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Academic literature on the topic 'Niobium'

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Published: 4 June 2021
Last updated: 31 July 2024

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Journal articles on the topic "Niobium"

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Liu, Shuang, Lang Yang, Hao Yi, and Shaoxian Song. "Simultaneous Recovery of Niobium and Sulfur from Carbonate Niobite Ore with Flotation." Minerals 12, no. 4 (March 31, 2022): 432. http://dx.doi.org/10.3390/min12040432.

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Exploring new ways to acquire niobium resources is essential to resolve niobium supply risks, due to the fact that, at present, 99% of niobium is controlled by only two countries. In the present work, a flotation technique was applied to separate niobium from low-grade niobite ore. To maximize the utilization of the original ore resources, pre-flotation was conducted to recover sulfur and eliminate the adverse effects of sulfide on niobite flotation. The obtained sulfur grade and recovery were 33.74% and 92.04%, respectively, and its concentration ratio was 40x. As for the niobite flotation, a closed-circuit experiment with one rougher flotation, three cleaner flotations, and two scavenger flotations was carried out to achieve the maximum niobite recovery. To further improve the niobite recovery, a leaching process with diluted HCl was employed; the final obtained Nb2O5 grade and recovery were 30.19% and 65.04%, respectively, and the concentration ratio reached 242x. Moreover, the economic evaluation implies that the flotation process can attract great positive interest.
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Papulovskiy, Evgeny, Aleksandr Shubin, and Olga Lapina. "Theoretical Modeling Of The Structure Of Surface Niobium Sites Based On Solid-State 93nb Nmr." Siberian Journal of Physics 11, no. 2 (June 1, 2016): 77–91. http://dx.doi.org/10.54362/1818-7919-2016-11-2-77-91.

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In this work niobium oxide clusters on the surface of Al2O3 are modeled using DFT calculations. 93Nb NMR parameters of modeled clusters were computed with the GIPAW method. The niobia system under consideration represents high niobium loading on the surface of the support. The niobium atoms are highly coordinated and linked to the other niobia polyhedra by one or two bonds. The most of the niobium oxide particles has a coordination number of six. The correlations found between 93Nb NMR parameters and coordination environment are discussed.
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Prasetyoko, Didik, Zainab Ramli, Salasiah Endud, and Hadi Nur. "Characterization and Catalytic Performance of Niobic Acid Dispersed over Titanium Silicalite." Advances in Materials Science and Engineering 2008 (2008): 1–12. http://dx.doi.org/10.1155/2008/345895.

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Niobic acid,Nb2O5⋅nH2O, has been supported on the titanium silicalite by impregnation method. The obtained materials were characterized by X-ray diffraction, infrared, and ultra-violet—visible diffuse reflectance spectroscopy, temperature programmed reduction, pyridine adsorption, and field emission scanning electron microscopy techniques. It was demonstrated that the tetrahedral titanium species still retained after impregnation of niobic acid. The results revealed that niobium species interacted with hydroxyl groups on the surface of TS-1. The niobium species in the catalysts are predominantly polymerized niobium oxides species or bulk niobium oxide with the octahedral structure. All catalysts showed both Brønsted and Lewis acid sites. The catalysts have been tested for epoxidation of 1-octene with aqueous hydrogen peroxide. It was found that the presence of niobic acid in the catalysts enhanced the rate of the formation of epoxide at the initial reaction time. Diol as a side product was also observed due to the acidic properties of the catalysts.
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Habazaki, H., M. Yamasaki, T. Ogasawara, K. Fushimi, H. Konno, K. Shimizu, T. Izumi, R. Matsuoka, P. Skeldon, and G. E. Thompson. "Thermal degradation of anodic niobia on niobium and oxygen-containing niobium." Thin Solid Films 516, no. 6 (January 2008): 991–98. http://dx.doi.org/10.1016/j.tsf.2007.06.127.

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5

Bliznyuk, Antonina, and Valentin Kozin. "NIOBIUM’S BEHAVIOR IN AQUEOUS HYDRO­FLUORIC ACID SOLUTION." Ukrainian Chemistry Journal 87, no. 8 (September 24, 2021): 116–26. http://dx.doi.org/10.33609/2708-129x.87.08.2021.116-126.

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Thanks to the unique combination of physicochemical properties, niobium and its compounds are widely used in various fields of science and technology. The main areas of niobium’s applications are the production of superconductors, nuclear energy, chemical engineering, metallurgy, manufacture of optically active materials, thin-film lithium batte­ries, fuel cells. The aim of this work is to study the processes that take place on the niobium electrode in aqueous solutions of hydrofluoric acid, as well as to establish the composition of niobium compounds that are formed. The paper presents the results of studies the behavior of the niobium electrode in aqueous solutions 0.25 N. hydrofluoric acid. The kinetic para­meters of the processes occurring at the phase boundary are determined. It was found that the anodic polarization of the niobium electrode is accompanied by the formation of a passive layer, the destruction of which is facilitated by increasing the polarization potential and fluorine anions, in the presence of which complex fluoroiobate anions [NbF7]2- and [NbOF5]2-are formed. Cathodic polarization of niobium is accompanied by the formation of hydrides on its surface, which causes an increase in the overvoltage of hydrogen evolution. The anodic polarization of the niobium electrode in a solution of hydrofluoric acid causes the formation on its surface of a passive layer, which is destroyed with increasing potential. In the Nbo–NbO2–0.25 –0.25 n HF system, [NbF7]2-anions are formed, as evidenced by bands in the region of 500 nm on the electron absorption spectra. The rate constants of [NbF7]2- and [NbOF5]2- formation are estimated at 3.78 • 10-3 s-1 and 5.18 • 10-3 s-1, respectively. The reduction of hydrogen at the niobium cathode from a solution of hydrofluoric acid is accompanied by the formation of hydrides, which causes an increase in the overvoltage of hydrogen evolution and high values of the angular coefficients of the Tafel dependence.
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Eckert,, J. "Niobium and Niobium Compounds." High Temperature Materials and Processes 11, no. 1-4 (January 1993): 97–118. http://dx.doi.org/10.1515/htmp.1993.11.1-4.97.

