Dissertationen zum Thema „Tungsten“
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1
Erdogan, Metehan. „Recovery Of Tungsten From Tungsten Bearing Compounds“. Phd thesis, METU, 2013. http://etd.lib.metu.edu.tr/upload/12615540/index.pdf.
Annotation:
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 parameterstemperature, 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.
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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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)
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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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.
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.
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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000863481.pdf: 2321316 bytes, checksum: aa11a4318131811b9ac2636856e02252 (MD5)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.
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.
Annotation:
Orientador: José Arana VarelaCo-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
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.
Annotation:
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
Doutor
8
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.
Annotation:
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.
9
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/.
10
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.
11
Poon, Michael. „Deuterium retention in tungsten“. Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape11/PQDD_0008/MQ40899.pdf.
12
Stewart, Lisa Joanne. „Tungsten-substituted DMSO reductase“. Thesis, University of Nottingham, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.368244.
13
Selcuk, Cem. „Reactive sintering of tungsten“. Thesis, University of Nottingham, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.405300.
14
Laine, A. D. „Inverse photoemission of tungsten“. Thesis, University of Liverpool, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.380177.
15
Christian, Joel B. „Tungsten fuel cell catalysts“. Diss., Online access via UMI:, 2007.
16
Wilder, Corey B. „Study of tungsten(IV) and tungsten(VI) imido complexes synthesis, structural analysis, and reactivity /“. [Gainesville, Fla.] : University of Florida, 2005. http://purl.fcla.edu/fcla/etd/UFE0011630.
17
Buzi, Luxherta. „Influence of the Particle Flux on Surface Modifications of Tungsten“. Thesis, Université de Lorraine, 2015. http://www.theses.fr/2015LORR0117/document.
Annotation:
Le tungstène est le matériau choisi pour le divertor d'ITER en raison de ses propriétés thermiques et physiques. Les densités de flux et les énergies des particules, et la température de surface pourront varier de plusieurs ordres de grandeur le long de la surface du divertor, soit respectivement 1020-1024 m2s-1, 0.1-100 eV, et 370-1370K. Exposé à de telles conditions, le tungstène peut subir de l'érosion, des fissurations et d'autres modifications de surface affectant ses propriétés thermomécaniques. Une autre préoccupation est la rétention des atomes de tritium implantés dans la surface et leur diffusion dans l'épaisseur du matériau. Nombre d'études ont porté sur la rétention et les modifications de surface induite par le plasma, mais se concentraient principalement sur l'effet de l'énergie des ions, leur fluence et la température de surface, mais très peu portaient sur l'influence du flux de plasma, avec des résultats erratiques et peu cohérents entre eux. L'objectif de cette thèse est de fournir une image cohérente du comportement du tungstène exposé à des conditions pertinentes pour les futurs réacteurs de fusion. Une investigation systématique évaluant l'impact de la densité de flux de plasma et de la température de l'exposition sur les modifications de surface et l'accumulation d'hydrogène dans tungstène a été effectuée au moyen d'expériences menées dans les dispositifs plasma linéaires, PSI-2 à Jülich, Pilot-PSI et Magnum-PSI à DIFFER, et PISCES-A à UCSD. La corrélation entre densité de flux de particules, température d'exposition, modifications de surface et rétention de l'hydrogène dans le tungstène a été étudiée pour différentes microstructures de matériau. Des échantillons de trois types de tungstène poly-cristallin (traité thermiquement à 1273 et 2273 K) et monocristallin (orientation 110) ont été exposés à des plasmas de deutérium et des températures de surface de 530 à 1170 K à deux gammes différentes de flux d'ions deutérium (~1022 et ~1024 m2s-1). Toutes les expositions ont été effectuées à la même énergie d'ions incidents de 40 eV et une fluence de particules de 1026 m2. Les échantillons ont été analysés post mortem en utilisant diverses techniques d'imagerie et d'analyse de surface (microscopie, spectroscopie de désorption thermique (TDS) et analyse par faisceau d'ions). L'augmentation du flux de particules de deux ordres de grandeur a provoqué la formation de bulles au-dessus de 700 K, températures pour lesquelles elles sont généralement absentes à faible flux. De petites cloques de respectivement quelques dizaines de nm et jusqu'à une taille latérale de 1 micron ont été détectées sur des échantillons de tungstène poly-cristallin recuit et monocristallin. Au contraire, les cloques sont absentes sur les échantillons recristallisés, sauf à faible flux et basse température où des vésicules d'environ 10 micron et des cavités sont apparues le long des joints de grains. La rétention totale de deutérium a été mesurée par TDS. A faible température d'exposition la fraction retenue était un à deux ordres de grandeur plus élevée après l'exposition à faible flux qu'à haut flux. Au contraire, une tendance opposée de la rétention totale à des températures d'exposition élevées a été observée. Par conséquent, le maximum de la rétention de deutérium totale a été observé pour une température supérieure dans le cas du flux incident de particules élevée (~850 K) comparée à l'exposition