Showing papers on "Tungsten published in 2018"
TL;DR: Micrometre-sized particles of two niobium tungsten oxides have high volumetric capacities and rate performances, enabled by very high lithium-ion diffusion coefficients.
Abstract: The maximum power output and minimum charging time of a lithium-ion battery depend on both ionic and electronic transport. Ionic diffusion within the electrochemically active particles generally represents a fundamental limitation to the rate at which a battery can be charged and discharged. To compensate for the relatively slow solid-state ionic diffusion and to enable high power and rapid charging, the active particles are frequently reduced to nanometre dimensions, to the detriment of volumetric packing density, cost, stability and sustainability. As an alternative to nanoscaling, here we show that two complex niobium tungsten oxides-Nb16W5O55 and Nb18W16O93, which adopt crystallographic shear and bronze-like structures, respectively-can intercalate large quantities of lithium at high rates, even when the sizes of the niobium tungsten oxide particles are of the order of micrometres. Measurements of lithium-ion diffusion coefficients in both structures reveal room-temperature values that are several orders of magnitude higher than those in typical electrode materials such as Li4Ti5O12 and LiMn2O4. Multielectron redox, buffered volume expansion, topologically frustrated niobium/tungsten polyhedral arrangements and rapid solid-state lithium transport lead to extremely high volumetric capacities and rate performance. Unconventional materials and mechanisms that enable lithiation of micrometre-sized particles in minutes have implications for high-power applications, fast-charging devices, all-solid-state energy storage systems, electrode design and material discovery.
515 citations
TL;DR: Density functional theory (DFT) calculation suggests that the unique structure of the W1 N1 C3 moiety plays an important role in enhancing the HER performance, and gives new insights into the investigation of efficient and practical W-based HER catalysts.
Abstract: Tungsten-based catalysts are promising candidates to generate hydrogen effectively. In this work, a single-W-atom catalyst supported on metal-organic framework (MOF)-derived N-doped carbon (W-SAC) for efficient electrochemical hydrogen evolution reaction (HER), with high activity and excellent stability is reported. High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and X-ray absorption fine structure (XAFS) spectroscopy analysis indicate the atomic dispersion of the W species, and reveal that the W1 N1 C3 moiety may be the favored local structure for the W species. The W-SAC exhibits a low overpotential of 85 mV at a current density of 10 mA cm-2 and a small Tafel slope of 53 mV dec-1 , in 0.1 m KOH solution. The HER activity of the W-SAC is almost equal to that of commercial Pt/C. Density functional theory (DFT) calculation suggests that the unique structure of the W1 N1 C3 moiety plays an important role in enhancing the HER performance. This work gives new insights into the investigation of efficient and practical W-based HER catalysts.
430 citations
TL;DR: An ultrafast multiscale exfoliation method is reported which exploits the piezoelectricity of stratified materials that are noncentrosymmetric in nature to trigger electrically-induced mechanical failure across weak grain boundaries associated with their crystal domain planes.
Abstract: While the remarkable properties of 2D crystalline materials offer tremendous opportunities for their use in optics, electronics, energy systems, biotechnology, and catalysis, their practical implementation largely depends critically on the ability to exfoliate them from a 3D stratified bulk state. This goal nevertheless remains elusive, particularly in terms of a rapid processing method that facilitates high yield and dimension control. An ultrafast multiscale exfoliation method is reported which exploits the piezoelectricity of stratified materials that are noncentrosymmetric in nature to trigger electrically-induced mechanical failure across weak grain boundaries associated with their crystal domain planes. In particular, it is demonstrated that microfluidic nebulization using high frequency acoustic waves exposes bulk 3D piezoelectric crystals such as molybdenum disulphide (MoS2 ) and tungsten disulphide (WS2 ) to a combination of extraordinarily large mechanical acceleration (≈108 m s-2 ) and electric field (≈107 V m-1 ). This results in the layered bulk material being rapidly cleaved into pristine quasi-2D-nanosheets that predominantly comprise single layers, thus constituting a rapid and high throughput chip-scale method that opens new possibilities for scalable production and spray coating deposition.
