1,721,044 research outputs found
Further Improvement of Battery Performance via Charge Transfer Enhanced by Solution-based Antimony Doping into Tin Dioxide Nanofibers
No full textWe synthesized antimony (Sb)-doped tin dioxide (SnO2) nanofibers by a one-pot solution doping electrospinning process, and demonstrated that the electrical and lithium (Li)-ion conductivities of SnO2 nanofibers can substantially be increased by such a facile doping process. Owing to improved conductivities, our Sb-doped SnO2 nanofibers exhibited greatly facilitated charge transport features as battery anodes. The current study on the effect of dopant concentration revealed that 10 at.% doping produced optimized electrical and Li-ion conductivities from current-voltage characteristics and Nyquist plots. The Sb-doped SnO2 nanofibers retained over 95% Coulombic efficiency at all variable current rates from a low current rate of 100 mA g(-1) to a high current rate of 1000 mA g(-1), while pure SnO2 nanofibers had lower Coulombic efficiency values around 85% at the low current rate of 100 mA g(-1). Especially, doped nanofibers exhibited a much more stable capacity retention during 100 cycles than undoped SnO2 nanofibers. We herein confirmed that the increase in charge transport properties by the facile solution doping can directly lead to the further improved performance of Li-ion batteries with one-dimensional nanofiber electrodes.11107sciescopu
A STUDY ON RESIDUAL-STRESSES IN SURFACE HARDENING BY HIGH-FREQUENCY INDUCTION-HEATING
No full textThe transient heat flow and thermal stress during surface hardening by high frequency induction heating were analyzed using the finite element method. Using the modified two-dimensional finite model, the thermal and residual stresses during high frequency induction hardening were successively calculated. The thermal stresses were induced mainly by the temperature gradient and martensitic phase transformation; the phase transformation was found to have a greater influence on the residual stress than the temperature gradient. The simulation results revealed that there is a compressive residual stress within the hardening area and there is a maximum tensile residual stress near the exterior of the hardened zone. The effect of transformation plasticity was considered by using an additional strain in the numerical analysis of the high frequency induction hardening. The difference between the residual stresses considering and not considering the transformation plasticity was large, so it cannot be considered a negligible factor. In the non-hardening region, however, the stresses were distributed similarly
A STUDY OF RESIDUAL-STRESSES IN THE SURFACE HARDENING OF A BLADE MOLD BY HIGH-FREQUENCY INDUCTION-HEATING
No full textHigh frequency induction heating is a method of surface treatment which restricts the hardening area using the skin effect. Since the penetration depth of the magnetic field in the workpiece is dependent on the frequency, the required size of hardening area can be obtained by selecting an appropriate frequency. High frequency induction heating is able to harden a large area at once, in which the shapes of the coil and workpiece and the distance between them are important factors for the hardening area shape and the distribution of residual stresses. In this study, the transient heat flow and thermal stress were analysed for the high frequency induction surface hardening of a blade mould by using the modified two-dimensional finite element method. Besides the volume change in the phase transformation, the effect of transformation plasticity was also considered as an additional strain in the numerical analysis of the high frequency induction hardening process. The hardening area was fairly uniform in the mould surface except around the corner where the distance between the coil and workpiece was slightly larger than on the other parts. The thermal stress was induced mainly by the temperature gradient and martensitic phase transformation, while the latter was found to have a greater influence on the residual stress than the former. Simulation results revealed that compressive residual stresses occur in the hardening area, while the maximum tensile residual stress occurs near the boundary of the hardened zone
A STUDY OF THE RESIDUAL-STRESS REDUCTION METHOD THROUGH THE MECHANICAL LOADING CYCLE IN METAL-TO-CERAMIC BRAZED JOINTS
No full textThe transient thermal and residual stresses in the metal-to-ceramic brazed joints were analysed by using the finite element method (FEM). The thermal and residual stresses which were induced mainly by the difference in the thermal expansion coefficients between the brazed materials were successively calculated. The high tensile residual stress occurred in the brazed joint interface, which has the potential to cause internal cracks in the brazed joints. In order to reduce the tensile residual stress in the brazed joint, the mechanical loading cycle was adopted during the brazing thermal cycle. The calculation results revealed that the tensile residual stress in the brazed ceramics can be reduced by the mechanical loading cycle and that the magnitude of the applied load and the temperature at which the mechanical loading cycle started greatly influence the reduction amount of the tensile residual stress. For a comparison of the simulation results, the residual stress in the brazed joints was measured by using the X-ray diffraction method. The results calculated by the FEM analysis showed a similar tendency to the results measured by the X-ray diffraction method. In the case of brazed joints with 0.1 mm thick filler metal, the residual stress in the ceramic part after the mechanical loading cycle showed a lower tensile stress compared to that of brazed joints without the mechanical loading cycle. The larger the applied load, the smaller was the tensile residual stress occurring in the metal-to-ceramic brazed joint.