de faible flux (~650 K). Globalement les résultats sur la rétention de deutérium étaient similaires pour toutes les microstructures de tungstène étudiées. La rétention diminue à haute température et son maximum est plus bas pour des expositions à haut flux. Or, en raison du décalage de la rétention maximale vers des températures plus élevées, la quantité de deutérium piégée pour des températures supérieures à 800 K était plus élevée à haut flux qu'à faible flux, soit ~ un ordre de grandeur inférieur à la rétention maximum à faible fluxTungsten is the selected material to be used in the ITER divertor due to its favorable thermal and physical properties. Particle flux densities and energies, and surface temperature will vary by several orders of magnitude along the divertor surface, with values in the range 1020-1024 m2s-1, 0.1-100 eV and 370-1370 K, respectively. Exposed to such conditions, tungsten may undergo erosion, cracking and other surface modifications affecting its thermal and mechanical properties. Another concern is the retention of implanted radioactive fuel atoms (tritium) in the material surface and their diffusion through the bulk. A considerable amount of studies have addressed retention and plasma induced surface modifications, focusing mainly on the effect of ion energy, ion fluence and surface temperature while very little knowledge exists on the influence of the plasma flux. These results are largely scattered and occasionally bear a lack of consistency. The aim of this thesis is to provide a coherent picture of the behavior of tungsten exposed to plasma conditions relevant for future fusion reactors. A systematic investigation assessing the impact of the plasma flux density and exposure temperature on surface modifications and hydrogen accumulation in tungsten was performed by means of experiments carried out in the linear plasma devices PSI2 at Forschungszentrum Juelich, Pilot-PSI and Magnum-PSI at DIFFER, and PISCES-A at UCSD. The correlation between the particle flux density, exposure temperature, surface modifications and hydrogen retention in tungsten was investigated for different material microstructures. Three types of polycrystalline tungsten (thermally treated at 1273 and 2273 K) and single crystal tungsten samples (110 crystal orientation) were exposed to deuterium plasmas at surface temperatures of 530-1170 K to two different ranges of deuterium ion fluxes (low and high flux: ~1022 and ~1024 m2s-1). All the exposures were performed at the same incident ion energy of 40 eV and particle fluence of ~1026 m2. The exposed samples were analyzed postmortem utilizing various surface imaging and analyses techniques (microscopy, thermal desorption spectroscopy and ion beam analysis). Increasing the particle flux by two orders of magnitude caused blister formation at temperatures above 700 K for which blistering is usually absent under low flux exposure conditions. Small blisters of several tens of nanometers and up to 1 micrometer of lateral size were detected on the annealed polycrystalline and in single crystal tungsten samples, respectively. On the contrary, blisters were absent on the recrystallized samples except for the low flux and low temperature case where large blisters of about 10 micrometer and cavities along the grain boundaries appeared. The total deuterium retention was measured by means of thermal desorption spectroscopy (TDS). In the cases with low exposure temperatures, the retained fraction of deuterium was one to two orders of magnitude higher after exposure to the low flux compared to the high flux. On the contrary, an opposite tendency of the total deuterium retention at high exposure temperatures was observed. Hence, the maximum of the total deuterium retention was observed to occur at a higher temperature in the case of high incident particle flux (~850 K) compared to low flux exposures (~650 K). Overall, experimental results on deuterium retention were similar for all the investigated tungsten microstructures. Deuterium retention decreased at high temperatures and the maximal retention was lower for high flux exposures. However, due to the shift of the maximal retention to higher temperatures, the amount of deuterium retained at temperatures above 800 K was higher at high flux rather than at low flux, being still about one order of magnitude lower than the maximal retention at low flux
18
Martin, Jeffrey Thomas. „Organometallic nitrosyl hydrides of tungsten“. Thesis, University of British Columbia, 1987. http://hdl.handle.net/2429/27449.
Annotation:
Although hydrides of metal carbonyls are widely known, the number of hydrides in the related family of metal nitrosyls is extremely small. The preparation of a series of nitrosyl hydrides from the treatment of [CpW(NO)I₂]₂ (Cp=ƞ⁵-C₅H₅) with Na[H₂Al(OCH₂CH₂OCH₃)₂] is described. The addition of one or two equivalents of the aluminum reagent results in the formation of [CpW(NO)IH]₂ or [CpW(NO)H₂]₂ respectively. The reaction of [CpW(NO)IH]₂ with a Lewis base (L=P(OPh)₃, P(OMe)₃, PPh₃ or PMe₃) gives the monometallic CpW(NO)IHL, while [CpW(NO)H₂]₂ reacts with P(OPh)₃ or P(OMe)₃ to yield [CpW(NO)HL]₂ which undergoes further reaction to give CpW(NO)H₂L. Proton NMR spectroscopy shows that all bimetallic species contain bridging hydride ligands and are therefore best, formulated as [CpW(NO)1]₂(µ-H)₂, [CpW(NO)H]₂(µ-H)₂ and [CpW(NO)L]₂(µ-H)₂.
The ¹H NMR spectrum of [CpW(NO)H]₂(µ-H)₂ shows that there is
no hydride ligand exchange on the NMR time scale and that
¹jH(terminal)W ≃ ¹jH(bridging)w > ²jHW. From this finding, it is
possible to develop new criteria for assessing the static or fluxional nature of hydride ligands for several families of organotungsten hydrides (Cp₂W, CpW(CO)₃, W(CO)₃ and CpW(NO)x (x=l or 2)). Within each family, the magnitude of ¹JHW strongly reflects the type of metal hydride bonding, i.e.
[Formula Omitted]
and suggests that bridge bonding involves all the atoms in the
bridge and therefore the "fused" notation is introduced.