313 citations
TL;DR: In this paper, a critical review of the methods that have been reported in the literature for improving the ductility of tungsten in order to understand the critical factors that control the ductile (or lack thereof) in Tungsten.
Abstract: Pure tungsten and tungsten alloys with minor alloying additions are known to be brittle at room temperature and have high ductile-to-brittle transition temperatures (DBTT). Improving the ductility of tungsten can have significant impact on both the manufacturing of and the range of applications of tungsten. Although there has been a significant volume of reported research on improving the ductility of tungsten over the span of several decades, it remains a difficult challenge. This is at least partially attributable to the fact that the understanding on the mechanical properties of tungsten and their dependence on microstructure has been insufficient. This article attempts to offer a critical review of the methods that have been reported in the literature for improving the ductility of tungsten in order to understand the critical factors that control the ductility (or lack thereof) in tungsten. It is clear from the literature that all tungsten materials that have been reported to be ductile at room temperature, or to have drastically reduced DBTT, are the result of thermomechanically processed (TMP) material with deformed and textured microstructures. Alloying tungsten with rhenium is essentially the only known method to improve the ductility of tungsten by alloying (excluding the class of alloys known as heavy alloys which are composites of tungsten with nickel and iron). Although there have been a large number of research reports in recent years on the effect of additives, including oxides, carbides, and others, the results are inconclusive to date or insignificant with respect to the effects of those additives on the ductility of tungsten independent of the effects of thermomechanical working. Using ultrafine-grained or nanocrystalline microstructure to improve the ductility of tungsten is another approach that has appeared promising. However, the results to date have not shown that the ductility of tungsten can be improved by reducing the grain size alone, without the benefits of thermomechanical processed or deformed microstructures. Another objective of this review is to examine the correlation between the ductility of tungsten and different microstructures resulting from different processing methods and compositions.
170 citations
TL;DR: In this article, the influence of the SLM processing parameters on the melting and solidification behavior of tungsten and alloys was investigated, and the best results were obtained with a high energy density of the laser and lowest oxygen level in build chamber of the ProX® DMP 320, where the optimal processing conditions resulted in closed porosity.
Abstract: Selective laser melting (SLM) is an additive manufacturing technique which enables fabrication of three dimensional objects by selectively melting successive layers of metallic powder. By utilizing a high energy density laser, complex geometries of even refractory metals like tungsten can be realized. However, due to its intrinsic properties (high melting point, good thermal conductivity, high ductile-to-brittle transition temperature and high surface tension) SLM of tungsten is a challenging task, mainly resulting in cracked and/or porous parts. In order to overcome these drawbacks, the influence of the SLM processing parameters on the melting and solidification behavior of tungsten and tungsten alloys was investigated. The best results were obtained with a high energy density of the laser and lowest oxygen level in build chamber of the ProX® DMP 320, where the optimal processing conditions resulted in parts with closed porosity. Microstructural development, crack formation as well as the resulting texture in the finished parts was evaluated with respect to the material composition and the used scanning strategy.
148 citations
140 citations
TL;DR: This work highlights a powerful way to design more efficient metal–carbon composites catalysts for HER through rational design of a tungsten nitride–carbon composite.
Abstract: Practical application of hydrogen production from water splitting relies strongly on the development of low-cost and high-performance electrocatalysts for hydrogen evolution reaction (HER). The previous researches mainly focused on transition metal nitrides as HER catalysts due to their electrical conductivity and corrosion stability under acidic electrolyte, while tungsten nitrides have reported poorer activity for HER. Here the activity of tungsten nitride is optimized through rational design of a tungsten nitride–carbon composite. More specifically, tungsten nitride (WN) coupled with nitrogen-rich porous graphene-like carbon is prepared through a low-cost ion-exchange/molten-salt strategy. Benefiting from the nanostructured WN, the highly porous structure and rich nitrogen dopant (9.5 at%) of the carbon phase with high percentage of pyridinic-N (54.3%), and more importantly, their synergistic effect, the composite catalyst displays remarkably high catalytic activity while maintaining good stability. This work highlights a powerful way to design more efficient metal–carbon composites catalysts for HER.
