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Kinetics of thermal decomposition of niobium hydride

Gabriel, S. B.; Brum, M. C.; Candioto, Katia Cristiane Gandolpho; Sandim, Hugo Ricardo Zschommler; Suzuki, Paulo Atsushi; Nunes, Carlos Angelo
Fonte: ELSEVIER SCI LTD; OXFORD Publicador: ELSEVIER SCI LTD; OXFORD
Tipo: Artigo de Revista Científica
ENG
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High-purity niobium powders can be obtained from the well-known hydride-dehydride (HDH) process. The aim of this work was the investigation of the structural phase transition of the niobium hydride to niobium metal as function of temperature, heating rate and time. The niobium powder used in this work was obtained by high-temperature hydriding of niobium machining chips followed by conventional ball milling and sieving. X-ray diffraction measurements were carried out in vacuum using a high-temperature chamber coupled to an X-ray diffractometer. During the dehydriding process, it is possible to follow the phase transition from niobium hydride to niobium metal starting at about 380 degrees C for a heating rate of 20 degrees C/min. The heating rate was found to be an important parameter, since complete dehydriding was obtained at 490 degrees C for a heating rate of 20 degrees C/min. The higher dehydriding rate was found at 500 degrees C. Results contribute to a better understanding of the kinetics of thermal decomposition of niobium hydride to niobium metal. (C) 2011 Elsevier Ltd. All rights reserved.; CNPq (Brazil); CNPq (Brazil)

Construção e avaliação de eletrodos de Nióbio/Óxido de Nióbio para determinações potenciométricas; Construction and evalution of Niobium/Niobium Oxide electrodes for potentiometric determination

Jardim, Wolney de Jesus
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 17/10/2008 PT
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A construção de sensor potenciométrico, utilizando Nióbio acoplado a eletrodo de referência de prata/cloreto de prata num mesmo instrumento, possibilita o acompanhamento da variação de potencial que ocorre durante uma reação ácido-base em meio aquoso. Foi utilizado eletrodo de vidro combinado, cuja membrana de vidro foi danificada fisicamente, porém com sua referência interna em pleno funcionamento. O eletrodo de Nióbio foi confeccionado com metal polido ou então com a superfície modificada com óxido eletrodepositado. O crescimento de óxido sobre o Nióbio foi obtido por eletrólise em meio a H3PO4 diluído. O metal ou o par metal/óxido foi fixado no eletrodo de vidro contendo uma solução eletrolítica. O eletrodo de Nióbio não apresenta boa sensibilidade quando utilizado como indicador em potenciometria direta, mas é sensível às variações de potenciais que ocorrem em titulações ácido-base. O eletrodo de Nióbio metálico pode substituir o eletrodo de vidro combinado na determinação do teor de acidez de vinagres.; The construction of potentiometric sensors, using Niobium combined with the reference electrode silver / silver chloride in a single instrument, allows the variation of potential monitoring that occurs during an acid-base reaction in aqueous media. It was used a combined electrode glass...

Influência de um revestimento de nióbio sobre a resistência à sulfetação das ligas FeCr e FeCrY; Influence of a niobium coating on sulfidation resistance of FeCr and FeCrY alloys

Geribola, Guilherme Altomari
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 01/12/2014 PT
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Nióbio e suas ligas são utilizados atualmente em muitas aplicações industriais por oferecerem excelente resistência à degradação em diversos meios corrosivos. Estes meios incluem atmosferas gasosas em temperaturas elevadas, como as encontradas em plantas de gaseificação de carvão existentes em usinas termelétricas para geração de energia. As atmosferas encontradas nestes meios são misturas gasosas complexasque contêm, entre outros compostos, oxigênio e enxofre. Os sulfetos são compostos menos estáveis, possuem pontos de fusão mais baixos e apresentam, freqüentemente, maiores desvios de estequiometria em relação ao óxido correspondente. Apesar de existirem estudos relacionados à aplicação de metais refratários em atmosferas sulfetantes a temperaturas elevadas, o uso de compostos de nióbio ainda não foi devidamente avaliado como revestimento protetor, havendo poucos dados disponíveis na literatura. O objetivo deste trabalho foi avaliar o efeito proporcionado por um filme de nióbio, obtido por pulverização catódica,sobre o comportamento de sulfetação isotérmica das ligas Fe-20Cr e Fe-20Cr-1Y.Os testes de sulfetação foram realizados a 500, 600 e 700°C pelo período de 2h em atmosfera H2/2%H2S. A avaliação da resistência à sulfetação foi feita por meio do ganho de massa por unidade de área exposta. Observou-se que o comportamento de sulfetação a 500ºC das ligas FeCr e FeCrY sem e com revestimento é similar. Nesta condição...