Treatment of CpW(NO)(CH₂SiMe₃)₂ with low pressures of H₂
(60-80 psig) in the presence of Lewis bases (L=P(0Ph)₃, PMePh₂)
gives the unusually stable alkyl hydride compounds
CpW(NO)(H)(CH₂SiMe₃)L. This chemistry is then extended to the Cp* (Cp*=ƞ⁵ -C₅Me₅) analogues, including the preparation of the
appropriate starting materials. Upon thermolysis of
Cp*W(NO)(H)(CH₂SiMe₃)(PMe₃) in C₆H₆, the intermolecular C-H
activation product Cp*W(N0)(H)(C₆H₅)(PMe₃) is cleanly formed.
However, intermolecular activation of CH₄, C₆H₁₂ or n-C₆H₁₄ does
not occur under similar experimental conditions.
Hydrogenolysis of Cp*W(NO)(CH₂SiMe₃)₂ at high pressures (≃920 psig) with no Lewis base present results in the formation of isolable [Cp*W(NO)H]₂(µ-H)₂ and
[Cp*W(N0)H](µ-H)₂[Cp*W(N0)(CH₂SiMe₃)]. The latter is a new example of the rare class of dinuclear alkyl hydride complexes. Proton NMR spin tickling experiments on this compound allow the complete assignment of all couplings in the spectrum and show
that ¹jH(terminal)W' ¹JH(bridging)W and ²jHW have the same sign.Science, Faculty of
Chemistry, Department of
Graduate
19
Segar, Richard William Moore. „Activated tungsten inert gas welding“. Thesis, University of Cambridge, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.621314.
20
Li, F. X. „Chemical vapour deposition of tungsten and tungsten silicide layers for applications in novel silicon technology“. Thesis, Queen's University Belfast, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.269129.
21
Verbrugghe, Nathalie. „Lithographie optique, dépôts de films minces de tungstène et trioxyde de tungstène dédiés aux capteurs de gaz semiconducteurs“. Thesis, Littoral, 2019. http://www.theses.fr/2019DUNK0527/document.
Annotation:
Porté par les préoccupations actuelles en matière de sécurité et de qualité environnementale ainsi que par les efforts de recherche entrepris dans ce domaine, le marché mondial des capteurs de gaz est en pleine expansion. Dans le contexte de la commercialisation d'un capteur de gaz, une phase d'amélioration de ses performances, et notamment de sa sensibilité et de sa stabilité, est naturellement nécessaire. Cependant, il s'avère également pertinent d'envisager d'en diminuer le coût de fabrication. Pour cela, il convient de développer une technologie utilisant d'une part des matériaux bas coût et d'autre part permettant de réduire la consommation électrique du dispositif. Dans cette optique, ce travail de thèse a porté sur la réalisation et la caractérisation d'un capteur de gaz oxyde semi-conducteur entièrement basé sur le tungstène et le trioxyde de tungstène pour la détection d'hydrogène sulfuré en milieu industriel. Le principal onjectif était de fabriquer un capteur faible coût en utilisant des techniques d'élaboration simples et des matériaux peu onéreux. Pour cela, notre travail a consisté, dans un premier temps, à développer un élément chauffant en tungstène pouvant fonctionner jusqu'à 500°C. Les procédés mis au point pour la conception de l'élément chauffant ont été utilisés dans l'élaboration des électrodes permettant de mesurer la résistance électrique du film de trioxyde de tungstène. Ensuite, nous avons travaillé sur l'optimisation du procédé de pulvérisation cathodique radio fréquence pour l'élaboration de l'élément sensible en trioxyde de tungstène. Des essais sous gaz ont montré des résultats prometteurs pour la détection d'hydrogène, de dioxyde d'azote et d'ammoniacDriven by current safety and environmental quality concerns and research efforts in this area, the global market for gas sensors is expanding rapidly. In the context of the marketing of a gas sensor, a phase of improvement in its performance, and in particular its sensitivity and stability, is naturally necessary. However, it is also relevant to consider reducing the cost of manufacturing. To achieve this, it is necessary to develop a technology that uses low-cost materials and reduces the device's power consumption. In this perspective, this thesis work focused on the realization and characterization of a semiconductor oxide gas sensor entirely based on tungsten and tungsten trioxide for the detection of hydrogen sulfide in an industrial environment. The main objective was to manufacturate a low-cost sensor using simple processing techniques and low-cost materials. To achieve this, our work initially consisted in developing a tungsten heating element that can operate up to 500°C. The processes developed for the conception of the heating element were used in the development of the electrodes for measuring the electrical resistance of the tungsten trioxide film. Then, we worked on the optimization of the radio frequency sputtering process for the development of the tungsten trioxide sensing element. Gas measurements have shown promising results for the detection of hydrogen sulfide, nitrogen dioxide and ammonia
22
Dyson, Glynn. „The low-temperature chemical vapour deposition of tungsten carbide coatings utilising the pyrolysis of tungsten hexacarbonyl“. Thesis, Loughborough University, 1998. https://dspace.lboro.ac.uk/2134/33243.
Annotation:
A detailed study has been made of the atmospheric pressure chemical vapour deposition (CVD) of tungsten carbide coatings onto powder metallurgy (PM) BT42 grade high speed steel (HSS) indexable cutting tool inserts. The pyrolysis of tungsten hexacarbonyl (W(CO)6) deposition route was utilised in conjunction with a laboratory-scale hot-wall CVD reactor. After numerous coating runs, deposition conditions were established under which rudimentary tungsten carbide coatings could be deposited at 350°C. The characteristics of these coatings were determined using an established characterisation procedure. This involved the following techniques: X-ray diffraction, ball cratering, Auger electron spectroscopy (AES), optical microscopy, fractography/scanning electron microscopy (SEM), profilometry, scratch adhesion testing and micro-indentation hardness testing.
