Amount Of Tungsten Research Articles

Synthesis of three-dimensional ordered mesoporous W-doped KIT-6 for oxidative desulfurization catalyst of fuels

A W-KIT-6 catalyst is prepared by inserting tungsten into the KIT-6 framework to reduce the amount of tungsten and improve the catalyst stability and using it for the oxidative desulfurization (ODS) reaction. Raman and UV–visible spectroscopic analyzes confirm that tungsten is successfully embedded in the KIT-6 framework, and WO3 is formed at high tungsten content. X-ray photoelectron spectroscopy uncovers that tungsten is present in the form of W6+ and W5+ in the framework. High-resolution transmission electron microscopy, nitrogen adsorption-desorption measurements and small-angle X-ray diffraction confirm the ordered structure of the W-KIT-6 catalyst. The true amount of tungsten in the catalyst is measured by inductively coupled plasma spectrometry. The dispersion of tungsten in the catalyst is analyzed by transmission electron microscopy element mapping. The W-KIT-6 catalytic activity is evaluated in the ODS reaction using simulated oil. Under optimal conditions, the sulfur removal effect can reach 100%. Catalyst recovery experiments show that the catalytic activity remains unaltered after 15 cycles, indicating the good stability of the catalyst. The catalytic reaction mechanism is also analyzed.

First efforts in numerical modeling of tungsten migration in WEST with SolEdge2D-EIRENE and ERO2.0

The first simulations of tungsten migration in WEST are performed with the SolEdge2D-EIRENE and ERO2.0 codes to support experimental investigations into the erosion of plasma-facing components and plasma impurity content. The impact of varying the background density on (i) the amount of tungsten penetrating the confined plasma, (ii) the promptly redeposited fraction, and (iii) the erosion and deposition patterns on the wall, is investigated under the working assumptions of a simplified toroidally symmetric wall contour, typical L-mode values of the transport coefficients, and deuterium plasma with a 1% oxygen content. The lower divertor is found to be the main zone of net tungsten erosion and deposition. This pattern is reduced at high background density due to the higher promptly redeposited fraction.

Multiple Generations of Wolframite Mineralization in the Echassieres District (Massif Central, France)

The Echassières district in central France contains complex rare-element ore deposits, whose formation is related to exotic igneous events and several hydrothermal episodes that are not entirely understood to date. Tungsten mineralization consists of three generations of wolframite, characterized by distinct Fe/Mn ratios (8.4; 3.5 and 0.3, for wolframite a, b and c, respectively), formed during three separate hydrothermal episodes related to the Variscan orogeny. Wolframite a occurs in quartz veins of the La Bosse stockwork where it crystallized before the Barrovian metamorphism that affected these veins and the host rock. After metamorphism, before intrusion of the Beauvoir and Colettes granites, wolframite b crystallized in the stockwork during massive topazification. High concentrations of wolframite c occur in the proximal quartz veins in the Mazet area, while only scant amounts are found in the La Bosse stockwork. In both settings, wolframite c precipitated from the fluid responsible for greisen alteration that massively affected the Beauvoir granite. In the La Bosse stockwork, greisen alteration is characterized by hydrothermal topaz that is texturally and chemically distinct from that precipitated during topazification. Supergene alteration responsible for kaolinization of Beauvoir and Colettes granites caused remobilization of a non-negligible amount of tungsten (W) during replacement of wolframite by W-rich goethite in all units of the Echassières district. This model for multiple W mineralizing events is novel and can prove essential in distinguishing potential economic deposits worldwide.

Effect of temperature on microstructure evolution and localized corrosion resistance of high tungsten hyper duplex stainless steel

The high tungsten hyper duplex stainless steel grade A890 7A, the newest addition to cast duplex grades has a very different composition compared to previous grades. The alloy is extremely corrosion-resistant, and it is necessary to understand the intermetallic formation of the new alloy for its proper processing and use. The high amount of tungsten, manganese, and larger chromium significantly influence the microstructural evolution and sigma formation of the material. The present work analyses the sigma phase formations of the alloy after prolonged soaking and solutionizing at various temperature ranges. Optical microscopic and x-ray diffractometry results revealed the temperature range for sigma formation to be between 770 °C–1100 °C. Electron microscopic revealed the island like a discrete formation of sigma leaving chromium deficient regions in the immediate vicinity. Highest sigma precipitation observed in the samples solutionized at temperatures in the range 850 °C–900 °C, and the sigma precipitations appeared to be very fine. As the soaking temperature increased, the quantity of sigma phase reduced and sigma appeared to be coarser. The composition analysis of sigma phase using energy dispersive spectroscopy (EDS) revealed more extensive diffusion of Cr, Mo and W into the phase with increase in soaking temperature and reduction in percentage of sigma.

