Bibliografie tematiche / Tungsten

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Letteratura scientifica selezionata sul tema "Tungsten"

Autore: Grafiati
Pubblicato: 4 giugno 2021
Ultima modifica: 31 luglio 2024

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Articoli di riviste sul tema "Tungsten"

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. 1 (5 gennaio 2022): 53–61. http://dx.doi.org/10.3365/kjmm.2022.60.1.53.

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Abstract (sommario):
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. 2 (1 giugno 2015): 1311–14. http://dx.doi.org/10.1515/amm-2015-0120.

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Abstract (sommario):
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 (aprile 2011): 283–87. http://dx.doi.org/10.4028/www.scientific.net/amr.228-229.283.

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Abstract (sommario):
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 (settembre 2010): 215–19. http://dx.doi.org/10.4028/www.scientific.net/msf.659.215.

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Abstract (sommario):
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. 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 (gennaio 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 novembre 2011): 519–25. http://dx.doi.org/10.17221/345/2011-pse.

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Abstract (sommario):
  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. 2 (1 giugno 2015): 1403–5. http://dx.doi.org/10.1515/amm-2015-0141.

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Abstract (sommario):
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. 1 (19 dicembre 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. 1 (1 gennaio 2023): 141–57. http://dx.doi.org/10.3329/jsr.v15i1.58211.

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Abstract (sommario):
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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Più fonti

Tesi sul tema "Tungsten"

1

Erdogan, Metehan. "Recovery Of Tungsten From Tungsten Bearing Compounds". Phd thesis, METU, 2013. http://etd.lib.metu.edu.tr/upload/12615540/index.pdf.

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Abstract (sommario):
Extensive research in recent years has failed to develop any essentially new method of large scale tungsten production. A new tungsten powder production technique from calcium tungstate (CaWO4) has recently been reported. In this thesis, this technique was further explored from the aspects of electrochemical reduction mechanism and kinetics, applicability to scheelite concentrates and industrial production. Cyclic voltammetry, constant potential and constant current electrochemical reduction tests were performed to determine the reversible cell potential. Analyses of the experimental results revealed that at least 2.2 V was required to compensate the potentials for the accompanying cell reaction and the electrode polarizations. A cell reaction was proposed by associating the experimental results and the Gibbs Energy changes of the possible reactions. An experiment (mixture) design was created to optimize the process parameters of the electrochemical reduction of CaWO4 to W in molten CaCl2-NaCl eutectic mixture. Temperature, applied voltage and the length of Kanthal wire winding of the CaWO4 pellets were selected as the process parameters and allowed to vary between the predetermined minimum and maximum values. The rates of the electrochemical reductions were interpreted from the variations of current and total charge vs. time graphs under different conditions. The analysis pointed out 640oC and 2.81 V from the created mixture design for the fastest reduction and it was seen that the effect of Kanthal wire winding on the output current was less pronounced when compared to the other two parameters. Another set of experiments was performed by full factorial design to investigate the cleaning procedure needed to remove calcium containing byproducts after electrochemical reduction experiments. Three levels were determined prior to the experiments for the selected three parameters
temperature, acid concentration and exposure time. Main effect and interaction graphs for calcium percent as a function of process parameters were plotted. Calcium contents of the samples were determined by XRF measurements. A 300 g/day capacity tungsten production line was manufactured to take the process one step closer to industrialization. Problems at larger scale were addressed as incomplete reduction, oxidation of graphite and corrosion of cathode materials. After careful research, AISI 316 Ti steel was found to impart sufficient resistance to highly corrosive environment. Oxidation of graphite anode inside the cell was lowered to acceptable levels by continuous nitrogen flow. Metallic tungsten powder was obtained from rich and flotation concentrates of Uludag Etibank Volfram Plant (closed in 1989) together with mainly iron. It was seen that tungsten and iron do not make compounds at the temperatures used for reduction (600-750oC). A basic diffusion model in the electrolyte was developed to better understand the decrease in current values and incomplete reduction encountered during large scale production. The model was used to simulate the recorded current vs. time graphs of selected experiments.
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2

Zacharias, Marisa Aparecida [UNESP]. "Síntese, caracterização e estudos de precursores e de óxidos de molibdênio e de tungstênio". Universidade Estadual Paulista (UNESP), 2000. http://hdl.handle.net/11449/105673.

