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Artigos de revistas sobre o tema "Tungsten"

Autor: Grafiati

Publicado: 4 de junho de 2021

Última modificação: 31 de julho de 2024

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1

Kwon, Hanjung, e Jung-Min Shin. "Sintering Behavior and Hardness of Tungsten Prepared by Hard Metal Sludge Recycling Process without Ammonium Paratungstate". Korean Journal of Metals and Materials 60, n.º 1 (5 de janeiro de 2022): 53–61. http://dx.doi.org/10.3365/kjmm.2022.60.1.53.

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In this paper, we suggest a novel recycling process for hard metal sludge that does not use ammonium paratungstate. Ammonia, which in the conventional recycling process is essential for removing sodium and crystallized tungstate, was not used in the novel process. Instead of ammonia, acid was used to remove the sodium and crystallized tungstate resulting in the formation of tungstic acid (H2WO4). Tungsten powders were successfully synthesized by hydrogen reduction of the tungstic acid through H2O decomposition, WO3 to WO2 reduction, and tungsten metal formation. The tungsten powders prepared from tungstic acid were spherical in shape and had a higher sintering density than the facet-shaped tungsten powders prepared from tungsten oxide. The spherical shape of the tungsten powders enhanced their sinterability and resulted in an increase in the size of grains. This is a result of the high diffusion rate of the atoms along the particle surfaces. Despite having a higher density, the hardness of the sintered tungsten was lower than that of tungsten from tungsten oxide. High energy milling effectively reduced grain size and improved hardness. The hardness of the tungsten prepared from milled tungstic acid was enhanced to a value (max. 471 HV) higher than the best previously reported value (389 HV). In sum, tungsten can be hardened, thereby improving its sinterability and reducing grain size, with tungstic acid prepared using the proposed recycling process.

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2

Pee, J. H., G. H. Kim, H. Y. Lee e Y. J. Kim. "Extraction Factor Of Tungsten Sources From Tungsten Scraps By Zinc Decomposition Process". Archives of Metallurgy and Materials 60, n.º 2 (1 de junho de 2015): 1311–14. http://dx.doi.org/10.1515/amm-2015-0120.

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Abstract Decomposition promoting factors and extraction process of tungsten carbide and tungstic acid powders in the zinc decomposition process of tungsten scraps which are composed mostly of tungsten carbide and cobalt were evaluated. Zinc volatility was suppressed by the enclosed graphite crucible and zinc volatilization pressure was produced in the reaction graphite crucible inside an electric furnace for ZDP (Zinc Decomposition Process). Decomposition reaction was done for 2hours at 650°, which 100% decomposed the tungsten scraps that were over 30 mm thick. Decomposed scraps were pulverized under 75μm and were composed of tungsten carbide and cobalt identified by the XRD (X-ray Diffraction). To produce the WC(Tungsten Carbide) powder directly from decomposed scraps, pulverized powders were reacted with hydrochloric acid to remove the cobalt binder. Also to produce the tungstic acid, pulverized powders were reacted with aqua regia to remove the cobalt binder and oxidize the tungsten carbide. Tungsten carbide and tungstic acid powders were identified by XRD and chemical composition analysis.

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3

Fu, Xiao Ming, Chen Chen Xie e Liang Yi Zhou. "Submicron Tungsten Powder Prepared through the Circulatory Oxidization-Reduction Method". Advanced Materials Research 228-229 (abril de 2011): 283–87. http://dx.doi.org/10.4028/www.scientific.net/amr.228-229.283.

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Tungstic oxide is prepared with pure ammonium paratungstate in the air. And then Tungsten powder is obtained with tungstic oxide through deoxidation in the hydrogen gas (Rate of purity: 99.99 %, dew point: -40 °C), and tungsten powder is oxidized in the air. Tungstic oxide is reduced into tungsten powder in the hydrogen gas. The above routes are repeated. The samples are characterized by the laser particle size distribution measuring instrument and the electron probe scan instrument. The results show that submicron tungsten powder is obtained through circulatory oxidation twice and reductiuon three times. The volume percentage of the particle size distribution of submicron tungsten powder between 0.1 μm and 0.5 μm is 94.81 %.

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4

Nagy, Áron Kázmér, Judit Pfeifer, István Endre Lukács, Attila Lajos Tóth e Csaba Balázsi. "Electrospinning – A Candidate for Fabrication of Semiconducting Tungsten Oxide Nanofibers". Materials Science Forum 659 (setembro de 2010): 215–19. http://dx.doi.org/10.4028/www.scientific.net/msf.659.215.

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The excellent gas sensing properties of the tungsten oxides have been manifested first of all in nanostructure and 1D, and 2D open structured forms. For optimal performance the sensing layer substrates should be of large specific surface. In this paper we report on electrospinning – a candidate for fabrication of large specific surface tungsten oxide nanofibers. Fibrous tissues doped with tungstic acid hydrate (H2WO4.H2O) and tungsten oxide one third hydrate (WO3.1/3H2O) has been created and characterized by X-ray diffraction, scanning electron microscope and energy dispersive spectroscopy in order to learn about the changes the materials suffer during the process.