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Leont’ev, L. I., V. I. Zhuchkov, O. V. Zayakin, A. V. Sychev, and L. Yu Mikhailova. "Potential for obtaining and applying complex niobium ferroalloys." Izvestiya. Ferrous Metallurgy 65, no. 1 (February 11, 2022): 10–20. http://dx.doi.org/10.17073/0368-0797-2022-1-10-20.

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This paper provides information regarding the application of niobium in industry and the scale of its production in the world and the Russian Federation. Most of the niobium deposits in Russia consist of pyrochlore, apatitepyrochlore and columbitepyrochlore types of ores. They contain a significant amount of phosphorus. Therefore, all enrichment schemes for these ores contain a dephosphorization stage which increases the price of the product and reduces the degree of niobium extraction. The paper explores the possibility of improving the end-to-end production scheme: niobium ore – beneficiation – niobium ferroalloy. The bulk of ferroniobium is intended for steel microalloying and can be replaced by complex ferroalloys with a reduced niobium content. The paper considers the issues of obtaining complex niobium ferroalloys from a rough concentrate with a weak content of niobium. It has been established that the addition of 25 – 40 % of silicon or 12 – 30 % of aliminum to the twocomponent metal system Fe – Nb causes the transfer of niobium ferroalloys (15 – 20 % Nb) from the refractory category to lowmelting materials. The crystallization temperatures are less than 1400 °C. The substantiation of using a complex niobium ferroalloy instead of ferroniobium is given. This alloy has reduced niobium content and increased silicon or aluminum content. Higher service characteristics of the complex ferroalloy are noted in comparison with ferroniobium (temperature of the initiation of crystallization and density). They indicate an increased assimilation of niobium when using a complex ferroalloy for steel microalloying. The paper presents data on the possibility of dephosphorization of niobium concentrates in the process of pyrometallurgical production of a complex ferroalloy. An improved scheme for the production of niobiumcontaining ferroalloys is proposed. This consists of the use of niobium concentrate for melting the intermediate ferroalloy containing a reduced concentration of niobium oxides and an increased concentration of silicon (aluminum). This ferroalloy can be used effectively for steel microalloying with niobium.
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Störmer, H., E. Ivers-Tiffée, C. Schnitter, and D. Gerthsen. "Microstructure and dielectric properties of nanoscale oxide layers on sintered capacitor-grade niobium and V-doped niobium powder compacts." International Journal of Materials Research 97, no. 6 (June 1, 2006): 794–801. http://dx.doi.org/10.1515/ijmr-2006-0128.

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Abstract Electrolytic anodization was used to form amorphous niobium oxide layers on niobium and V-doped niobium powder compacts which act as dielectric layers, e. g. in niobium-based solid electrolyte capacitors. The microstructure development within the layered structure niobium-niobium oxide was studied by scanning- and transmission electron microscopy in order to investigate the influence of processing parameters. It could be shown that the thickness as well as the quality of the oxide layers on niobium vary in a considerable range, depending on processing parameters. Examination of the influence of heat treatments on the structural properties of the oxide layers revealed remarkable changes at the niobium – niobium oxide interface upon heat impact exceeding 300 °C. In contrast, the interface remains stable with respect to the as-anodized sample when annealing was performed at lower temperature.
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Liu, Cheng Jun, Ya He Huang, Hong Liang Liu, and Mao Fa Jiang. "Effects and Mechanisms of Niobium on the Fracture Toughness of Heavy Rail Steel." Advanced Materials Research 163-167 (December 2010): 110–16. http://dx.doi.org/10.4028/www.scientific.net/amr.163-167.110.