Evaluation of brazed monolayer CBN grinding wheel on high-speed steel (HSS)

Shaping and forming of high-speed steel (HSS) tool with complicated geometry has been a challenge for the cutting tool industry. HSS grades generally display high hardness at high temperature and high wear resistance due to its constituent elements like a high amount of tungsten with the addition of chromium, vanadium and cobalt. HSS being used extensively in the manufacturing industry for machining difficult-cut-materials due to its high hardness and abrasion resistance. CBN grinding wheel is being used extensively for shaping the HSS. In this work, cBN brazed wheel with monolayer configuration is being used to grind HSS. Usually, reasonably uniform grit distribution, adequate spacing between the grits, 50-70% grit protrusion over the brazed surface and strong chemical bond strength are key features of brazed CBN wheel to perform satisfactorily. In the current investigation, the brazed CBN wheel showed limitations of its capability while grinding HSS in dry condition. The high chip load due to adverse grinding combinations, high attrition wear of grit due to its interaction with constituent elements like tungsten, chromium, vanadium and cobalt, fracturing and pull out of the grits are the limitation of the brazed wheel. The paper also concluded with facts to overcome limitations of brazed CBN wheel.

A novel Ni-based bulk metallic glass containing high amount of tungsten and boron

Glass forming ability (GFA) and thermal stability of (Ni51W31.6B17.4)100-xCox (x = 0–35) alloy system have been investigated. It is found that as the cobalt content is increased critical casting thicknesses improve significantly. Critical casting thickness of 20, 25 and 30 at. % cobalt alloys are determined as 0.5, 1, and 1 mm, respectively. However, further increase of cobalt content degrades the GFA. The Ni-based bulk metallic glasses discovered in this study are the first ones ever developed which contain more than 10 at. % boron. It is also determined that after annealing the fully amorphous samples above their first and second crystallization temperatures, nickel solid solution and CoWB phase precipitate. This is the first study where precipitation of ultra-hard CoWB phase in a bulk metallic glass is reported.

High tough W-added silicon nitride ceramics

Abstract Silicon nitride ceramics with varying amounts of tungsten were fabricated by sintering with various nitrogen pressure using yttria and alumina as sintering aids. It has been found that the chemical composition of the ceramics is sensitive to the nitrogen pressure during the sintering process, and the adverse interfacial reactions between W and Si3N4 could be perfectly inhibited by altering nitrogen pressure. The weak interfacial bonding strength between the tungsten particle and silicon nitride matrix dramatically promotes crack deflection, branch and grain pullout during the fracture process. As a consequence, with increasing W fraction, the fracture toughness of silicon nitride ceramics increases noticeably. Nevertheless, excessive W fraction lowers the relative density and degrades the performance of the ceramics. The silicon nitride ceramics with high fracture toughness about 11 MPa m1/2 and high flexural strength about 1 GPa were fabricated.