122 citations
TL;DR: The mechanical properties of the SLM-produced tungsten are comparable to that produced by the conventional fabrication methods, with hardness values exceeding 460 HV0.05 and an ultimate compressive strength of about 1 GPa, which offers new potential applications of refractory metals in additive manufacturing.
117 citations
110 citations
TL;DR: 2D h-W2 N3 demonstrates an excellent catalytic activity for cathodic HER with an onset potential of -30.8 mV as well as an overpotential of -98.2 mV for 10 mA cm-2 .
Abstract: 2D transition metal nitrides, especially nitrogen-rich tungsten nitrides (Wx Ny , y > x), such as W3 N4 and W2 N3 , have a great potential for the hydrogen evolution reaction (HER) since the catalytic activity is largely enhanced by the abundant WN bonding. However, the rational synthesis of 2D nitrogen-rich tungsten nitrides is challenging due to the large formation energy of WN bonding. Herein, ultrathin 2D hexagonal-W2 N3 (h-W2 N3 ) flakes are synthesized at atmospheric pressure via a salt-templated method. The formation energy of h-W2 N3 can be dramatically decreased owing to the strong interaction and domain matching epitaxy between KCl and h-W2 N3 . 2D h-W2 N3 demonstrates an excellent catalytic activity for cathodic HER with an onset potential of -30.8 mV as well as an overpotential of -98.2 mV for 10 mA cm-2 .
98 citations
15 Mar 2018
TL;DR: A simple method for the synthesis of high performance co-sensitized TiO2 nanotube photocatalysts for application in solar energy conversion has been proposed in this work.
Abstract: Tungsten-copper co-sensitized TiO2 nanotube films on titanium substrate, used as photoanodes in photoelectrochemical (PEC) water splitting to produce hydrogen, have been synthesized via anodization and chemical bath deposition (CBD) methods. Field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD) were used to study the morphology and elemental composition of the synthetic samples. UV-Vis diffuse reflection spectroscopy (UV-Vis DRS) was sued to investigate the optical features of the samples. The impact of copper and tungsten ratio on the photocatalytic behavior of co-sensitized TiO2 nanotube photoelectrodes in PEC water splitting has been investigated. High photocatalytic activity has been exhibited by the co-sensitized TiO2 nanotube samples due to the synergistic effects of the copper and tungsten. Sample T4 had the highest photoelectrochemical activity compared with other samples. In addition, this sample exhibited outstanding photochemical stability even after four runs in the photocatalytic test. A simple method for the synthesis of high performance co-sensitized TiO2 nanotube photocatalysts for application in solar energy conversion has thus been proposed in this work. The advantages of these new photoanodes for practical applications are low cost, ease of synthesis, high activity in visible light and excellent stability.
TL;DR: In this article, a review of various approaches to improving the beneficiation efficiency of tungsten ores are reviewed, including selective flotation of scheelite from other calcium containing minerals such as calcite and fluorite using more selective reagents.
TL;DR: In this paper, an easy route by sol-gel method, without using any template, for the synthesis of flower shaped tungsten (W) supported TiO2/SiO2 catalyst for the triglyceride transesterification was demonstrated.
TL;DR: In this paper, the effects of crystal structure, dislocation structure, and microstructure to describe competing factors in the plasticity and fracture of tungsten at low temperatures are assessed.
Abstract: The physical, chemical, and mechanical properties of tungsten are at the far limits of all engineering materials. These unique properties, particularly ultra-high strength, density, and melting point, create enticing prospects for using tungsten in extreme engineering environments for nuclear, military and space applications. However, these environments also require materials that resist fracture, which presents a significant challenge for tungsten, particularly at low temperatures. This review discusses several significant factors that affect the ductile to brittle transition and low temperature ductility of tungsten. The effects of crystal structure, dislocation structure, and microstructure to describe competing factors in the plasticity and fracture of tungsten at low temperatures are assessed. In particular, the dislocation structure and the mechanisms of dislocation mobility are shown to be critical to understanding plasticity at low temperatures.
