Showing papers on "Tungsten published in 2021"

Oxygen-evolving catalytic atoms on metal carbides.

Abstract: Single-atom catalysts have shown promising performance in various catalytic reactions. Catalytic metal sites supported on oxides or carbonaceous materials are usually strongly coordinated by oxygen or heteroatoms, which naturally affects their electronic environment and consequently their catalytic activity. Here, we reveal the stabilization of single-atom catalysts on tungsten carbides without the aid of heteroatom coordination for efficient catalysis of the oxygen evolution reaction (OER). Benefiting from the unique structure of tungsten carbides, the atomic FeNi catalytic sites are weakly bonded with the surface W and C atoms. The reported catalyst shows a low overpotential of 237 mV at 10 mA cm−2, which can even be lowered to 211 mV when the FeNi content is increased, a high turnover frequency value of 4.96 s−1 (η = 300 mV) and good stability (1,000 h). Density functional theory calculations show that either metallic Fe/Ni atoms or (hydro)oxide FeNi species are responsible for the high OER activity. We suggest that the application of inexpensive and durable WCx supports opens up a promising pathway to develop further single-atom catalysts for electrochemical catalytic reactions Metal oxides or carbonaceous supported atomic metal sites coordinated by oxygen or heteroatoms exhibit enhanced electrocatalytic activity. Stabilization of single-atom catalysts on tungsten carbides without heteroatom coordination for efficient oxygen evolution reaction is demonstrated.

Single-photon detection in the mid-infrared up to 10 μm wavelength using tungsten silicide superconducting nanowire detectors

Abstract: We developed superconducting nanowire single-photon detectors based on tungsten silicide, which show saturated internal detection efficiency up to a wavelength of 10 μm. These detectors are promising for applications in the mid-infrared requiring sub-nanosecond timing, ultra-high gain stability, low dark counts, and high efficiency, such as chemical sensing, LIDAR, dark matter searches, and exoplanet spectroscopy.

Mechanical Properties of Atomically Thin Tungsten Dichalcogenides:: WS2, WSe2, and WTe2

Abstract: Two-dimensional (2D) tungsten disulfide (WS2), tungsten diselenide (WSe2), and tungsten ditelluride (WTe2) draw increasing attention due to their attractive properties deriving from the heavy tungsten and chalcogenide atoms, but their mechanical properties are still mostly unknown. Here, we determine the intrinsic and air-aged mechanical properties of mono-, bi-, and trilayer (1-3L) WS2, WSe2, and WTe2 using a complementary suite of experiments and theoretical calculations. High-quality 1L WS2 has the highest Young's modulus (302.4 ± 24.1 GPa) and strength (47.0 ± 8.6 GPa) of the entire family, overpassing those of 1L WSe2 (258.6 ± 38.3 and 38.0 ± 6.0 GPa, respectively) and WTe2 (149.1 ± 9.4 and 6.4 ± 3.3 GPa, respectively). However, the elasticity and strength of WS2 decrease most dramatically with increased thickness among the three materials. We interpret the phenomenon by the different tendencies for interlayer sliding in an equilibrium state and under in-plane strain and out-of-plane compression conditions in the indentation process, revealed by the finite element method and density functional theory calculations including van der Waals interactions. We also demonstrate that the mechanical properties of the high-quality 1-3L WS2 and WSe2 are largely stable in air for up to 20 weeks. Intriguingly, the 1-3L WSe2 shows increased modulus and strength values with aging in the air. This is ascribed to oxygen doping, which reinforces the structure. The present study will facilitate the design and use of 2D tungsten dichalcogenides in applications such as strain engineering and flexible field-effect transistors.

Simultaneously Realizing Superior Energy Storage Properties and Outstanding Charge-Discharge Performances in Tungsten Bronze-Based Ceramic for Capacitor Applications.

Abstract: The development of lead-free ceramics with appropriate energy storage properties is essential for the successful practical application of advanced electronic devices. In this study, a site engineering strategy was proposed to concurrently decrease grain size, increase the band-gap, and enhance the relaxor nature in Ta-doped tungsten bronze ceramics (Sr2NaNb5-xTaxO15) for the improvement of the dielectric breakdown strength and the polarization difference. As a result, the ceramic with x = 1.5, that is, Sr2NaNb3.5Ta1.5O15, exhibited superior energy density (∼3.99 J/cm3) and outstanding energy efficiency (∼91.7%) (@380 kV/cm) as well as good thermal stability and remarkable fatigue endurance. In addition, the ceramic demonstrated an ultrashort discharge time (τ0.9 < 57 ns), a high discharge current density (925.8 A/cm2) along with a high power density (78.7 MW/cm3). The energy storage properties in combination with good stability achieved in this work indicate the powerful potential of Sr2NaNb5-xTaxO15 tungsten bronze ceramics for high-performance capacitor applications. This material can be considered as a complement to the widely studied perovskite-based relaxor ceramics and should be further investigated in the future.