Avoidance of impurity-induced current quench using lower hybrid current drive

This work reports observations of a tokamak plasma that experienced a thermal quench due to a large, transient high-Z influx but avoided a current quench. This is argued to be caused by the presence of lower hybrid range of frequency (LHRF) waves that sustain a non-thermal, current-carrying electron population. In Alcator C-Mod L-mode plasmas at kA, m−3, nearly all of the current can be sustained non-inductively by injecting 700 kW of LHRF power at 4.6 GHz and . A sudden influx of a large amount of tungsten, , triggers a cooling wave that propagates at 2–3 m s−1 all the way into the core, dropping on-axis Te from 3 keV to temperatures less than measurement floor of 50 eV. An off-axis reheat begins after 100 ms, but Te profiles remain hollow for 300–350 ms after the injection. Throughout this temperature evolution, the plasma density, current and shape remain unchanged to within 10%. Following the expulsion of the tungsten, the plasma returns to its baseline conditions and the plasma ends as planned with a controlled current ramp-down. Energy balance analysis shows the LHRF power continues to be absorbed in the plasma after the thermal quench, as a significant fraction of it is needed to be consistent with radiated power measurements. Examination of current relaxation time, , and fast-electron slowing down time, , indicate the LHRF must contribute to driving current, despite the low temperatures, as the current remains nominally stationary despite ms and ms for relativistic electrons. These measurements represent an important existence proof of a possible technique for avoidance of disruptions caused by sudden, unplanned influx of impurities in the form of dust or flakes of high-Z wall material. Implications and suggestions for future experimental and modeling and simulation work are summarized.

Influence of tungsten loading on CO2 /O2 reforming of methane over Co-W-promoted NiO-Al2 O3 nanocatalyst designed by sol-gel-plasma

Co-W–promoted NiAl2O4 nanocatalyst with various amount of tungsten (0, 1, 3, and 7 wt.%) was fabricated via hybrid sol-gel-plasma method. The nanocatalysts were evaluated by XRD, FESEM, EDX, BET, and FTIR analyses. The samples were utilized in CO2/O2 reforming of methane to syngas. EDX results proved the existence of all the applied elements in synthesis. FESEM and BET results illustrated that tungsten addition led to lower surface area, larger particle size, and roughly worse particles scattering. Therefore, Co-NiAl2O4 (NCW0A) presented higher yield; however, yields were reduced for the other samples due to the covering impact of tungsten. As a result of time on streams performance (2880 minutes and at 750°C), the 7 wt.% tungsten promoted sample exhibited stable but lower yield (YH2 = 64%). Moreover, NCW1A exhibited more stable and higher yield than NCW0A. Optimum operating parameters were obtained as GHSV = 24 l/gcat.h, CH4/CO2 = 1, and CH4/CO2/O2 = 1/1/0.08. TG-DTG, EDX, and FESEM analyses were applied for the used samples. TG-DTG graphs demonstrated that by rising of tungsten loading, lighter and lower amount of coke was formed. Some agglomerations were observed in the EDX images of NCW0A and NCW1A while lower agglomeration was found for the tungsten-rich sample. Carbon fiber formation was detected in the FESEM images of the used NCW0A while for the others, amount of the deposited coke and carbon fibers decreased.

Sol-gel synthesis of Co-W promoted NiAl2O4 spinel nanocatalyst used in combined reforming of methane: Influence of tungsten content on catalytic activity and stability

A stable process for green fuel production by means of a combined CO2 reforming of methane and partial oxidation was evaluated during this research work. The goal was achieved by using Co-W promoters with NiO spinel on Al2O3 support. Sol-gel technique based on the privileged characterization such as homogeneous distribution was used for the synthesis of enhanced Co-W catalyst on NiAl2O4 spinel. Structural and morphological attributes of fabricated samples were investigated through XRD, FESEM, EDX, BET and FTIR techniques. Eventually, homogeneous distribution of particles, less than 50 nm, high specific surface area and homogeneous structure were observed. Catalysts stability and resistance to carbonaceous deposits in operated conditions are evaluated by TG-DTG technique. In this study, reduction of deposited coke after the reaction was achieved by raising the tungsten amount in catalyst. According to obtained results, CoNiAl2O4 promoter with 1 wt% W (CoW1/NiAl2O4) nanocatalyst has obtained higher conversion along with high H2 and CO yields. Also, CoW1/NiAl2O4 was considered as an optimum nanocatalyst for methane combined reforming by illustrating the tremendous stability at 750 °C and during the 48 h time on stream performance.

