Showing papers on "Tungsten published in 2023"

Oxygen vacancy-induced spin polarization of tungsten oxide nanowires for efficient photocatalytic reduction and immobilization of uranium(VI) under simulated solar light

Abstract: Tungsten oxide nanowires (WO3−x) with rich oxygen vacancies (OVs) were fabricated through a facile hydrothermal method, which had both high adsorptive capability and photocatalytic activity. 95.1% of total U(VI) (C0 = 10 mg/L) was removed by WO3−x at pH 5, and 79.9% was transformed to U(IV) to achieve reductive immobilization after photocatalysis under simulated solar light. Band structure and optical characterizations indicated WO3−x had narrower band gap energy, but higher charger carrier separation and transfer rates compared with conventional WO3. Density functional theory (DFT) calculations further demonstrate the spin polarization state electrons of W 5d in WO3−x due to the construction of OVs, thus greatly inhibiting recombination of electron-hole pairs. In addition, the electron density increases in WO3−x and the photogenerated e– in the conduction band of WO3−x has higher reduction ability than WO3, leading to more efficient electron transfer from WO3−x to UO22+ after photo-excitation for U(VI) reduction.

High-Mobility Flexible Transistors with Low-Temperature Solution-Processed Tungsten Dichalcogenides

Abstract: The investigation of high-mobility two-dimensional (2D) flakes beyond molybdenum disulfide (MoS2) will be necessary to create a library of high-mobility solution-processed networks that conform to substrates and remain functional over thousands of bending cycles. Here we report electrochemical exfoliation of large-aspect-ratio (>100) semiconducting flakes of tungsten diselenide (WSe2) and tungsten disulfide (WS2) as well as MoS2 as a comparison. We use Langmuir–Schaefer coating to achieve highly aligned and conformal flake networks, with minimal mesoporosity (∼2–5%), at low processing temperatures (120 °C) and without acid treatments. This allows us to fabricate electrochemical transistors in ambient air, achieving average mobilities of μMoS2 ≈ 11 cm2 V–1 s–1, μWS2 ≈ 9 cm2 V–1 s–1, and μWSe2 ≈ 2 cm2 V–1 s–1 with a current on/off ratios of Ion/Ioff ≈ 2.6 × 103, 3.4 × 103, and 4.2 × 104 for MoS2, WS2, and WSe2, respectively. Moreover, our transistors display threshold voltages near ∼0.4 V with subthreshold slopes as low as 182 mV/dec, which are essential factors in maintaining power efficiency and represent a 1 order of magnitude improvement in the state of the art. Furthermore, the performance of our WSe2 transistors is maintained on polyethylene terephthalate (PET) even after 1000 bending cycles at 1% strain.

Highly efficient reduced tungsten oxide-based hydrogen gas sensor at room temperature

Abstract: Reduced tungsten oxide nanoparticles (WO2.72) was synthesized from tungsten trioxide by calcination method. The prepared samples were systematically characterized via field-emission scanning electroscope (FESEM), Raman spectroscopy, and X-ray diffraction (XRD). Then, the prepared WO2.72 was spin coated on Si/SiO2 substrate, and the sensor was developed with interdigital electrode. The gas sensing property of the developed sensor toward H2 gas was investigated. The result shows that the fabricated WO2.72 sensor possesses excellent H2 gas sensor response of 27% at room temperature. Moreover, the WO2.72 sensor exhibited outstanding long-term stability and repeatability at 500 ppm. Besides, it exhibited stable sensor response in wide range of humidity reaveviling its potential candidacy for real application of H2 gas monitoring. Therefore, this study paves way for development of effective, stable and fast responsing H2 gas sensor at room temperature that is very important in environmental remediation.

Cavitation Erosion Characteristics of the EN AW-6082 Aluminum Alloy by TIG Surface Remelting

Abstract: Components made of aluminum alloys operating under cavitation erosion conditions have low performance and therefore a reduced lifetime. The degradation of these components is a consequence of the repetitive implosion of cavitation bubbles adjacent to the solid surface. In this paper, the effect of the rapid re-melting and solidification modification of the surface microstructure of parts of an Al-based alloy strengthened by artificial ageing on the reduction of material loss through cavitation erosion was investigated. The heat source used was the electric arc generated between a tungsten electrode and the workpiece (i.e., TIG). Local surface melting was performed at different values of linear energy (El = 6600–15840 J/cm), varying the current between 100 A and 200 A, at a constant voltage of 10 V. The obtained results showed an increase in the surface microhardness at values of 129–137 HV0.05 and a decrease in the erosion rate from 0.50 µm/min, characteristic of the artificial ageing heat treatment, to 0.10–0.32 µm/min, specific to TIG re-melted layers. For the study of the cavitational erosion mechanism, investigations were carried out by optical microscopy and scanning electron microscopy. The results showed that the improvement of the cavitational erosion resistance by surface melting was a consequence of the increase in microstructural homogeneity and grains refinement.