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5

Nielsen, K. H., K. Wondraczek, U. S. Schubert e L. Wondraczek. "Large-area wet-chemical deposition of nanoporous tungstic silica coatings". Journal of Materials Chemistry C 3, n.º 38 (2015): 10031–39. http://dx.doi.org/10.1039/c5tc02045j.

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6

Labbe, Ph. "Tungsten Oxides, Tungsten Bronzes and Tungsten Bronze-Type Structures". Key Engineering Materials 68 (janeiro de 1992): 293–0. http://dx.doi.org/10.4028/www.scientific.net/kem.68.293.

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7

Kumar, A., e N. C. Aery. "Effect of tungsten on growth, biochemical constituents, molybdenum and tungsten contents in wheat". Plant, Soil and Environment 57, No. 11 (8 de novembro de 2011): 519–25. http://dx.doi.org/10.17221/345/2011-pse.

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  The effect of various concentrations (3, 9, 27, 81, and 243 mg/kg) of tungsten (W) on growth performance, biochemical constituents and tungsten and molybdenum (Mo) contents in wheat was observed. Lower doses (up to 9 mg/kg) of tungsten showed promotory effects whereas higher doses retarded. An increment in growth, biomass, chlorophyll and carbohydrate contents was observed. Tungsten contents in root and shoot showed a very strong linear dependence on the soil applied W contents. Mo contents in plant tissue showed an increase with an increase in the W contents in plant tissue up to a threshold after which it showed an abrupt decrease. The activity of peroxidase enzyme decreased with lower application of W. Higher administration of tungsten (27–243 mg/kg) resulted in increased total phenol, free proline and activity of enzyme peroxidase.

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8

Pee, J. H., G. H. Kim, H. Y. Lee e Y. J. Kim. "Extraction Factor Of Pure Ammonium Paratungstate From Tungsten Scraps". Archives of Metallurgy and Materials 60, n.º 2 (1 de junho de 2015): 1403–5. http://dx.doi.org/10.1515/amm-2015-0141.

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Abstract Typical oxidation process of tungsten scraps was modified by the rotary kiln with oxygen burner to increase the oxidation rate of tungsten scraps. Also to accelerate the solubility of solid oxidized products, the hydrothermal reflux method was adapted. By heating tungsten scraps in rotary kiln with oxygen burner at around 900° for 2hrs, the scraps was oxidized completely. Then oxidized products (WO3 and CoWO4) was fully dissolved in the solution of NaOH by hydrothermal reflux method at 150° for 2hrs. The dissolution rate of oxidized products was increased with increasing the reaction temperature and concentration of NaOH. And then CaWO4 and H2WO4 could be generated from the aqueous sodium tungstate solution. Ammonium paratungstate (APT) also could be produced from tungstic acid using by aqueous ammonium solution. The morphologies (cubic and plate types) of APT was controlled by the stirring process of purified solution of ammonium paratungstate.

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9

Tran-Nguyen, D. H., D. Jewell e D. J. Fray. "Electrochemical preparation of tungsten, tungsten carbide and cemented tungsten carbide". Mineral Processing and Extractive Metallurgy 123, n.º 1 (19 de dezembro de 2013): 53–60. http://dx.doi.org/10.1179/1743285513y.0000000049.

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10

Kumari, J., e P. Mangala. "Enhanced Anticarcinogenic and Antimicrobial Response of Synthesized Tungsten Oxide Nanoparticles". Journal of Scientific Research 15, n.º 1 (1 de janeiro de 2023): 141–57. http://dx.doi.org/10.3329/jsr.v15i1.58211.

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In the present study, we fabricated tungsten trioxide nanoparticles (WO3 NPs) from a tungsten complex [W(C13H10NO)3] of ligand N-salicylideneaniline with tungstic acid as the precursor. Nanoparticles were synthesized using the direct thermal decomposition method. These nanoparticles were evaluated for cytotoxicity influence on human breast cancer MCF7 cell line (adenocarcinoma). The observed results suggested that WO3 can destroy 50 % of viable cells after 24 h of incubation at 37 °C. Based on these results, we concluded that WO3 nanoparticles could be a potential drug carrier candidate against human breast cancer cells based on the amount of the drug. In addition, WO3 nanoparticles exhibited significant antimicrobial and antifungal activity.

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11

Zhudra, A. P. "Tungsten carbide based cladding materials". Paton Welding Journal 2014, n.º 6 (28 de junho de 2014): 66–71. http://dx.doi.org/10.15407/tpwj2014.06.13.

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12

Baghel, Manas Singh, Dr L. Boriwal, Dharmesh Barodiya, Monil Jain e Mohd Altaf Ansari. "Micro Additive Manufacturing in Tungsten". International Journal of Research Publication and Reviews 5, n.º 4 (abril de 2024): 1622–30. http://dx.doi.org/10.55248/gengpi.5.0424.0942.

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13

Luchting, Wolfgang A., César Vallejo e Robert Mezey. "Tungsten". Chasqui 18, n.º 2 (1989): 100. http://dx.doi.org/10.2307/29740189.