A novel perception toward welding of stainless steel by activated TIG welding: a review

Abstract: Stainless steel is a widely used material in various industries such as aerospace, chemical processing and transportation. Tungsten Inert Gas (TIG) or Gas Tungsten Arc Welding (GTAW) process is ext...

Review: Oxygen-deficient tungsten oxides

Abstract: Oxygen-deficient/non-stoichiometric tungsten oxides are a distinct class between two only stoichiometric tungsten oxides, i.e., WO3 and WO2. The WO3 could be termed as a parent structure while understanding the non-stoichiometric tungsten oxides. The oxygen vacancies (Ovacs) induced in the parent (WO3) structures cause the re-adjustment of atomic arrangement to compensate for the oxygen deficiency and follow the crystal chemistry. The degree of Ovacs determines the range of WO3-x. The W18O49 (WO2.722) is the highest oxygen-deficient stable phase. These non-stoichiometric oxides proved superior to WO3 for various applications. Thus, the composition, chemistry, crystallography, synthesis, and formation mechanisms of such materials have been elaborated. Further, the superiority of the materials in view of few applications is well discussed. Finally, the importance of non-stoichiometry/Ovacs in metal oxides for various functional applications can be understood.

New insights into microstructure of neutron-irradiated tungsten

Abstract: The development of appropriate materials for fusion reactors that can sustain high neutron fluence at elevated temperatures remains a great challenge. Tungsten is one of the promising candidate materials for plasma-facing components of future fusion reactors, due to several favorable properties as for example a high melting point, a high sputtering resistivity, and a low coefficient of thermal expansion. The microstructural details of a tungsten sample with a 1.25 dpa (displacements per atom) damage dose after neutron irradiation at 800 °C were examined by transmission electron microscopy. Three types of radiation-induced defects were observed, analyzed and characterized: (1) voids with sizes ranging from 10 to 65 nm, (2) dislocation loops with a size of up to 10 nm and (3) W-Re-Os containing σ- and χ-type precipitates. The distribution of voids as well as the nature of the occurring dislocation loops were studied in detail. In addition, nano-chemical analyses revealed that the σ- and χ-type precipitates, which are sometimes attached to voids, are surrounded by a solid solution cloud enriched with Re. For the first time the crystallographic orientation relationship of the σ- and χ-phases to the W-matrix was specified. Furthermore, electron energy-loss spectroscopy could not unambiguously verify the presence of He within individual voids.

Engineered tungsten oxide-based photocatalysts for CO2 reduction: Categories and roles

Abstract: Photocatalytic technology can convert CO2 molecules into clean fuels by solar energy, which can alleviate the energy and environmental crisis caused by the consumption of fossil fuels and the greenhouse effect. It is extremely challenging to develop semiconductor photocatalytic materials to achieve high-efficiency catalysis of CO2 reduction with a suitable band gap, effective use of sunlight, and better oxidation-reduction capability for photogenerated holes and electrons. Tungsten oxides mainly exist in the form of WO3, W18O49 (or WO2.72), WO3·0.33H2O, etc., and their visible light response and suitable band structure have certain potential in the photocatalytic CO2 reduction process. At the same time, in view of their shortcomings such as the negative conduction band position, the small amount of CO2 adsorption, and the serious recombination of photogenerated electron holes, the crystal plane/crystal phase/structure/defect/composition can be adjusted to treat their surfaces/interfaces to improve their catalytic activity. In this review, we first briefly introduce the different methods of controlling tungsten oxide. Then, the activities and mechanisms of different types of tungsten oxides-based photocatalysts in catalytic CO2 reduction are summarized. Finally, solutions to the problems for the material design and application of tungsten oxide-based photocatalysts in high-efficiency catalytic CO2 reduction are proposed, and future prospects are discussed.

