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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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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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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 FilhoBanca: 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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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 FilhoBanca: 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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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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000871485.pdf: 4448809 bytes, checksum: 076304fcbd569aa83db5f6ca2b2bbcff (MD5)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 FilhoBanca: 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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Humphries, Martin J. "Studies in niobium imido chemistry." Thesis, University of Oxford, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.302068.
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Malyshev, Dimitriy. "Photochemical Synthesis of Niobium Nanoparticles." Thèse, Université d'Ottawa / University of Ottawa, 2014. http://hdl.handle.net/10393/30999.
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This thesis focuses on the development of method to the photochemical synthesis of niobium nanoparticles (NbNP) using Irgacure 907 (I-907) photoinitiator. This investigation is composed of two parts; whereas the mechanistic study of formation of particles was investigated first, and then followed by particles property characterization. By studying the mechanism of formation we were able to obtain knowledge on how to control the size of NbNP. This knowledge provided us with ability to generate a library of nanoparticles with the varying sizes. Furthermore, the study of I-907 photoproducts has given insight for an alternative method for the synthesis of NbNP using a milder reducing agent, 4-(methylthio)benzaldehyde (MSBA).
Exposure of NbNP to air causes their oxidation leading to the formation of niobium oxide nanoparticles (NbONP). The oxidation of NbONP was characterized with variety of techniques (XPS, EDS and HRTEM) that demonstrated the core-shell structure of the nanoparticles. These methods indicated that the core is metallic Nb0 and the shell is the niobium oxide, Nb2O5. Since Nb2O5 is known be a strong Brønsted acid, we tested the Brønsted activity of NbONP with pH sensitive dye coumarin-6 (C6) (monitored using fluorescence and UV-vis). The results of these spectroscopic experiments indicated that NbONP can protonate C6, thus serving as confirmation for the acidity of NbONP. Furthermore, particles with varying sizes were tested with C6 to check if the difference in size affects the acidity. It was observed that the particles with the larger sizes have the strongest acidity and the particles of smaller sizes are less acidic.
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Kim, Yoomi. "Oxidation of niobium-aluminium alloys." Thesis, University of Cambridge, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.624866.
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Moro, Ramiro Alfredo. "Ferroelectricity in free niobium clusters." Diss., Available online, Georgia Institute of Technology, 2004:, 2003. http://etd.gatech.edu/theses/available/etd-04062004-164744/unrestricted/moro%5Framiro%5Fa%5F200312%5Fphd.pdf.
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Bach, David [Verfasser], and D. [Akademischer Betreuer] Gerthsen. "EELS investigations of stoichiometric niobium oxides and niobium-based capacitors / David Bach. Betreuer: D. Gerthsen." Karlsruhe : KIT-Bibliothek, 2009. http://d-nb.info/1014222036/34.
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Marana, Naiara Letícia [UNESP]. "Preparação e caracterização estrutural de complexos quirais de nióbio, utilizando álcoois terpênicos quirais como ligantes." Universidade Estadual Paulista (UNESP), 2013. http://hdl.handle.net/11449/99713.
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marana_nl_me_bauru.pdf: 1709941 bytes, checksum: 717fd3e0400bc82b06520df05560ea02 (MD5)Compostos de nióbio tem despertado interesse na comunidade científica devido as suas aplicações como, por exemplo, na preparação de β-mercaptanas, síntese de 3,4-dihidropinimidinonas (reação de Biginelli), síntese de β-cetoésteres, acilação de Friedel-Crafts, acilação de alcoóis e fenóis, entre outras. Dentre os compostos utilizados como catalisadores em reações orgânicas, o pentacloreto de nióbio (NbCI5) é o que apresenta um maior destaque, entretanto, mais recentemente, o desenvolvimento de catalisadores quirais de Nióbio vem ganhando destaque no cenário científico, através da complexação de alcoois quirais a alcóxidos de Nióbio [Nb(OMe)5 e Nb(OEt)5]. Deste modo, este trabalho teve como objetivo o desenvolvimento de novos catalisadores quirais de nióbio, utilizando alcoois terpêuticos quirais como ligantes, através da realização de um estudo teórico/experimental da conformação destes catalisadores. Para a obtenção destes complexos foram utilizados o pentaetóxido de nióbio [Nb(OEt)5] e diferentes álcoois terpêuticos quirais [(+)-mentol, (-)-mentol, (+)-pinanodiol e (-)-pinanodiol]. Ao final deste trabalho, concluiu-se que a conformação adotada do Nb(OEt)5 é do tipo monomérica bipirâmide trigonal quando o composto se encontra em solução e dimérica, em sua forma pura, o que pode ser confirmada com espectros de infravermelho e ressonância magnética nuclear (RMN) de 13C e 1H e comparado com os espectros obtidos teoricamente. Através dos estudos teórico/experimentais, verificou-se que, para os complexos de pinanodiol, duas estruturas são formadas, sendo que a maior proporção é a octaédrica e de menor proporção a bipirâmide trigonal. Para os complexos formados com o mentol, foi possível determinar que são formadas três estruturas após a complexação, sendo uma octaédrica e duas na conformação de bipirâmide trigonal