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14

LOWDEN, RICK. "TUNGSTEN". Chemical & Engineering News 81, n.º 36 (8 de setembro de 2003): 142. http://dx.doi.org/10.1021/cen-v081n036.p142.

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15

Fereday, Richard J. "Tungsten". Coordination Chemistry Reviews 81 (novembro de 1987): 51–100. http://dx.doi.org/10.1016/0010-8545(87)85013-0.

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16

Dunbar, Kim R., e Gary M. Finniss. "Tungsten". Coordination Chemistry Reviews 127, n.º 1-2 (setembro de 1993): 65–97. http://dx.doi.org/10.1016/0010-8545(93)80055-a.

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17

Jasper, Bruno, Jan W. Coenen, Johann Riesch, Till Höschen, Martin Bram e Christian Linsmeier. "Powder Metallurgical Tungsten Fiber-Reinforced Tungsten". Materials Science Forum 825-826 (julho de 2015): 125–33. http://dx.doi.org/10.4028/www.scientific.net/msf.825-826.125.

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The composite material tungsten fiber-reinforced tungsten (Wf/W) addresses the brittleness of tungsten by extrinsic toughening through introduction of energy dissipation mechanisms. These mechanisms allow the release of stress peaks and thus improve the materials resistance against crack growth. Wf/W samples produced via chemical vapor infiltration (CVI) indeed show higher toughness in mechanical tests than pure tungsten. By utilizing powder metallurgy (PM) one could benefit from available industrialized approaches for composite production and alloying routes. In this contribution the PM method of hot isostatic pressing (HIP) is used to produce Wf/W samples. A variety of measurements were conducted to verify the operation of the expected toughening mechanisms in HIP Wf/W composites. The interface debonding behavior was investigated in push-out tests. In addition, the mechanical properties of the matrix were investigated, in order to deepen the understanding of the complex interaction between the sample preparation and the resulting mechanical properties of the composite material. First HIP Wf/W single-fiber samples feature a compact matrix with densities of more than 99% of the theoretical density of tungsten. Scanning electron microscopy (SEM) analysis further demonstrates an intact interface with indentations of powder particles at the interface-matrix boundary. First push-out tests indicate that the interface was damaged by HIPing.

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18

Gu, Gang, Bo Zheng, W. Q. Han, Siegmar Roth e Jie Liu. "Tungsten Oxide Nanowires on Tungsten Substrates". Nano Letters 2, n.º 8 (agosto de 2002): 849–51. http://dx.doi.org/10.1021/nl025618g.

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19

Bell, David A., John L. Falconer e Carol M. McConica. "Desorption of Tungsten Fluorides from Tungsten". Journal of The Electrochemical Society 142, n.º 7 (1 de julho de 1995): 2401–4. http://dx.doi.org/10.1149/1.2044309.

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20

Patrick, Chris. "Smaller-grained tungsten is stronger tungsten". Scilight 2020, n.º 40 (2 de outubro de 2020): 401104. http://dx.doi.org/10.1063/10.0002130.

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21

Posthill, J. B., M. C. Hogwood e D. V. Edmonds. "Precipitation at Tungsten/Tungsten Interfaces in Tungsten–Nickel–Iron Heavy Alloys". Powder Metallurgy 29, n.º 1 (janeiro de 1986): 45–51. http://dx.doi.org/10.1179/pom.1986.29.1.45.

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22

Jenuš, P., A. Abram, S. Novak, M. Kelemen, M. Pečovnik, T. Schwarz-Selinger e S. Markelj. "Deuterium retention in tungsten, tungsten carbide and tungsten-ditungsten carbide composites". Journal of Nuclear Materials 581 (agosto de 2023): 154455. http://dx.doi.org/10.1016/j.jnucmat.2023.154455.

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23

He, Xue Liang, Zeng Lin Zhou, Qiao Juan Deng, Yan Li, Zhi Lin Hui e Fu Wang. "Tungsten Matrix Material for Diffusion Barium Tungsten Cathode". Materials Science Forum 913 (fevereiro de 2018): 846–52. http://dx.doi.org/10.4028/www.scientific.net/msf.913.846.

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As the core component of the diffusion cathode, the performance of porous tungsten matrix material will directly affect the output performance and life of microwave source. Therefore, the preparation of porous tungsten matrix is the key process of making a cathode material. In this paper, the industrial tungsten powder was used as raw material, whose particle size was modulated by fluidic classification firstly. Then via cold isostatic pressing and hydrogen sintering in high temperature, the porous tungsten sintered body was obtained. Finally, by the process of copper infiltration, machining and copper removal, the porous tungsten matrix was achieved. The result showed that compared with raw material tungsten powder, the classified tungsten powder’s particle size distribution was narrowed and its tap density obviously increased, indicating that it had better particle stacking performance. Setting the temperature between 1900°C and 2050°C the high temperature hydrogen sintering experiment was conducted, and it was found that the volume shrinkage ratio of tungsten sintered body increased with the sintering temperature, and correspondingly, its total porosity decreased from 24.4% at 1900°C to 20.8% at 2050°C. It was characterized by MIP (mercury intrusion porosimetry) that at high temperature between 1950~2050°C, the porous tungsten matrix with an open porosity of 21±1%, 1.30~1.60μm average pore size, a close cell ratio less than 1% and the skeleton strength greater than 150MPa was obtained. Thus this porous tungsten matrix is an ideal material to be applied to highly reliable diffusion bariated tungsten cathode manufacturing.