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Abstract (sommario):
Made available in DSpace on 2014-06-11T19:35:05Z (GMT). No. of bitstreams: 0 Previous issue date: 2000-02-21Bitstream added on 2014-06-13T19:44:56Z : No. of bitstreams: 1 zacharias_ma_dr_araiq.pdf: 3695623 bytes, checksum: f2762446db235d48a685f25509e7eeb2 (MD5)
O presente trabalho tem como objetivo a obtenção de óxidos de molibdênio e de tungstênio com propriedades texturais controladas, particularmente com elevadas áreas específicas. Tais óxidos serão posteriormente empregados como precursores nas sínteses de nitretos e carbetos de molibdênio e de tungstênio, materiais potencialmente promissores na decomposição catalítica da hidrazina em sistemas micropopulsivos de satélites. Sabe-se da literatura que uma rede inorgânica de óxidos pode ser proveniente de vários precursores. Visando alcançar o objetivo do trabalho proposto, procurou-se primeiramente obter os óxidos, via processo sol-gel, a partir da decomposição térmica dos alcóxidos de molibdênio e de tungstênio. No decorrer do desenvolvimento do projeto de pesquisa achou-se também conveniente testar a decomposição térmica de outros precursores. Estas novas rotas exigem as sínteses de complexos de molibdênio (VI) e de tungstênio (VI) com ácidos a-hidroxicarboxílicos, de ácidos molíbdico e túngstico e dos saia de amônio dos referidos metais. Os materiais sintetizados foram, sempre que possível, analisados por espectroscopia na região infravermelho, difração de raios X e medidas de adsorção de nitrogênio na sua temperatura de condensação. Algumas amostras foram submetidas à análise elementar para a determinação dos teores de C, N e H. Efetuou-se a decomposição térmica de todos os precursores, sendo os óxidos obtidos analisados pelas mesmas técnicas utilizadas anteriormente. Os óxidos de molibdênio apresentaram uma fase cristalina ortorrômbica, exceto em algumas amostras onde se observou além desta fase, a presença de uma pequena quantidade de material amorfo.Com relação ao óxido de molibdênio, o maior valor de área específica de um foi de 8m2/g para uma amostra proveniente da hidrólise controlada de um alcóxido metálico...
The present work hás a objective the obtaining of molibdenum and tungsten oxides with texturais controlled properties, particularly with high specific areas. Such oxides will be used later on as precursors in the nitrides and carbides synthesis of molibdenium and tungsten, materials potentially promissing in the catalytic decomposition of the hydrazine in micropopulsives system of satellites. It's known about the literature that an inorganic net of oxide can come from several precursors. Seeking to reach the objective of the proposed work, it was firstly tried to obtain the oxides through sol-gel process, starting from the thermal decomposition of the molybdenum and tungsten alcoxides. In elapsing of the development in the research project it was also convenient to test the thermal decomposition of others precursors. These new routes demand the syntheses of molibdenium(VI) and tungsten(VI) complexes with the a-hidroxycarboxylic acids, of molybdic and tungstic acids and of the ammonium salts of the referred metals.The synthesized materials were, whenever possible, analysed by spectroscopy in the infrared region, of X-rays diffraction and measures of adsorption of nitrogen in its condensation temperature. Some samples were submitted the elementary analysis for the determination of texts of C, N and H. The thermal decomposition of all precursors was made, being the obtained oxides analysed same techniques previously used. The molibdenium oxides presented crystalline orthorhombic phase, except in some samples where it was observed besides this phase, the presence of a small amount of amorphous material. With relationship to molibdenium oxide, the largest value of specific area went of 8m2/g to a coming sample of the controlled hydrolysis of a metallic alcoxide. It was also obtained of area around 8m2/g for the ocide, coming from a of molybdic acid sample... (Complete abstract, click electronic address below)
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3

Gianni, Lorenzo. "Electrodialytic recovery of tungsten and cobalt from tungsten carbide scrap". Master's thesis, Alma Mater Studiorum - Università di Bologna, 2022.

