Papers by Keyword: Tungsten

Abstract: Molecular dynamics (MD) simulation was used to explore how models of W-He respond to irradiation induced damage. Displacement cascades up to 10 keV recoil energy were simulated for W-Σ17 and W-Σ17-He models. The pre-existing He bubbles within and around the grain boundary region have a major effect on the number and distribution of surviving Frenkel pairs. Frenkel pairs increased as the energy of the primary knock-on atom (PKA) increased across all models. Models containing pre-existing He bubbles showed a significant reduction in the number of surviving vacancies/SIAs compared to those without He bubbles. A large portion of point defects accumulate at the grain boundary which acts as a sink for defects during the recrystallization phase. The presence of He bubbles within or near the grain boundary region facilitates the defects generation, absorbs residual point defects, and form clusters. When He bubbles are located around the grain boundary, the number of surviving vacancies/SIAs decreased by 23% to 60% compared to models without He bubbles. However, for models with He bubbles located within the grain boundary structure, a much more extensive reduction occurred compared to models without He bubbles, which is between the range of 76% to 92%.

Abstract: This study investigates the mechanical properties and microstructure of sintered tungsten under varying sintering conditions. Bending strength tests revealed that sintering at 1400 °C resulted in low flexural strength due to inadequate temperature, whereas sintered tungsten at 1500 °C exhibited improved strength attributed to grain growth. However, temperatures exceeding 1600 °C led to excessive grain growth and a subsequent decline in strength, indicative of grain coarsening and potential localized bonding. Additionally, analysis of holding times at 1500 °C demonstrated that extended durations promoted neck bonding between grains, contributing to the formation of interconnected grains and enhanced mechanical properties. This study underscores the importance of optimizing sintering parameters to control grain growth and achieve desired mechanical properties in sintered tungsten materials.

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: The results of the development of the technology for growing super-large single crystals of refractory metals, which were developed at the E.O. Paton Electric Welding Institute of the NAS of Ukraine. Based on proven technology and acquired skills, a new generation of equipment was created that allows the growth of single crystals of refractory alloys in the form of bodies of rotation. Experiments were conducted on growing a single crystal of tungsten in the form of a hollow cylinder, from which it is possible to make such a product as a crucible. Technological parameters and energy regimes were established, which allowed for control of the thickness of the wall to be welded. As a result of the experiments, an ingot with a welded wall height of 68 mm, a thickness of 20–22 mm, and an outer diameter of 85 mm was grown. The structure of the obtained samples was studied.

Abstract: Tungsten (W) reinforced diamond-like carbon (DLC) nanocomposite thin films were deposited on silicon substrates by magnetron sputtering in a CH₄/Ar discharge. The W content of the films was varied by varying the W target power (20, 40, 60, 80, and 100 W). The evolution of the W-DLC nanocomposites was studied by high-resolution transmission electron microscopy, X-ray energy dispersive spectroscopy, X-ray photoelectron spectroscopy, 3D optical profilometry and Raman spectroscopy. Increasing the W target power resulted in an almost liner increase in the W content, reduced the hardness and the sp³/sp² ratio in the films, while it increased the surface roughness and promoted formation of WC nanoparticles. Tribological properties were studied by conducting sliding reciprocating testing. Wear tracks were analyzed with Raman spectroscopy and 3D optical profilometry. Increasing the W content in the films (increasing target power) resulted in a reduction of both, the friction coefficient and wear rate. The film deposited at 80 W target power (~8 at. % W) exhibited the lowest friction coefficient (0.15) and wear rate (6x10^-7 mm³N^-1m^-1). The observed low friction and wear rate were attributed to the particular nanocomposite structure of the films involving a fine distribution of WC nanoparticles surrounded by a sp² dominant carbon network. The present W-DLC nanocomposite films offer a highly desirable combination of low friction and low wear rate.

Abstract: Tungsten (W) and Cerium (Ce) doped nanoTitanium oxide (TiO₂) nanophotocatalyst were prepared by the sol-gel method and their photodegradation effect against atrazine herbicide were investigated. The doping of the nanocatalyst took place at 50 °C within a time interval of 120 minutes. The prepared gel was dried and calcined in the oven at 350 °C for 75 minutes. The XRD result revealed that the synthesized nanocatalyst was 16.7 nm in size with a mostly monoclinic structure. With FTIR spectra, characteristic peaks of TiO₂ were found at 516 cm^-1, Ti-O-Ce at 1104 cm^-1, and W-O with a single bond at 1609 cm^-1. Scanning electron microscope analysis revealed the surface morphology of synthesized nanophotocatalyst. The photocatalytic activity of synthesized nanocatalyst was tested on the degradation of atrazine herbicide (ATZ) under visible and UV light in a batch reactor. The efficiency of nanocatalyst was compared for effective utilization. About 46.5 % of photocatalytic activity was observed without UV light irradiation within 120 minutes. The photocatalytic activity of W-Ce co-doped TiO₂ to degrade atrazine further increased up to 99.1 % when the solution was irradiated under UV light. Factors like pH, time, and concentration of nanocatalyst were optimized to check the photocatalytic activity of nanocatalyst on ATZ. It was concluded that nanocatalyst showed an efficient photocatalytic degradation at pH 6 within 120 mins time interval after exposure to UV light.

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 paper presents the results of tests of HPC (high performance composites) samples consisting of aramid and glass fabrics modified by agglomerates of WC and WO₃ nanopowders. According to the test results, introduction of WC and WO₃ powders into the composite plate structure makes it more rigid and elastic, increasing its ability to dissipate energy.

Abstract: The paper provides an assessment of the safety processes of high-modulus energy sources systems during the initiation of flat and cylindrical high-modulus energy sources. The expressions, which establish the relationship between the parameters of flat and hollow cylindrical charges of explosives under the only condition of equality of the developed pressure pulse on the surface of the charge of explosives, provided all other things being equal, were obtained. In contrast to the earlier studies, which assert the existence of a direct relationship between the parameters during the initiation of flat and cylindrical surfaces, the current study demonstrates energy consumption during the initiation of cylindrical surfaces is higher than the initiation of flat surfaces, all other things being equal.

Abstract: The conditions for the synthesis of Al-Cr-W alloys during the aluminothermic reduction of a mineral tungsten concentrate - scheelite were considered. The alloys were identified as an aluminum matrix by the methods of elemental and X-ray phase analyzes. It is shown that the alloy synthesized from scheelite concentrate contains small amounts of iron and oxygen impurities (1.2 wt. %). It has been established that the alloys have a composite structure: inclusions of continuously solid solutions based on chromium and tungsten, as well as chromium aluminides Al₃(Cr, W, Fe)2, which have increased microhardness values (12.9 GPa) are distributed in the aluminum matrix.