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24

Cao, Yaowu, e Qinghai Guo. "Tungsten speciation and its geochemical behavior in geothermal water: A review". E3S Web of Conferences 98 (2019): 07005. http://dx.doi.org/10.1051/e3sconf/20199807005.

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Tungsten and most of its compounds remain one of the least regulated substances. As the potential toxicity of tungsten has been reported, the stereotypes about tungsten are gradually being broken. Areas with intense magmatic hydrothermal activity are likely threatened by geothermal tungsten (up to 1037 μg/L of tungsten was detected in the geothermal waters from a magmatic hydrothermal system in Tibet, Daggyai), and the geothermal developers should be cautious during the utilization of geothermal resource. This paper reviews the studies on transformation of aqueous tungsten species, distribution of tungsten in geothermal waters, and critical geochemical processes (or parameters) controlling geothermal tungsten concentrations. The mobility of aqueous tungsten depends on environmental pH, its complexation with sulfide, and its sorption onto Fe(III) oxides/oxyhydroxides. More attention still needs to be paid to environmental geochemistry of tungsten, in view that there are limited literatures reporting the thermodynamic properties of tungsten compounds at high temperatures and the models delineating the geochemical behavior of tungsten.

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25

Yordanov, Krastin, Aneliya Stoyanova e Jaroslav Argirov. "Determining the Properties and Structure of Welded Copper Plates and Establishing their Connection with the Temperature Field Distribution in the Studied Zones". Advanced Materials Research 1111 (julho de 2015): 217–22. http://dx.doi.org/10.4028/www.scientific.net/amr.1111.217.

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The aim of our study is to determine the properties and structure of the material after welding thin copper plates in a shielding medium of inert gas (argon) with unsmeltable tungstic electrode by determining the temperature fields during welding. This welding method is well-known as tungsten inert gas (TIG) welding.

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26

Nikolaenko, Irina V., Nikolay Kedin e Gennadii Shveikin. "Two-Step Synthesis of Ultrafine and Nanosized Powders of Tungsten Oxide and Carbide". Advances in Science and Technology 88 (outubro de 2014): 9–14. http://dx.doi.org/10.4028/www.scientific.net/ast.88.9.

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In this work a new method of nanoand ultrafine powder of tungsten oxide and carbide synthesis by means of combinating carbon carrier supported classic liquid-phase precipitation and low-temperature microwave treatment was offered. The full range of intermediate substances obtained during thermolysis, reduction and carbidization precursors to final products were presented. The thermolysis of tungstic acid with the formation of tungsten oxide and carbide ultrafine particles of different modifications were studied. It was shown, that cooling ammonium tungstate solution to 4 °C, and use of carbon carrier on the precipitation stage can increase specific surface area from 20 to 100 m2g-1. With the use of SEM precursors particles size were examined (∼200 nm) and the morphology of initial, intermediate and final products was shown.

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27

Liu, Lingna, Yi Hou, Xiuzhao Yin, Fang Zhang e Zifei Peng. "Preparation and investigation of co-doped VO2 powders". Functional Materials Letters 12, n.º 02 (abril de 2019): 1950015. http://dx.doi.org/10.1142/s1793604719500152.

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In this paper, tungsten-and molybdenum-doped vanadium dioxide (VO[Formula: see text] powders were prepared by hydrothermal reaction using vanadium pentoxide (V2O[Formula: see text], H2O2, white tungstic acid (WPTA) and sodium molybdate (Na2MoO[Formula: see text] as raw materials. The microstructure and composition of VO2 powders were characterized by means of XRD, XPS, DSC and FT-IR. We made a preliminary study on the thermal-induced phase transition properties of powders. The experimental results show that the co-doped samples are monoclinic rutile. Tungsten and molybdenum atoms exist in the lattice at the positive six valence. When the W and M W were 3% and 2%, respectively, the transition temperature of co-doped samples were close to room temperature can reach 25.5∘C.

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28

Linyuan, Zhao, Yang Mingqing e Lv Yong. "Solvothermal Synthesis and Near-Infrared Shielding Properties of Cs0.3WO3/WO3 Composites". International Journal of Nanoscience 19, n.º 04 (6 de fevereiro de 2020): 1950032. http://dx.doi.org/10.1142/s0219581x19500327.

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The Cs[Formula: see text]WO3/WO3 composite with near-infrared shielding properties was synthesized by the solvothermal method using tungstic acid and cesium salt as raw materials. The as-prepared composites were tested by X-ray powder diffraction, scanning electron microscopy, energy spectrum analysis, transmission electron microscopy, electron energy loss spectroscopy, and ultraviolet-visible near-infrared spectroscopy. The effects of different reaction conditions on the structure and near-infrared shielding properties of the synthesized composites were investigated. The best near-infrared light transmittance of as-prepared composites can reach up to 9%, which provides a feasible solution for the near-infrared shielding material. The new homogeneous composites of cesium tungsten bronze and tungsten oxide are good candidates for solar filters.

