Tungsten Content Research Articles

Linear and nonlinear electric and magneto-optical absorption coefficients and relative refractive index changes in WxMo1−xS2 monolayer: Role of tungsten contents

In this work, we study the electric and magneto-optical absorption coefficients (ACs) and relative refractive index changes (RRICs) in W[Formula: see text]Mo[Formula: see text]S2 ternary alloys under the control of tungsten contents using the compact density matrix approach. With the influence of external electric and magnetic fields, the results show that there are a series of resonant peaks for both intra-band and inter-band transitions. With an increase in W-concentration and electric and magnetic fields, the resonant peaks give a blue (red) shift and reduce (increase) their amplitudes. These results suggest a potential application of monolayer W[Formula: see text]Mo[Formula: see text]S2 in future nanoscale electronic and magneto-optical devices.

A contribution to the understanding of hydrochemical properties of thermo-mineral water on the L’dži locality (eastern part of North Macedonia)

Regarding the aspect of mineral, thermo-mineral, and thermal waters, on the territory of the Republic of North Macedonia, there are 65 registered locations, of which 8 are categorized as spas. This includes the Kežovica spa, also known as the Štipska spa. In the vicinity of Kežovica Spa is the thermo-mineral L’Dži spring with mineralization around 1.3 g/L and the water temperature at the time of sampling was 50.1°C. Spring L’Dži is generated by a fault structure and is linked to a granite massif of Mesozoic age. These are alkaline waters (pH=8.3) and the hydrochemical type is chloride-sodium. Regarding the trace elements, the water of the L’Dži spring contains a large amount of boron and silica. Water also contains an increased content of arsenic (200 µg/L) and tungsten (169 µg/L). Elevated concentrations of As and W are characteristic of alkaline thermal waters in reducing conditions. Often elevated concentrations of Mo are accompanied by elevated concentrations of As and W, which is also the case.

Broadening active temperature window for NH3-SCR on tungsten-promoted MnCeOx nanorod catalysts

xW/MnCe nanorod catalysts with various tungsten contents were synthesised using the incipient wetness impregnation method for selective catalytic reduction (SCR) of nitrogen oxides with NH3 (i.e. NH3-SCR reaction). Tungsten addition considerably widened the active temperature window and enhanced the SO2/H2O tolerance of the catalysts. The optimum catalytic performance was achieved when the tungsten content was 15 wt% with NOx conversion being ≥ 80% in the range of 175–450 °C. The MnCe nanorods approximately retained their morphology after tungsten loading. Microcrystalline WO3 formed when the W content was 15%, resulting in increments in the amount of Ce3+ and Mn4+, which is in favour of the NH3-SCR reaction on the catalyst surface. Moreover, the broad active temperature windows of the tungsten-modified MnCe nanorod catalysts were related to the balance between the redox and acidic properties. Tungsten addition enhanced the acidity of the MnCe catalyst while suppressing its reducibility. Both the Brønsted and Lewis acid sites are active, and the formation of reactive bridging nitrate species promote the performance of 15 W/MnCe catalyst. Overall, this study provided an easy method of adjusting the active temperature window of Mn–Ce nanorod catalysts through W modification.

High filler content acrylonitrile‐butadiene‐styrene composites containing tungsten and bismuth oxides for effective lead‐free x‐ray radiation shielding

AbstractAcrylonitrile‐butadiene‐styrene (ABS) based composites with a high content of tungsten and bismuth oxide were developed using an innovative process to obtain lead‐free x‐ray shielding materials. ABS was chosen for its good mechanical properties and its widespread availability as a recycled material. The composites underwent flexural tests, Shore D hardness tests, thermogravimetric and morphological analysis, and their x‐ray attenuation properties were determined through numerical simulations and experimental measurements. Despite their high filler content (up to 75 wt%), the composites showed good filler dispersion within the polymeric matrix and maintained their mechanical properties. Across the investigated energy range (50–150 kV), the lead equivalence for x‐ray shielding was achieved with composite plates containing 75 wt% of tungsten and bismuth oxide, at thickness values corresponding to a weight increase of only 29% and 36%, respectively, in comparison to lead. These findings pave the way for a new generation of lead‐free x‐ray shielding materials. Moreover, their mechanical properties, including flexibility for potential application in wearable personal protective equipment, can be tailored by adjusting the filler content.Highlights High filler content lead‐free ABS composites with WO3 and Bi2O3 were developed. They show good polymer/filler interfacial adhesion and flexural properties. Numerical simulations of their x‐ray shielding properties were performed. Experimental tests with polychromatic sources confirmed good x‐ray attenuation. Results pave the way for the development of new lead‐free x‐ray shielding systems.