Vacuum plasma spraying of functionally graded tungsten/EUROFER97 coatings for fusion applications

As structural materials for future fusion power plants, reduced activation ferritic martensitic steels as EUROFER97 can be used. Unfortunately, the interaction of the plasma with the steel would result in a limited lifetime, so protective layers are investigated. An excellent protective material is tungsten, as it shows unique properties with respect to low sputtering, high melting points and low activation. However, the mismatch of thermo-physical properties between tungsten and EUROFER97 can lead to large stress levels and even failure.A possible way to overcome this problem is the use of functionally graded material (FGM). The paper will describe the manufacture of these FGMs by vacuum plasma spraying and their characterization. First of all, two different feeding lines have been used to produce the coatings. A major problem lies in different melting points of tungsten and steel. So the particle size distribution has to be adjusted to achieve sufficient melting of both materials during the spray process. In a second step, the feeding rates were optimized to obtain the wanted amount of tungsten and steel phases in the graded structures. In a thermal spray process, the gradient cannot be made continuously, however it has to be applied in a step-wise manner. In this investigation, samples with 3 and 5 different concentrations (excluding the pure steel and tungsten part) have been produced. The microstructures of these layers have been investigated. In addition, hardness was measured and the residual stress state was determined by the hole drilling method.

Preconcentration and Determination of Tungsten Using Cold-Induced Aggregation Microextraction Technique Via Ionic Liquid in Environmental and Biological Samples

Spectrophotometry in combination with cold induced aggregation microextraction was used to preconcentrate and determine tungsten in environmental and biological samples. The preconcentration and extraction of tungsten was performed in the presence of 5-(2′,4′-dimethylphenylazo)-6-hydroxypyrimidine-2,4-dione (DMPAHPD) as complexing agent. In the present procedure, sodium hexafluorophosphate (NaPF6) was transferred to the sample solution containing minimum amounts of 1-hexyl-3-methylimidazolium hexafluorophosphate [Hmim][PF6] as extraction solvent. The preconcentration and extraction efficiency were affected and optimized by parameters as amount of ionic liquid, ionic strength pH, and temperature. The applicability was evaluated to detect trace amount of tungsten in various types of environmental and biological samples. The calibration curve was linear in the concentration range 2.5-80 ng mL-1 with correlation coefficient (r2) of 0.9994 under the optimum experimental conditions. The relative standard deviation (RSD) was 1.73 % for 40 ng mL-1 (n = 10) tungsten. The detection limit (LOD) of 0.8 ng mL-1 and enhancement factor of 300 were obtained.

Hydrometallurgical processing of spent selective catalytic reduction (SCR) catalyst for recovery of tungsten

This paper deals with the recovery of tungsten as synthetic CaWO4 from spent V2O5-WO3/TiO2 (selective catalytic reduction, SCR) catalyst. The newly developed process included the systematic experimental steps (roasting, decomposition (using HCl solution), leaching (using NaOH), and precipitation) to recover tungsten as CaWO4. The results revealed that the effect of roasting of spent SCR catalyst was significant for the extraction of tungsten. Furthermore, CaO addition in the roasting process promoted chemical equilibrium for the formation of CaWO4, and extraction efficiency of tungsten was increased simultaneously. Decomposition process revealed that 4 mol·L−1 of HCl solution was the best condition with considerable degree of removal (92.5%) of vanadium along with negligible loss of tungsten. The most appropriate concentration of NaOH (aq) to dissolve tungstic acid (H2WO4) from the decomposed sample was 1 mol L−1 (>99% tungsten yield) in accordance with minimized concentration of foreign metals (Si, Al, Fe). The maximum amount of tungsten (>99%) was obtained from the sodium tungstate solution as synthetic CaWO4 using CaCl2 (molar ratio (CaCl2/WO3): 1). The best experimental conditions for the precipitation were under following conditions: temperature, 50 °C; equilibrium pH, 8–10; molar ratio (CaCl2/WO3), “1”. The content of CaWO4 in the final product was 96.1 wt%. The overall yield of tungsten from the feedstock using the proposed process was 96.4%.