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Abstract (sommario):
Critical raw materials (CRMs) are essential for a wide range of European industrial ecosystems. Access to critical resources is necessary for Europe’s ambition to achieve climate neutrality and deliver the Green Deal. However, supply of material from primary sources is putting extreme pressure on the planet through greenhouse gas emissions, biodiversity loss and water stress. In this scenario, promoting circular economy by obtaining resources from secondary sources is therefore essential to reduce the environmental burden posed by raw material primary extraction and to secure the supply chain of CRMs. This work is a preliminary assessment on the potential of the electrodialytic (ED) treatment in alkaline condition on a tungsten carbide scrap powder obtained from end-of-life cutting tools industry for the recovery of two CRMs: Tungsten (W) and Cobalt (Co). Modular ED reactors with 2 or 3 cell compartments have been used to perform eleven ED experiments (each lasting 24 h), with either NaOH or NH4OH and at 100, 150 or 200 mA to individuate the best reactor configuration, alkaline reagent, and current intensity. The alkaline reagents were placed at different concentrations in the anode compartment (in case of 2-compartments reactor) or in the central compartment (in case of a 3-compartments reactor) along with 450 mL of deionized water and the solid matrix with a solid:liquid ratio of 1/50. Inductively coupled plasma-atomic emission spectroscopy was used to quantify the amount of W and Co obtained in solution at the end of the experiments. The experiments showed that the 2-compartments ED cell setup at 100 mA and with NaOH 0.1 M resulted in the highest W dissolution ( 651 mg), and that the 3-compartments ED cell setup at 100 mA and with NaOH 0.01 M resulted in the highest Co dissolution ( 372 mg) and electromigration (85%). Further investigation is needed to optimize the operational parameters.
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4

Ogundipe, Adebayo. "Environmental release of tungsten and other elements from tungsten heavy alloys addressing the environmental viability of tungsten heavy alloys". Saarbrücken VDM Verlag Dr. Müller, 2006. http://d-nb.info/989277992/04.

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5

Pimenta, Juliana de Oliveira [UNESP]. "Influência do tratamento térmico assistido por pressão nas propriedades óptica e elétrica do trióxido de tungstênio". Universidade Estadual Paulista (UNESP), 2015. http://hdl.handle.net/11449/138511.

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The aim of this work is to study the influence of a pressure-assisted heat treatment on the electrical and optical properties of nanoparticulate tungsten trioxide (WO3) obtained by microwave assisted hydrothermal method. The behavior of WO3 as gas sensor and its pholominescence emission were used to evaluate the electrical and optical properties, respectively. Samples were heat-treated under an air pressure of 2 MPa at 180ºC for 32 h. The oxides obtained were previously characterized by X-ray diffraction (XRD), nitrogen adsorption volumetric (BET), X-ray Photoelectron Spectroscopy (XPS), and field emission scanning electron microscopy (FEG-SEM) and micro Raman Spectroscopy. Using combined techniques, the structure, morphology, size and chemical composition of the synthetized materials were characterized in details. A comparison between samples that underwent the pressure-assisted heat treatment and samples that underwent a conventional heat treatment was established. The originality of the work is to understand how the pressure-assisted heat treatment chames the tungsten trioxide behavior without the addition of dopants. The photoluminescence emission intensity increased after the pressure treatment, and the maximum emission changed from 460 nm (blue) to 549 nm (green). The spectrum exhibited a red shift at higher wavelengths. This displacement and change in intensity can be correlated to a decrease in oxygen vacancies after the pressure-assisted heat treatment. In addition, the electrical properties were investigated as a n-type gas sensor for NO2 and H2 that are reducing and oxidizing gases, respectively. Samples became more resistive to electric current impeding the investigation of the sensing properties of the oxide under study.
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6

Pimenta, Juliana de Oliveira. "Influência do tratamento térmico assistido por pressão nas propriedades óptica e elétrica do trióxido de tungstênio /". Araraquara, 2015. http://hdl.handle.net/11449/138511.