TL;DR: In this paper, large-scale molecular dynamics simulations of post-implantation helium behavior in tungsten single crystals reveal orientation-dependent depth profiles, surface evolution patterns, and other crystallographic and diffusion-related characteristics of helium behavior during the first microsecond.
TL;DR: In this article, the effect of process parameters like hatch spacing and scan speed on the densification of tungsten by the selective laser melting (SLM) technique was investigated.
Abstract: Selective Laser Melting (SLM) is a promising technique for the fabrication of complex net shaped parts of many metals. However, the high melting temperature of tungsten makes fabricating complex parts via SLM difficult. A study was undertaken to understand the effect of process parameters like hatch spacing and scan speed on the densification of tungsten by the SLM technique. Experiments were conducted at hatch spacing of 15 and 30 μm and scan speeds in the range 200–1400 mm/s. A constant laser power of 90 W and a powder layer thickness of 30 μm were used. Rectangular cuboids of 7.8 ± 1.4 mm × 10.1 ± 0.1 mm × 10.1 ± 0.04 mm were printed using various process parameters and analyzed for densification. The densification of tungsten was found to increase with an increase in energy density. A maximum density of 75% theoretical was achieved at energy density of 1000 J/mm3.
TL;DR: In this paper, the authors used tungsten carbide (W2C@WC) electrodes for hydrogen evolution studies (HER) in 0.5 M H2SO4.
Abstract: Pyrolysis of hexacarbonyl tungsten, W(CO)6, in 1-octadecene has been used to prepare colloidal tungsten, W, nanoparticles (NPs). The obtained W NPs has been spin-coated on graphite (C) electrodes. Heat treatment of the W/C electrodes at elevated temperatures (≥900 °C) allows the preparation of metallic W and tungsten carbide (W2C@WC) thin films. The obtained W2C@WC electrodes were used for hydrogen evolution studies (HER) in 0.5 M H2SO4. Cyclic voltammetry tests for 1000 cycles showed that W2C@WC exhibit long term stability without significant drop in current density. The overpotential defined at 10 mA/cm2 is 310 mV vs. RHE giving an excellent catalytic activity for HER. Materials characterization has been achieved using transmission electron microscopy (TEM), scanning electron microscopy (SEM), and electrochemical impedance spectroscopy (EIS). Here, EIS studies were used to access the charge-transfer resistance of tungsten carbide electrodes.
TL;DR: In this article, a novel B-site cation ordered double perovskite, SrCo0.4Fe 0.4O3−δ (SCFW0.2W0.
Abstract: Here, using the materials genome strategy, we can account for the comprehensive effects of composition, structure, active sites and adsorption energy, and identify a novel B-site cation ordered double perovskite, SrCo0.4Fe0.2W0.4O3−δ (SCFW0.4), as a superior OER electrocatalyst, which shows outstanding activity and excellent operational stability.
TL;DR: In this paper, the effect of tungsten doping on the activity of α-MnO2 for ozone decomposition was investigated, and the results indicated that doping of Tungsten made the morphology change from nanorods to nanoparticles with great increase of specific surface area.
Abstract: Ozone is a universal air pollutant and its stable decomposition under humid condition is still a challenge. In this work, the effect of tungsten doping on the activity of α-MnO2 for ozone decomposition was first investigated. Tungsten was doped into MnO2 with addition of tungstate in a hydrothermal reaction solution. The as-synthesized catalysts were characterized by XRD, SEM, TEM, BET, XPS, ICP-AES, Raman, H2-TPR, O2-TPD, NH3-TPD and EPR. The results indicated that doping of tungsten made the morphology change from nanorods to nanoparticles with great increase of specific surface area. In addition, more oxygen vacancies were formed, and the surface acidity was greatly enhanced, accordingly the tungsten-doped MnO2 exhibited enhanced activity and stability at room temperature under dry and particularly under humid condition (RH = 65%). It indicates that the doping with a high valence metal such as W6+ into MnO2 is a promising method to obtain efficient ozone-decomposition catalyst.