Design of Highly Stable Tungsten-Doped IZO Thin-Film Transistors With Enhanced Performance

High-performance thin-film transistors (TFTs) were obtained by incorporating small amount of tungsten ( ${W}$ ) into amorphous indium zinc oxide (IZO)-based thin films via a solution process. Compared with original IZO TFTs, 0.2-wt% ${W}$ -doped IZO TFTs exhibit improved bias stress stability and field-effect mobility of 30.5 cm2/ $\text{V}\cdot \text{s}$ . Meanwhile, the bias stress stability of IZO TFTs can be further enhanced with 0.5-wt% W-doping. The pulsed current–voltage ( ${I}$ – ${V}$ ) method is employed to study the hysteresis and charging behavior of the ${W}$ -doped IZO TFTs. The X-ray photoelectron spectroscopy analysis and the pulsed ${I}$ – ${V}$ measurement results suggest that these desirable performances could be attributed to the suppression of excessive oxygen vacancies and improved interface quality because of ${W}$ -doping. The results represent an effective strategy to achieve high-performance solution-processed amorphous oxide-based TFTs with desirable stability by ${W}$ -doping.

Tungsten doped mesoporous SBA‐16 as novel heterogeneous catalysts for oxidation of cyclopentene to glutaric acid

Novel heterogeneous tungsten species in mesoporous silica SBA‐16 catalysts based on ship‐in‐a‐bottle methodology are originally reported for oxidizing cyclopentene (CPE) to glutaric acid (GAC) using hydrogen peroxide (H2O2). For all W‐SBA‐16 catalysts, isolated tungsten species and octahedrally coordinated tungsten oxide species are observed while WO3 crystallites are detected for the W‐SBA‐16 catalysts with Si/ W = 5, 10, and 20. The specific surface areas and the corresponding total pore volumes decrease significantly as increasing amounts of tungsten incorporated into the pores of SBA‐16. Using tungsten‐substituted mesoporous SBA‐16 heterogeneous catalysts, high yield of GAC (55%) is achieved with low tungsten loading (for Si/W = 30, ~13 wt%) for oxidation of CPE. The W‐SBA‐16 catalysts with Si/W = 30 can be reused five times without dramatic deactivation. In fact, low catalytic activity provided by bulk WO3 implies that the highly distributed tungsten species in SBA‐16 and the steric confinement effect of SBA‐16 are key elements for the outstanding catalytic performance.

Non-destructive measurement of the tungsten content in the binder phase of tungsten heavy alloys

Measurement of the magnetic properties is well-established to non-destructively monitor composition and microstructure of cemented carbides. The present study demonstrates that this method can also be applied to ferromagnetic tungsten heavy alloys. Compositional changes during heat treatment may have effects on the magnetic properties of W-Ni-Fe heavy alloys, as an example, which would allow for simple non-destructive measurement. We report that increasing tungsten content in Ni-Fe(-W) samples and higher annealing temperatures for Densimet 180® grade 95W-Ni-Fe heavy alloy samples cause a decrease of their respective weight-specific saturation magnetization. XRD analyses show that higher heat treatment temperatures result in larger lattice parameters of the binder phase. Likewise, larger amounts of tungsten dissolved in the nickel-iron samples also widen the γ-Ni-Fe lattice. This suggests that the decrease in saturation magnetization of heavy alloys annealed at higher temperatures is caused by more dissolved tungsten in the binder phase. As EDX measurements may overestimate the tungsten concentration in the binder phase, another method for determining the amount of dissolved tungsten was developed. A relationship between saturation magnetization and tungsten content in the binder could be established through the Ni-Fe(-W) samples with known amounts of tungsten. In view of these results, we propose saturation magnetization measurements as a simple non-destructive tool for additional quality control in the production of ferromagnetic tungsten heavy alloys.

WxC-β-SiC Nanocomposite Catalysts Used in Aqueous Phase Hydrogenation of Furfural.

This study investigates the effects of the addition of tungsten on the structure, phase composition, textural properties and activities of β-SiC-based catalysts in the aqueous phase hydrogenation of furfural. Carbothermal reduction of SiO2 in the presence of WO3 at 1550 °C in argon resulted in the formation of WxC-β-SiC nanocomposite powders with significant variations in particle morphology and content of WxC-tipped β-SiC nano-whiskers, as revealed by TEM and SEM-EDS. The specific surface area (SSA) of the nanocomposite strongly depended on the amount of tungsten and had a notable impact on its catalytic properties for the production of furfuryl alcohol (FA) and tetrahydrofurfuryl alcohol (THFA). Nanocomposite WxC-β-SiC catalysts with 10 wt % W in the starting mixture had the highest SSA and the smallest WxC crystallites. Some 10 wt % W nanocomposite catalysts demonstrated up to 90% yield of THFA, in particular in the reduction of furfural derived from biomass, although the reproducible performance of such catalysts has yet to be achieved.