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29

Luo, Yunbo, e Faming Zhang. "A Novel Process of Tungsten Flotation for Sustainable Exploitation of Tungsten Resources". Chiang Mai Journal of Science 50, n.º 5 (30 de setembro de 2023): 1–12. http://dx.doi.org/10.12982/cmjs.2023.056.

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Tungsten as key metal in various fields is indispensable metal resource for global economy. Sustainable exploitation of tungsten resources is still challenging. This work makes attempt to solve the difficulty in flotation separation of tungsten minerals from Yaogangxian tungsten ore. Systematical analysis of mineralogical properties of tungsten ore was performed. A process for tungsten flotation from tungsten ore was developed for exploitation of tungsten resources. The major valuable element in the ore is tungsten, and the grade of tungsten is 0.22%. The distribution of scheelite is nonuniform, and it is majorly distributed in 0.02~0.32 mm. The intergrowth and inclusion of scheelite occur with other minerals such as calcite, diopside, grossularite, and fluorite. The liberation of scheelite reaches 92.40% for -0.074 mm accounting for 75.48%. Process factors including Na2CO3, flotation collector, modified sodium silicate solution, and lead nitrate are studied, and the optimized conditions are Na2CO3 1600 g/t, GY-107 (640 g/t for roughing and 240 g/t for scavenging), modified sodium silicate solution 4200 g/t, and lead nitrate 400 g/t. The open-circuit and closed-circuit flotation processes for tungsten separation are designed, and it is verified for effective separation of tungsten minerals. For the closed-circuit flotation, the grade of tungsten concentrate is 7.30%, while the recovery reaches 85.89%. This work provides technical insights into tungsten separation from tungsten ore.

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30

Fu, Xiao Ming. "Fine Cemented Carbide Particles Prepared with Activated Tungsten Oxide". Advanced Materials Research 510 (abril de 2012): 619–22. http://dx.doi.org/10.4028/www.scientific.net/amr.510.619.

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Fine cemented carbide in the diameter of less than 1 μm is obtained activated tungsten oxide. The samples are characterized by laser particle size analyze, electron microscope and sclerometer. The experimental results show that the size of tungsten particles and tungsten carbide prepared with activated tungsten becomes small remarkably, and coarse tungsten particles decrease. The properties of cemented carbide prepared with activated tungsten oxide are better than those of cemented carbide made with blue tungsten oxide. Especially, the hardness of cemented carbide prepared with activated tungsten oxide increases by about 7 %.

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31

Han, Zhengdong, Artem Golev e Mansour Edraki. "A Review of Tungsten Resources and Potential Extraction from Mine Waste". Minerals 11, n.º 7 (29 de junho de 2021): 701. http://dx.doi.org/10.3390/min11070701.

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Tungsten is recognized as a critical metal due to its unique properties, economic importance, and limited sources of supply. It has wide applications where hardness, high density, high wear, and high-temperature resistance are required, such as in mining, construction, energy generation, electronics, aerospace, and defense sectors. The two primary tungsten minerals, and the only minerals of economic importance, are wolframite and scheelite. Secondary tungsten minerals are rare and generated by hydrothermal or supergene alteration rather than by atmospheric weathering. There are no reported concerns for tungsten toxicity. However, tungsten tailings and other residues may represent severe risks to human health and the environment. Tungsten metal scrap is the only secondary source for this metal but reprocessing of tungsten tailings may also become important in the future. Enhanced gravity separation, wet high-intensity magnetic separation, and flotation have been reported to be successful in reprocessing tungsten tailings, while bioleaching can assist with removing some toxic elements. In 2020, the world’s tungsten mine production was estimated at 84 kt of tungsten (106 kt WO3), with known tungsten reserves of 3400 kt. In addition, old tungsten tailings deposits may have great potential for exploration. The incomplete statistics indicate about 96 kt of tungsten content in those deposits, with an average grade of 0.1% WO3 (versus typical grades of 0.3–1% in primary deposits). This paper aims to provide an overview of tungsten minerals, tungsten primary and secondary resources, and tungsten mine waste, including its environmental risks and potential for reprocessing.

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Zhang, Lian Meng, Ming Gao, Guo Qiang Luo, Zhuo Chen e Qiang Shen. "Preparation of Tungsten-Epoxy Composites and FGMs with Density Gradient". Materials Science Forum 631-632 (outubro de 2009): 461–64. http://dx.doi.org/10.4028/www.scientific.net/msf.631-632.461.

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FGMs with density gradient are of great interest in field of dynamic high-pressure physics. In this paper, tungsten particles reinforced epoxy resin composites, and FGMs with density gradient were prepared by calendering technique. Microstructures of tungsten-epoxy composites with various tungsten contents were analyzed, and the density distribution of the FGMs was characterized. The results show that the distribution of tungsten particles in tungsten-epoxy composites is homogeneous, and the combination of tungsten particles with epoxy matrix is good. The density of tungsten-epoxy composites varies from 1.26gcm-3 to 4.0gcm-3, and the thickness of each layer is about 200μm. Tungsten-epoxy FGMs with density gradient were obtained by laminating thin layers of tungsten-epoxy composites with different tungsten contents. The highly enough bonding strength between these transition layers and good parallelism were achieved. The density distribution of the tungsten-epoxy FGMs can meet the demand of the power function equation of density and thickness.