Production and heat treatment of cast graphitic steels with additions of niobium

Soufen, C. A.; Casteletti, L. C.; Neto, A. Lombardi; Totten, G. E.
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Conferência ou Objeto de Conferência Formato: 127-130
ENG
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The optimal combination of the mechanical characteristics of austempered spheroidal graphitic cast steel together with modern casting techniques yielded an economically promising product. The maximum potential of the usage of these steels is related to fabrication and characterization techniques, among which, one of the most important is the cooling diagram (TTT curve). In this work, 3 heats of graphitic steels with the following nominal compositions were cast: 1.0 % C, 2.3 % Si, 0.4 % Mn, and with niobium contents of. 0.0 %, 0.5 % and 1.0 %. TTT curves were determined by dilatometric testing and test specimens of these steels were austempered. The samples were then characterized by hardness testing and optical and SEM microscopy. Tensile, impact (no notch) and wear testing were also performed. The addition of niobium produced significant alterations in the TTT diagrams. Increasing niobium content moves the pearlite transformation nose to the right and the bainitic transformation nose to the left. Tensile strength of these alloys was high, in the range of 1700 MPa and impact values were around of 45 Joules for alloy with 1 % Nb, 49 Joules for alloy with 0.5 % Nb and fracture did not occur for the alloy without the addition of Nb.

Diffusion phenomena of the oxygen and nitrogen in niobium by mechanical spectroscopy

Florêncio, O.; Silva, P. S.; Grandini, Carlos Roberto
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Conferência ou Objeto de Conferência Formato: 1346-1353
ENG
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The short-range diffusion phenomenon (Snoek Effect) was investigated by mechanical spectroscopy measurements between 300 K and 650 K, in a polycrystalline niobium sample, containing oxygen and nitrogen, using a torsion pendulum. Experimental spectra of anelastic relaxation were obtained under three conditions: as-received sample; annealed sample and subsequently annealed in an oxygen atmosphere for three hours at 1170 K in partial pressure of 5°10 -5mbar. The experimental spectra obtained were decomposed in elementary Debye peaks and the anelastic relaxation processes were identified. With anelastic relaxation parameters and the lattice parameters, the interstitial diffusion coefficients of the oxygen and nitrogen in niobium were calculated for each kind of preferential occupation (octahedral and tetrahedral). The results were compared with the literature data, and confirmed that the best adjustment is for the preferential occupation octahedral model for low concentrations of interstitial solutes, but at higher concentration of oxygen were observed deviations of experimental data for the interstitial diffusion coefficients of oxygen in niobium when compared with the literature data, this could be related to the possible occurrence of a double occupation of interstitial sites in the niobium lattice by oxygen interstitials. © (2010) Trans Tech Publications.

Caracterização mecânica e microestrutural de aços médio carbono microligados ao nióbio e molibdênio; Mechanical and microstructural characterization of an niobium and molybdenum microalloyed medium carbon steels

Adilto Pereira Andrade Cunha
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 24/07/2013 PT
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Neste trabalho foi estudada a influência da adição de molibdênio e nióbio na microestrutura e propriedades mecânicas de aços com 0,5 e 0,6 %C, utilizado na fabricação de rodas ferroviárias. A deformação dos aços foi aplicada através da laminação, em escala de laboratório, simulando o forjamento no processo real de fabricação. As amostras foram aquecidas a 1250 °C para solubilização do nióbio, sendo então laminadas em 4 passes, a partir de 1200 °C, sofrendo uma deformação total (redução em altura) de 67%, seguida de resfriamento ao ar. Posteriormente, os aços C5 e C5Nb foram submetidos a um tratamento térmico de têmpera e revenimento. Foram analisadas amostras dos aços por microscopia óptica, eletrônica de varredura e transmissão e também foram realizados ensaios mecânicos em todas as condições. Após a laminação entre 1200 e 1120 °C, observou-se que a adição de molibdênio e nióbio promoveu um aumento da resistência mecânica em 171 e 119 MPa no limite de escoamento e 61 e 66 MPa no limite de resistência à tração, nos aços C5Nb e C6Nb, respectivamente, devido à precipitação de carbonetos de nióbio, mantendo a mesma ductilidade e tenacidade para o aço C5Nb, mas houve uma queda dessas propriedades para os aço C6Nb. Após a laminação com posterior têmpera e revenimento a 500°C...