Surface Characterization and Corrosion Resistance of 36Cr-Ni-Mo4 Steel Coated by WC-Co Cermet Electrode Using Micro-Electro Welding

In this paper the influence of spark energy on corrosion resistance, hardness, surface roughness and morphology of WC-Co coated 36Cr-Ni-Mo4 steel by Micro-Electro Welding (MEW) was investigated. Frequencies of 5, 8 and 11 kHz, currents of 15, 25 and 35 A and duty cycles of 10, 30 and 50 % were applied for coating of the samples using a WC-Co cermet electrode. The results indicate that increasing the current, Duty cycle and frequency of the process increases spark energy. As spark energy increases, efficiency of coating increases to 80% and then decreases. X-ray diffraction (XRD) analysis was used to identify the phases. The results indicated that other than the peaks obtained for the metallic Iron with BCC (Body Centered Cubic) structure, Tungsten Carbide, Cr7C3 and Titanium Carbide phases were also seen on the surface. Vickers micro hardness method was used for hardness measurement of the samples. Surface hardness increases to 817.33 HV0.05 with spark energy increasing up to 1.03 mJ, and then reducing. Optical Microscopy (OM) and scanning electron microscopy (SEM) to study Microstructural and atomic force microscopy (AFM) to study the topography, morphology and roughness were used. Polarization technique in 3.5 wt % NaCl solution was used to evaluate the corrosion properties. The results of the energy dispersive X-ray spectroscopy (EDS) analysis indicate that with increasing spark energy, the amount of Tungsten in surface increases to 41.95 wt % and then decreases. As spark energy increases up to 2.17 mJ, thickness of coating increases to 8.31 μm and then decreases. As spark energy increases, surface roughness is also increased. Corrosion test results indicated that the lowest corrosion rate (2.6 × 10−8 mpy) is related to the sample with the highest level of efficiency.

Reprint of: Arc erosion of full metal plasma facing components at the inner baffle region of ASDEX Upgrade

At the inner baffle of the AUG divertor massive polished inserts of tungsten and P92 steel were installed to measure the erosion by arcing. For tungsten most of the traces are less than 0.4µm deep and a similar amount of tungsten is deposited close to the traces. Few craters up to 4µm resulting in an average erosion rate of 2×1013 at cm−2s−1 are observed. The behaviour for P92 steel is quite different: most of the traces are 4µm deep, up to 80µm were observed. An average erosion rate of 400×1013 at cm−2s−1, i.e. more than a factor of hundred higher compared to tungsten, is found. Therefore, erosion by arcing has to be taken into account to determine the optimal material mix for future fusion devices.

Multi-property improvement of TiO2-WO3 mixed oxide films deposited on 316L stainless steel by electrophoretic method

Titanium dioxide (TiO2) is widely employed in many domains, such as photo-catalysis, self-cleaning and bio-medical applications due to its photocatalytic properties and high chemical stability. However, its mechanical and tribological properties as well as its resistance to corrosion can be improved by the addition of the other elements. The aim of the present work is to study the impact of adding WO3 in TiO2-WO3 composites coating on the mechanical and tribological properties as well as on the corrosion resistance. In this work, TiO2-WO3 composites were obtained with using different amounts of WO3. Structural properties of the coatings were analyzed using X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDXS) and scanning electron microscopy (SEM). Besides, mechanical properties were investigated by nano-indentation measurements. Micro-scratch tester was performed to evaluate the tribological properties. Potentiodynamic polarization and electrochemical impedance spectroscopy of composite coating were measured through electrochemical tests. Obviously, thin film with the highest amount of tungsten (Ti50W50)Ox was characterized by the best mechanical properties compared to the result obtained for the pure TiO2 coating. In addition, the increase of the WO3 content in the coating allowed improving the tribological properties.