Papers by Keyword: Tungsten Oxide

Abstract: O₂ plasma treatment induces a transformation in the structure of WO₃ thin films, converting them into a crystalline structure. Amorphous WO₃ thin films were deposited on silicon produced by pulsed DC reactive magnetron sputtering at room temperature. The as-deposited films were treated with oxygen plasma powered by an RF generator. During the plasma treatment, the pressures were set at 1 x 10^-1 to 1x 10^-2 mbar, while the RF supplied powers at 100 W and 200 W. The effects of plasma treatment induced modifications of structure and physical properties of WO₃ thin films. Several techniques were used to characterize microstructure, phase composition and surface morphology of the films including X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM). An RF generator powered the O₂ plasma treatment on the as-deposited films. During the plasma treatment, the pressures were set at 1.0x10^-1and 1.0x10^-2 while the RF powers was supplied at 100 and 200 watt, respectively. The film's crystal structure changed at 200W plasma power and 1 x 10^-2 mbar operating pressure. The O₂ plasma treatment significantly changed the thickness of the films, probably as a result of changes in the packing density and surface etching. The experimental results suggest that the plasma treatment excitation process after crystallization can transform the films' amorphous structure into a crystalline structure.

Abstract: Electrochemical research is devoted to the development of a method of processing secondary raw materials containing tungsten in the form of a pseudoalloy of the carbide type WC–Co in sulfate solutions. The target processing products are: powders of tungsten oxides of lower oxidation states, which can be reduced to metallic tungsten with lower costs. Using the methods of linear and cyclic voltammetry, it was established that the selective dissolution of the cobalt component of the pseudoalloy in the studied solutions occurs at potentials more positive than 0.2 V, carbon is removed from the working electrode at a potential > 0.8 V. At the same time, tungsten is oxidized to the higher oxide WO₃. It was determined that in sulfuric acid, with an increase in its concentration from 1 to 5 mol∙dm-3, the current density decreases, which is associated with the formation of a solid surface layer of tungsten oxide on the surface of the anode, which passivates the surface. It was established experimentally that when adding 1 mol∙dm^-3 of H₂SO₄ hexamine (C₆H₁₂N₄) with a concentration of 0.9 mol∙dm^-3 to a solution, it is possible to block the process of formation of a passivating film and obtain powders of tungsten oxides of lower oxidation states.

Abstract: Thin films of tungsten oxide were deposited on glass substrates by the radio frequency (RF) reactive sputtering from a high purity tungsten metal target (99.9%) with a diameter of 10 cm. The reactive sputtering was carried out in an argon-oxygen gas mixture containing 20% of O₂ and 80% of Ar. The used RF power is 200 W while fixing the deposition time at 120 min. Finally, the prepared films were annealed at different temperatures (350 °C, 400 °C, 450 °C, 500°C and 550 °C) for 1 hour under air and under vacuum. X-ray diffractograms showed that the deposited thin films crystallized in Hexagonal/Monoclinic WO₃ phase. It was found that the crystallite size varies with the annealing temperature and the lattice parameters is a= 7.3064Å, b = 7.5292Å, c = 7.6875Å and a=b= 7.3242Å, c= 7.6624 Å, for h-WO₃ and m-WO₃ structures, respectively. Scanning Electron Microscopy (SEM), Raman spectra confirmed the formation of WO₃ thin films. In addition, optical transmittance data revealed that the optical bandgap of the films decreases with increasing the annealing temperature. Electrical measurements revealed that annealing in air results in more resistive samples, which should be taken into account in future investigations, especially as buffer layers for efficient photovoltaic solar cells. Keywords: Vacuum, Tungsten oxide, Raman spectroscopy, RF Sputtering method, RF Power, Annealing temperature.

Abstract: Electrochemical research is focused on the tungsten extraction during acid electrochemical treatment of WC-Co pseudoalloy in chloride solutions. The target resulted products of the treatment are: tungsten oxide (VI), tungsten powder with a given particle size distribution (2…3 μm). Based on the analysis of kinetics, the mechanism of dissolution of the WC-Co pseudoalloy in a solution of 2.5 mol∙dm-3 HCl and with the addition of HF was proposed. It was found that a well-soluble higher tungsten chloride is formed on the surface of the pseudoalloy, which is eventually hydrolyzed in aqueous solution to form tungsten oxides. The dispersion control levers were investigated and the technological parameters of obtaining tungsten metal powder from low-temperature ionic alloys (NaCl-KCl-CsBr-NaF) were determined, which make it possible to obtain tungsten metal powder of a given particle size distribution. It is stated that the use of tungsten powder (W or WO3) for the modification of aramid fiber can significantly increase the heat resistance of aramid fabric and reduce its wear

Abstract: The oxide layers on titanium were formed by plasma electrolytic oxidation technique in acid aqueous electrolytes containing sodium tungstate and copper acetate. The coatings with WO₃-CuO or WO₃-CuWO₄ oxide layers have been formed in the electrolytes with H₂C₂O₄ (pH~6) or H₂SO₄ (pH~4) accordingly. The coatings with WO₃-CuWO₄ have a developed surface architecture. The surface is constructed from coral-like structures with lamellar nanocrystals containing copper tungstate and tungsten oxide. The layers of tungsten oxide nanocrystals occupy the depressions between these structures. The band gap of the mixed WO₃CuWO₄ oxide layers is 2.8 eV.