Adsorption of phosphoric acid on niobium oxide coated cellulose fiber: preparation, characterization and ion exchange property

Pavan,Flávio A.; Francisco,Maria Suzana P.; Landers,Richard; Gushikem,Yoshitaka
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/08/2005 EN
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The preparation procedures for a hybrid organic-inorganic cellulose-niobium oxide (Cel/Nb2O5) and its derivative, Cel/Nb2O5/phosphate, are described. The precursor reagent of the metal oxide was the very convenient water soluble niobium oxalate compound, NH4[NbO(C2O4)2)(H 2O)2].nH2 O. Phosphate ion was adsorbed on the Cel/Nb2O5 by immersing this solid in an aqueous solution of phosphoric acid. Textural analyses carried out by using scanning electron microscopy (SEM) connected to an energy dispersive detector (EDS) revealed that the niobium oxide particles are, within the magnification used, uniformly dispersed on the cellulose matrix surface. Phosphoric acid is adsorbed on the material surface through the Nb-O-P linkage. The X-ray photoelectron and 31P NMR spectra showed that the adsorbed phosphate on the surface is the (H2PO4)- species. The ion exchange isotherms obtained using the material Cel/Nb2O5/H2PO4- showed good affinity for retaining Na+, K+ and Ca2+ when in contact with these ions in an aqueous solution.

THE INFLUENCE OF NIOBIUM ON THE ACIDITY AND STRUCTURE OF GAMMA-ALUMINA-SUPPORTED VANADIUM OXIDES

Sathler,M.N.B.; Eon,J.G.
Fonte: Brazilian Society of Chemical Engineering Publicador: Brazilian Society of Chemical Engineering
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/06/1998 EN
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Gamma-alumina-supported niobium oxide was used as a support for vanadium oxides. The influence of the addition of niobium oxide was studied by looking for changes in the structure and acid-base character of superficial species. Vanadium oxide was deposited using the continuous adsorption method; niobium oxide was impregnated using the incipient wetness method. The catalysts were characterized by XPS, UV-visible and IR spectroscopy. Catalytic tests were performed using propane oxidation reaction at 400oC. For coverage below the monolayer, both vanadium and niobium oxides were observed in slightly condensed superficial species. The presence of vanadium oxide on the support was found to increase the Lewis acidity and create some Bronsted acidity. Higher catalytic activity and selectivity for propene were associated with vanadium oxides. The presence of niobium did not contribute to the modification of the chemical properties of superficial vanadium but did decrease the adsorption of vanadium on the alumina.

Niobium carbide synthesis by solid-gas reaction using a rotating cylinder reactor

Fontes,F. A. O.; Gomes,K. K. P.; Oliveira,S. A.; Souza,C. P.; Sousa,J. F.
Fonte: Brazilian Society of Chemical Engineering Publicador: Brazilian Society of Chemical Engineering
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/09/2004 EN
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A rotating cylinder reactor was designed for the synthesis of niobium carbide powders at 1173 K. Niobium carbide, NbC, was prepared by carbothermal reduction starting from commercial niobium pentoxide powders. The reactor was heated using a custom-made, two-part, hinged, electric furnace with programmable temperature control. The design and operational details of the reactor are presented. The longitudinal temperature gradient inside the reactor was determined. Total reaction time was monitored by a gas chromatograph equipped with an FID detector for determination of methane concentrations. The results show that time of reaction depended on rotation speed. NbC was also prepared in a static-bed alumina reactor using the same conditions as in the previous case. The niobium carbide powders were characterized by X-ray diffraction and compared with commercially available products. Morphological, particle size distribution and surface area analyses were obtained using SEM, LDPS and BET, respectively. Therefore, the present study offers a significant technological contribution to the synthesis of NbC powders in a rotating cylinder reactor.

