查看更多>>摘要：Consumers are increasingly demanding the range and safety of the electric vehicles. Nickel-rich layered lithium transition-metal oxide cathode material with Ni content exceeding 80% has attracted extensive attention due to its high capacity. To suppress the decrease of cyclic and thermal stability due to the in-crease of nickel content, LiNi0.87Co0.06Mn0.07O2 particles with transition metal concentration gradient from the interior to the surface are realized. An efficient and low-cost method is proposed involves firstly forming the shell layer with low nickel content by a dry mechanofusion process and subsequently adopting a novel particle size-controllable calcination course. Through which a concentration gradient layer with a thickness of 1 mu m is successfully formed, and the particle size of primary particles is effectively controlled at the range of 250-300 nm. The relationship between the calcination conditions, the morphology, particle size of primary particles and the electrochemical performance have been established. Capacity of 211.9 mAh/g and initial coulomb efficiency of 90.29% have been achieved by LiNi0.87Co0.06Mn0.07O2 with superficial transition metal concentration gradient, and the capacity retention rate at 1 C reached 86.1% after 400 cycles in a pouch cell. In addition, the thermal decomposition temperature is elevated from 220 degrees C to 242 degrees C, the safety of the Ni-rich material has been also effectively improved. (C) 2021 Published by Elsevier B.V.
查看更多>>摘要：The application scope and market demand for additive-manufactured high-entropy alloys (AM HEAs) have broadened of late. However, a long-standing problem associated with AM HEAs is their limited ductility. In this study, a dual-phase AlCoCuFeNi HEA, consisting of body-centered cubic (BCC) solid solution matrix with uniformly dispersed face-centered cubic (FCC) structured precipitates, was fabricated by selective electron beam melting (SEBM). SEBM involved a preheating process can enable the formation of Cu-rich FCC phases with needle-like and spherical morphologies, as well as nanotwins that in-situ precipitated from the metastable BCC(B2) matrix. The compressive strength and ductility of the SEBM HEA were superior to those of the HEAs processed by selective laser melting (SLM) AM technique. Furthermore, using selective electron beam remelting (SEB-RM) during SEBM could result in a higher relative density, finer microstructure, and enhanced compressive properties. Particularly, the SEB-RM sample exhibited a better compressive strength of 2572 MPa, a yield strength of 870 MPa, and a strain of 18.3%. The improved mechanical properties of SEBRM samples could be ascribed to the refined grains and the formation of FCC precipitates, mostly along the grain boundaries. This provides new insights into the dual-phase HEAs-fabricated via a combination of the SEBM additive manufacturing process and selective electron beam remelting-that exhibit in-situ strengthening. (c) 2021 Elsevier B.V. All rights reserved.
查看更多>>摘要：Bramble-like NaVMoO6/C nanofibers with remarkable lithium-storage property are fabricated via a simple electrospinning method. The NaVMoO6 nanoparticles with average size of 84 nm are uniformly embedded into the carbon nanofibers at loading of 77.2 wt%. The unique architecture of the resulting nanocomposite has great advantages like enhanced surface-to-volume ratio, reduced ion transport lengths and strengthened electron transfer along the longitudinal direction. As a new-type anode for lithium-ion batteries (LIBs), NaVMoO6/C composite demonstrates a stable capacity of 1013 and 682 mAh g(-1) at the current density of 0.1 and 1 A g(-1), respectively. Furthermore, the structure evolution mechanism during the first discharge process is carefully researched by ex-situ X-ray diffraction and X-ray photoelectron spectroscopy. It is found that the NaVMoO6 crystals begin to change after being embedded with a few equivalent Li+ when discharging to 2.2 V. With the continuous intercalation of Li+ ions, the main crystal form of the electrode is V2O5 at the potential of about 2.0 V. At low potential (approximate to 1.2 V vs. Li/Li+), the formed V2O5 is transformed into LiVO2. In addition, the volume expansion of the NaVMoO6 particles is alleviated due to the confining effect of carbon nanofibers. Consequently, NaVMoO6/C nanofibers demonstrate a high reversible capacity even at high rate. (C) 2021 Elsevier B.V. All rights reserved.