MnCo2O4 Nanowires Anchored on Reduced Graphene Oxide Sheets as Effective Bifunctional Catalysts for Li–O2 Battery Cathodes
No full textA hybrid composite system of MnCo2O4 nanowires (MCO NWs) anchored on reduced graphene oxide (RGO) nanosheets was prepared as the bifunctional catalyst of a Li-O-2 battery cathode. The catalysts can be obtained from the hybridization of one-dimensional MCO NWs and two-dimensional RGO nanosheets. As O-2-cathode catalysts for Li-O-2 cells, the MCO@RGO composites showed a high initial discharge capacity (ca. 11092.1 mAhgcarbon(-1)) with a high rate performance. The Li-O-2 cells could run for more than 35 cycles with high reversibility under a limited specific capacity of 1000 mAhgcarbon(-1) with a low potential polarization of 1.36 V, as compared with those of pure Ketjenblack and MCO NWs. The high cycling stability, low potential polarization, and rate capability suggest that the MCO@ RGO composites prepared here are promising catalyst candidates for highly reversible Li-O-2 battery cathodes.113938sciescopu
Patterned Catalyst Arrays of Pd/SnO2 Core-Shell Nanowires for Electrooxidations of Biomass-Derived Alcohols
No full textPatterned arrays of catalyst nanowires are demonstrated as high-performance electrode platforms in this research. Palladium catalysts synthesized on various patterned arrays of tin dioxide nanowire frameworks exhibit superior performance for electrooxidations of methanol, ethanol, ethylene glycol, and glycerol in alkaline media. This could be attributed to the effective diffusion of the liquid-phase alcohol reactants through the hollow channels formed between the patterned electrode arrays. Comparable electrocatalytic investigations modifying the pattern geometries of these nanowire electrodes enable the design of promising electrode platforms for electrochemical energy conversion applications.11108sciescopu
Formation of Carbon-coated ZnFe2O4 Nanowires and Their Highly Reversible Lithium Storage Properties
No full textIn this paper, carbon-decorated ZnFe2O4 nanowires, having one-dimensional geometry with diameters of 70-150 nm and lengths of several micrometers, were prepared and used as a highly reversible lithium ion anode material. They can be obtained from calcination of glucose-coated ZnFe2(C2O4)(3) nanowires, which were prepared in glucose containing microemulsion solutions. The physicochemical properties of carbon-coated ZnFe2O4 nanowires were investigated by scanning electron microscopy, X-ray diffraction, Raman spectroscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. The carbon-coated ZnFe2O4 nanowires showed a substantially increased discharge capacity of ca. 1285.1 mA h g(-1) at the first cycle as compared with non-carbon-coated ZnFe2O4 nanowires (ca. 1024.3 mA h g(-1)) and ZnFe2O4 nanoparticles (ca. 1148.7 mA h g(-1)). Moreover, the discharge capacity of the carbon-coated ZnFe2O4 nanowires was maintained with no degradation even after 100 charge/discharge cycles. The high cycling durability, rate capability, and coulombic efficiency suggest that the carbon-coated ZnFe2O4 nanowires prepared here can be promising anode candidates for a highly reversible lithiumstorage electrode.113123sciescopu
An Overview of One-dimensional Metal Nanostructures for Electrocatalysis
No full textNanostructures of metals are of great importance in the area of catalysis due to their distinct physicochemical properties compared to their bulk counterparts. Size and morphology dependent properties of metal nanostructures provide a rational approach toward designing a highly efficient catalytic materials. In particular, one-dimensional (1D) metallic nanostructures in the shapes of wires, rods and tubes have recently been studied with great interest due to their potential uses as electrocatalysts for oxidations of fuels and reduction of oxidants in fuel cell applications. Compared to the conventional nanoparticle catalysts that are generally supported on carbon, these 1D materials can offer significant opportunities to improve catalytic performance under fuel cell reaction conditions by their structural characteristics such as preferential exposure of reactive crystal facets, high stability, and facile electron transport. Great advances in the synthesis of electrocatalysts based on the metallic nanowires and nanotubes have been made with enhanced electrocatalytic activity and durability. This review summarizes the research progress made on synthesizing 1D metal electrocatalysts using different synthetic strategies, including template-assisted method, electrospinning, and template-free wet-chemical synthesis, with an emphasis on the electrocatalytic performance of these 1D nanomaterials.111312sciescopu
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