the moderate degradation rates and acceptable biocompatibility, Zn-based alloys have attracted more and more attention as biodegradable materials. However, the inferior strength and ductility significantly limit their further applications. In this work, biodegradable Zn-2Cu-0.2Mn-xLi (x = 0, 0.1 and 0.38) alloys were developed with enhanced comprehensive mechanical properties. Also, these novel alloys were found to possess extraordinary antibacterial activity and good biocompatibility. Annealing and hot extrusion were performed on the as-cast alloys. The microstructures, mechanical properties, corrosion behavior, antibacterial ability, hemocompatibility and cytocompatibility of the alloys were systematically studied. Microstructure analysis indicates that primary e-CuZn4 particles are distributed in the Zn grains in all ascast alloys. Addition of Li leads to formation of beta-LiZn4 phase in eutectics and beta-LiZn4 precipitates within the Zn grains. In the as-annealed alloy, secondary epsilon-CuZn4 precipitates and fine beta-LiZn4 precipitates appear in the Zn matrix of the Li-containing alloys. All the as-extruded alloys reveal fibrous morphology and develop (0001) basal texture. Mechanical property test shows that all as-extruded alloys exhibit excellent strength and ductility which can fully meet the benchmark requirement for biodegradable materials. It is worth to notice that, Zn-2Cu-0.2Mn-0.38Li alloy has a tensile yield strength, ultimate tensile strength and elongation as high as 424 +/- 28.3 MPa, 445 +/- 11.1 MPa and 76 +/- 3.35%, respectively. The 24-day in vitro immersion test in the SBF solution shows that the corrosion rates were 0.212 +/- 0.007 mm/year for Zn-2Cu-0.2Mn, 0.197 +/- 0.005 mm/year for Zn-2Cu-0.2Mn-0.1Li and 0.184 +/- 0.008 mm/year for Zn-2Cu-0.2Mn-0.38Li, respectively. It indicates that addition of Li improves the corrosion resistance of the alloys. All as-extruded alloys have antibacterial rates of >= 99% and hemolysis rates of < 5%, exhibiting strong antibacterial activity and good hemocompatibility. The MC3T3-E1 cells show more than 95% viability in 25% extracts of all asextruded alloys in all culturing days. In addition, in this low concentration of extracts, the cells in the alloy groups exhibit good spreading morphology and high ALP expression, suggesting good cytocompatibility. (c) 2022 Elsevier B.V. All rights reserved.
查看更多>>摘要：In this work, a facile chemical co-precipitation method to prepare nickel-cobalt layered double hydroxide (Ni, Co-LDH) is reported. Through the addition of NaHCO3, carbonate ions (CO32-) are introduced into the LDH in a controlled way. The doping of CO(3)(2- )causes the original nanosheet structure to bend and inter-connect, which increases the contact area between the electrode and the electrolyte, enhancing the energy storage characteristics of materials. Appropriate CO(3)(2- )doping effectively increases the specific capacity of Ni, Co-LDH. When the doping ratio of carbonate is 5% (Ni, Co-LDH/CO3-5%), the specific capacity is improved from 1432 F g(-1) (undoped) to 1970 F g(-1) at 1 A g(-1). Furthermore, the electrode exhibits satisfactory rate capability, retaining 82.8% of the specific capacity at 20 A g(-1). Moreover, an asymmetric supercapacitor (ASC), assembled with Ni, Co-LDH/CO3-5% as the positive electrode and activated carbon as the negative electrode, possesses a high energy density of 54.8 Wh kg(-1) at a power density of 374.9 W kg(-1) and remains 80.8% after 10000 cycles at 10 A g(-1), demonstrating excellent cyclic stability. (C) 2022 Elsevier B.V. All rights reserved.
查看更多>>摘要：It is of great significance to improve the performance of electrocatalysts by constructing suitable heterogeneous interfaces to adjust the electronic structure of their surfaces. Here, we design and synthesize Co-Fe alloy nanoparticles (NPs) modified nitrogen-doped cubic carbon box (NC) supported MoS2 nanosheets (NC@ MoS2@Co-Fe) as a bi-functional electrocatalytic electrode material, which possesses excellent electrocatalytic oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) performance. The NC@ MoS2@Co-Fe exhibits remarkable bifunctional electrocatalytic activities with an ORR half-wave potential of 0.73 V in 0.1 M KOH electrolyte and an OER overpotential of 400 mV, driving a current density of 10 mA cm-2. The advanced catalytic performance can be attributed to the unique heterojunction structure of the catalyst. The size of the Co-Fe alloy NPs supported on MoS2 can be tuned to avoid the excessive growth of alloy NPs and to expose more catalytic active sites. Meanwhile, the loaded Co-Fe alloy NPs should be covered with a calcined carbon layer derived from the organic ligand to prevent oxidation passivation and particle aggregation. The structure formed by Co-Fe alloy NPs and NC@MoS2 optimizes the electronic structure of the active center and accelerates the electrocatalytic reaction rate, thus synergistically improving the bi-functional electrocatalytic activity of the NC@MoS2@Co-Fe catalyst and can be applied to rechargeable zinc air batteries.
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.
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