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33

Hu, Ya Fang, Jian Can Yang e Zhen Liu. "Effect of Doping Elements on High Temperature Properties of Tungsten Products". Materials Science Forum 847 (março de 2016): 59–64. http://dx.doi.org/10.4028/www.scientific.net/msf.847.59.

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The tungsten products including tungsten electrode, tungsten filament, tungsten crucible have been widely used in national production. To study their properties at high temperature can provide a basis for improving the production process and the quality of processing as well as reducing production defects, which has important significance for the optimization of the performance and life extension of tungsten products. In this paper the development of tungsten and tungsten products is briefly introduced, the effects of many kinds of doped elements and doped compounds on high temperature mechanical properties is summarized, the research status of high temperature properties of tungsten products described in detail. And the development direction and application prospects for optimizing the high temperature performance of tungsten products has been out looked,in order to provide a reference for the research on the mechanical properties under high temperature of tungsten products.

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Абдуллин, Х. А., А. А. Азаткалиев, М. Т. Габдуллин, Ж. К. Калкозова, Б. Н. Мукашев e А. С. Серикканов. "Получение наноразмерных порошков оксида вольфрама и вольфрама". Физика твердого тела 61, n.º 1 (2019): 163. http://dx.doi.org/10.21883/ftt.2019.01.46907.158.

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AbstractNanopowder tungsten oxide and metallic tungsten are obtained via pyrolysis of ammonium metatungstate. Two methods are used for the synthesis of tungsten oxide: the use of a fibrous matrix and pyrolysis of aerosol particles. Tungsten oxide particles are formed during the pyrolysis in air. Metallic tungsten nanoparticles are obtained via subsequent thermal reduction of tungsten oxide in hydrogen. The structure and morphology of the samples are studied with X-ray diffraction and scanning electron microscopy. Tungsten nanopowders with average sizes from 7 to 30 nm are obtained depending on synthesis temperature. The electrochemical characteristics of electrodes coated with tungsten nanoparticles are studied with cyclic voltammetry, impedance spectroscopy, and galvanostatic charge–discharge methods. An electrode with W nanoparticles exhibited a specific low-frequency capacitance of about 90 F/g due to thin tungsten oxide film on the surface of tungsten nanoparticles.

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Upadhyay, R. K., e L. A. Kumaraswamidhas. "Tungsten/tungsten nitride performance at elevated temperature". Materials at High Temperatures 31, n.º 2 (29 de janeiro de 2014): 102–8. http://dx.doi.org/10.1179/1878641314y.0000000003.

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Lipski, A. R., e R. S. Lefferts. "Making tungsten targets using tungsten oxide powder". Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 655, n.º 1 (novembro de 2011): 41–43. http://dx.doi.org/10.1016/j.nima.2011.06.016.

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Lin, Jun, Atsuhiro Tsukune, Toshiya Suzuki e Masao Yamada. "Conversion of tungsten nitride to pure tungsten". Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films 16, n.º 2 (março de 1998): 611–14. http://dx.doi.org/10.1116/1.581077.

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Yang, L., B. D. Wirth, Danny Perez e Arthur F. Voter. "Mobility of tungsten clusters on tungsten surfaces". Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms 453 (agosto de 2019): 61–66. http://dx.doi.org/10.1016/j.nimb.2019.05.078.

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Choi, D. S., S. K. Kim e R. Gomer. "Diffusion of tungsten on stepped tungsten surfaces". Surface Science 234, n.º 3 (agosto de 1990): 262–72. http://dx.doi.org/10.1016/0039-6028(90)90559-q.

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Reiser, Jens, Lauren Garrison, Henri Greuner, Jan Hoffmann, Tobias Weingärtner, Ute Jäntsch, Michael Klimenkov et al. "Ductilisation of tungsten (W): Tungsten laminated composites". International Journal of Refractory Metals and Hard Materials 69 (dezembro de 2017): 66–109. http://dx.doi.org/10.1016/j.ijrmhm.2017.07.013.

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Brown, David A., William K. Glass, Hani J. Toma e W. Earle Waghorne. "Dithiocarbamates of tungsten(III)and tungsten(IV)". Journal of the Chemical Society, Dalton Transactions, n.º 11 (1987): 2531. http://dx.doi.org/10.1039/dt9870002531.

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El-Kurdi, Said, Abdal-Azim Al-Terkawi, BerndâM Schmidt, Anton Dimitrov e Konrad Seppelt. "Tungsten(VI) and Tungsten(V) Fluoride Complexes". Chemistry - A European Journal 16, n.º 2 (11 de janeiro de 2010): 595–99. http://dx.doi.org/10.1002/chem.200902307.