Niobium compounds have shown interesting results due to their applications in organic synthesis, such as preparation of β-mercaptans, in Biginelli reactions, β-keto esters synthesis, Friedel-Crafts acylation, among others. Niobium pentachloride (NbCI5) is the most used as catalyst in organic synthesis; however, recently, the development of chiral Niobium catalysts has been gaining attention in the scientific area, by complexing from chiral alcohols to Niobium of the alcoxides [Nb(OMe)5 and Nb(OEt)5]. Thus, this work aimed to the development and analysis of chiral niobium catalysts Nb(OEt)5 using terpenic alcohols as ligands [(+)-menthol, (-)-menthol, (-)-pinanediol and (+)-pinanediol], through theoretical/experimental study of conformation of these chiral compounds. At the end of this study, it was concluded that the conformation adopted by Nb(OEt)5 is a monomer type trigonal bipyramid when the compound is in solution and when it is in pure state is a dimmer, that was confirmed by infrared an nuclear magnetic resonance (NMR) spectra, and compared them with theoretical results. Through theoretical/experimental calculations, it was found that, for the pinanediol complexes, two structures can be formed and the structure in a greater proportion formed is an octahedral type, and the less proportion formed is a trigonal bypyramid. For the menthol compounds, the analysis showed that three structures can be formed and the structure in a greater proportion is an octahedral type and two trigonal bipyramid ones
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Santos, Willian Henrique dos. "Estudos sobre a síntese e caracterização de derivados cumarínicos e xantênicos promovida pelo pentacloretro de nióbio /." Bauru, 2017. http://hdl.handle.net/11449/148920.
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Orientador: Luiz Carlos da Silva FilhoBanca: Kleber Thiago de Oliveira
Banca: Fabio Gorzoni Doro
Banca: Valdecir Farias Ximenes
Banca: Manoel Lima de Menezes
Resumo: A demanda por fontes de energias renováveis já é uma necessidade mundial, pois, o crescimento populacional e industrial trouxe concomitantemente um aumento no consumo de energia. Infelizmente, a matriz energética dos países que estão em pleno desenvolvimento se baseia na queima de combustíveis fósseis, o que traz sérios problemas ambientais e para a saúde da população. Tendo em vista esta necessidade, este trabalho retrata o estudo sobre o uso do pentacloreto de nióbio (NbCl5) como ácido de Lewis em reações multicomponentes para a síntese de compostos derivados de cumarinas e xantenos, compostos com potencial aplicação como corantes sensibilizadores em dispositivos fotovoltaicos. Os compostos de interesse foram obtidos através dos reagentes de partida: 4-hidróxicumarina, derivados fenólicos 3,5-dimetóxifenol e 3,4,5-trimetóxifenol, aldeídos aromáticos e 1,3-ciclo-hexanodiona. Foram estudadas as condições reacionais (% NbCl5, solvente utilizado e tempo reacional) para se estabelecer protocólos de síntese para a formação dos produtos de interesse na presença do pentacloreto de nióbio. O pentacloreto de nióbio demonstrou ser capaz de promover as reações estudadas neste trabalho. Esta nova possibilidade de obtenção destes compostos é de fundamental importância, pois, estes compostos possuem um leque muito amplo de aplicações, das quais algumas foram citadas neste trabalho.
Abstract: The demand for renewable energy sources is already a worldwide need, because, the population and industrial growth concurrently brought an increase in energy consumption. Unfortunately, the energy matrix of the countries that are in full development is based on burning fossil fuels, which causes serious environmental problems and the health of the population. In view of this need, this work shows that the study about the use of niobium pentachloride (NbCl5) as Lewis acid in multicomponent reactions for the synthesis of coumarin and xanthene derivatives of compounds with potential application as sensitizing dyes in photovoltaic devices. These compounds were obtained from the starting materials: 4-hydroxycoumarin, phenolic derivatives (3,5-dimethoxyphenol and 3,4,5-trimethoxyfenol, aromatic aldehydes and 1,3-cyclohexanedione. The reaction conditions (% NbCl5, solvent and reaction time) to establish protocols synthesis for the formation of the products in the presence of niobium pentachloride were studied.Niobium pentachloride has been shown to be capable of promoting the reactions studied in this work. This new method of obtaining these compounds is of fundamental importance, considering that these compounds have a wide range of applications, some of which have been cited in this work
Doutor
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Marana, Naiara Letícia. "Preparação e caracterização estrutural de complexos quirais de nióbio, utilizando álcoois terpênicos quirais como ligantes /." Bauru, 2013. http://hdl.handle.net/11449/99713.