Formation of the gradient of structural-phase states of high-speed steel during surfacing. Part 1. Solving the Stefan problem with two movable boundaries

The article considers theoretical study of solidification of the binary iron–tungsten system at a tungsten content of 18 wt. %. Such tungsten content is typical for heat-resistant alloys used in plasma-arc surfacing on the rolls surface. The axisymmetric Stefan thermal problem is solved for two movable cylindrical boundaries that separate three regions. In region 1, the melt is at the melting point; in region 2, the substance is in a two‒phase state, and in region 3 – a solid. The liquidus temperature was set at the interface of regions 1 and 2, and the solidus temperature – at the interface of regions 2 and 3. At these boundaries, a condition for the heat flows balance was given, from which a system of kinetic equations was obtained. This system was solved by numerical methods, without hypothesizing that the fronts of phase transformations move according to the law R ~ t1/2. Solution of the system of kinetic equations shows that the solidus boundary moves almost linearly. The liquidus boundary moves according to the parabolic law. For regions of the micrometer range in size, the processes of phase transformations take place in a time of about 5 ns, whereas for regions of the order of 10 μm in size – in a time of about 50 ms. Dependences of temperature fields on the radial coordinate at various points in time show that with increasing time, the dimensions of region 2 decrease, and as soon as coordinates of the liquidus and solidus boundaries become close, thecrystallization process stops. Further development of the model consists in taking into account the rotation of one of the media. The results obtained will serve as a material for the study of the Mullins-Sekerka two-front instability.

Stress evolution in sputtered vanadium-tungsten alloys

While metal alloy films are used in many applications, there remains a rather limited series of studies of their stress evolution during growth as compared to elemental films. Here, we provide measurements of the sputter deposition stress evolution of VxW1-x alloys, which is a system that forms a body centered cubic solid solution across all its compositions. By increasing either the tungsten content or the growth rate, we note an increasing trend towards a compressive stress state. Since the crystallite size is approximately the same for all alloys and growth rates, we conclude that the increasing tungsten content enhances the effect of energetic particle deposition (atomic peening) on the stress facilitating this change. The results suggest that stress can be understood in terms of the same physical processes that have been proposed previously to explain stress in elemental films. These mechanisms, described in the text include effects of non-energetic growth kinetics, microstructural evolution and energetic particle bombardment.

Microstructure, mechanical properties, and energetic characteristics of novel peritectic W x NbTiZr medium entropy alloys

Novel W x NbTiZr medium entropy alloys (MEAs) with tungsten concentrations of 15–25 at.% were produced using arc vacuum melting. The microstructure formation, mechanical behaviours and energetic characteristics were studied. Peritectic reaction occurs in these alloys, resulting in BCC1 and BCC2 phases with close lattice parameters, along with unique pearl chain structures. The average grain sizes of these alloys are less than 10 μm. W0.75NbTiZr alloy exhibited the most significant grain refinement, resulting in a remarkable combination of strength and ductility. When subjected to high-speed impact, the W x NbTiZr projectiles reacted with air and release high amounts of energy. These W x NbTiZr MEAs exhibit high density, exceptional mechanical properties, and significant energy release, showcasing their immense potential as high-strength energetic structural materials

Application of W-Doped VO2 Phase Transition Mechanism and Improvement of Hydrophobic Self-Cleaning Properties to Smart Windows