Mechanical and microstructural characterization of Nodular Cast Iron (NCI) with Niobium Additions

Souza,Tânia Nogueira Fonseca; Nogueira,Rogéria Alves Perilo Sousa; Franco,Francis José Saldanha; Aguilar,Maria Teresa Paulino; Cetlin,Paulo Roberto
Fonte: ABM, ABC, ABPol Publicador: ABM, ABC, ABPol
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/10/2014 EN
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Nodular cast irons (NCIs) involve the inoculation and nodulization of 0.03 to 0.06wt% Magnesium, as well as the addition of Molybdenum, Chromium, Nickel, Copper and Vanadium, although the presence of Niobium is not common. The literature reports that Niobium leads to better mechanical properties of the NCIs, and recent results indicate that 0.5wt% Niobium increases the strength and the Charpy notch toughness of NCIs, but decreases its hardness, in relation to a similar NCI without Niobium. The present report studies the addition of 0.23, 0.47, 0.67, and 0.85wt% Niobium to a NCI covering the effects on the microstructures, yield and tensile strengths, tensile elongations and Charpy toughness. The NCIs were prepared in a 120 kg medium frequency induction furnace, and samples were obtained following the ASTM A842 standard; the various test specimens were extracted from these samples according to specific standards for each test. Fracture analysis was performed in fractures specimens after the Charpy tests. It was shown that the volume fraction of pearlite increases as the Niobium content is raised, leading to increments in the yield and tensile strengths and hardness of these materials. Modest increment of tensile ductility and Charpy toughness are observed only for an addition of 0.23% Niobium. Fracture analysis revealed typical brittle cleavage surfaces and decohesion between grains and grain - graphite nodules interfaces...

Comportamento da adição do carbeto de nióbio (nBC) na matriz metálica do aço ferrítico 15kH2mfa; Behavior of adition of niobium carbide (nBc) in metallic matrix of ferritic steel 15kH2mfa

Silva Júnior, José Ferreira da
Fonte: Universidade Federal do Rio Grande do Norte; BR; UFRN; Programa de Pós-Graduação em Ciência e Engenharia de Materiais; Processamento de Materiais a partir do Pó; Polímeros e Compósitos; Processamento de Materiais a part Publicador: Universidade Federal do Rio Grande do Norte; BR; UFRN; Programa de Pós-Graduação em Ciência e Engenharia de Materiais; Processamento de Materiais a partir do Pó; Polímeros e Compósitos; Processamento de Materiais a part
Tipo: Tese de Doutorado Formato: application/pdf
POR
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The 15Kh2MFA steel is a kind of Cr-Mo-V family steels and can be used in turbines for energy generation, pressure vessels, nuclear reactors or applications where the range of temperature that the material works is between 250 to 450°C. To improve the properties of these steels increasing the service temperature and the thermal stability is add a second particle phase. These particles can be oxides, carbides, nitrites or even solid solution of some chemical elements. On this way, this work aim to study the effect of addition of 3wt% of niobium carbide in the metallic matrix of 15Kh2MFA steel. Powder metallurgy was the route employed to produce this metallic matrix composite. Two different milling conditions were performed. Condition 1: milling of pure 15Kh2MFA steel and condition 2: milling of 15Kh2MFA steel with addition of niobium carbide. A high energy milling was carried out during 5 hours. Then, these two powders were sintered in a vacuum furnace (10-4torr) at 1150 and 1250°C during 60 minutes. After sintering the samples were normalized at 950°C per 3 minutes followed by air cooling to obtain a desired microstructure. Results show that the addition of niobium carbide helps to mill faster the particles during the milling when compared with that steel without carbide. At the sintering...