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Orientador: Luiz Carlos da Silva FilhoBanca: Alexandre Fontes da Fonseca
Banca: Álvaro Cunha Neto
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 da Unesp
Resumo: Compostos de nióbio tem despertado interesse na comunidade científica devido as suas aplicações como, por exemplo, na preparação de β-mercaptanas, síntese de 3,4-dihidropinimidinonas (reação de Biginelli), síntese de β-cetoésteres, acilação de Friedel-Crafts, acilação de alcoóis e fenóis, entre outras. Dentre os compostos utilizados como catalisadores em reações orgânicas, o pentacloreto de nióbio (NbCI5) é o que apresenta um maior destaque, entretanto, mais recentemente, o desenvolvimento de catalisadores quirais de Nióbio vem ganhando destaque no cenário científico, através da complexação de alcoois quirais a alcóxidos de Nióbio [Nb(OMe)5 e Nb(OEt)5]. Deste modo, este trabalho teve como objetivo o desenvolvimento de novos catalisadores quirais de nióbio, utilizando alcoois terpêuticos quirais como ligantes, através da realização de um estudo teórico/experimental da conformação destes catalisadores. Para a obtenção destes complexos foram utilizados o pentaetóxido de nióbio [Nb(OEt)5] e diferentes álcoois terpêuticos quirais [(+)-mentol, (-)-mentol, (+)-pinanodiol e (-)-pinanodiol]. Ao final deste trabalho, concluiu-se que a conformação adotada do Nb(OEt)5 é do tipo monomérica bipirâmide trigonal quando o composto se encontra em solução e dimérica, em sua forma pura, o que pode ser confirmada com espectros de infravermelho e ressonância magnética nuclear (RMN) de 13C e 1H e comparado com os espectros obtidos teoricamente. Através dos estudos teórico/experimentais, verificou-se que, para os complexos de pinanodiol, duas estruturas são formadas, sendo que a maior proporção é a octaédrica e de menor proporção a bipirâmide trigonal. Para os complexos formados com o mentol, foi possível determinar que são formadas três estruturas após a complexação, sendo uma octaédrica e duas na conformação de bipirâmide trigonal
Abstract: Niobium compounds have shown interesting results due to their applications in organic synthesis, such as preparation of β-mercaptans, in Biginelli reactions, β-keto esters synthesis, Friedel-Crafts acylation, among others. Niobium pentachloride (NbCI5) is the most used as catalyst in organic synthesis; however, recently, the development of chiral Niobium catalysts has been gaining attention in the scientific area, by complexing from chiral alcohols to Niobium of the alcoxides [Nb(OMe)5 and Nb(OEt)5]. Thus, this work aimed to the development and analysis of chiral niobium catalysts Nb(OEt)5 using terpenic alcohols as ligands [(+)-menthol, (-)-menthol, (-)-pinanediol and (+)-pinanediol], through theoretical/experimental study of conformation of these chiral compounds. At the end of this study, it was concluded that the conformation adopted by Nb(OEt)5 is a monomer type trigonal bipyramid when the compound is in solution and when it is in pure state is a dimmer, that was confirmed by infrared an nuclear magnetic resonance (NMR) spectra, and compared them with theoretical results. Through theoretical/experimental calculations, it was found that, for the pinanediol complexes, two structures can be formed and the structure in a greater proportion formed is an octahedral type, and the less proportion formed is a trigonal bypyramid. For the menthol compounds, the analysis showed that three structures can be formed and the structure in a greater proportion is an octahedral type and two trigonal bipyramid ones
Mestre
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Cabanel, Régis. "Elaboration, caractérisation et propriétés électroniques de couches minces de nitrure de niobium et d'oxyde de niobium." Grenoble INPG, 1986. http://www.theses.fr/1986INPG0051.
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Etude, entre 1 et 300 k, de la conductivite de couches minces granulaires. Mise en evidence d'une supraconductivite dans des films avec coefficient de temperature negatif. Mesures de reflexion optique dans le visible; la correlation avec les mesures de conductivite electrique
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Cabanel, Régis. "Elaboration, caractérisation et propriétés électroniques de couches minces de nitrure de niobium et d'oxyde de niobium." Grenoble 2 : ANRT, 1986. http://catalogue.bnf.fr/ark:/12148/cb37596198b.