A passive responsive smart window is an emerging energy-saving building facility that does not require an active energy supply due to its passive excitation characteristics, which can fundamentally reduce energy consumption. Therefore, achieving passive excitation is the key to the application of such smart windows. In this paper, VO2 is used as a critical raw material for the preparation of smart windows, and we researched the feasibility of its phase transition function and hydrophobic self-cleaning function. VO2 has the characteristic of undergoing a reversible phase transition between metal and insulator under certain temperature conditions and can selectively absorb spectrum at different wavelengths while still maintaining a certain visible light transmission rate, making it a reliable material for smart window applications. The one-step hydrothermal method was used in this work, and different concentrations of tungsten (W) elements were utilized for doping to reduce the VO2 phase transition temperature to 35 °C and even below, thus adapting to the ambient outdoor temperature of the building and enabling the smart window to achieve a combined solar modulation capability of 14.5%. To ensure the environmental adaptability and anti-fouling self-cleaning function of the smart window, as well as to extend the usage period of the smart window, we have modified the smart window material to be hydrophobic, resulting in an environmental surface contact angle of 152.93°, which is a significant hydrophobic improvement over the hydrophilic properties of inorganic glass itself. The realization of the ideal phase transition function and the self-cleaning function echoes the social trend of environmental protection, enriches the use of scenarios and achieves energy saving and emission reduction.

The effects of tungsten addition on the microstructure and anti‑sulfurization of silver

In pursuit of cost-effective and resource-saving applications for Ag paste, this study delves into the characterization of ordinary pure Ag paste, commercial PdAg paste, and WAg paste with varying tungsten content. The emergence of a secondary phase, Ag2WO4, at the grain boundaries was identified as the crucial anti-corrosion component. Experimental findings reveal that W doped Ag paste exhibit superior properties regarding anti-corrosion behavior, as evidenced by electrochemical polarization curves and weatherability tests. Furthermore, 2.5% W doped Ag paste achieves a comparable anti‑sulfurization standard to that of the 5% Pd doped Ag paste. Consequently, tungsten demonstrates significant potential for sulfide resistance, serving as a more economical material choice that not only lowers costs but also conserves resources for industrial applications.

Effect of tungsten on structure of chromium-based heat-resistant alloys

The effect of tungsten on the structure and properties of Cr–32Ni–W alloys was studied. Characteristic tungsten concentrations were separated: up to 3%, 3–10%, and more than 10%, which determine the structure of the alloys. The mechanical properties of the alloys are determined. The area of rational application of the alloy Cr–32Ni–W is shown.

Study of the process of preparing amorphous Fe–W(La) alloy plating by induced co-deposition

To obtain high-performance Fe–W alloy plating instead of environmentally hazardous chromium plating, the effects of the cathode material, electrolyte pH, temperature, current density, plating time and rotational speed on the cathode current efficiency and alloy plating are investigated in this paper. The results show that the pH and current density of the plating solution greatly influence the morphology and current efficiency of the cathode. The current efficiency of the cathode can reach 63.56%, and the tungsten content can reach 55% at pH = 8, 60 °C, 12 A/dm2, 100 r/min, 75 min, 0.1 mol/l of Fe2+ and 0.2 mol/l of W6+. After XRD analysis, the plating is found to consist of the Fe7W6 amorphous phase. In addition, La is added to the Fe–W alloy under optimal conditions. By analyzing the polarization curve, the potential of the Fe–W(La) alloy is positively shifted by 0.039 V compared with the Fe–W alloy, which has good corrosion resistance.