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Heavy rail steel was prepared by the process of vacuum induction furnace smelting, forge work and rolling. Effects and mechanisms of niobium on the fracture toughness of heavy rail steel were investigated. In addition, the appropriate range of niobium content for heavy rail steel was determined. With the niobium content increasing, both the austenite grain size and pearlite laminae distance of heavy rail steel were decreased gradually at first and then increased rapidly. When the niobium content was low, the precipitates containing niobium predominantly appeared in the cementite, which improved the toughness of heavy rail steel by fining the austenite grain size and pearlite laminae distance; when the niobium content > 0.024%, the fine dispersed precipitates containing niobium mainly occurred in the ferrite, which improved the toughness of heavy rail steel by pining dislocations and inhibiting crack growth; with the niobium content increasing, both the quantity and size of precipitates containing niobium were increased gradually; when the niobium content > 0.073%, most precipitates containing niobium could not pin dislocations and inhibit crack growth because the particles size was too big, thus the fracture toughness of heavy rail steel was bad. So the optimum range of the niobium content could improve the fracture toughness of heavy rail steel. In the present study, when the niobium content was about 0.053%, the fracture toughness of heavy rail steel was the best. The maximum plane-strain fracture toughness was 49.88 MPam1/2.
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ZURER, PAMELA S. "NIOBIUM." Chemical & Engineering News 81, no. 36 (September 8, 2003): 106. http://dx.doi.org/10.1021/cen-v081n036.p106.

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Dissertations / Theses on the topic "Niobium"

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Kajuch, Jan. "Synthesis, consolidation and properties of niobium(5) silicon(3) and laminated niobium(5) silicon(3)/niobium composites." Case Western Reserve University School of Graduate Studies / OhioLINK, 1993. http://rave.ohiolink.edu/etdc/view?acc_num=case1060712767.

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Rigney, Joseph David. "Ductile-phase toughening of in situ niobium silicide-niobium composites." Case Western Reserve University School of Graduate Studies / OhioLINK, 1994. http://rave.ohiolink.edu/etdc/view?acc_num=case1061304077.

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Beebe, Melissa R. "Highly-Correlated Electron Behavior in Niobium and Niobium Compound Thin Films." W&M ScholarWorks, 2017. https://scholarworks.wm.edu/etd/1499450045.

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Electron correlations are the root of many interesting phenomena in materials, including phase transitions such as superconductivity and insulator-to-metal transitions, which are of great interest both for scientific understanding and for many applications. Such phase transitions can often be tailored in thin films, in which the geometry of the material is limited in one dimension. By studying how the physical structure of a thin film affects its correlated electron response, it is possible to obtain useful insight into both the nature of the electron correlations present in the material and how to control them for various applications. Niobium, an elemental superconductor, has the highest critical temperature and lower critical field of the naturally-occurring superconductors, making it attractive for many applications, particularly in the superconducting radio frequency (SRF) community. Several niobium-based compounds are also superconductors of interest; while the bulk materials are fairly well-understood, there is still a great deal to learn regarding the effects of the microstructure of thin films of these materials on their superconducting properties. Another niobium compound, niobium dioxide, exhibits a phase transition from a room-temperature insulating state to a high-temperature metallic state. Such insulator-to-metal transitions are not well-understood, even in bulk, and there is a great deal of debate over the mechanism that drives them. Experimental studies on niobium dioxide thin films are still somewhat rare and thus have the potential to contribute a great deal to the understanding of the mechanisms behind the transition. This dissertation presents structure-property correlation studies on niobium and niobium compound superconducting thin films such as those discussed above, and also reports on the first experimental studies of the light-induced insulator-to-metal transition in niobium dioxide.
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Santos, Giovanny Carvalho dos [UNESP]. "Estudos sobre a síntese de derivados quinolínicos promovida pelo pentacloreto de nióbio para utilização como corantes sensibilizadores em dispositivos fotoeletroquímicos de gratzel." Universidade Estadual Paulista (UNESP), 2015. http://hdl.handle.net/11449/154719.

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Made available in DSpace on 2018-07-27T18:26:15Z (GMT). No. of bitstreams: 0 Previous issue date: 2015-02-24. Added 1 bitstream(s) on 2018-07-27T18:30:35Z : No. of bitstreams: 1 000871607.pdf: 7216802 bytes, checksum: 9abe1632634a9de4ee04f393445edbc7 (MD5)
Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
O desenvolvimento de novas estragégias sintéticas para uma eficiente produção de compostos orgânicos é de grande importância. Dentre estes compostos, os derivados quinolínicos apresentam uma variedade de aplicações em diversas áreas e estão presentes em diversas áreas e estão presentes em diversos produtos naturais e drogas. Assim, neste trabalho estudamos a síntese desses derivados utilizando o pentacloreto de nióbio como promotor em reações multicomponentes realizadas entre p-nitroanilina, fenilacetileno e derivados de benzaldeído, a temperatura ambiente, onde obtiveram-se bons rendimentos (54-98%) em um bom tempo reacional. Analisamos também a eficácia do pentacloreto de nióbio comparado a outros catalisadores, que demonstrou então que este é um bom promotor nesta reação. Foi realizada em seguida da redução do grupo nitro presente nos derivados quinolínicos sintetizados. Todos os compostos sintetizados foram submetidos a análises de caracterização estrutural, fotoquímica e fotofísica e os derivados aminoquinolínicos apresentaram maior potencial para aplicação como corantes sensibilizadores de dispositivos fotoeletroquímicos de Gratzel e para utilização em outros dispositivos eletrônicos orgânicos
The development of new synthetic strategies for an efficient production of organic compounds is very importante. Among these compounds, quinolites show a variety of applications in various areas and ares present in many natural products and drugs. Thus, in this work we have studied the synthesis of such derivatives by using niobium pentachloride as promoter in multicomponent reactions carried out between p-nitroaniline, phenylacetylene and benzaldehyde derivatives, at room temperature, which were obtained good yields (54-98%) in a good reaction time. We also analyze the effectiveness of niobium pentachloride compared to other catalysts, which showed that the NbCl5 is a good promoter in this reaction. We them carried the reduction of the nitro group present in the synthesized compounds were submitted to analysis of structural, photochemistry and photophysics characterization, aminoquinolines derivatives showed the highest potential for application as sensitizing dyes in photoelectrochemical devices of Gratzel and for use in order organic electronic devices
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5