Microstructure and hardening induced by neutron irradiation in single crystal, ITER specification and cold rolled tungsten

Abstract: In this work, we have performed neutron irradiation and sub-sequent microstructural and micro-hardness measurements on a series of tungsten grades. The neutron irradiation was performed in BR2 reactor up to 0.2 dpa at 600, 800 and 1200 °C. The selected irradiation temperatures correspond to a large range of the operation of tungsten in ITER as armour for the divertor. The applied fast neutron flux is representative of ITER irradiation conditions in terms of damage rate. The primary purpose of the study was to establish the relation between the initial microstructure, the resulting irradiation-induced microstructure and corresponding irradiation hardening. The microstructure was studied using transmission electron microscopy (TEM) and hardening was assessed by micro-hardness measurements. The obtained TEM results were used to predict the hardening employing the dispersed barrier model and strength coefficients established for the single crystal from the open literature. Based on the performed analysis, it appeared that the main contribution to the hardening at high irradiation temperature originates from the voids, while the dislocation loops provide a comparable contribution (30–50%) only under irradiation at 600 °C. Excellent agreement between the model prediction and experimentally measured hardness increase was obtained for the single crystal and ITER specification grade without any additional adjustment, while the hardening induced in the cold rolled plate was essentially overestimated by the model. This result suggests that the cold rolled tungsten plate exhibits an alternative mechanisms of the plastic deformation besides the conventional dislocation glide and multiplication, and this alternative mechanism is impacted by the irradiation less severely compared to the prediction coming from the dispersed barrier model.

Gold-like activity copper-like selectivity of heteroatomic transition metal carbides for electrocatalytic carbon dioxide reduction reaction.

Abstract: An overarching challenge of the electrochemical carbon dioxide reduction reaction (eCO2RR) is finding an earth-abundant, highly active catalyst that selectively produces hydrocarbons at relatively low overpotentials. Here, we report the eCO2RR performance of two-dimensional transition metal carbide class of materials. Our results indicate a maximum methane (CH4) current density of -421.63 mA/cm2 and a CH4 faradic efficiency of 82.7% ± 2% for di-tungsten carbide (W2C) nanoflakes in a hybrid electrolyte of 3 M potassium hydroxide and 2 M choline-chloride. Powered by a triple junction photovoltaic cell, we demonstrate a flow electrolyzer that uses humidified CO2 to produce CH4 in a 700-h process under one sun illumination with a CO2RR energy efficiency of about 62.3% and a solar-to-fuel efficiency of 20.7%. Density functional theory calculations reveal that dissociation of water, chemisorption of CO2 and cleavage of the C-O bond-the most energy consuming elementary steps in other catalysts such as copper-become nearly spontaneous at the W2C surface. This results in instantaneous formation of adsorbed CO-an important reaction intermediate-and an unlimited source of protons near the tungsten surface sites that are the main reasons for the observed superior activity, selectivity, and small potential.

A Review of Tungsten Resources and Potential Extraction from Mine Waste

Abstract: Tungsten is recognized as a critical metal due to its unique properties, economic importance, and limited sources of supply. It has wide applications where hardness, high density, high wear, and high-temperature resistance are required, such as in mining, construction, energy generation, electronics, aerospace, and defense sectors. The two primary tungsten minerals, and the only minerals of economic importance, are wolframite and scheelite. Secondary tungsten minerals are rare and generated by hydrothermal or supergene alteration rather than by atmospheric weathering. There are no reported concerns for tungsten toxicity. However, tungsten tailings and other residues may represent severe risks to human health and the environment. Tungsten metal scrap is the only secondary source for this metal but reprocessing of tungsten tailings may also become important in the future. Enhanced gravity separation, wet high-intensity magnetic separation, and flotation have been reported to be successful in reprocessing tungsten tailings, while bioleaching can assist with removing some toxic elements. In 2020, the world’s tungsten mine production was estimated at 84 kt of tungsten (106 kt WO3), with known tungsten reserves of 3400 kt. In addition, old tungsten tailings deposits may have great potential for exploration. The incomplete statistics indicate about 96 kt of tungsten content in those deposits, with an average grade of 0.1% WO3 (versus typical grades of 0.3–1% in primary deposits). This paper aims to provide an overview of tungsten minerals, tungsten primary and secondary resources, and tungsten mine waste, including its environmental risks and potential for reprocessing.

Tungsten-Based Catalysts for Environmental Applications

Abstract: This review aims to give a general overview of the recent use of tungsten-based catalysts for wide environmental applications, with first some useful background information about tungsten oxides. Tungsten oxide materials exhibit suitable behaviors for surface reactions and catalysis such as acidic properties (mainly Bronsted sites), redox and adsorption properties (due to the presence of oxygen vacancies) and a photostimulation response under visible light (2.6–2.8 eV bandgap). Depending on the operating condition of the catalytic process, each of these behaviors is tunable by controlling structure and morphology (e.g., nanoplates, nanosheets, nanorods, nanowires, nanomesh, microflowers, hollow nanospheres) and/or interactions with other compounds such as conductors (carbon), semiconductors or other oxides (e.g., TiO2) and precious metals. WOx particles can be also dispersed on high specific surface area supports. Based on these behaviors, WO3-based catalysts were developed for numerous environmental applications. This review is divided into five main parts: structure of tungsten-based catalysts, acidity of supported tungsten oxide catalysts, WO3 catalysts for DeNOx applications, total oxidation of volatile organic compounds in gas phase and gas sensors and pollutant remediation in liquid phase (photocatalysis).