23
Donati, George Luís. „Trends in tungsten coil atomic spectrometry“. Winston-Salem, NC : Wake Forest University, 2010. http://dspace.zsr.wfu.edu/jspui/handle/10339/73044.
24
Wahlberg, Sverker. „Nanostructured Tungsten Materials by Chemical Methods“. Licentiate thesis, KTH, Funktionella material, FNM, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-42702.
Annotation:
Tungsten based-materials are used in many different technical fields, particularly in applications requiring good temperature and/or erosion resistance. Nanostructuring of tungsten alloys and composites has the potential to dramatically improve the materials’ properties, enhancing the performance in present applications or enabling totally new possibilities. Nanostructured WC-Co composites have been the focus of researchers and industries for over two decades. New methods for powder fabrication and powder consolidation have been developed. However, the fabrication of true nanograined WC-Co materials is still a challenge. Nanostructured tungsten composites for applications as plasma facing materials in fusion reactors have in recent years attracted a growing interest. This Thesis summarizes work on the development of chemical methods for the fabrication of two different types of nanostructured tungsten based materials; WC-Co materials mainly aimed at cutting tools applications and W-ODS composites with rare earth oxide particles, intended as plasma facing materials in future fusion reactors. The approach has been to prepare powders in two steps: a) synthesis of uniform powder precursors containing ions of tungsten and the doping elements by co-precipitation from aqueous solutions, and b) further processing of the precursors into W or WC based nano-composite powders. Highly homogenous W and Co containing powder precursors for WC-Co composites were prepared via two different routes. Keggin-based precursors ((NH4)8[H2Co2W11O40]) with agglomerates of sizes up to 50 μm, were made from sodium tungstate or ammonium metatungstate and cobalt acetate. The powder composition corresponded to 5.2 % Co in the final WC-Co composites. In a second approach, paratungstate-based precursors (Cox(NH4)10-2x[H2W12O42]) were prepared from ammonium paratungstate (APT) and cobalt hydroxide with different compositions corresponding to 3.7 to 9.7 % Co in WC-Co. These particles had a plate-like morphology with sides of 5-20 μm and a thickness of less than 1 μm. Both precursors were processed and sintered into highly uniform microstructures with fine scale (<1μm). The processing of paratungstate-based precursors was also further investigated. Nanostructured WC-Co powders with grains size of less than 50 nm by decreasing processing temperatures and by applying gas phase carburization. W-ODS materials were fabricated starting from ammonium paratungstate and rare earth elements (Y or La). Paratungstate-based precursors were prepared with different homogeneity and particle sizes. The degree of the chemical uniformity varied with the particle size from ca 1 to 30 μm. Tungsten trioxide hydrate-based precursors made from APT and yttrium nitrate under acidic conditions had dramatically higher homogeneity and smaller particle size. The crystallite size was decreased to a few nanometers. These precursors were further processed to composite nanopowder and sintered to a nanostructured W-1.2%Y2O3 composite with 88% relative density. In summary, APT can be converted to highly homogenous powder precursors of different compositions. The transformations are carried out in aqueous suspensions as a solvent mediated process, in which the starting material dissolves and the precursor precipitates. Powders with fine scale morphologies are obtained, e.g. plate-like particles with thickness less than 1 μm or spherical particles with size of a few nanometers. These precursors were processed further in to nano-sized composite powders and sintered to highly uniform tungsten composites with fine microstructures.QC 20111013
25
Garner, Sally Elizabeth. „Ion insertion in tungsten trioxide electrodes“. Thesis, University of Leicester, 1997. http://hdl.handle.net/2381/30079.
Annotation:
The role of ion insertion into the electrochromic metal oxide WO3 has been studied using a combination of electrochemical, gravimetric and spectroscopic techniques. The electrochemical quartz crystal microbalance (EQCM) was used to investigate the effect of electrolyte composition by studying the identity of the cations and anions involved and the concentration of the electrolyte used. It was found that the effect of electrolyte concentration and choice of anion did not affect film reduction and re-oxidation. The two cations studied, Li- and Na+, however cause marked differences in film redox behaviour. The effect of film history was studied using a combination of EQCM and spectrophotometry. The initial cycle at a slow scan rate (5 mV s-1) showed responses different to those of subsequent cycles. Results indicated that at completion of the first cycle there is both injected charge and mass remaining in the WO3 film. This effect has been termed the "break-in" effect and has been seen for all experiments initially cycled at this slow scan rate, irrespective of anion or cation, or the electrolyte concentration. It is possible to correlate current (or charge), mass change and absorbance data together in a novel way, to give information regarding electrons, ions and solvent and electron and ion distribution (via the extinction coefficient, ). Also, the effect of long term cycling (>10,000 cycles) has been investigated with respect to cation insertion. This shows that Li+ insertion yields stable WO3 films after many cycles, whereas Na+ insertion does not. The effect of experimental time scale also has been studied using cyclic voltammetry and chronoamperometry, together with the EQCM. Again, the "break-in" effect was recorded using chronoamperometry, indicating that the effect is not only seen for cyclic voltammetric experiments. Under all experimental conditions used, there is a second, neutral species being inserted and extracted alongside the cations.