Santos, Giovanny Carvalho dos. "Estudos sobre a síntese de derivados quinolínicos promovida pelo pentacloreto de nióbio para utilização como corantes sensibilizadores em dispositivos fotoeletroquímicos de gratzel /." Bauru, 2015. http://hdl.handle.net/11449/154719.

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Orientador: Luiz Carlos da Silva Filho
Banca: Valdecir Farias Ximenes
Banca: Marco Antonio Barbosa Ferreira
O Programa de Pós Graduação em Ciência e Tecnologia de Materiais, PosMat, tem caráter institucional e integra as atividades de pesquisa em materiais de diversos campi
Resumo: O desenvolvimento de novas estragégias sintéticas para uma eficiente produção de compostos orgânicos é de grande importância. Dentre estes compostos, os derivados quinolínicos apresentam uma variedade de aplicações em diversas áreas e estão presentes em diversas áreas e estão presentes em diversos produtos naturais e drogas. Assim, neste trabalho estudamos a síntese desses derivados utilizando o pentacloreto de nióbio como promotor em reações multicomponentes realizadas entre p-nitroanilina, fenilacetileno e derivados de benzaldeído, a temperatura ambiente, onde obtiveram-se bons rendimentos (54-98%) em um bom tempo reacional. Analisamos também a eficácia do pentacloreto de nióbio comparado a outros catalisadores, que demonstrou então que este é um bom promotor nesta reação. Foi realizada em seguida da redução do grupo nitro presente nos derivados quinolínicos sintetizados. Todos os compostos sintetizados foram submetidos a análises de caracterização estrutural, fotoquímica e fotofísica e os derivados aminoquinolínicos apresentaram maior potencial para aplicação como corantes sensibilizadores de dispositivos fotoeletroquímicos de Gratzel e para utilização em outros dispositivos eletrônicos orgânicos
Abstract: The development of new synthetic strategies for an efficient production of organic compounds is very importante. Among these compounds, quinolites show a variety of applications in various areas and ares present in many natural products and drugs. Thus, in this work we have studied the synthesis of such derivatives by using niobium pentachloride as promoter in multicomponent reactions carried out between p-nitroaniline, phenylacetylene and benzaldehyde derivatives, at room temperature, which were obtained good yields (54-98%) in a good reaction time. We also analyze the effectiveness of niobium pentachloride compared to other catalysts, which showed that the NbCl5 is a good promoter in this reaction. We them carried the reduction of the nitro group present in the synthesized compounds were submitted to analysis of structural, photochemistry and photophysics characterization, aminoquinolines derivatives showed the highest potential for application as sensitizing dyes in photoelectrochemical devices of Gratzel and for use in order organic electronic devices
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6

Ray, Arunim. "Niobium microalloyed rail steels." Thesis, University of Cambridge, 2017. https://www.repository.cam.ac.uk/handle/1810/265387.

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Rail steels rely primarily on possessing adequate wear and rolling contact fatigue resistance. These properties, together with the toughness, can in principle be optimized by implementing thermomechanical processing assisted by controlled niobium additions. The purpose of the current work is to develop a Nb-microalloying strategy in the context of high-carbon pearlitic and cementite-free bainitic steels. The conventional methods do not leave the critical regions of a rail section in a suitably processed state. An attempt has been made for the first time, to create a pancaked austenite grain structure, with an examination of the consequences on the final product. One of the major difficulties is to ensure that niobium does not segregate during manufacturing, since niobium is a strong carbide former and rail steels traditionally contain large carbon concentrations. Niobium solubility in austenite has been assessed critically and thermodynamic calculations for microsegregation have been taken into account. The aim is to ensure that any primary niobium carbide precipitated from solute-enriched liquid during non-equilibrium solidification, can be taken into solution in austenite during reheating, to mitigate potential effects of coarse precipitates on the final mechanical properties. Rail steels containing 0.01-0.02 wt% Nb have been designed and characterised. In as-cast condition, primary niobium carbides as large as ~10 µm can be observed, which dissolve slowly during reheating. An attempt has been made to develop a model to estimate the dissolution kinetics of the carbides. Dissolved niobium in reheated austenite precipitates during hot deformation as fine niobium carbides (< 50 nm) which inhibit austenite recrystallisation by pinning the austenite grain boundaries. Nb-microalloying increases the ‘no-recrystallisation temperature’ of deformed austenite during multi-pass compression tests. The topology of grain deformation has been analysed in terms of stereological calculations and dilatometric experiments have shown that transformation kinetics tend to accelerate when the austenite is deformed below the no-recrystallisation temperature, however the effect is relatively small. The microstructure and mechanical properties of the as-rolled Nb-microalloyed steels have been characterised along with their rolling-sliding wear performance and compared with their non-microalloyed counterparts. Increased austenite grain boundary area and increased dislocation activity due to pancaking, hinder bainite growth which leads to an increased retained austenite volume fraction. This in turn, leads to slightly improved ductility, improved toughness and improved wear resistance in Nb-microalloyed bainitic alloys. Microstructural refinement in Nbmicroalloyed pearlitic alloys does not have any significant effect on tensile and toughness properties, but wear resistance improves significantly. A Bayesian neural network model has been developed to estimate the wear of rails. Predicted trends have been found consistent with metallurgical experience and the perceived noise levels are consistent with reasonable repeatability of the wear testing method used. The model can be applied widely to estimate wear because of its capacity to indicate uncertainty, including both the perceived level of noise in the output, and an uncertainty associated with fitting the function in the local region of input space.
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Oshiro, Paula Beatriz. "Estudos sobre a síntese de 4H-Cromenos promovida pelo pentacloreto de nióbio para utilização como corantes sensibilizadores em células solares /." Bauru, 2015. http://hdl.handle.net/11449/154718.