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Abstract (sommario):
Orientador: José Arana Varela
Co-orientador: Sergio Mazurek Tebcherani
Banca: Evaldo Toniolo Kubaski
Banca: Máximo Siu Li
Banca: Sônia Maria Zanetti
Banca: Anderson André Felix
Resumo:Este trabalho é referente ao estudo investigativo da influência de um tratamento térmico assistido por pressão nas respostas de propriedade elétrica, como sensor de gás e propriedade ótica de fotoluminescência de nanopartículas de trióxido de tungstênio (WO3), obtidas por processo hidrotermal assistido com micro-ondas adaptado. As condições de tratamento foram de 180 ºC sob pressão de 2 MPa durante 32 horas. Os óxidos obtidos foram previamente caracterizados por difração de raios X (DRX), volumetria de adsorção de nitrogênio (BET), espectroscopia de fotoelétrons excitados por raios X (XPS), microscopia eletrônica de varredura por emissão de campo (FEG-SEM) e espectroscopia micro Raman. Pelas técnicas combinadas foi possível caracterizar detalhadamente os materiais sintetizados, como sua estrutura, forma, tamanho e composição química. Foi possível comparar a respostas do material quando o óxido é submetido ao tratamento térmico assistido por pressão com o óxido obtido somente com tratamento térmico convencional. A originalidade do trabalho está em compreender como o tratamento térmico assistido por pressão está alterando as respostas do trióxido de tungstênio, sem a necessidade da adição de dopantes. Quando analisado a propriedade ótica após esse tratamento com pressão, o trióxido de tungstênio apresentou um aumento na intensidade de emissão, passando da emissão de maior contribuição em 460 nm (azul) para a emissão em 549 nm (verde). O espectro ainda apresenta um deslocamento para o vermelho, em comprimentos de onda maiores. Este deslocamento e mudança na intensidade podem estar correlacionados a diminuição de vacâncias de oxigênio após o tratamento térmico assistido por pressão. Também foram estudadas as propriedades elétricas como sensor de gás do tipo-n para gases redutores e oxidantes (H2 e NO2, respectivamente). As amostras tratadas...
Abstract: The aim of this work is to study the influence of a pressure-assisted heat treatment on the electrical and optical properties of nanoparticulate tungsten trioxide (WO3) obtained by microwave assisted hydrothermal method. The behavior of WO3 as gas sensor and its pholominescence emission were used to evaluate the electrical and optical properties, respectively. Samples were heat-treated under an air pressure of 2 MPa at 180ºC for 32 h. The oxides obtained were previously characterized by X-ray diffraction (XRD), nitrogen adsorption volumetric (BET), X-ray Photoelectron Spectroscopy (XPS), and field emission scanning electron microscopy (FEG-SEM) and micro Raman Spectroscopy. Using combined techniques, the structure, morphology, size and chemical composition of the synthetized materials were characterized in details. A comparison between samples that underwent the pressure-assisted heat treatment and samples that underwent a conventional heat treatment was established. The originality of the work is to understand how the pressure-assisted heat treatment chames the tungsten trioxide behavior without the addition of dopants. The photoluminescence emission intensity increased after the pressure treatment, and the maximum emission changed from 460 nm (blue) to 549 nm (green). The spectrum exhibited a red shift at higher wavelengths. This displacement and change in intensity can be correlated to a decrease in oxygen vacancies after the pressure-assisted heat treatment. In addition, the electrical properties were investigated as a n-type gas sensor for NO2 and H2 that are reducing and oxidizing gases, respectively. Samples became more resistive to electric current impeding the investigation of the sensing properties of the oxide under study.
Doutor
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7

Zacharias, Marisa Aparecida. "Síntese, caracterização e estudos de precursores e de óxidos de molibdênio e de tungstênio /". Araraquara : [s.n.], 2000. http://hdl.handle.net/11449/105673.