Small Changes, Big Impact: Tungsten Bronzes with Extremely Large Second Harmonic Generation Achieved by the Transition Metal Doping on the B‐Site

Abstract: Two novel transition metal‐doped tungsten bronze oxides, Pb2.15Li0.85Nb4.85Ti0.15O15 (PLNT) and Pb2.15Li0.55Nb4.85W0.15O15 (PLNW), are synthesized by high‐temperature solid‐state reactions. The Rietveld method using the high‐resolution synchrotron radiation indicates that PLNT and PLNW crystallize in the orthorhombic polar noncentrosymmetric space group, Pmn21 (no. 31). As a class of tungsten bronze oxide, PLNT and PLNW retain a unique rigid framework composed of d0 transition metal cation (Ti4+ or W6+)‐doped highly distorted NbO6 octahedra along with the subsequently generated Pb/LiO12 and PbO15 polyhedra. Interestingly, the d0 transition metal‐doped tungsten bronzes, PLNT and PLNW, exhibit extremely large second‐harmonic generation (SHG) responses of 56 and 67 × KH2PO4, respectively. The observed immeasurably strong SHG is mainly attributed to a net polarization originating from the alignment of highly distorted NbO6 octahedra with doped transition metals in the frameworks. It is believed that doping transition metal cations at the B‐site of the tungsten bronze structures should be an innovative strategy to develop novel high‐performance nonlinear optical materials.

Exploring the Influence of the Evolution of Discharge Plasma Channel on the Characteristics of Electric Explosion Products

Abstract: Electrical explosion method as a powerful tool for one-step synthesizing metallic nanoparticles has raised widely interests. In this paper, experiments were performed with three metal wires, namely copper, tungsten and titanium who are the typical representation of non-refractory and refractory metals. High-speed photography along with electrophysical and optical diagnostics were applied to characterize the electrical explosion. Accordingly, SEM and TEM was used to characterize the micro-morphology of explosion products. XRD was used to detect the phase compositions. Experiment results indicated that the products morphology and particle size distribution were influenced by the dynamic behaviors of the exploding wires. Electrothermal instability (ETI) and secondary breakdown were observed in copper wire explosion, the prominent discrepancies of temperature and density among stratified vapor and plasma channel enlarged the inhomogeneity of particle size. The sufficient plasma process maintained the metal vapor at a relatively high temperature and enhance the coalescence process after nucleation in titanium explosion, and the median diameter of particles increased as a result. The core-corona structure happened in tungsten wire explosion led to special heating mechanism (heat transport and/or radiation instead of Joule heating) which may be responsible for the formation of large-size agglomerates. In order to produce high-quality nanoparticles, except suitable experimental conditions, it is necessary to achieve homogeneous explosions. The critical dynamics behaviors including ETI (stratification), breakdown mode (inner or surface), and coexistent multi-states products (melts/vapor/plasma) under low-density current which caused the inhomogeneity should be further considered and eliminated in nanoparticle production.

High-temperature tensile and thermal shock characterization of low-temperature rolled tungsten

Abstract: A developed tungsten (W) grade was prepared by powder metallurgy technology plus multi-step low-temperature rolling. The relative density, thermal conductivity, microstructure, tensile properties of original and high-temperature annealed states, micro-hardness and transient thermal shock resistance were characterized. The results of tensile test with a strain rate of 2 × 10-4 s−1 show that the ductile–brittle transition temperature (DBTT) of rolled-W in the original and recrystallized state are 150–200 °C and 250–300 °C, respectively. The rolled-W presents high strength and great plasticity simultaneously. For example, the maximum ultimate tensile strength (UTS) below DBTT is as high as ∼ 1189 MPa, and the maximum total elongation (TE) above DBTT reaches 28.9 %. In particular, the TE of recrystallized W achieves an incredible 81.4 % at 500 °C, which is the highest value among all the published literatures so far. The results of transient thermal shock tests indicate that the rolled-W has an outstanding transient thermal shock resistance. It can withstand the thermal bombardment at an absorbed power densities (APD) of 0.33 GW·m−2 without causing any surface damages, and still no cracks are observed as the APD rises to 0.88 GW·m−2. Moreover, the failure mechanism of rolled-W was also studied in details. This work plays an important role in establishing a dependable China Fusion Engineering Test Reactor (CFETR) data-library on a unitary W grade, which can provide an effective reference for the identification of material performance under the high heat flux and subsequent numerical simulation.

Investigation of interfacial strength in nacre-mimicking tungsten heavy alloys for nuclear fusion applications

Abstract: Tungsten heavy alloys have been proposed as plasma facing material components in nuclear fusion reactors and require experimental investigation in their confirmation. For this purpose, a 90W-7Ni-3Fe alloy has been selected and microstructurally manipulated to present a multiphase brick-and-mortar structure of W-phase 'bricks' surrounded by a ductile 'mortar'. This work draws inspiration from nature to artificially imitate the extraordinary combination of strength and stiffness exhibited by mollusks and produce a nacre-mimicking metal matrix composite capable of withstanding the extremely hostile environment of the reactor interior and maintaining structural integrity. The underlying mechanisms behind this integrity have been probed through high-resolution structural and chemical characterization techniques and have revealed chemically diffuse phase boundaries exhibiting unexpected lattice coherency. These features have been attributed to an increase in the energy required for interfacial decohesion in these systems and the simultaneous expression of high strength and toughness in tungsten heavy alloys.