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Orientador: Luiz Carlos da Silva Filho
Banca: Daniel Rinaldo
Banca: Antonio Eduardo Miller Crotti
O Programa de Pós Graduação em Ciência e Tecnologia de Materiais, PosMat, tem caráter institucional e integra as atividades de pesquisa em materiais de diversos campi
Resumo: Os derivados de 4H-cromemos constituem uma importante classe de produtos naturais, e o interesse em sua química se dá por conta dos inúmeros efeitos biológicos e farmacêuticos, assim como sua utilização como intermediários nas sínteses de inúmeros produtos naturais e reagentes medicinais. Esses derivados podem ser obtidos através das reações multicomponentes (RMC). As RMC's ocorrem entre três ou mais reagentes em uma única etapa reacional, ao mesmo tempo frasco. São reações com economia de tempo e energia. O pentacloreto de nióbio é um ácido de Lewis forte, que apresenta grande aplicabilidade em reações orgânicas, incluindo as reações multicomponentes. Dentre os diversos métodos de síntese de derivados de 4H-cromenos, desenvolveu-se neste trabalho a síntese através da reação multicomponente entre derivados de benzaldeído, 3,5-dimetóxifenol e acetoacetato de metila, utilizando pentacloreto de nióbio como ácido de Lewis. As reações foram realizadas a temperatura ambiente, sob atmosfera inerte (n2) e utilizando diclorometano anidro (CH2Cl2) como solvente, com um tempo reacional de 72 horas. Os produtos obtidos foram isolados por coluna cromatográfica em sílica gel e submetidos a análises de caracterização estrutural, fotoquímica e fotofísica para um estudo de sua potencial aplicação como corantes sensibilizadores de dispositivos fotoeletroquímicos de Gratzel. A análise dos resultados obticos demonstram que o pentacloreto de nióbio é um bom promotor da reação multicomponente, obtendo-se bons rendimentos (62 a 91%)
Abstract: 4H-chromete derivatives constitute an important class of natural products, and the the interest in its chemical occurs because of the numerous biological and pharmaceutical effects, as well their use a intermediates in the synthesis of numerous natural products and medicinal reagents. These derivatives can be obtained thorugh the multicomponent reactions (MCR). The MCR's occur between three or more reagents in one reaction step only, in the same pot. These reactions have time and energy saving. The niobium pentachloride is strong Lewis acid, which has wide applicabiblity in organic reactions, including multicomponent reactions. Among, the various methods of synthesis of 4H-chromene derivatives, developed in this work, the synthesis by multicomponent reactions between benzaldehyde derivatives, 3,5-dimethoxyphenol and methyl acetoacetate, using niobium pentachloride as the Lewis acid, is described. The reactions were carried out at room temperature, under inert atmosphere (N2), using dichloromethane anhydrous (CH2Cl2) as solvent with a reaction time of 72 hours. The obtained products were isolated by column chromatography on silica gel and subject to analysis of structural characterization, photophysics and photochemistry for a study of their potential use as sensitizing dyes of Gratzel photoelectrochemical devices. Our results show that niobium pentachloride is a good promoter to multicomponent reaction studied, obtaining high yields (62-91%)
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8

Oshiro, Paula Beatriz [UNESP]. "Estudos sobre a síntese de 4H-Cromenos promovida pelo pentacloreto de nióbio para utilização como corantes sensibilizadores em células solares." Universidade Estadual Paulista (UNESP), 2015. http://hdl.handle.net/11449/154718.