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43

Malyshev, V. V., e N. F. Kushchevska. "Production of Tungsten and Tungsten Carbide Powders". Powder Metallurgy and Metal Ceramics 58, n.º 3-4 (julho de 2019): 237–42. http://dx.doi.org/10.1007/s11106-019-00069-w.

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44

Yang, Chen, Qinghai Guo, Yaowu Cao e Georgii A. Chelnokov. "Hydrocalumite as well as the Formation of Scheelite Induced by Its Dissolution, Removing Aqueous Tungsten with Varying Concentrations". International Journal of Environmental Research and Public Health 19, n.º 14 (15 de julho de 2022): 8630. http://dx.doi.org/10.3390/ijerph19148630.

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As a toxic element, tungsten (W) in elevated concentrations, originating from human activities or geological sources, poses a severe threat to the environment. However, there has been a lack of robust remediation techniques focusing on aqueous tungsten contamination with varying initial concentrations, because only recently have the toxicity and the environmental threat of tungsten been fully realized. In this study, the removal of tungsten from an aqueous solution by hydrocalumite was investigated for the first time. Systematic removal experiments were carried out at designated contact time, temperature, and initial tungsten concentration. The results showed that hydrocalumite is capable of effectively removing tungsten under various conditions, especially at high initial tungsten concentrations, with the maximum uptake capacity being up to 1120.5 mg (tungsten)/g (hydrocalumite). The mechanisms of tungsten removal were studied based on the measured chemical compositions of the solution samples and their PHREEQC simulations as well as the solid sample characterization by XRD, SEM–EDX, and XPS. At low initial tungsten concentrations (below 1 mmol/L), anion exchange between the tungsten in solution and the Cl in the hydrocalumite interlayers played a critical role in tungsten removal. At high initial tungsten concentrations (higher than 5 mmol/L), the removal of W from the solution was solely caused by the precipitation of scheelite (CaWO4), facilitated by the substantial release of Ca2+ from hydrocalumite dissolution. At moderate tungsten concentrations (1–5 mmol/L), however, both mechanisms were responsible for the uptake of tungsten, with scheelite precipitation being more important. Hydrocalumite is promising for wide use in the treatment of high-tungsten natural waters or wastewaters.

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Mao, Yiran, Jan W. Coenen, Chao Liu, Alexis Terra, Xiaoyue Tan, Johann Riesch, Till Höschen, Yucheng Wu, Christoph Broeckmann e Christian Linsmeier. "Powder Metallurgy Produced Aligned Long Tungsten Fiber Reinforced Tungsten Composites". Journal of Nuclear Engineering 3, n.º 4 (8 de dezembro de 2022): 446–52. http://dx.doi.org/10.3390/jne3040030.

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For the future fusion reactor, tungsten is the main candidate material as the plasma-facing material. However, considering the high thermal stress during operation, the intrinsic brittleness of tungsten is one of the issues. To overcome the brittleness, tungsten fiber reinforces tungsten composites (Wf/W) developed using extrinsic toughening mechanisms. The powder metallurgy process and chemical vapor deposition process are the two production routes for preparing Wf/W. For the powder metallurgy route, due to technical limitations, previous studies focused on short random distributed fiber-reinforced composites. However, for short random fiber composites, the strength and reinforcement effect are considerably limited compared to aligned continuous fiber composites. In this work, aligned long tungsten fiber reinforced tungsten composites have been first time realized based on powder metallurgy processes, by alternately placing tungsten weaves and tungsten powder layers. The produced Wf/W shows significantly improved mechanical properties compared to pure W and conventional short fiber Wf/W.

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46

Fu, Xiao Ming. "Ultrafine Tungsten Powder Obtained with Violet Tungsten Oxide Using Circulatory Oxidization-Reduction Method". Applied Mechanics and Materials 127 (outubro de 2011): 101–4. http://dx.doi.org/10.4028/www.scientific.net/amm.127.101.

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Violet tungsten oxide is prepared with pure ammonium paratungstate in the argon gas. Tungsten powder is obtained with violet tungsten oxide through deoxidation in the hydrogen gas (Rate of purity: 99.99 %, dew point: -40 °C), and tungsten powder is oxidized in the air. Tungsten oxide is reduced with tungsten powder in the hydrogen gas. The samples are characterized with the laser particle size distribution measuring instrument and field-emission scanning electron microscope. The results show that ultrafine tungsten powder is obtained through circulatory oxidation twice and reduction three times. The percentage of the particle size distribution of ultrafine tungsten powder is 95.73 % between 0.1 μm and 1.0 μm.

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Wasel, Ola, e Jennifer Freeman. "Comparative Assessment of Tungsten Toxicity in the Absence or Presence of Other Metals". Toxics 6, n.º 4 (9 de novembro de 2018): 66. http://dx.doi.org/10.3390/toxics6040066.