High carrier mobility in graphene doped using a monolayer of tungsten oxyselenide

Abstract: Doped graphene could be of use in next-generation electronic and photonic devices. However, chemical doping cannot be precisely controlled in the material and leads to external disorder that diminishes carrier mobility and conductivity. Here we show that graphene can be efficiently doped using a monolayer of tungsten oxyselenide (TOS) that is created by oxidizing a monolayer of tungsten diselenide. When the TOS monolayer is in direct contact with graphene, a room-temperature mobility of 2,000 cm2 V−1 s−1 at a hole density of 3 × 1013 cm−2 is achieved. Hole density and mobility can also be controlled by inserting tungsten diselenide interlayers between TOS and graphene, where increasing the layers reduces the disorder. With four layers, a mobility value of around 24,000 cm2 V−1 s−1 is observed, approaching the limit set by acoustic phonon scattering, resulting in a sheet resistance below 50 Ω sq−1. To illustrate the potential of our approach, we show that TOS-doped graphene can be used as a transparent conductor in a near-infrared (1,550 nm) silicon nitride photonic waveguide and ring resonator. A monolayer of tungsten oxyselenide, created by oxidizing a layer of tungsten diselenide, can be used to efficiently dope graphene, leading to a room-temperature mobility of 2,000 cm2 V–1 s–1 at a hole density of 3 × 1013 cm–2.

Ductile to brittle transition temperature of advanced tungsten alloys for nuclear fusion applications deduced by miniaturized three-point bending tests

Abstract: A large campaign of characterization of the ductile to brittle transition temperature (DBTT) and microstructure has been performed on several commercial and lab-scale pure tungsten grades, potassium doped tungsten alloys, and particle reinforced tungsten grades (with particles of TiC, Y2O3, or ZrC), all integrated in a large-scale neutron irradiation campaign. The DBTT is deduced based on miniaturized three-point bending tests to provide reference data for the assessment of the irradiation effects on the tungsten alloys. This miniaturized geometry is designed to minimize the operational cost of neutron irradiation, to speed up post-irradiation examination, and to reduce the amount of nuclear waste. The resulting DBTT ranges from around −15 up to 450 °C, depending on the material. The potassium doped tungsten alloys have the lowest DBTT, followed by rolled ZrC reinforced tungsten grade, commercial pure tungsten grades, lab-scale pure tungsten grades, and other particle reinforced tungsten grades. The crack plane orientation and microstructure with respect to grain shape and grain boundaries significantly affect the DBTT for forged/rolled tungsten products with elongated grains. The L-T orientation has a lower DBTT compared to the T-L orientation. Moreover, the DBTT difference in the L-T and T-L orientation raises with increasing the grain aspect ratio. An attempt is made to establish a relationship between the density of low and high angle grain boundaries and DBTT value. The obtained relationship is discussed in the frame of mechanical processing (i.e., rolling or forging) to optimize the DBTT by optimized manufacturing. The results are compared to recent computational predictions of the DBTT in tungsten.

Enhanced mechanical and electrical properties of in situ synthesized nano-tungsten dispersion-strengthened copper alloy

Abstract: In this study, a novel dispersion-strengthened copper-tungsten alloy with improved mechanical properties, electrical conductivity, and thermal stability was prepared by mechanical alloying. Cu-WO3 powder blend was milled to obtain a uniform dispersion of WO3 in copper and the WO3 particles were subsequently reduced to tungsten to obtain the Cu–W composite. The tungsten nanoparticles dispersed in the copper matrix have an average size of 32 nm, without agglomeration, and are highly stable. The cold-rolled Cu-5 vol% W reached a tensile strength of 596 MPa, elongation of 7.7%, and electrical conductivity of 84% IACS (International annealing copper standard). In particular, the cold-rolled alloy retains the tensile strength of over 400 MPa and reasonable ductility even after annealing at 800 °C. The remarkable improvement in mechanical properties and thermal stability are attributed to the pinning effect of highly dispersed nano-sized W particles in the Cu matrix.