查看更多>>摘要：Enhancement of the magneto-mechanical properties in directional solidified Fe80Al20 alloys by doping Tb is demonstrated. The Delta E effect of 9.1%, large magnetostriction of 144 ppm, magnetostriction sensitivity of 0.28 ppm/Oe, Delta G effect of 5.4%, and magneto-mechanical coupling of 29.74% reached for Fe79.9Al20Tb0.1 alloy are beneficial for applications. The increased magnetostriction with increasing the Tb content x from 0 to 0.1 is related to the increased degree of (110) texture with Tb doping. Notably, the increased magnetostriction sensitivity, resulted from the increased magnetostriction with Tb-doping, leads to the enhancement of Delta E and Delta G effects. Nevertheless, the degraded (110) texture for higher Tb content (x = 0.15) results in the reduction of magneto-mechanical properties. Summarized with the experimental measured and theoretically estimated results, the micro eddy-current mechanism mainly governs the change of damping capacity with H for frequency of vibrations similar to 2.0 kHz resulting from the magnetic domain wall motion. Moreover, the amplitude and temperature dependences of internal friction and elastic modulus data, measured by DMA, including damping capacity and Young's modulus, at a frequency of 0.1-30 Hz could characterize hysteretic damping and anelastic effects at heating. The result of this study suggests a cost-effective and simple method to obtain Fe80Al20 based alloy with excellent magneto-mechanical properties via proper Tb-doping. (C) 2021 Elsevier B.V. All rights reserved.
Shalnova, Svetlana A.Kuzminova, Yulia O.Evlashin, Stanislav A.Klimova-Korsmik, Olga G....
9页
查看更多>>摘要：Direct energy deposition (DED) is a promising additive manufacturing technique in the area of aerospace, automotive, shipbuilding and medical industries. DED allows producing large-scale parts that imply the use of a significant amount of powders. Powder reuse is an important task that leads to a reduction in the cost of the final products. In this work, Ti-6Al-4V samples were fabricated by DED technique with a mixture of unused and recycled powders in the recycled powder content of 0%, 10%, 25%, and 50%. The results show that the morphology of the powder does not change significantly due to a low number of powder uses. Chemical analysis reveals a slight decrease of V in the recycled powder. The evolution of macrostructure with increasing recycled powder content was not revealed. In the as-built samples, the columnar prior beta grains grow toward the build direction with a typical Widmanstatten structure consisting of the thin alpha' laths. The mix of Widmanstatten microstructure and basket weave microstructure appears after the annealing at 800 celcius. Furthermore, the horizontal and vertical annealed samples exhibit ductile fracture and inconspicuous anisotropy of tensile and impact mechanical properties. (c) 2021 Elsevier B.V. All rights reserved.
查看更多>>摘要：Red-emitting Ca3Si2O7:Eu3+ and Ca3Si2O7:Eu3+, M+ (M = Li, Na, K) phosphors were prepared via a solid-state reaction. The effects of Eu3+ doping concentration and alkali metal ions M+ co-doping on the structure and luminescence performance of Ca3Si2O7:Eu3+ were investigated. X-ray diffraction patterns demonstrated that the Ca3Si2O7:Eu3+ phase synthesized at 1400 degrees C was consistent with the standard Ca3Si2O7 structure. Characteristic emission peaks of Ca3Si2O7:Eu3+ phosphors were revealed at 593 nm and 617 nm under excitation at 394 nm, which relate to the 4f electron transitions of Eu3+ ions. After co-doping M+ as a charge compensator, the luminescence intensity of red-emitting Ca3Si2O7:Eu3+, M+ phosphors were significantly improved by 2.62-, 1.80-, and 2.92-fold for Li+, Na+, K+ co-doping, as well as the luminescence lifetime compared with that of Eu3+-doped Ca3Si2O7. Moreover, actual LEDs with excellent chromaticity parameters were manufactured via coating the as-prepared phosphor onto a 395 nm n-UV chip. All results indicate that the Ca3Si2O7:Eu3+, M+ red-emitting phosphor has an excellent potential application as a red component in white light-emitting diodes. (C) 2021 Elsevier B.V. All rights reserved.
查看更多>>摘要：Graphene quantum dots (GQDs) as excellent conductive materials could effectively enhance the electron transmission efficiency of W18O49 nanofibers after their combination. In order to investigate the effect of different crystal phase WO3 on the optoelectric properties of GQDs/W18O49 composites, the orthogonal phase WO3 (o-WO3), hexagonal phase WO3 (h-WO3) and tetragonal phase WO3 (t-WO3) had been used to produce GQDs/W18O49/WO3 homojunction with GQDs/W18O49. After comparing them, it was found that the photocurrent intensity of GQDs/W18O49/t-WO3 was 2.35 times, 1.68 times and 1.08 times as high as that of GQDs/W18O49, GQDs/W18O49/o-WO3 and GQDs/W18O49/h-WO3 at 1.2 V versus Hg/Hg2Cl2, respectively. And the t-WO3 could effectively decrease the band gap, reduce the interfacial resistance, prolong the electron lifetime, accelerate the electron conduction and increase the photocurrent magnitude of the homojunction. The photoelectric performance of the composites could be adjusted by regulating the ratios of GQDs/W18O49 and t-WO3, the ratio 2:1 of GQDs/W18O49/t-WO3 composites presented a higher photocurrent density and lower interfacial resistance than other proportions. The physical mechanism of such enhanced photoconduction in this homostructure have been discussed. (C) 2021 Elsevier B.V. All rights reserved.