Testo completo
Abstract (sommario):
Resumo: O presente trabalho tem como objetivo a obtenção de óxidos de molibdênio e de tungstênio com propriedades texturais controladas, particularmente com elevadas áreas específicas. Tais óxidos serão posteriormente empregados como precursores nas sínteses de nitretos e carbetos de molibdênio e de tungstênio, materiais potencialmente promissores na decomposição catalítica da hidrazina em sistemas micropopulsivos de satélites. Sabe-se da literatura que uma rede inorgânica de óxidos pode ser proveniente de vários precursores. Visando alcançar o objetivo do trabalho proposto, procurou-se primeiramente obter os óxidos, via processo sol-gel, a partir da decomposição térmica dos alcóxidos de molibdênio e de tungstênio. No decorrer do desenvolvimento do projeto de pesquisa achou-se também conveniente testar a decomposição térmica de outros precursores. Estas novas rotas exigem as sínteses de complexos de molibdênio (VI) e de tungstênio (VI) com ácidos a-hidroxicarboxílicos, de ácidos molíbdico e túngstico e dos saia de amônio dos referidos metais. Os materiais sintetizados foram, sempre que possível, analisados por espectroscopia na região infravermelho, difração de raios X e medidas de adsorção de nitrogênio na sua temperatura de condensação. Algumas amostras foram submetidas à análise elementar para a determinação dos teores de C, N e H. Efetuou-se a decomposição térmica de todos os precursores, sendo os óxidos obtidos analisados pelas mesmas técnicas utilizadas anteriormente. Os óxidos de molibdênio apresentaram uma fase cristalina ortorrômbica, exceto em algumas amostras onde se observou além desta fase, a presença de uma pequena quantidade de material amorfo.Com relação ao óxido de molibdênio, o maior valor de área específica de um foi de 8m2/g para uma amostra proveniente da hidrólise controlada de um alcóxido metálico... (Resumo completo, clicar acesso eletrônico abaixo)
Abstract: The present work hás a objective the obtaining of molibdenum and tungsten oxides with texturais controlled properties, particularly with high specific areas. Such oxides will be used later on as precursors in the nitrides and carbides synthesis of molibdenium and tungsten, materials potentially promissing in the catalytic decomposition of the hydrazine in micropopulsives system of satellites. It's known about the literature that an inorganic net of oxide can come from several precursors. Seeking to reach the objective of the proposed work, it was firstly tried to obtain the oxides through sol-gel process, starting from the thermal decomposition of the molybdenum and tungsten alcoxides. In elapsing of the development in the research project it was also convenient to test the thermal decomposition of others precursors. These new routes demand the syntheses of molibdenium(VI) and tungsten(VI) complexes with the a-hidroxycarboxylic acids, of molybdic and tungstic acids and of the ammonium salts of the referred metals.The synthesized materials were, whenever possible, analysed by spectroscopy in the infrared region, of X-rays diffraction and measures of adsorption of nitrogen in its condensation temperature. Some samples were submitted the elementary analysis for the determination of texts of C, N and H. The thermal decomposition of all precursors was made, being the obtained oxides analysed same techniques previously used. The molibdenium oxides presented crystalline orthorhombic phase, except in some samples where it was observed besides this phase, the presence of a small amount of amorphous material. With relationship to molibdenium oxide, the largest value of specific area went of 8m2/g to a coming sample of the controlled hydrolysis of a metallic alcoxide. It was also obtained of area around 8m2/g for the ocide, coming from a of molybdic acid sample... (Complete abstract, click electronic address below)
Orientador: Antonio Carlos Massabni
Coorientador: Sandra Helena Pulcinelli
Banca: Elizabeth Berwerth Stucchi
Banca: Carlos de Oliveira Paiva Santos
Banca: José Augusto Jorge Rodrigues
Banca: Ariovaldo de Oliveira Florentino
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Björklund, Kajsa. "Microfabrication of Tungsten, Molybdenum and Tungsten Carbide Rods by Laser-Assisted CVD". Doctoral thesis, Uppsala University, Department of Materials Chemistry, 2001. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-1593.

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Abstract (sommario):

Thin films of refractory metals and carbides have been studied extensively over many years because of their wide range of application. The two major techniques used are Chemical Vapour Deposition (CVD) and Physical Vapour Deposition (PVD). These can result in the deposition of two-dimensional blanket or patterned thin films. Laser-assisted Chemical Vapour Deposition (LCVD) can provide a maskless alternative for localised deposition in two and three dimensions. This thesis describes LCVD of micrometer-sized tungsten, molybdenum and tungsten carbide rods. The kinetics, phase composition and microstructure have been studied as a function of in situ measured laser induced deposition temperature.