26
Potter, Frances Helen. „Surface studies of the tungsten bronzes“. Thesis, University of Oxford, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.357429.
27
Parkin, G. „The chemistry of trimethylphosphine tungsten complexes“. Thesis, University of Oxford, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.355780.
28
Wahlberg, Sverker. „Tungsten-Based Nanocomposites by Chemical Methods“. Doctoral thesis, Stockholm, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-156604.
Annotation:
Tungsten based-materials find use in many different fields of engineering, particularly in applications where good temperature and/or erosion resistance is important. Nanostructuring of tungsten composites is expected to dramatically improve the materials’ properties and enhancing the performance in present applications but also enabling totally new possibilities. Nanostructured WC-Co materials have been the focus of researchers and engineers for over two decades. New fabrication methods have been developed. But, the fabrication of true nanograined WC-Co composites is still a challenge. Nanostructured tungsten-based materials for applications as plasma facing materials in fusion reactors have attracted a growing interest. This Thesis summarizes work on the development of chemical methods for the fabrication of two different types of nanostructured tungsten-based materials; WC-Co composites mainly for cutting tools applications and W-ODS materials with yttria particles, intended as plasma facing materials in fusion reactors. The approach has been to prepare powders in two steps: a) synthesis of uniform powder precursors containing ions of tungsten and cobalt or yttrium by precipitation from aqueous solutions and b) processing of the precursors into WC- or W-based nano-composite powders. Highly homogenous W- and Co- containing precursors for WC-Co composites were prepared via two different routes. Keggin-based precursors ((NH4)8[H2Co2W11O40]) were made from sodium tungstate or ammonium metatungstate and cobalt acetate. The powder composition corresponded to 5.2 % Co in the final WC-Co material. In a second approach, paratungstate-based precursors (Cox(NH4)10-2x[H2W12O42]) were prepared from ammonium paratungstate (APT) and cobalt hydroxide with different compositions corresponding to 3.7 to 9.7 % Co in WC-Co. Both precursors were processed and sintered into uniform microstructures with fine scale (<1μm). The processing of paratungstate-based precursors was also further investigated. WC-Co powders with grains size of less than 50 nm were obtained by decreasing processing temperatures and by applying gas phase carburization. W-ODS materials were fabricated starting from ammonium paratungstate and yttrium salts. Paratungstate-based precursors were prepared with different homogeneities and particle sizes. The degree of the chemical uniformity varied with the particle size from ca 1 to 30 μm. Tungsten trioxide hydrate-based precursors made from APT and yttrium salts under acidic conditions had higher uniformity and smaller particle size. The tungsten oxide crystallite size was decreased to a few nanometers. Yttrium was included either by doping or in a nanocomposite structure as yttrium oxalate. The nanocomposite precursor was found to be more reactive during hydrogen reduction, facilitating its conversion to pure W-Y2O3 nanopowder. The doped precursor were further processed to nanopowders and sintered to highly uniform W-1.2%Y2O3 composites. In summary, APT was converted to highly homogenous or uniform powder precursors ofdifferent compositions. The transformations were carried out in aqueous suspensions as a water-mediated process. These precursors were processed further in to nano-sized powders and sintered to highly uniform tungsten composites with fine microstructures.QC 20141201
29
McLaren, M. G. „Ion bombardment induced deposition of tungsten“. Thesis, University of Salford, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.308526.
30
Whitby, Raymond Lee Derek. „Nanocomposites of carbon and tungsten disulphide“. Thesis, University of Sussex, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.394897.
31
Gardner, Jonathan. „Ferroelectricity in empty tetragonal tungsten bronzes“. Thesis, University of St Andrews, 2017. http://hdl.handle.net/10023/10592.
Annotation:
In this work, in-depth structural and electrical characterisation is used to study a family of “empty” tetragonal tungsten bronzes (TTBs), A2₄A1₂B1₂B2₈O₃₀. An initial investigation into the effect of the A1-cation size on the properties of empty Ba₄R₀.₆₇◻₁.₃₃Nb₁₀O₃₀ TTBs (where R is the A1-cation and R = La, Nd, Sm, Gd, Dy and Y; ◻ = vacancy) was performed. These were determined to be metrically tetragonal by powder x-ray diffraction, with decreasing R cation size inducing increased crystal anisotropy. This tetragonal structural distortion, driven by contraction in the ab-plane, is shown to stabilise c-axis ferroelectricity; a direct correlation between tetragonality and the ferroelectric Curie temperature, T[sub]C, is demonstrated. Further examination of the relaxor ferroelectric (RFE) to ferroelectric (FE) crossover in Ba₄(La₁₋ₓNdₓ)₀.₆₇◻₁.₃₃Nb₁₀O₃₀ TTBs using detailed structural studies employing variable temperature, high resolution neutron, synchrotron X-ray and electron diffraction revealed a common superstructure with 2√2 × √2 × 2 cell with respect to the basic tetragonal aristotype cell. However, they display different degrees of order/disorder which can disrupt polar order (ferroelectricity). La-rich analogues exhibit a disordered regime between the low and high temperature ferroelectric and non-polar phases. Although polar, this disordered regime is non-ferroelectric, however, large polarisation may be established with an applied electric field, but relaxes back to the disordered phase upon removal of the field. Substitution of Nd for La at the A1-site leads to destabilisation of the disordered phase and reintroduces “normal” ferroelectric behaviour. Finally, isovalent substitution of Sr²⁺∙ for Ba²⁺ is shown to lead to the development of relaxor behaviour at higher dopant concentrations in Ba₄₋ₓSrₓDy₀.₆₇◻₁.₃₃Nb₁₀O₃₀, (x = 0, 0.25, 0.5, 1, 2, 3; ◻ = vacancy). With increasing x the unit cell contracts in both the ab- plane and c-axis coinciding with a decrease in T[sub]C and development of relaxor behaviour for x ≥ 2. This observation is rationalised by differing cation occupancies: for x ≤ 1, Sr²⁺ principally occupies the A2-site while for x ≥ 2 significant Sr²⁺ occupation of the A1-site leads to the observed RFE characteristics. The FE to RFE crossover is discussed in the context of a previously proposed TTB crystal chemical framework with the A1-site tolerance factor identified as the dominant influence on relaxor behaviour.