Heat flow losing via earth's surface around of Khulj hot spring

In this paper, we extracted values of geomagnetic anomaly sourced in the lithosphere from the total intensity of geomagnetic that is measured on the 750 points on an area (100x100 km2) around the Khulj hot springs. The two-dimensional map of the distribution of the anomaly geomagnetic corresponding to this area was made via these extracted values of anomaly geomagnetic. The method of spectral analysis was used to estimate the Curie Point Depth, which is lost magnetic characteristics of the lithosphere with a temperature of 580o C and the depth of layer sourcing anomaly geomagnetic with high content of iron, nickel, and tungsten by these values of geomagnetic anomaly. On the Fig. 5, the isothermal Curie surface with the temperature of 580o C was visualized in three dimensions by these values of Curie Point Depth. The heat flows lost on Earth’s surface was also detected by the method of the gradient of temperature from the Curie Point Depth. And the two-dimensional map of heat flow around the Khulj hot spring was illustrated by the values of heat flows. Moreover, the average value of the heat flow for whole the area (100x100 km2) was about 60[mW/м2], and it was estimated at about 70[mW/м2], at the Khulj hot springs. When we carried out a same study near Ulaanbaatar in 2018, the average heat flows lost on Earth’s surface was determined about 40-50[mW/м2].

Effect of solid solution tungsten on the radiation-induced amorphization in bulk M23C6 fabricated by vacuum induction melting

To provide a mechanistic understanding of the stability of the M23C6 phase under irradiation, the crystalline to amorphous (c-a) transition behavior in bulk M23C6 specimens with a variation in tungsten (W) content subjected to helium ion irradiation was investigated. The Cr-W-C ternary ingots with a W concentration range of 0–11.6 at.% were fabricated by vacuum-induced furnace melting. Microstructure characterization revealed that the dominant phase in the ingots was M23C6 regardless of the W concentration, and a small amount of metallic-Cr, (Cr, W), and W-rich carbide co-existed as the minor phase. The lattice parameter of M23C6 increases with an increase in W concentration, and the maximum value is 1.083 nm when the W content is 11.6 at.%. Based on this, the chemical formula of the M23C6 particle in F82H steel was represented by Cr20W3C6 or Cr19W4C6 because its lattice parameter was estimated to be 1.08–1.09 nm. From the grazing incident X-ray diffraction analysis before and after irradiation, the amorphous peak was only observed in the specimen of W concentration 11.6 at.% after irradiation, which was further confirmed by transmission electron microscopy analyses. It is clarified that the c-a transition behavior in M23C6 is dependent on the W content, the amorphization of M23C6 can be mitigated when the W concentration is 6.8 at.% or less under the present study condition.

Influence of tungsten oxide concentration on structural, morphological, compositional, linear and non-linear optical properties, and vibrational properties on NiO:WO3 thin films

Mixed nickel-tungsten oxide, NiO:WO3 (90:10, 85:15) thin films with different tungsten oxide (WO3) concentrations of 10 and 15% were deposited using the radio frequency (RF) sputtering technique. An X-ray diffraction analysis reported the amorphous nature of the films. A SEM study showed smooth morphology. EDAX confirms the compositional purity, in which the nickel content decreases, while the tungsten and oxygen content increase with an increased WO3 concentration. The average transmittance of the NiO:WO3 (90:10, 85:15) films decreases from 79 to 75% as a consequence of increased thickness. The Urbach energy (Eu) enhances because of increased defects (localized states) inside the films induced by tungsten oxide addition. The energy bandgap decreases from 2.66 to 2.48 eV due to the formation of new localized energy states inside the band gap (Eg). The refractive index (n) acquired from different proposed models for the entire UV–Vis–NIR region has increased with increasing WO3 concentration, implying the escalation in densification (or packing density) of prepared films. The optical parameters like n, k, ε1, ε2, electronic polarizability (αp), optical conductivity (σop), electric conductivity (σe), volume and the surface energy loss function (VELF AND SELF) vary with WO3 concentration. The dispersion energy parameters (Eo, Ed), resulting from the Wemple and Didomenico (WD) model, decreases. The optical non-linear susceptibility, χ(3), decreased with increasing WO3 concentration. The photoluminescence (PL) emissions were perceived at 368 nm and 423 nm, assignable to 3 d8 Ni2+ ions transitions. Micro-Raman detected peaks at 570 cm−1 and 1100 cm−1 ascribing Ni–O bond vibrations, whereas the peak spotted at 870 cm−1 is ascribed to a W–O bond vibration. The deposited films are good enough for electrochromic and optoelectronic device fabrications.