查看更多>>摘要：Ti-4Al-4Mo-4Sn-xSi (wt%) (x = 0, 0.2, 0.5) alloys were fabricated by hot extrusion of compacts of blends of TiH2, AlMo60 master alloy and other required elemental powders followed by heat treatments involving vacuum annealing, solution treatment, air cooling and aging. The microstructure of the alloys consists of alpha plates, lamellae of alpha and transformed beta structure (beta(t)), beta(t) blocks as well as grain boundary alpha layers. With the addition of 0.2 wt%Si, the Si atoms exist in equal concentration in both alpha and beta(t) regions as solute atoms, and they retard the growth of alpha phase, causing a decrease of the average thickness of alpha plates and lamellae and slight increase of the volume fraction of beta(t) lamellae and blocks. The solid solution strengthening and enhanced alpha/beta interface hardening brought by the 0.2 wt%Si cause the yield strength of the Ti-4Al-4Mo-45n alloy to increase significantly from 1030 to 1130 MPa with a slight decrease of the tensile ductility (7.4% vs 6.8%) and without changing the fracture behavior. With the addition of 0.5 wt%Si, the extra Si causes nanometer sized silicide (Ti5Si3) precipitates to form in both alpha and beta(t) regions and further microstructural refinement. The additional alpha/beta interface hardening and precipitation hardening cause the yield strength of the alloy to increase further to 1177 MPa, but the tensile ductility deteriorates clearly with the elongation to fracture decreasing to 4.9%. The main reason for this ductility decrease is the premature fracture of grain boundary alpha layers caused by the higher flow stress which can induce more strain localization at the grain boundary alpha layers. (C) 2021 Elsevier B.V. All rights reserved.
查看更多>>摘要：Electrolysis of water is an environmentally friendly and promising hydrogen generation technology, which is one of the best ways to deal with the global energy crisis and environmental pollution. However, the slow anode reaction of water electrolysis is the bottleneck of limiting the efficient hydrogen production. Therefore, it is a key problem to explore an efficient and economical electrocatalyst to assist the anode reaction. Herein, a series of self-supporting M-NiCo2S4/Ni3S2 (M=Mn, Fe, Cu, Zn) nanostructures grown on a nickel foam (NF) skeleton were prepared through one-step hydrothermal strategy. In this process, doping engineering is employed to adjust the electronic structure of catalyst and improve the performance of the catalyst. Among them, the introduction of Fe not only greatly changed the morphology, but also provided rich active sites. Specifically, the Fe-NiCo2S4/Ni3S2 electrode can achieve current densities of 50 and 100 mA cm(-2) at overpotential of 159 and 210 mV in alkaline media for oxygen evolution reaction (OER). In addition, driving current densities of 50 and 100 mA cm(-2) in 1.0 M KOH with 0.5 M urea only requires the ultra-small voltage of 1.37 and 1.39 V (vs. RHE) for urea oxidation reaction (UOR), indicating that UOR can well replace OER to reduce electrical energy consumption. The experimental results and density functional theory calculations (DFT) demonstrate that the superior activity of the catalyst can be attributed to the optimal water adsorption energy, faster electron transfer rate, more active site exposure and good electrical conductivity. This work extends the application of doping engineering in water electrolysis and provides a novel preparation method of efficient catalyst for OER and UOR. (C) 2021 Elsevier B.V. All rights reserved.
查看更多>>摘要：Great efforts have been made to enhance the photocatalytic efficiency of g-C3N4. The construction of Z-scheme g-C3N4-based ferroelectric heterostructures was considered to be an effective strategy to promote rapid carrier separation. However, the mechanism of charge transfer in the synergistic effect between Zscheme g-C3N4-based heterojunction and ferroelectric polarization has not been thoroughly studied. Herein, g-C3N4-based ferroelectric catalysts with various bismuth ferrite (BiFeO3) contents have been prepared with a simple approach, and the direct Z-scheme heterojunction between BFO and g-C3N4 has been proved by experiments. Meanwhile, our study verified that the direct Z-scheme g-C3N4-based ferro-electric heterostructure plays a positive role in photocatalytic activity, and the charge transfer mechanism of this structure was discussed in detail, which provides a new strategy for improving the performance of g-C3N4-based ferroelectric catalysts. (C) 2021 Elsevier B.V. All rights reserved.
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