Avaliação cinética e potencial do Nb2O5 obtido a partir de um complexo de nióbio para formação do oleato de metila através da reação de esterificação do ácido oleico; Evaluation of the kinetic and potential Nb2O5 obtained from a niobium complex to the formation of methyl oleate by esterification of oleic acid

Oliveira, Samuel Alves de
Fonte: Universidade Federal do Rio Grande do Norte; BR; UFRN; Programa de Pós-Graduação em Engenharia Química; Pesquisa e Desenvolvimento de Tecnologias Regionais Publicador: Universidade Federal do Rio Grande do Norte; BR; UFRN; Programa de Pós-Graduação em Engenharia Química; Pesquisa e Desenvolvimento de Tecnologias Regionais
Tipo: Dissertação Formato: application/pdf
POR
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Among the heterogeneous catalysts materials made from niobium show up as an alternative to meet the demand of catalysts for biodiesel production. This study aims to evaluate the potential of a heterogeneous catalyst derived from a complex of niobium in the reaction of methyl esterification of oleic acid. The catalyst was synthesized after calcination at different temperatures of a niobium complex ((NH4)3[NbO(C2O4)3].H2O) generating a niobium oxide nanostructure with a different commercial niobium oxide used to synthesize the complex. The commercial niobium oxide, the complex niobium and niobium catalyst were characterized by thermogravimetry (TG and DTA), surface area analysis (BET), scanning electron microscopy (SEM) and X-ray diffraction (XRD), showing the catalyst has researched morphological and crystallographic indicating a catalytic potential higher than that of commercial niobium oxide characteristics. Factorial with central composite design point, with three factors (calcination temperature, molar ratio of alcohol/oleic acid and mass percentage of catalyst) was performed. Noting that the optimal experimental point was given by the complex calcination temperature of 600°C, a molar ratio alcohol/oleic acid of 3.007/1 and the catalyst mass percentage of 7.998%...

Serum titanium, niobium, and aluminum levels after instrumented spinal arthrodesis in children

Cundy, T.; Antoniou, G.; Sutherland, L.; Freeman, B.; Cundy, P.
Fonte: Lippincott Williams & Wilkins Publicador: Lippincott Williams & Wilkins
Tipo: Artigo de Revista Científica
Publicado em //2013 EN
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STUDY DESIGN. A prospective cohort study. OBJECTIVE. To determine serum titanium, niobium, and aluminum levels in pediatric patients within the first postoperative year after instrumented spinal arthrodesis. SUMMARY OF BACKGROUND DATA. Instrumented spinal arthrodesis is a common procedure to correct scoliosis and kyphosis. Titanium-based instrumentation is increasingly favored due to enhanced biomechanical properties, but concerns have arisen regarding metal debris release and the potential for local and systemic complications. METHODS. The pattern of systemic metal release over time was evaluated by measuring serum titanium, niobium, and aluminum levels preoperatively and 1 week, 1 month, 6 months, and 12 months after instrumented spinal arthrodesis using a titanium alloy. Serum metal levels were measured using high-resolution inductively coupled plasma mass spectrometry. RESULTS. Thirty-two patients were included in the study group. Mean age at surgery was 14.7 years. Preoperative and postoperative concentrations of serum titanium and niobium were significantly different (P = 0.0001). Median postoperative serum concentrations of titanium and niobium were elevated 2.4- and 5.9-fold above the normal range respectively with 95% and 99% of samples elevated postoperatively. A significant and rapid rise in serum titanium and niobium levels was observed within the first postoperative week...

Serum titanium, niobium and aluminium levels two years following instrumented spinal fusion in children: does implant surface area predict serum metal ion levels?

Cundy, T.P.; Cundy, W.J.; Antoniou, G.; Sutherland, L.M.; Freeman, B.J.C.; Cundy, P.J.
Fonte: Springer Verlag Publicador: Springer Verlag
Tipo: Artigo de Revista Científica
Publicado em //2014 EN
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PURPOSE: Measurement of serum metal ion levels is used to determine systemic exposure to implant-derived metal debris that may be generated by processes of wear and corrosion. The aim of this study is to investigate predictors of serum metal ion levels in children undergoing instrumented spinal arthrodesis using a titanium alloy, focusing on implant characteristics and instrumentation construct design variables. METHODS: This prospective longitudinal cohort study involved 33 children. Serum samples were obtained preoperatively:and at five defined interval periods over the first:two post-operative years. Samples were analysed using high resolution:inductively coupled plasma mass spectrometry to measure titanium, niobium and aluminium concentrations. Instrumentation characteristics were catalogued and construct surface area (SA) measurements calculated using an implant-specific software algorithm tool. RESULTS: Significantly elevated levels of serum titanium and niobium were observed (p< 0.0001), with >95 % of post-operative levels abnormally elevated. Significant predictors of serum titanium and niobium levels included time since surgery, surgical procedure (posterior or anterior fusion), number of levels fused, number of pedicle screws inserted...