Abstract: Tungsten oxide (WO₃) is a transition metal oxide with a wide range of applications such as displays, rear-view mirrors, electrochromic (EC) smart windows and gas sensors. Many techniques were adopted for the fabrication of WO₃, namely magnetron sputtering, spray pyrolysis and sol-gel synthesis techniques. In this work, WO₃ films were deposited on indium tin oxide (ITO) coated glasses by sol-gel spin-coating method. The film thickness was varied by depositing different number of layers. The WO₃ film thickness and optical transmittance were determined using step profilometer and ultraviolet-visible (UV-Vis) spectrophotometer, respectively. WO₃ film thicknesses increased from 38 nm to 606 nmwith increasing number of deposited layers.The optical transmittance of the WO₃ films in visible range decreased with increasing film thickness. The optical transmittance were at least 70 % up to 10 deposited layers.WO₃is a promising EC material in the application ofEC devices (ECDs).The application of WO₃ in the EC devices will be discussed.

Abstract: The chemical synthesis is a leading route for the purposeful design of nanomaterials, whereas the tungsten oxides are employed in a variety of special applications. The production of nanomaterials by traditional synthetic methods is still a cumbersome multistep procedure. Here we propose an improved method to produce tungsten oxide nanoparticles via a pyrolytic process. A tungsten-containing precursor was prepared by liquid extraction using n-trioctylamine (C₈H₁₇)₃N solution in toluene. We have shown that the conditions of thermal treatment of the W-based precursor determine the crystalline structure and nanomorphology of the final product. Monoclinic WO₃ nanocrystallites are produced conducting the pyrolysis above 450 °C. The proposed method is a facile and versatile route to produce and control the phase composition and morphology of tungsten oxide-based nanomaterials.

Abstract: The catalytic performance strongly relies on the composition, structure, and property of the material used. Earth-abundant tungsten oxides family (WO_x≤3) has received considerable attention in photocatalysis, electrochemistry and catalytic hydrogenation due to its highly tunable structure and unique physicochemical properties. Substantial efforts have been made by us to improve the photocatalytic activity of WO_x≤3 by enhancing light harvesting, charge transfer and separation, including defect engineering, morphology control, and hetero-junction construction. Additionally, the semiconductor-to-metal transition of WO_x≤3 has been found with the increase of defect concentration, suggesting H₂ can be activated on them in a similar way of a metal catalyst. As a result, WO_2.72 also can function as a versatile and efficient catalyst for the saturation of olefins and selective transform of nitroarenes to anilines.

Abstract: The reduction of pure WO₃ and Ce/WO₃ has been studied by using temperature programmed reduction (TPR), X-ray diffraction (XRD), and FESEM analysis. The reduction behavior were examined by non-isothermal reduction up to 900 oC then continued with isothermal reduction at 900 oC for 45 min under (40% v/v) carbon monoxide in nitrogen (CO in N₂) atmosphere. The TPR results shows that reduction peak of Ce/WO₃ were shifts to lower temperature as compared with to the pure WO₃. In addition, TPR results indicate that addition with ceria give better reducibility compared to pure WO₃. Based on the characterization of the reduction products after hold 45 min using XRD, pure WO₃ were completely converted to WO₂ and W metal phases. While, after addition of Ce to the WO₃, the reduction was enhanced to W phases and some suboxide W₅O₁₄ and W₃O₅ with no WO₂ phase remained and carbide observed. This is associated to the formation of alloy complex Ce₂WO₆ which gave remarkable effect to the reduction.

Abstract: In this study, tungsten silicide powders mechanochemically synthesized using WO₃-SiO₂-Mg powder blends. Stoichiometric proportions and excess amounts of initial powders were used to indicate the effects of final composition of synthesized tungsten silicide powders. Since the initial powder compositions affect the reaction times, all compositions were mechanically alloyed for 1 hour. In addition, thermodynamic calculations of all compositions were theoretically conducted. The dominant phases are WSi₂ and MgO for all mechanically alloyed powders. Results show that the excess amount additions of initial powders directly effects the amount and formation of resultant phases in the synthesized powder compositions.