Preparation and Properties of Textured Ni–W Coatings Electrodeposited on the Steel Surface from a Pyrophosphate Bath

Ni–W alloys with a (2 2 0) or (1 1 1) preferred orientation growth and amorphous structure were prepared from a pyrophosphate bath using the electrodeposition method. Structure transformation can be the result of the bath temperature (Tb) and the concentration of sodium tungstate (CW) in the bath. Increasing the Tb and CW can change the crystal growth from (2 2 0) to (1 1 1). At a higher Tb and CW, an amorphous Ni–W alloy can be obtained. The tungsten content in the coatings should be responsible for the structure change. The three textured Ni–W alloys with a (2 2 0) texture, (1 1 1) texture and amorphous structure were annealed at different temperatures ranging from 200 to 700 °C. The microhardness, corrosion resistance and HER of the as-deposited and annealed Ni–W alloys were comparatively studied. The results show that the microhardness of the amorphous Ni–W alloy is the highest and reaches 1028 HV after annealing at 400 °C. The (2 2 0)-textured Ni–W alloy has the best corrosion resistance, which is further improved after annealing, while the HER activity of the (1 1 1) textured Ni-W alloy is superior.

Investigation of gamma shielding parameters of VMQ/W/TiO2 polymer composites

Vinyl Methyl Silicone Rubber (VMQ) matrix with Tungsten (W) and Titanium dioxide (TiO2) as multi-filler materials was studied with varying Tungsten content (0, 30, 50, 70 phr (parts per hundred rubber)) and investigated for gamma radiation shielding applications. The mass attenuation coefficient of VMQ/W/TiO2 composites for 80, 356 and 662 keV were obtained using XCOM database. Various radiation shielding parameters, such as the linear attenuation coefficient, half-value layer, tenth-value layer and relaxation length were evaluated using the values of mass attenuation coefficient and density. It is found that the attenuation coefficient increases with increase in filler density, whereas the HVL, TVL and relaxation length of the composites found to decrease. The mass attenuation coefficient and HVL of VMQ/70W/30 TiO2 phr are found to be 2.88 cm2/g and 0.1 cm for 80 keV gamma rays. The results confirm that the examined shielding parameters are associated with photon energies and chemical composition. Hence, the performance of VMQ/W/TiO2 rubber based composites show superior shielding properties and the experimental results are found to be better than barite at 356 & 662 keV and slightly lower than lead and barite at 80 keV.

Development of flux-cored wire of Fe – C – Si – Mn – Cr – W – V system with additives of carbon-fluorine-containing material and titanium

The paper considers research of quality of the electric arc coating obtained using flux-cored wire of the Fe – C – Si – Mn – Cr – W – V system with additives of carbon-fluorine-containing material and titanium. The formation of an electric arc coating was carried out using an automatic arc welding machine ASAW-1250 with a new chromium-containing flux-cored wire on plates made of St3 steel. To exclude mixing of the deposited metal with the substrate steel, multilayer surfacing was conducted. The surfacing mode was calculated and refined experimentally. The authors studied the composition and properties of the surface of the electric arc coating after surfacing. As a substitute for amorphous carbon they used a carbon-fluorine-containing material (dust of gas purification of aluminum production). Surfacing was carried out under a flux made from slag produced by silicomanganese with a high content of sulfur. A regression analysis of influence of the deposited layer’s chemical composition on its hardness and wear rate was carried out and mathematical models of the investigated performance characteristics of the electric arc coating were obtained. With an increase in the content of chromium, tungsten, carbon and silicon, hardness of the deposited metal and its resistance to abrasive wear increase. The results of the conducted research make it possible to develop measures ensuring the required level of performance characteristics of the electric arc coating and can be used to make a forecast of hardness of the deposited layer and its wear resistance when the chemical composition of the metal changes, to predict the operational resistance of rolling rolls deposited with wires of the PP-Np-35V9Kh3SF type. Mathematical models of hardness of the deposited layer and its wear resistance help to clarify the mechanism of hardening and formation of protective properties of the surface layers of rolling rolls by means of electric arc coatings deposited with flux-cored wires.