32
Deshpande, Pranav Kishore. „Infrared Processed Copper-Tungsten Carbide Composites“. University of Cincinnati / OhioLINK, 2002. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1025107651.
33
Nitta, Koji. „Electrodeposition of tungsten from molten salts“. Kyoto University, 2009. http://hdl.handle.net/2433/126410.
Annotation:
Kyoto University (京都大学)0048
新制・課程博士
博士(エネルギー科学)
甲第14961号
エネ博第204号
新制||エネ||46(附属図書館)
27399
UT51-2009-M875
京都大学大学院エネルギー科学研究科エネルギー基礎科学専攻
(主査)教授 萩原 理加, 教授 尾形 幸生, 准教授 野平 俊之
学位規則第4条第1項該当
34
Khosla, Chetna Templeton J. L. „Intermediate oxidation state tungsten acetylacetonate complexes“. Chapel Hill, N.C. : University of North Carolina at Chapel Hill, 2009. http://dc.lib.unc.edu/u?/etd,2296.
Annotation:
Thesis (Ph. D.)--University of North Carolina at Chapel Hill, 2009.Title from electronic title page (viewed Jun. 26, 2009). "... in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Department of Chemistry." Discipline: Chemistry; Department/School: Chemistry.
35
Belyaeva, A. I., A. A. Galuza, I. V. Kolenov, V. G. Konovalov, Alla Aleksandrovna Savchenko und O. A. Skoryk. „Effect of sputtering on the samples of iter-grade tungsten preliminarilly irradiated by tungsten ions: optical investigations“. Thesis, Національний науковий центр "Харківський фізико-технічний інститут", 2014. http://repository.kpi.kharkov.ua/handle/KhPI-Press/48176.
36
Osman, Joseph Michael. „Optical switching and memory using tungsten oxide“. Related electronic resource: Current Research at SU : database of SU dissertations, recent titles available full text, 2002. http://wwwlib.umi.com/cr/syr/main.
37
Kukkola, J. (Jarmo). „Gas sensors based on nanostructured tungsten oxides“. Doctoral thesis, Oulun yliopisto, 2013. http://urn.fi/urn:isbn:9789526202082.
Annotation:
Abstract The aim of this thesis is to study whether nanostructured particles of WO3 could be competitive counterparts of traditional, more bulky materials in resistive gas sensor applications. Pristine and various surface decorated derivatives of three different types of WO3 nanoparticles applied on the surface of lithographically defined Si chips were used in the work to analyse the electrical behaviour of thin films when exposed to different gas atmospheres. Nanosized particles of WO3, obtained by capillary force-induced collapse of porous anodic tungsten oxide in water, were demonstrated as a sensing medium for the detection of H2 and NO analytes. Commercially available nanoparticles of WO3 were also studied. After decorating their surface with metal/metal oxide nanoparticles (Ag, PdOx and PtOx), stable aqueous dispersions were made and used for the inkjet printing of conductive patterns on test chips. Surface decoration was found to affect substantially the gas response behaviour of the materials with the largest differences in response to H2 and NO. The third type of tungsten oxide applied consisted of hydrothermally synthesized nanowires that were also surface decorated with PdO as well as with PtOx. The nanowires were suspended in water and drop cast on test chips for gas sensing measurements. The nanowire based devices allowed ultrasensitive detection of H2 even at room temperature. The results summarized in this thesis indicate that resistive gas sensors based on nanostructured tungsten oxides are excellent alternatives to existing devices utilizing porous thick films or bulky thin films. Their high sensitivity, low operating temperature and low electrical power consumption may enable the construction of portable sensors, for example by inkjet printing, thus having great potential for fast prototyping but also for large scale production at low costTiivistelmä Väitöstyön tavoitteena on tutkia nanorakenteisten WO3 hiukkasten kilpailukykyä suhteessa perinteisiin suuremman kidekoon materiaaleihin resistiivisissä kaasusensorisovelluksissa. Työssä tutkittiin kolmella eri tekniikalla valmistettujen WO3 nanopartikkeleiden alkuperäisistä ja pintakäsitellyistä versioista muodostettujen ohutkalvojen sähköisiä ominaisuuksia erilaisten kaasukehien funktiona. Veden kapillaarivoimien aikaan saaman huokoisen anodisen volframioksidirakenteen romahduksen kautta saatujen WO3 nanopartikkeleiden osoitettiin toimivan havaintoväliaineena H2 ja NO kaasuille. Myös kaupallisia WO3 nanopartikkeleita tutkittiin. Partikkelien pinta päällystettiin metalli- ja metallioksidinanopartikkeleilla (Ag, PdOx and PtOx), jonka jälkeen niistä muodostettiin vakaita vesipohjaisia seoksia johtavien kuvioiden mustesuihkutulostukseen testisubstraateille. Pintakäsittelyn havaittiin vaikuttavan merkittävästi materiaalien kaasuvasteisiin erityisesti H2:n ja NO:n tapauksessa. Kolmannen tyyppinen väitöskirjassa tutkittu volframioksidimateriaali koostuu hydrotermisesti syntetisoiduista nanojohdoista, jotka ovat pintakäsitelty PdO tai PtOx nanopartikkeleilla. Nanojohdot sekoitettiin veteen ja pipetoitiin testisubstraateille kaasumittauksia varten. Tämän tyyppiset kaasusensorit olivat erityisen herkkiä H2 kaasulle jopa huoneenlämmössä. Väistökirjan tulosten mukaan nanorakenteiset volframioksidimateriaalit ovat erinomainen vaihtoehto perinteisille huokoisille paksukalvoille ja suhteellisen paksuille ohutkalvoille kaasusensorisovelluksissa. Niiden suuri herkkyys, alhainen toimintalämpötila ja matala sähkönkulutus voivat mahdollistaa kannettavien kaasusensorien valmistuksen, esimerkiksi mustesuihkuteknologilla, nopeaan testaukseen ja suuren mittakaavan tuotantoon alhaisin kustannuksin
38
Walker, Daniel James. „Fluorinations of tungsten and molybdenum carbonyl complexes“. Thesis, University of Leicester, 1997. http://hdl.handle.net/2381/30011.