First Results of Cavitation Erosion Behavior of Plasma Nitrided Niobium: Surface Modification

Kertscher,Ricardo; Moraes,Juliana Martins de; Henke,Sérgio; Allenstein,Angela Nardelli; Silva,Regis Henrique Gonçalves e; Dutra,Jair Carlos; Brunatto,Silvio Francisco
Fonte: ABM, ABC, ABPol Publicador: ABM, ABC, ABPol
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2015 EN
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This work presents the first results of the plasma nitriding study performed in pure niobium in order to increase its cavitation erosion resistance. Samples were prepared from 98.9% purity and 90% reduction cold-rolled niobium bars. Annealing treatment of the cold-worked niobium samples was carried out in vacuum furnace at 1.33 Pa pressure, in the temperature of 1000 °C, for a time of 60 min. Annealed samples showing hardness of 80 HV were cut to dimensions of 20 × 30 × 4 mm3. Nitriding treatment was conducted at 1080 °C, gas mixture of 90% N2 + 10% H2, flow rate of 5 × 10–6Nm3s–1, and pressure of 1200 Pa (9 Torr), for a total time of 4 h comprised by two treatment steps of 2 h each. For comparison purpose, results for nitrided and non-nitrided niobium are confronted. Samples were characterized by XRD, nanoindentation, microhardness, SEM, and 2D surface topography and 3D interferometry profile analysis techniques. Cavitation testing was conducted according to ASTM G32-09. Comparatively, promising results based on the formation of niobium nitride phases in treated surfaces are presented and discussed in the present work.

Niobium oxides and niobates physical properties; Propriedades físicas de óxidos de nióbio e de niobatos

Nico, Cláudio Miguel Silva
Fonte: Universidade de Aveiro Publicador: Universidade de Aveiro
Tipo: Tese de Doutorado
ENG
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Niobium oxides have been pointed as an alternative to tantalum in the production of solid electrolytic capacitors, with advantages regarding the dielectric constant, density and price. In this work, it is intended to create a new family of niobium oxides based capacitors, adapting the technology and production line currently used with tantalum. Despite the known potentialities of niobium oxides, and many types of niobates, in several technological applications, the understanding of these oxide systems is still noticeably insufficient. Hence, a careful bibliographic review is shown, which evidences the complexity of these materials, the difficulty in identifying of their different phases and polymorphs, as well as in the interpretation of their properties. In this context, several fundamental studies on niobium oxides are presented, namely structural, microstructural, optical and electrical characterizations, which allow not only to contribute in an important way for the general knowledge of the physical properties of these materials, but also to advance to a sustained development of the niobium oxides based solid electrolytic capacitors. Several processing parameters were studied, clearing the way towards the creation of a prototype. It was also decided to perform a preliminary study on the synthesis and characterization of other oxide systems based in niobium...

Niobium and niobium-iron coatings on API 5LX 70 steel applied with HVOF

Brandolt,Cristiane de Souza; Souza Junior,Jair Garcia de; Kunst,Sandra Raquel; Vega,Maria Rita Ortega; Schroeder,Roberto Moreira; Malfatti,Célia de Fraga
Fonte: ABM, ABC, ABPol Publicador: ABM, ABC, ABPol
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/08/2014 EN
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The present study aimed to create and characterize niobium and niobium-iron 60% coatings applied to steel API 5L X70 using the hypersonic thermal spray process (HVOF). The morphologies of the coatings were analyzed using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and profilometry, while the coatings' hardnesses was evaluated using the Vickers hardness test. The coatings' corrosion resistance was evaluated by monitoring their open circuit potential and potentiodynamic polarization and performing electrochemical impedance spectroscopy in a 0. 05 M NaCl solution. The results showed that the niobium-iron coating contained minor porosity regions, while such defects occurred over large regions of the niobium coating. In terms of corrosion resistance, the coatings obtained in this work promoted a reduction in the substrate's corrosion rate, but the presence of discontinuities such as porosity compromised the barrier effects of these coatings.