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)
Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
Os derivados de 4H-cromemos constituem uma importante classe de produtos naturais, e o interesse em sua química se dá por conta dos inúmeros efeitos biológicos e farmacêuticos, assim como sua utilização como intermediários nas sínteses de inúmeros produtos naturais e reagentes medicinais. Esses derivados podem ser obtidos através das reações multicomponentes (RMC). As RMC's ocorrem entre três ou mais reagentes em uma única etapa reacional, ao mesmo tempo frasco. São reações com economia de tempo e energia. O pentacloreto de nióbio é um ácido de Lewis forte, que apresenta grande aplicabilidade em reações orgânicas, incluindo as reações multicomponentes. Dentre os diversos métodos de síntese de derivados de 4H-cromenos, desenvolveu-se neste trabalho a síntese através da reação multicomponente entre derivados de benzaldeído, 3,5-dimetóxifenol e acetoacetato de metila, utilizando pentacloreto de nióbio como ácido de Lewis. As reações foram realizadas a temperatura ambiente, sob atmosfera inerte (n2) e utilizando diclorometano anidro (CH2Cl2) como solvente, com um tempo reacional de 72 horas. Os produtos obtidos foram isolados por coluna cromatográfica em sílica gel e submetidos a análises de caracterização estrutural, fotoquímica e fotofísica para um estudo de sua potencial aplicação como corantes sensibilizadores de dispositivos fotoeletroquímicos de Gratzel. A análise dos resultados obticos demonstram que o pentacloreto de nióbio é um bom promotor da reação multicomponente, obtendo-se bons rendimentos (62 a 91%)
4H-chromete derivatives constitute an important class of natural products, and the the interest in its chemical occurs because of the numerous biological and pharmaceutical effects, as well their use a intermediates in the synthesis of numerous natural products and medicinal reagents. These derivatives can be obtained thorugh the multicomponent reactions (MCR). The MCR's occur between three or more reagents in one reaction step only, in the same pot. These reactions have time and energy saving. The niobium pentachloride is strong Lewis acid, which has wide applicabiblity in organic reactions, including multicomponent reactions. Among, the various methods of synthesis of 4H-chromene derivatives, developed in this work, the synthesis by multicomponent reactions between benzaldehyde derivatives, 3,5-dimethoxyphenol and methyl acetoacetate, using niobium pentachloride as the Lewis acid, is described. The reactions were carried out at room temperature, under inert atmosphere (N2), using dichloromethane anhydrous (CH2Cl2) as solvent with a reaction time of 72 hours. The obtained products were isolated by column chromatography on silica gel and subject to analysis of structural characterization, photophysics and photochemistry for a study of their potential use as sensitizing dyes of Gratzel photoelectrochemical devices. Our results show that niobium pentachloride is a good promoter to multicomponent reaction studied, obtaining high yields (62-91%)
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Siqueira, Mayara de Souza. "Estudo sobre a síntese dos derivados de 4H-piranos e 1,4-di-hidropiridinas via reação multicomponente de Hantzsch promovida pelo pentacloreto de nióbio /." Bauru, 2017. http://hdl.handle.net/11449/150660.

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Orientador: Luiz Carlos da Silva Filho
Banca: Rosangela da Silva de Laurentiz
Banca: Gilbert Bannach
Resumo: Compostos heterocíclicos constituem a maior e mais variada família de compostos orgânicos. Dentre esses compostos temos os derivados de 4H-piranos e 1,4-di-hidropiridinas (1,4-DHPs), que são importantes classes de moléculas bioativas. O interesse em sua química se dá por conta dos inúmeros efeitos biológicos e farmacêuticos que estes derivados apresentam, assim como sua utilização como intermediários reacionais nas sínteses de inúmeros produtos naturais. Existem diversas metodologias para a síntese de derivados dessas moléculas. O objetivo deste trabalho foi investigar a utilização do NbCl5 como ácido de Lewis na síntese de derivados de 4H-piranos e 1,4-di-hidropiridinas através de reações multicomponentes, via metodologia de Hantzsch. Reações entre acetoacetato de metila e diferentes aldeídos aromáticos foram realizados na presença de NbCl5. As reações mostraram que o NbCl5 é um bom ácido de Lewis para a síntese de derivados de 4H-piranos, em uma única etapa e com rendimentos satisfatórios (77 a 91%). Foi realizado um estudo detalhado verificando o efeito do solvente, da concentração molar de NbCl5 e o efeito dos substituintes presentes nos aldeídos aromáticos nessas reações, com relação ao tempo reacional e rendimento das reações. Observamos que quando as reações foram realizadas em EtOH e MeOH como solventes, não ocorre a formação dos derivados de 4H-piranos. Também foi observado que não houve diferença nos rendimentos e tempos reacionais quando utilizado diferentes substi... (Resumo completo, clicar acesso eletrônico abaixo)
Abstract: Heterocyclic compounds constitute the largest and most varied family of organic compounds. Among these compounds are derivatives of 4H-pyrans and 1,4-dihydropyridines (1,4-DHPs), which are an important class of bioactive molecules and interest in their chemical occurs due to the numerous biological and pharmaceutical effects, as well as their use as intermediates in the total syntheses of many natural products. There are various methodologies for the synthesis of derivatives of these molecules. The objective of this work was to investigate the use of NbCl5 as Lewis acid in the synthesis of derivatives of 4H-pyrans and 1,4-dihydropyridines through multicomponent reactions, using Hantzsch's methodology. Reactions between methyl acetoacetate and different aromatic aldehydes were performed in the presence of NbCl5. The reactions showed that NbCl5 is a good Lewis acid for the synthesis of 4H-pyran derivatives in a single step and in satisfactory yields (77 to 91%). A detailed study was carried out verifying the solvent effect, the molar concentration of NbCl5 and the effect of the substituents present on the aromatic aldehydes in these reactions, with respect to the reaction time and yield of the reactions. We note that when the reactions were carried out in EtOH and MeOH as solvents, the formation of 4H-pyran derivatives does not occur. It was also observed that there was no difference in yields and reaction times when different substituents were used in the aromatic aldehydes. A... (Complete abstract click electronic access below)
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Song, Gang. "Hydrogen in thin niobium films." [S.l. : s.n.], 2000. http://deposit.ddb.de/cgi-bin/dokserv?idn=961906529.