Annotation:
The dimeric complexes (n5-C5H5)M(CO)3 2 (where M = W or Mo) and (H3C{ti5-C5H4})Mo(CO)3 2 have been treated with XeF2 in organic solvents. All three materials react to form air sensitive products which solid-phase IR studies show to contain highly oxidised metal carbonyl components. The product from the fluoridation of (H3C{T 5-C5H5})Mo(CO)3 2 is insufficiently stable in solution for it to be characterised further. 19F NMR studies show that (n5-C5H5)W(CO)3 2 reacts to form the new complex (T 5-C5H5)WF5, but that the molybdenum analogue reacts to form an unidentified product which, although it produces an AB4 pattern in the 19F NMR, does not appear structurally related to (n5-C5H5)WFs. (n5-C5H5)W(CO)3 2 was found to react with AgF in anhydrous HF solution to give (t 5-C5H5)WF5. Solid-phase IR studies showed that a highly oxidised metal carbonyl, identical to that obtained in the XeF2 reaction, was also formed. Reaction of (T 5-C5H5)M(CO)3(CH3) (where M = W or Mo) with anhydrous HF was found to yield the complexes (n5-C5H5)M(CO)3 2 (where M = W or Mo). The molybdenum product was characterised by X-ray crystallography, whilst the tungsten dimer was characterised using mass spectroscopy. The mechanism for this redox process is unknown, but is believed to involve formation of the complexes (T 5-C5H5)M(CO)3F, as intermediates. Although solid-phase IR shows that both Mo(CO)6 and W(CO)6 react with XeF2 to give oxidised metal carbonyls, the products appear very different. W(CO)6 yields a variety of salts of the W202F9 " anion, none of which dissociate fully in solution, and which thus give separate 19F NMR spectra, for the anion. One of these salts may contain the W2(CO)8 2+ cation, which has been characterised in the product mixture by +EI MS. Mo(CO)6 reacts to form a molybdenum fluoride whose 19F NMR spectrum has been observed, but which has not been identified.
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Hong, Kunquan. „Synthesis of one-dimensional tungsten oxide nanostructures“. Click to view the E-thesis via HKUTO, 2008. http://sunzi.lib.hku.hk/HKUTO/record/B39558551.
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洪昆權 und Kunquan Hong. „Synthesis of one-dimensional tungsten oxide nanostructures“. Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2008. http://hub.hku.hk/bib/B39558551.
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Hu, Rong, und 胡蓉. „Synthesis and characterization of tungsten oxide nanostructures“. Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2008. http://hub.hku.hk/bib/B41508774.
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Espinosa, Daniel C. „Visualization of gas tungsten arc weld pools“. Thesis, Monterey, California. Naval Postgraduate School, 1991. http://hdl.handle.net/10945/28643.
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Thiebaut, Benedicte. „Co-ordinatively unsaturated complexes of tungsten (II)“. Thesis, Heriot-Watt University, 1998. http://hdl.handle.net/10399/606.
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Bain, Michael. „The deposition and characterisation of CVD tungsten“. Thesis, Queen's University Belfast, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.326383.
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Macpherson, I. „Some metallaborane chemistry of molybdenum and tungsten“. Thesis, University of Leeds, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.376799.
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Polya, D. A. J. „Chemical behaviour of tungsten in hydrothermal fluids“. Thesis, University of Manchester, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.378304.
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Shen, Peikang. „A study of modified tungsten trioxide electrodes“. Thesis, University of Essex, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.315727.
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Shonfield, Peter K. A. „Molybdenum and tungsten complexes for moleular electronics“. Thesis, University of Bristol, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.264635.
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Thummavichai, Kunyapat. „Tungsten oxide nanostructures and their electrochromic performance“. Thesis, University of Exeter, 2018. http://hdl.handle.net/10871/33858.