INVESTIGATION OF MAGNETIC HYSTERESIS PROPERTIES OF ISOTROPIC MAGNETICALLY HARD ALLOYS OF THE Fe-Cr-Co SYSTEM ALLOYED WITH TUNGSTEN

Hard magnetic alloys Fe-30Cr-20Co (wt.%) alloyed with tungsten in an amount of up to 3 wt.% were obtained by powder metallurgy. A study of magnetic properties showed that tungsten additions increase the values of the coercivity Hc and the maximum energy product (BH)max, but at the same time reduce the residual induction Br. This effect increases with increasing tungsten content in the material. The maximum values of Hc (55.8 kA/m) and (BH)max (17.2 kJ/m3) are observed in the alloy alloyed with 3 wt.% W. At the same time, the alloys studied in the work turned out to be sensitive to thermal conditions processing. According to X-ray phase analysis, after a full processing cycle, alloys contain a noticeable proportion of non-magnetic ɣ-phase, but the magnetic properties correspond to the level of cast analogues. During compression tests, all samples of tungsten alloyed alloys failed before reaching a deformation rate of 20%, while the unalloyed Fe-30Cr-20Co (wt.%) alloy deformed without failure under these conditions. Thus, tungsten additives reduce the ductility of the material.

Deciphering the role of W content, triple junctions, and heat treatment on the corrosion performance of Ni–W alloy coatings used for automotive applications

In this study we focus on understanding the influence of tungsten (W) content, heat treatment and grain size on the corrosion behaviour of Ni–W coatings. Using pulse and pulse reverse electrodeposition techniques, Ni–W coatings with different W contents (3, 7.5, 12, 17, 20 and 25 at.%) were deposited from a standard ammonia-citrate bath. Coatings were heat treated at 700 °C in vacuum for 1 h and then characterized to determine the surface morphology, grain size, and phase transformations. To evaluate the corrosion performance of the coatings, potentiodynamic polarization tests were performed in 0.6 M NaCl solution. Polarization test results indicated that as-deposited Ni–W coatings had better corrosion resistance compared to heat treated coatings. In the as-deposited condition, corrosion resistance increased up to 17 at.% W. However, further addition of W decreased the corrosion resistance due to high volume fraction of triple junctions and intercrystalline regions. On the other hand, heat treated coatings suffered from micro-galvanic corrosion due to the precipitation of Ni4W and NiW phases, and therefore showed higher corrosion rates compared to as-deposited coatings. The changes observed in the corrosion behaviour of as-deposited and heat treated Ni–W coatings were rationalized based on surface composition, mixed potential theory, and triple junction corrosion theory.

Selectively extracting H2WO4 of high purity from the H2SO4 decomposition product of scheelite through hydrogen peroxide coordination followed by purification using ion-exchange and solvent extraction and thermal decomposition

The discharge of ammonium-containing wastewater and saline wastewater, which are among the main sources of water pollution in China, is difficult to avoid in traditional tungsten extraction processes. Sulfuric acid decomposition of scheelite can address the issue of saline wastewater discharge, but effectively dissolving tungsten from the sulfuric acid decomposition product without causing ammonia pollution remains a challenge. To tackle these problems, this work proposes a novel process of selectively extracting tungsten from sulfuric acid decomposition products using hydrogen peroxide coordination. Under the optimum preparation conditions, 99.0% of tungsten in scheelite was transformed into tungstic acid. The extraction efficiency of tungsten from the product by hydrogen peroxide reached 99.4%, while tungsten content in residue is <1%. The conversion of tungsten from the product to peroxotungstic acid was investigated. After the purification using ion-exchange and solvent extraction, high-purity tungstic acid was obtained through thermal decomposition, with the content of each impurity element being lower than 15 mg/l. This study offers a new approach to producing high-purity tungstic acid from the sulfuric acid decomposition product of scheelite while eliminating the issues of ammonium-containing wastewater and saline wastewater.