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Books on the topic "Niobium"

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Cunningham, Larry D. Columbium (niobium) and tantalum. Washington, D.C: U.S. Department of the Interior, Bureau of Mines, 1991.

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Gupta, C. K. Extractive metallurgy of niobium. Boca Raton: CRC Press, 1994.

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Möller, Peter, Petr Černý, and Francis Saupé, eds. Lanthanides, Tantalum and Niobium. Berlin, Heidelberg: Springer Berlin Heidelberg, 1989. http://dx.doi.org/10.1007/978-3-642-87262-4.

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Leite, Rogério C. de Cerqueira, 1931-, ed. Nióbio, uma conquista nacional. São Paulo: Livraria Duas Cidades, 1988.

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Petrasek, Donald W. Creep behavior of tungsten/niobium and tungsten/niobium-1 percent zirconium composites. Washington, DC: U.S. Dept. of Energy, Nuclear Energy, Reactor Systems Development and Technology, 1988.

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TMS Symposium on Niobium and Niobium Alloys in Superconducting Applications (1987 Denver, Colo.). Superconducting applications of niobium: Containing papers presented at the TMS Symposium on Niobium and Niobium Alloys in Superconducting Applications, February 24-27, 1987. Edited by Carlson O. Norman. London: Elsevier Applied Science, 1988.

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Miller, Frederick W. Columbium availability--market economy countries: A minerals availability appraisal. [Washington, DC] (2401 E St. NW, Washington 20241): U.S. Dept. of the Interior, Bureau of Mines, 1986.

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Miller, Frederick W. Columbium availability--market economy countries: A minerals availability appraisal. Washington, DC: U.S. Dept. of the Interior, 1986.

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Wong, Thomas M., and Thomas M. Wong. Niobium: Properties, production, and applications. Hauppauge, N.Y: Nova Science Publishers, 2010.

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Wong, Thomas M. Niobium: Properties, production, and applications. Hauppauge, N.Y: Nova Science Publishers, 2010.

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Book chapters on the topic "Niobium"

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Kurtz, Wolfgang, and Hans Vanecek. "Niobium." In W Tungsten, 103–6. Berlin, Heidelberg: Springer Berlin Heidelberg, 1987. http://dx.doi.org/10.1007/978-3-662-08690-2_17.

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Münker, Carsten. "Niobium." In Encyclopedia of Earth Sciences Series, 1–3. Cham: Springer International Publishing, 2016. http://dx.doi.org/10.1007/978-3-319-39193-9_262-1.

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Münker, Carsten. "Niobium." In Encyclopedia of Earth Sciences Series, 983–85. Cham: Springer International Publishing, 2018. http://dx.doi.org/10.1007/978-3-319-39312-4_262.

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Crowson, Phillip. "Niobium." In Minerals Handbook 1992–93, 179–84. London: Palgrave Macmillan UK, 1992. http://dx.doi.org/10.1007/978-1-349-12564-7_28.

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Crowson, Phillip. "Niobium." In Minerals Handbook 1994–95, 189–94. London: Palgrave Macmillan UK, 1994. http://dx.doi.org/10.1007/978-1-349-13431-1_30.

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Crowson, Phillip. "Niobium." In Minerals Handbook 1996–97, 264–71. London: Palgrave Macmillan UK, 1996. http://dx.doi.org/10.1007/978-1-349-13793-0_31.

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Brookins, Douglas G. "Niobium." In Eh-pH Diagrams for Geochemistry, 110–11. Berlin, Heidelberg: Springer Berlin Heidelberg, 1988. http://dx.doi.org/10.1007/978-3-642-73093-1_44.

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Shabalin, Igor L. "Niobium." In Ultra-High Temperature Materials I, 531–607. Dordrecht: Springer Netherlands, 2014. http://dx.doi.org/10.1007/978-94-007-7587-9_8.

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Mishra, B., and P. Termsuksawad. "Niobium." In Review of Extraction, Processing, Properties & Applications of Reactive Metals, 83–134. Hoboken, NJ, USA: John Wiley & Sons, Inc., 2013. http://dx.doi.org/10.1002/9781118788417.ch3.

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Labinger, J. A. "Nb Niobium." In Organometallic Compounds of the Lanthanides, Actinides and Early Transition Metals, 118–26. Boston, MA: Springer US, 1985. http://dx.doi.org/10.1007/978-1-4899-7164-7_17.

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Conference papers on the topic "Niobium"

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TSIRKUNOVA, N. G., A. A. LESHOK, and D. A. SASINOVICH. "NANOSTRUCTURES BASED ON POROUS NIOBIUM AND NIOBIA." In Proceedings of the International Conference on Nanomeeting 2007. WORLD SCIENTIFIC, 2007. http://dx.doi.org/10.1142/9789812770950_0107.