The Evolution of the Niobium Production in Brazil

Alves,Adilson Rangel; Coutinho,Aparecido dos Reis
Fonte: ABM, ABC, ABPol Publicador: ABM, ABC, ABPol
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/02/2015 EN
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Niobium (Nb) was initially applied in the industry in 1933 to stabilize stainless steels against intergranular corrosion. Around 1970, niobium started to be used in many technological applications, especially in heat treatments at high temperatures, in the form of superalloys and, over the past four decades, Nb has been employed on an industrial scale. During recent years, applications of niobium have increased steadily in various segments such as: micro-alloyed steels, super alloys, thin films, medical implants, titanium and aluminum alloys, superconductors and copper alloys, electrolytic and ceramic capacitors. The worldwide demand for Nb grew at an annual rate of 10% between the years 2000-2010, were the sectors of energy, automotive and construction of the largest consumers FeNb. In 2000 the brazilian production was 35,458 t of Nb and, in 2007, reached 82,000 t of concentrate Nb. Brazil has the world's largest reserves of Nb (98.53%), which totaled 842.4 million t. So, in this paper is made a study on the evolution of the production of niobium in Brazil and its main industrial and technological applications.

Ammonium complex of niobium as a precursor for the preparation of Nb2O5/Al2O3catalysts

Noronha, Fábio Bellot; Schmal, Martin; Mendes, Fabiana M. Teixeira; Perez, C. A. C.
Fonte: Instituto Nacional de Tecnologia Publicador: Instituto Nacional de Tecnologia
Tipo: Artigo de Revista Científica
EN
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CAtalysis today, 78 (1-4): 449-458 Fev 28, 2003.; Ammonium oxalate complex of niobium was investigated as an aqueous precursor for the preparation of x% Nb2O5/Al2O3 (x=5, 10, 20 and 30 wt.%) samples. Catalysts with the same Nb2O5 contents were also prepared from the traditional niobium oxalate/oxalic acid aqueous solution. The catalysts were characterized by X-ray diffraction (XRD), diffuse reflectance spectroscopy (DRS), temperatureprogrammed reduction (TPR), infrared spectroscopy of chemisorbed pyridine and X-ray photoelectron spectroscopy (XPS). A comparison with the preparation method using the niobium oxalate salt was performed. The results showed that the niobium precursor influence the species growing leading to phases with different reducibility. The XPS revealed the presence of multilayers of niobium oxide on the Nb2O5/Al2O3 samples prepared by using niobium ammonium oxalate complex, while the ones obtained from niobium oxalate led to Nb2O5 particles islands. The addition of niobium oxide decreased the fraction of Lewis acid sites and increased the fraction of Brønsted acid sites, independent of the precursor salt. However, the creation of BAS was more pronounced on the Nb2O5/Al2O3 samples prepared from niobium oxalate.

The Attempted synthesis of novel BIS(quadridentate) niobium(IV) complexes and the analyses of the products resulting from the attempted synthesis of tetrakis (8-hydroxyquinolinato) niobium (IV)

Pinkes, John R.
Fonte: Rochester Instituto de Tecnologia Publicador: Rochester Instituto de Tecnologia
Tipo: Tese de Doutorado
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Four previously reported quadridentate ligands were synthesized, and the attempts made to synthesize the corresponding bis(quadridentate)niobium( IV) complexes are documented. Attempts made to synthesize the previously reported tetrakis(bidentate) niobium ( IV) complexes of benzoyltrifluoroacetylacetone (Nb(BTA)O1 and of 8- hydroxyquinoline (Nb(8-Q)4)t are also discussed. Though neither of the desired complexes was synthesized, the resulting complexes from the attempted synthesis of the Nb(8-Q)4 complex, and their subsequent analyses, are examined in detail. Along with the ligand syntheses and the attempted coraplexations , modifications in the experimental techniques and the apparatus are also discussed .