Tungsten and molybdenum rods were deposited by hydrogen reduction of their corresponding hexafluorides, WF6 and MoF6, respectively. Single crystal and polycrystalline tungsten rods were obtained, depending on the H2/WF6 molar ratio and deposition temperature. The molybdenum rods were either single crystals or dendritic in form depending on experimental conditions. The field emission characteristics of the tungsten single crystals were investigated. The results showed LCVD to be a potential fabrication technique for field emitting cathodes.

Nanocrystalline tungsten carbide rods were deposited from WF6, C2H4 and H2. TEM analysis showed that the carbide rods exhibited a layered structure in terms of phase composition and grain size as a result of the temperature gradient induced by the laser beam. With decreasing WF6/C2H4 molar ratio, the carbon content in the rods increased and the phase composition changed from W/W2C to WC/WC1-x and finally to WC1-x/C.

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Björklund, Kajsa. "Microfabrication of tungsten, molybdenum and tungsten carbide rods by laser-assisted CVD /". Uppsala : Acta Universitatis Upsaliensis : Univ.-bibl. [distributör], 2001. http://publications.uu.se/theses/91-554-5197-7/.

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Williams, Paul Andrew. "The synthesis of novel tungsten precursors for the CVD of tungsten oxide". Thesis, University of Bath, 2000. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.323568.

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Libri sul tema "Tungsten"

1

Lassner, Erik, e Wolf-Dieter Schubert. Tungsten. Boston, MA: Springer US, 1999. http://dx.doi.org/10.1007/978-1-4615-4907-9.

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Smith, Gerald R. Tungsten. Washington, D.C: U.S. Department of the Interior, Bureau of Mines, 1991.

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United States. Agency for Toxic Substances and Disease Registry. Division of Toxicology. Tungsten. Atlanta, GA: Dept. of Health and Human Services, Public Health Service, Agency for Toxic Substances and Disease Registry, Division of Toxicology, 2005.

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International Conference on Tungsten and Tungsten Alloys (1st 1992 Arlington, Va.). Tungsten & tungsten alloys, 1992: Proceedings of the First International Conference on Tungsten and Tungsten Alloys. Princeton, N.J: The Federation, 1993.

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Czack, Gerhard, Gerhard Kirschstein, Wolfgang Kurtz e Frank Stein. W Tungsten. A cura di Wolfgang Huisl, Wolfgang Kurtz e Frank Stein. Berlin, Heidelberg: Springer Berlin Heidelberg, 1993. http://dx.doi.org/10.1007/978-3-662-10154-4.

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Jehn, Hermann, Schwäbisch Gmünd, Gudrun Bär, Erich Best e Ernst Koch. W Tungsten. A cura di Jörn von Jouanne, Elisabeth Koch e Ernst Koch. Berlin, Heidelberg: Springer Berlin Heidelberg, 1993. http://dx.doi.org/10.1007/978-3-662-08684-1.

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Best, Erich, Peter Kuhn, Wolfgang Kurtz e Hildegard List. W Tungsten. A cura di Hartmut Bergmann, Dieter Gras, Ingeborg Hinz, Ernst Koch, Wolfgang Kurtz e Ursula Vetter. Berlin, Heidelberg: Springer Berlin Heidelberg, 1986. http://dx.doi.org/10.1007/978-3-662-08687-2.

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Kurtz, Wolfgang, e Hans Vanecek. W Tungsten. A cura di Ernst Koch e Wolfgang Kurtz. Berlin, Heidelberg: Springer Berlin Heidelberg, 1987. http://dx.doi.org/10.1007/978-3-662-08690-2.

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Kurlov, Alexey S., e Aleksandr I. Gusev. Tungsten Carbides. Cham: Springer International Publishing, 2013. http://dx.doi.org/10.1007/978-3-319-00524-9.