Probing the composition dependence of residual stress distribution in tungsten-titanium nanocrystalline thin films

Abstract: Abstract Nanocrystalline alloy thin films offer a variety of attractive properties, such as high hardness, strength and wear resistance. A disadvantage is the large residual stresses that result from their fabrication by deposition, and subsequent susceptibility to defects. Here, we use experimental and modelling methods to understand the impact of minority element concentration on residual stresses that emerge after deposition in a tungsten-titanium film with different titanium concentrations. We perform local residual stress measurements using micro-cantilever samples and employ machine learning for data extraction and stress prediction. The results are correlated with accompanying microstructure and elemental analysis as well as atomistic modelling. We discuss how titanium enrichment significantly affects the stress stored in the nanocrystalline thin film. These findings may be useful for designing stable nanocrystalline thin films.

A comprehensive laboratory measurement on the thermal characteristics of Ag–CuO–tungsten oxide/water nanofluid in mono, hybrid and ternary cases and presenting a new correlation

Abstract: Background: This study investigates the thermal conductivities of the Ag–CuO–tungsten oxide/water ternary hybrid nanofluids (THNFs) with mixing ratios of 20, 45 and 35%, Ag-tungsten oxide/water, Ag-CuO/water, tungsten oxide-CuO/water hybrid nanofluids (HNFs) (with 50% mixing ratio), and Ag/water, CuO/water, and tungsten oxide/water mono nanofluids (MNFs) in a laboratory. Methods: Using the two-step method, the nanofluids (NFs) are fabricated by dispersing nanoparticles (NPs) in base fluids. THNFs are formed in volume fractions φ =0.1–0.4% and MNFs and HNFs are made in φ=0.1 and 0.3%. After ensuring NF stability, thermal conductivity (TC) is measured within T = 20–50 °C. The results show that raising temperature increases TC. Moreover, increasing φ increases TC; and increasing temperature has a greater effect in higher φ. The results suggest that the Ag/water MNF in the φ=0.4% and T = 50 °C has the highest TC with a 49.7% increase compared to the base fluid. Finally, a mathematical model is proposed for estimating the TC of Ag–CuO–tungsten oxide/water THNFs. Significant Findings: Comparison of the proposed equation's results with laboratory results shows that the proposed model for the Ag-CuO-tungsten oxide/water THNF was accurate within 20–50 °C and φ=0.1–0.4%.

Optimization of pulse bi-directional electrolysis in-situ synthesis of tungsten carbide by response surface methodology

Abstract: The response surface methodology was used to optimize the parameters of pulse bi-directional electrolysis (PBE) in-situ synthesis of tungsten carbide (WC) in NaF-KF molten salt system. The process of PBE synthesis of WC is a short process method of in-situ synthesis of WC powders in molten salt electrolyte. WC were used both as cathode and anode. A symmetrical bi-directional pulse is applied between the two electrodes. Tungsten ions dissolved by forward pulse, and WC were produced in situ with carbon near the electrode during reverse pulse. During the research, it was found that the factors affecting the phase of the experimental product were Current intensity, Pulse period and Electrolysis duration. In this paper, the cathode and anodic dissolved mass and the Proportion of WC in the product were used as the response values. The Box-Behnken center combined test and response surface analysis are used to optimize the factors that affect significantly, and the optimal process parameters were determined. Finally, the model was experimentally verified. Under the optimized experimental conditions, high-performance tungsten carbide nanopowders were prepared with short-process and high-efficiency.

A comparative study between pure bismuth/tungsten and the bismuth tungsten oxide for flexible shielding of gamma/X rays

Abstract: Thermoplastic vulcanizate based flexible W/Bi and bismuth tungsten oxide composites with different doping ratios from 20% to 100% are successfully fabricated. The ray attenuation abilities of the composites are determined at X-ray tube voltages of 80 KVp–120 KVp, and at gamma rays of 59 keV, 122 keV, 343 keV and 960 keV. The surface morphology and elements mapping of W/Bi and bismuth tungsten oxide particles within the polymer have confirmed a more uniform dispersion of bismuth tungsten oxide than W/Bi. Shielding parameters such as transmittance T, mass/linear attenuation coefficients μm and μ, as well as lead equivalent δPb are investigated experimentally and numerically by Monte Carlo code NECP-MCX as well as XCOM program. The transmittance of γ ray decreases exponentially with the areal density of the functional particles, and the best shielding of X-ray goes to 100 KVp tube voltage, followed by 80 KVp and 120 KVp. A comparison of the two series of composites are made that W/Bi always has advantages over bismuth tungsten oxide in attenuation coefficients and lead equivalent, because the extra containing oxygen atoms in bismuth tungsten oxide crystal actually provide very weak additional shielding. Test of mechanical property also reflects the advantage of using pure W/Bi over bismuth tungsten oxide in flexibility. As substitutes for Pb containing materials, these two types of composites could be of potential use in medical diagnosis, interventional surgery, or biological radiation protection, etc.