TL;DR: In this article, a thin solid amorphous silicon film is used as reductant for the gas phase precursor WF6 leading to the conversion to metallic W. The role of the Si surface preparation, the conversion temperature, and Si thickness on the formation process is investigated.
Abstract: The deposition of ultra-thin tungsten films and their related 2D chalcogen compounds on large area dielectric substrates by gas phase reactions is challenging. The lack of nucleation sites complicates the adsorption of W-related precursors and subsequent sulfurization usually requires high temperatures. We propose here a technique in which a thin solid amorphous silicon film is used as reductant for the gas phase precursor WF6 leading to the conversion to metallic W. The selectivity of the W conversion towards the underlying dielectric surfaces is demonstrated. The role of the Si surface preparation, the conversion temperature, and Si thickness on the formation process is investigated. Further, the in situ conversion of the metallic tungsten into thin stoichiometric WS2 is achieved by a cyclic approach based on WF6 and H2S pulses at the moderate temperature of 450 °C, which is much lower than usual oxide sulfurization processes.
TL;DR: In this paper, a double-layer diamond/Cu composite was fabricated by a novel method which coated diamond particles with tungsten as the inner layer through salt-bath plating and then deposited copper as the outer layer through electroless plating.
TL;DR: A review of current research efforts and various methods of scrap recovery, future prospects and sustainability of the tungsten industry, are presented in this paper, with a special emphasis on conversion and energy costs, purity of the scrap metal, recovery of all valuable constituents, as well as diminished environmental impact.
TL;DR: In this paper, a small fraction of tetragonal tungsten bronze (TTB) related KNb6O15F nano-sticks with NbO5F2 pentagonal bipyramids are introduced as conductive wires into H-Nb2O5 by simply doping KF.
TL;DR: In this article, the scheelite was classified into three types: prograde, retrograde, and semi-retrograde skarns, and the lattice strain model was used to estimate the relative distribution of rare earth element (REE) in scheelites and to predict the relative distributions of REE in the ore-forming fluids.
TL;DR: A facile new synthetic method of forming WO3 from tungsten sulfide, WS2 is reported and the negative differential resistance (NDR) property of both WO2 and WO4 is reported for the first time and NDR is explained with density of state approach.
Abstract: Tungsten oxide (WO3 ) is an emerging 2D nanomaterial possessing unique physicochemical properties extending a wide spectrum of novel applications which are limited due to lack of efficient synthesis of high-quality WO3 . Here, a facile new synthetic method of forming WO3 from tungsten sulfide, WS2 is reported. Spectroscopic, microscopic, and X-ray studies indicate formation of flower like aggregated nanosized WO3 plates of highly crystalline cubic phase via intermediate orthorhombic tungstite, WO3. H2 O phase. The charge storage ability of WO3 is extremely high (508 F g-1 at current density of 1 A g-1 ) at negative potential range compared to tungstite (194 F g-1 at 1 A g-1 ). Moreover, high (97%) capacity retention after 1000 cycles and capacitive charge storage nature of WO3 electrode suggest its supremacy as a negative electrode of supercapacitors. The asymmetric supercapacitor, based on the WO3 as a negative electrode and mildly reduced graphene oxide as a positive electrode, manifests high energy density of 218.3 mWhm-2 at power density 1750 mWm-2 , and exceptionally high power density, 17 500 mW m-2 , with energy density of 121.5 mWh m-2 . Furthermore, the negative differential resistance (NDR) property of both WO3 and WO3 .H2 O are reported for the first time and NDR is explained with density of state approach.
TL;DR: In this article, a strategy to improve the sluggish HER kinetics on 3D transition-metal hydroxides by incorporating tungsten through a one-step electrodeposition method is reported.