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Vallejo, César. Tungsten: A novel. Syracuse, N.Y: Syracuse University Press, 1988.

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Capitoli di libri sul tema "Tungsten"

1

Lassner, Erik, e Wolf-Dieter Schubert. "The Element Tungsten". In Tungsten, 1–59. Boston, MA: Springer US, 1999. http://dx.doi.org/10.1007/978-1-4615-4907-9_1.

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Lassner, Erik, e Wolf-Dieter Schubert. "Tungsten in Catalysis". In Tungsten, 365–75. Boston, MA: Springer US, 1999. http://dx.doi.org/10.1007/978-1-4615-4907-9_10.

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Lassner, Erik, e Wolf-Dieter Schubert. "Tungsten Scrap Recycling". In Tungsten, 377–85. Boston, MA: Springer US, 1999. http://dx.doi.org/10.1007/978-1-4615-4907-9_11.

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Lassner, Erik, e Wolf-Dieter Schubert. "Ecology". In Tungsten, 387–94. Boston, MA: Springer US, 1999. http://dx.doi.org/10.1007/978-1-4615-4907-9_12.

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Lassner, Erik, e Wolf-Dieter Schubert. "Economy". In Tungsten, 395–407. Boston, MA: Springer US, 1999. http://dx.doi.org/10.1007/978-1-4615-4907-9_13.

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Lassner, Erik, e Wolf-Dieter Schubert. "Tungsten and Living Organisms". In Tungsten, 409–16. Boston, MA: Springer US, 1999. http://dx.doi.org/10.1007/978-1-4615-4907-9_14.

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Lassner, Erik, e Wolf-Dieter Schubert. "Tungsten History". In Tungsten, 61–84. Boston, MA: Springer US, 1999. http://dx.doi.org/10.1007/978-1-4615-4907-9_2.

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Lassner, Erik, e Wolf-Dieter Schubert. "Important Aspects of Tungsten Chemistry". In Tungsten, 85–132. Boston, MA: Springer US, 1999. http://dx.doi.org/10.1007/978-1-4615-4907-9_3.

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Lassner, Erik, e Wolf-Dieter Schubert. "Tungsten Compounds and Their Application". In Tungsten, 133–77. Boston, MA: Springer US, 1999. http://dx.doi.org/10.1007/978-1-4615-4907-9_4.

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Lassner, Erik, e Wolf-Dieter Schubert. "Industrial Production". In Tungsten, 179–253. Boston, MA: Springer US, 1999. http://dx.doi.org/10.1007/978-1-4615-4907-9_5.

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Atti di convegni sul tema "Tungsten"

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Kobayashi, Nobuyoshi, Masayuki Suzuki e Masayoshi Saitou. "Tungsten Plug Technology: Substituting Tungsten for Silicon Using Tungsten Hexaflouride". In 1988 International Conference on Solid State Devices and Materials. The Japan Society of Applied Physics, 1988. http://dx.doi.org/10.7567/ssdm.1988.a-5-3.

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Creighton, J. R. "Non-selective tungsten chemical-vapor deposition using Tungsten hexacarbonyl". In AIP Conference Proceedings Vol. 167. AIP, 1988. http://dx.doi.org/10.1063/1.37175.

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MATĚJÍČEK, Jiří, Jakub KLEČKA, Jan CIZEK, Jakub VEVERKA, Monika VILÉMOVÁ, Tomáš CHRÁSKA e Vishnu GANESH. "Tungsten-steel and tungsten-chromium composites prepared by RF plasma spraying". In METAL 2020. TANGER Ltd., 2020. http://dx.doi.org/10.37904/metal.2020.3548.

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Mittelstadt, Chad R. "Silver Tungsten vs Silver Tungsten Carbide Contact Performance in Environmental Testing". In 2012 IEEE 58th Holm Conference on Electrical Contacts (Holm 2012). IEEE, 2012. http://dx.doi.org/10.1109/holm.2012.6336600.

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Avotina, Liga, Lada Bumbure, Annija Elizabete Goldmane, Edgars Vanags, Marina Romanova, Hermanis Sorokins, Aleksandrs Zaslavskis, Gunta Kizane e Yuri Dekhtyar. "Thermal behaviour of magnetron sputtered tungsten and tungsten-boride thin films". In 2022 International Conference on Applied Electronics (AE). IEEE, 2022. http://dx.doi.org/10.1109/ae54730.2022.9920033.