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Graham, Ronald A. "RRR Niobium Manufacturing Experience." In SINGLE CRYSTAL - LARGE GRAIN NIOBIUM TECHNOLOGY: International Niobium Workshop. AIP, 2007. http://dx.doi.org/10.1063/1.2770692.

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Antoine, Claire. "Single And Large Grain Activities At Fermilab." In SINGLE CRYSTAL - LARGE GRAIN NIOBIUM TECHNOLOGY: International Niobium Workshop. AIP, 2007. http://dx.doi.org/10.1063/1.2770683.

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Pagani, Carlo. "Overview of ILC." In SINGLE CRYSTAL - LARGE GRAIN NIOBIUM TECHNOLOGY: International Niobium Workshop. AIP, 2007. http://dx.doi.org/10.1063/1.2770675.

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Graham, Ronald A. "Single Crystal Technology for Making RRR Niobium Sheet." In SINGLE CRYSTAL - LARGE GRAIN NIOBIUM TECHNOLOGY: International Niobium Workshop. AIP, 2007. http://dx.doi.org/10.1063/1.2770676.

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Myneni, Ganapati Rao. "Physical and Mechanical Properties of Niobium for SRF Science and Technology." In SINGLE CRYSTAL - LARGE GRAIN NIOBIUM TECHNOLOGY: International Niobium Workshop. AIP, 2007. http://dx.doi.org/10.1063/1.2770677.

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Gnäupel-Herold, Thomas, Ganapati Rao Myneni, and Richard E. Ricker. "Investigations of Residual Stresses and Mechanical Properties of Single Crystal Niobium for SRF Cavities." In SINGLE CRYSTAL - LARGE GRAIN NIOBIUM TECHNOLOGY: International Niobium Workshop. AIP, 2007. http://dx.doi.org/10.1063/1.2770678.

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Ricker, R. E., D. J. Pitchure, and G. R. Myneni. "Interstitial Solutes and Deformation in Nb and Nb Single Crystals." In SINGLE CRYSTAL - LARGE GRAIN NIOBIUM TECHNOLOGY: International Niobium Workshop. AIP, 2007. http://dx.doi.org/10.1063/1.2770679.

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Batchelor, A. D., D. N. Leonard, P. E. Russell, F. A. Stevie, D. P. Griffis, and G. R. Myneni. "TEM and SIMS Analysis of (100), (110), and (111) Single Crystal Niobium." In SINGLE CRYSTAL - LARGE GRAIN NIOBIUM TECHNOLOGY: International Niobium Workshop. AIP, 2007. http://dx.doi.org/10.1063/1.2770680.

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Kneisel, P., G. R. Myneni, G. Ciovati, J. Sekutowicz, and T. Carneiro. "Development of Large Grain/Single Crystal Niobium Cavity Technology at Jefferson Lab." In SINGLE CRYSTAL - LARGE GRAIN NIOBIUM TECHNOLOGY: International Niobium Workshop. AIP, 2007. http://dx.doi.org/10.1063/1.2770681.

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Reports on the topic "Niobium"

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Van Rythoven, Adrian. Critical mineral: Niobium. Montana Bureau of Mines and Geology, March 2024. http://dx.doi.org/10.59691/uakl2872.

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Burakovsky, Leonid, Samuel R. Baty, Dean Laverne Preston, Sky K. Sjue, and Darby Jon Luscher. Thermoelasticity Model for Niobium. Office of Scientific and Technical Information (OSTI), August 2019. http://dx.doi.org/10.2172/1558934.

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Champion, David. Australian resource reviews: niobium 2018. Geoscience Australia, 2019. http://dx.doi.org/10.11636/9781925848304.

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Kuchnir, M., and R. E. Hiller. Welding of niobium to stainless. Office of Scientific and Technical Information (OSTI), November 1993. http://dx.doi.org/10.2172/10195094.

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Norman, J. H., and G. H. Reynolds. Chemical Vapor Synthesis of Niobium Aluminides. Fort Belvoir, VA: Defense Technical Information Center, October 1988. http://dx.doi.org/10.21236/ada202591.

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Smith, A. B., D. L. Smith, and R. J. Howerton. Evaluated nuclear-data file for niobium. Office of Scientific and Technical Information (OSTI), March 1985. http://dx.doi.org/10.2172/5817931.

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Mueller, G. E. Radioactivity analysis in niobium activation foils. Office of Scientific and Technical Information (OSTI), June 1995. http://dx.doi.org/10.2172/426967.

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D.F.Teter, P.K. Tubesing, D.J.Thoma, and E.J.Peterson. Density Prediction of Uranium-6 Niobium Ingots. Office of Scientific and Technical Information (OSTI), April 2003. http://dx.doi.org/10.2172/810685.

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Plodinec, M. J. Free energy of hydration of niobium oxide. Office of Scientific and Technical Information (OSTI), August 1996. http://dx.doi.org/10.2172/525049.

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Smolik, G. R., and K. A. McCarthy. Oxidation and volatilization of a niobium alloy. Office of Scientific and Technical Information (OSTI), July 1992. http://dx.doi.org/10.2172/6918220.

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