Abstract: Developing efficient, low-cost, and biocompatible electrocatalysts toward hydrogen evolution reaction (HER) in neutral environments is vital to the development of a hybrid water splitting–biosynthetic system to achieve high-efficiency solar-to-fuels conversion. We report here a strategy to improve the sluggish HER kinetics on 3d transition-metal hydroxides by incorporating tungsten through a one-step electrodeposition method. The prepared amorphous CoW(OH)x delivers high HER activity in neutral solution, which only requires overpotentials of −73.6 and −114.9 mV to achieve the current densities of −10 and −20 mA cm–2 in 1.0 M phosphate buffer solution (PBS), respectively. The activity can be ascribed to the synergistic effects between Co and W, where Co sites facilitate H2O dissociation to generate Had intermediates and W sites could effectively convert Had to H2. Meanwhile, the amorphous architecture features homogeneously dispersed Co and W atoms that avoid crystalline phase separation, further strengthe...
TL;DR: In this article, gas tungsten arc welding (GTAW) was applied to dissimilar lap joining of Al6061 and Zn-coated galvanized low carbon steels using Al-5 wt% Si filler metal.
TL;DR: In this paper, a Field-Assisted Sintering Technology (FAST) process with different fiber-matrix interfaces is used to produce fiber-reinforced tungsten composites.
Abstract: In future fusion reactors, tungsten is a main candidate material for plasma-facing components. However, the intrinsic brittleness of tungsten is an issue under the extreme fusion environment. To overcome this drawback, tungsten fiber-reinforced tungsten (Wf/W) composites are being developed relying on an extrinsic toughening principle. In this study Wf/W composites are produced by a Field-Assisted Sintering Technology (FAST) process with different fiber–matrix interfaces. The fracture behavior was studied by 3-point bending tests on notched samples. 4-point bending tests and tensile tests are performed to measure the flexural strength and tensile strength, respectively. Wf/W with a weak interface shows a typical pseudo-ductile fracture behavior, similar to ceramic matrix composites. A strong interface is beneficial to achieve higher flexural strength and tensile strength, but in turn, weakens the pseudo-ductile behavior.
TL;DR: In this paper, the authors investigated the fundamental mechanisms of the brittle-to-ductile transition in textured, pre-deformed, polycrystalline body-centred cubic metals.
Abstract: This paper attempts to elucidate fundamental mechanisms of the brittle-to-ductile transition (BDT) in textured, pre-deformed, polycrystalline body-centred cubic metals. For this purpose, five tungsten sheets have been rolled out from one and the same sintered ingot representing degrees of deformation of 1.8, 2.5, 3.0, 3.4, and 4.1 (logarithmic notation). Electron backscatter diffraction measurements display the evolution of the microstructure with increasing degree of deformation. The mean grain size of the five sheets in the normal direction is 1.1, 0.59, 0.48, 0.37, and 0.3 μm. Toughness tests based on the K-concept have been performed and the brittle-to-ductile transition temperature of the five sheets has been determined. The crack system used was the L-T crack system. The results have been benchmarked against the BDT temperature of a sintered ingot. The results show a decrease of the BDT temperature with increasing degree of deformation starting from 600 °C (873 K) for the sintered ingot via 115 °C (388 K), 85 °C (358 K), 75 °C (348 K), 60 °C (333K) down to − 65 °C (208 K) for the most heavily deformed tungsten plate. The results are discussed against the background of (i) rolling induced lattice defects such as (i-a) vacancies, (i-b) dislocations (i-c) grain boundaries, (ii) crystallographic texture, (iii) the state of stress, (iv) impurities, (v) sinter pores, and (vi) the geometrical arrangement of areas with low and high fracture toughness. The authors postulate that the BDT is still controlled by the kink-pair nucleation process of a screw dislocation and that the BDT temperature scales with the spacing of dislocation sources (e.g. grain boundary ledges, low angle boundaries, debris loops) along the crack front.
TL;DR: In this paper, a direct diffusion bonding method is designed to bond tungsten and copper without using an interlayer metal at a temperature close to the melting point of copper (TmCu).