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Rana, Ahsan Sarwar, Taimoor Naeem, Muhammad Zubair e Muhammad Qasim Mehmood. "Tungsten based optical absorber". In 2020 17th International Bhurban Conference on Applied Sciences and Technology (IBCAST). IEEE, 2020. http://dx.doi.org/10.1109/ibcast47879.2020.9044598.

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Rana, Ahsan Sarwar, Muhammad Qasim Mehmood, Heongyeong Jeong, Inki Kim e Junsuk Rho. "Ultra-Broadband Tungsten Absorber". In 2018 Progress in Electromagnetics Research Symposium (PIERS-Toyama). IEEE, 2018. http://dx.doi.org/10.23919/piers.2018.8597930.

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Ye, Yu, Zi Jing Wong, Xiufang Lu, Hanyu Zhu, Yuan Wang, Xianhui Chen e Xiang Zhang. "Monolayer Tungsten Disulfide Laser". In CLEO: Science and Innovations. Washington, D.C.: OSA, 2015. http://dx.doi.org/10.1364/cleo_si.2015.sm2f.7.

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Hirata, G. A., O. Contreras, M. H. Farías e L. Cota-Araiza. "Stoichiometric tungsten carbide coatings". In The 8th Latin American congress on surface science: Surfaces , vacuum, and their applications. AIP, 1996. http://dx.doi.org/10.1063/1.51119.

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Ives, Lawrence, George Miram, Lou Falce, Kim Gunther, Marc Curtis, Steve Schwartzkopf e Ron Witherspoon. "Sintered Tungsten Wire Cathodes". In 2007 IEEE International Vacuum Electronics Conference. IEEE, 2007. http://dx.doi.org/10.1109/ivelec.2007.4283272.

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Rapporti di organizzazioni sul tema "Tungsten"

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Dawson, K. M. Skarn tungsten. Natural Resources Canada/ESS/Scientific and Technical Publishing Services, 1995. http://dx.doi.org/10.4095/208024.

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Hatfield, Kendrich, Michael McBride e Donald Johnson. Tungsten Electrodeposition. Office of Scientific and Technical Information (OSTI), ottobre 2023. http://dx.doi.org/10.2172/2008256.

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Wohletz, K., T. Kunkle e W. Hawkins. KISMET tungsten dispersal experiment. Office of Scientific and Technical Information (OSTI), dicembre 1996. http://dx.doi.org/10.2172/432871.

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Sinclair, W. D. Vein-stockwork tin, tungsten. Natural Resources Canada/ESS/Scientific and Technical Publishing Services, 1995. http://dx.doi.org/10.4095/208012.

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Brau, James E. Silicon-tungsten Electromagnetic Calorimetry. Office of Scientific and Technical Information (OSTI), marzo 2018. http://dx.doi.org/10.2172/1426488.

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Hughes, A. Australian resource reviews: tungsten 2019. Geoscience Australia, 2020. http://dx.doi.org/10.11636/9781925848731.

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Joel B. Christian e Sean P. E. Smith. Tungsten Cathode Catalyst for PEMFC. Office of Scientific and Technical Information (OSTI), settembre 2006. http://dx.doi.org/10.2172/891991.

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Boyle, Timothy J., Ryan Falcone Hess, Michael Luke Neville e Panit Clifton Howard. Scandium separation from tungsten crucibles :. Office of Scientific and Technical Information (OSTI), febbraio 2013. http://dx.doi.org/10.2172/1088104.

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Dandekar, Dattatraya P. Spall Strength of Tungsten Carbide. Fort Belvoir, VA: Defense Technical Information Center, settembre 2004. http://dx.doi.org/10.21236/ada427318.

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Dannemann, Kathryn, e James Walker. Evaluation of Tungsten Alloy Rods. Fort Belvoir, VA: Defense Technical Information Center, maggio 2000. http://dx.doi.org/10.21236/ada415228.

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