Annotation:
The electrochromic behaviour of tungsten oxide (WOx) bulk forms has attracted huge research interest for decades owing to advantages of fast response time, good reversibility and high colouration efficiency compared with other electrochromic materials. Nanomaterials have certainly brought in new opportunities and opened the door for better, higher and smarter devices fabrication. This thesis will first investigate, explore, and understand the electrochromic performance of WOx in the nanoscale, and identify ways to enhance its performance via effective doping electrolyte selection and heat treatment. Moreover, the thesis will evaluate the prototype device performance based on our new understandings obtained in this project. The main findings are as follows: • Successfully synthesised crystalline WOx-based nanomaterials using a simple solvothermal technique, and achieved a series of La-, Ce- and Na-doped nanomaterials. The results show that the dopants caused distortion of the parental WOx¬ frameworks and increased the oxygen vacancy inside the structure, which is beneficial for the chromic properties. • The best electrochromic performance was obtained from Ce/W = 1 : 15 samples which presented 44.3% for optical contrast colouration efficiency of 67.3 cm2 C−1. • Conducted in-situ phase transition investigations using both WO3 nanoparticles and W18O49 nanowires, and found out that temperature was affecting the relaxation of W-O framework and phase transition. Based on the investigation, the 187.6 cm-1 band has identified as a fingerprint band for the phase transition from γ- to β- of the WO3 nanoparticle at 275 °C. W18O49 nanowires exhibit better thermal stability than the WO3 nanoparticles. • Intensive electrochemical investigations of La- and Ce-doped WOx structures were exhibit better diffusion kinetics, stability and colouration efficiency compare with plain WOx. These improvements are contributed to the improved oxygen vacancy (Vo). DLi+ of the Ce-doped samples were much higher than that of the plain W18¬O49 nanowires, by 177%, 102% and 84% for the 1:15, 1:10 and 1:5 samples respectively. DLi+ values of all La-doped samples were over 100% higher than those of the plain W18O49. The La-doped thin films increased the stability by 9%, 4% for intercalation, and 25% and 23% for de-intercalation, for La/W = 1:15 and 1:10 samples respectively, against the plain W18O49. • Provided experimental evidence to explain the degradation of chromic thin films, which is related to the Li+ trapping and loss of Vo in the WOx the structures. • The 350 °C annealed W18O49 thin film sample showed better diffusion kinetics by 25% for intercalation and 30% for de-intercalation compared with the un-annealed W18O49 samples. Stabilities also showed 31% improvement for the de-intercalation, against the un-annealed W18O49 sample. • Fabricated electrochromic device prototypes, and investigated the influence of various electrolytes, an optimal combination of LiClO4/PPC/PC polymer electrolyte has been developed, to improve the performance in ion kinetics and switching time of W18O49. These results have shown that WOx nanomaterials via further effective modification including doping with rare-earth elements or proper heat treatment are promising and practical candidate for the creation of fast, reliable and highly efficient electrochromic devices/smart windows for various applications.
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Kelley, Andrew III. „Tungsten carbide-cobalt by Three Dimensional Printing“. Thesis, Massachusetts Institute of Technology, 1998. http://hdl.handle.net/1721.1/32316.
Annotation:
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1998.Includes bibliographical references (p. 69-70).
Three Dimensional Printing is an additive manufacturing process for rapid prototyping ceramic and metallic parts [Sachs, et al, 1990]. Green (not sintered) tungsten carbide-cobalt parts must have a density greater than 50% of the theoretical density, 14.9 g/cc, for proper sintering and post-processing. Two approaches were assessed for feasibility and robustness: printing slurry into tungsten carbide-cobalt spray dried powder and printing a solvent in spray dried tungsten carbide powder that readily dissolves. For slurry administered to a powder bed of solid, spherical particles, it has been found that the resulting packing primitive packing fraction increases almost linearly with the volume loading of the slurry over a range of powder size. The increase in density is approximately half what would be calculated by assuming that the slurry fills all the porosity in the powder bed. The maximum green density achieved by printing slurry into a spray dried tungsten carbide-cobalt bed was 41%, midway between the lower bound calculated by assuming the vehicle in the slurry infiltrates only the large pores between the spray dried power and the upper bound calculated by assuming that the vehicle of the slurry also infiltrates the find pores within a spray dried granule. A re-dispersible spray dried powder (38-53 micron size range) was fabricated using only the Duramax 3007 dispersant as the binder. This powder redisperses in water. Administering a drop of water to this powder resulted in primitives with 47% packing density, but which had significant quantities of 80 micron voids.
(cont.) Several lines of evidence pointed to the hypothesis that the voids were the result of trapped air. Two methods were successfully employed to nearly eliminate such voids. In one approach, the droplet of water wvas administered to the powder bed under a vacuum of between 25 and 40 torr and air was admitted to the chamber to 1 atmosphere after different intervals of time ranging from 30 seconds to 10 minutes. In another approach, the ability of water to absorb CO₂ was used to "getter" any trapped gas into the liquid. Water was administered to a powder bed under a CO₂ environment at room temperature. After a 2 minute period, intended to allow the spray dried powder to substantially re-disperse, the temperture of the powder bed was lowered to 0-5 degrees Centigrade in order to increase the amount of CO₂ which could be absorbed in the water and "switch on" the gettering of the trapped gas.Controls were run with the same procedure in air. The primitives made under CO₂ were nearly void free and had densities as high as 52%, while the controls were not significantly different than primitives made at room temperature in air.
by Andrew Kelley, III.
S.M.