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Tungsten is a refractory metal that is used in a wide range of applications. It was initially perceived that tungsten was immobile in the environment, supporting tungsten as an alternative for lead and uranium in munition and military applications. Recent studies report movement and detection of tungsten in soil and potable water sources, increasing the risk of human exposure. In addition, experimental research studies observed adverse health effects associated with exposure to tungsten alloys, raising concerns on tungsten toxicity with questions surrounding the safety of exposure to tungsten alone or in mixtures with other metals. Tungsten is commonly used as an alloy with nickel and cobalt in many applications to adjust hardness and thermal and electrical conductivity. This review addresses the current state of knowledge in regard to the mechanisms of toxicity of tungsten in the absence or presence of other metals with a specific focus on mixtures containing nickel and cobalt, the most common components of tungsten alloy.

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Han, Chulwoong, Hyunwoong Na, Hanshin Choi e Yonghwan Kim. "High Purity Tungsten Spherical Particle Preparation From WC-Co Spent Hard Scrap". Archives of Metallurgy and Materials 60, n.º 2 (1 de junho de 2015): 1507–9. http://dx.doi.org/10.1515/amm-2015-0162.

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Abstract Tungsten carbide-cobalt hard metal scrap was recycled to obtain high purity spherical tungsten powder by a combined hydrometallurgy and physical metallurgy pathway. Selective leaching of tungsten element from hard metal scrap occurs at solid / liquid interface and therefore enlargement of effective surface area is advantageous. Linear oxidation behavior of Tungsten carbide-cobalt and the oxidized scrap is friable to be pulverized by milling process. In this regard, isothermally oxidized Tungsten carbide-cobalt hard metal scrap was mechanically broken into particles and then tungsten trioxide particle was recovered by hydrometallurgical method. Recovered tungsten trioxide was reduced to tungsten particle in a hydrogen environment. After that, tungsten particle was melted and solidified to make a spherical one by RF (Ratio Frequency) thermal plasma process. Well spherical tungsten micro-particle was successfully obtained from spent scrap. In addition to the morphological change, thermal plasma process showed an advantage for the purification of feedstock particle.

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Sevcenco, Ana-Maria, Loes E. Bevers, Martijn W. H. Pinkse, Gerard C. Krijger, Hubert T. Wolterbeek, Peter D. E. M. Verhaert, Wilfred R. Hagen e Peter-Leon Hagedoorn. "Molybdenum Incorporation in Tungsten Aldehyde Oxidoreductase Enzymes from Pyrococcus furiosus". Journal of Bacteriology 192, n.º 16 (18 de junho de 2010): 4143–52. http://dx.doi.org/10.1128/jb.00270-10.

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ABSTRACT The hyperthermophilic archaeon Pyrococcus furiosus expresses five aldehyde oxidoreductase (AOR) enzymes, all containing a tungsto-bispterin cofactor. The growth of this organism is fully dependent on the presence of tungsten in the growth medium. Previous studies have suggested that molybdenum is not incorporated in the active site of these enzymes. Application of the radioisotope 99Mo in metal isotope native radioautography in gel electrophoresis (MIRAGE) technology to P. furiosus shows that molybdenum can in fact be incorporated in all five AOR enzymes. Mo(V) signals characteristic for molybdopterin were observed in formaldehyde oxidoreductase (FOR) in electron paramagnetic resonance (EPR)-monitored redox titrations. Our finding that the aldehyde oxidation activity of FOR and WOR5 (W-containing oxidoreductase 5) correlates only with the residual tungsten content suggests that the Mo-containing AORs are most likely inactive. An observed W/Mo antagonism is indicative of tungstate-dependent negative feedback of the expression of the tungstate/molybdate ABC transporter. An intracellular selection mechanism for tungstate and molybdate processing has to be present, since tungsten was found to be preferentially incorporated into the AORs even under conditions with comparable intracellular concentrations of tungstate and molybdate. Under the employed growth conditions of starch as the main carbon source in a rich medium, no tungsten- and/or molybdenum-associated proteins are detected in P. furiosus other than the high-affinity transporter, the proteins of the metallopterin insertion machinery, and the five W-AORs.

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Deng, Pan, Lili Cheng, Alin Li, Zhiyong Zeng e Chunfa Liao. "Recent Advances in the Utilization of Tungsten Residue: A Mini Review of China". Metals 13, n.º 8 (17 de agosto de 2023): 1481. http://dx.doi.org/10.3390/met13081481.

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As a metal of strategic value, tungsten plays an important part in civil and military applications. Currently, China is the biggest tungsten producer all over the world, and the metallic smelting technologies for tungsten are well established. However, the harmless recovery and treatment procedures for tungsten residue remain rather underdeveloped. The treatment of tungsten residue generally includes the recovery of valuable metals (e.g., scandium, tantalum, and niobium) and the solidification of toxic elements (e.g., arsenic, lead, and chromium), which may control the transfer of these elements and metals. If treated improperly, the resource of tungsten residue may be wasted, and potential environmental risks could arise. Therefore, the safe disposition of tungsten residue has become the limit factor and an urgent problem to be solved for the sustainable development of tungsten-related industries. In this regard, we reviewed the industrial background of tungsten and the composition and toxicity characteristics of tungsten residue. In addition, particular attention was paid to the harmless utilization processes and technologies for tungsten residue, which were then systematically compared in terms of the applicable situations as well as their advantages and shortcomings. Finally, the development trend for the harmless utilization of tungsten residue was discussed, and some proposals for further studies were provided.

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