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Tin, Ma Khin Than. "Guanidinate complexes of niobium and tantalum." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp01/MQ38771.pdf.
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Watkin, John Graham. "Low-valent organometallic compounds of niobium." Thesis, University of Oxford, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.236173.
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Bailey, Nigel J. "ANSA bridged metallocene chemistry of niobium." Thesis, University of Oxford, 1998. http://ora.ox.ac.uk/objects/uuid:9bd76a85-ba44-42d8-affe-317bc98be368.
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This thesis is concerned with the synthesis and characterisation of new ansa bridged bis-η-cyclopentadienyl derivatives of niobium. Chapter 1 provides an introduction to the area of early transition metal bent metallocene derivatives and charts the development of ansa bridged metallocenes. Chapter 2 presents the synthesis and characterisation of some new ansa niobocene derivatives prepared from niobium(IV) chloride. The compounds [Nb(η-C5H4-CMe2- η-C5H4)(η2-BH4)],* [Nb(η-C5H4-CMe2-η-C5H4)(PMe3)H],* [Nb(η-C5H4-CMe2-η- C5H4)(PPh3)H], [Nb(η-C5H4-CMe2-η-C5H4)(SPh)2] and [Nb(η-C5H4-CMe2-η- C5H4)(CH2Ph)2]* are described. An asterisk indicates that the X-ray crystal structure was determined. Chapter 3 describes the synthesis and characterisation of some ansa niobocene derivatives containing ancillary imido ligands. The compounds [Nb(η-C5H4-CMe2-η- C5H4)(NSiMe3)Cl],* [Nb(η-C5H4-CMe2-η-C5H4)(NBu')X] (X = Cl,* Br,* I,* Me), [Nb(η-C5H4-CMe2-η-C5H4)(NHBu')Cl][BF4)]and[Nb(η-C5H4-CMe2-η-C5H4)(O)Cl]* are described. An asterisk indicates that the X-ray crystal structure was determined. Photoelectron spectra were recorded for [Nb(η-C5H4-CMe2-η-C5H4)(NBu')X] (X = Cl, Me) and compared to a geometry optimisation calculation obtained using density functional theory. In these formally twenty electron compounds the HOMO has negligible metal contribution and the eighteen electron rule is not violated. Chapter 4 describes the results of a preliminary investigation into ansa niobium(III) bis-η-cyclopentadienyl derivatives containing phosphorus donor ligands. The compound [Nb(η-C5H4-CMe2-η-C5H4)(PMe3)Cl] is characterised spectroscopically. The synthesis and full characterisation details of the compound [Nb(η-C5H4-CMe2-η- C5H4){P(OMe)3}Cl] are given, including the X-ray crystal structure. Chapter 5 provides the experimental details for the preceding Chapters and Chapter 6 contains the characterising data for the new compounds described in this thesis. Full details of the X-ray crystallographic structure determinations are given in Appendices A -1.
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Chandra, Ashwini. "On the Mechanism of Niobium Electropolishing." The Ohio State University, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=osu1330544777.
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Nico, Cláudio Miguel Silva. "Niobium oxides and niobates physical properties." Doctoral thesis, Universidade de Aveiro, 2015. http://hdl.handle.net/10773/14851.
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Doutoramento em Nanociências e NanotecnologiaNiobium 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, namely rare-earth orthoniobates (RENbO4), which interest has been related to their optical properties and protonic conductivity. Hence, single and polycrystalline samples of RENbO4 were synthesized and characterized structural, optical and electrically, leaving open an interesting future work.
Os óxidos de nióbio têm sido apontados como uma alternativa ao tântalo na produção de condensadores eletrolíticos sólidos, com vantagens relativamente à constante dielétrica, densidade e preço. Neste trabalho, pretende-se criar uma nova família de condensadores de óxidos de nióbio, adaptando a tecnologia e linha de produção atualmente utilizada com o tântalo. Apesar das já conhecidas potencialidades dos óxidos de nióbio, e vários tipos de niobatos, em diversas aplicações tecnológicas, o conhecimento destes sistemas óxidos é ainda manifestamente insuficiente. Assim, é apresentada uma cuidadosa revisão bibliográfica que evidencia a complexidade destes materiais, as dificuldades na identificação das suas várias fases e polimorfos, assim como na interpretação das suas propriedades. Neste contexto, são apresentados vários estudos fundamentais em óxidos de nióbio, nomeadamente caracterização estrutural, microestrutural, ótica e elétrica, que permitem não só contribuir de uma forma importante para o conhecimento geral das propriedades físicas destes materiais, como avançar para o desenvolvimento sustentado dos condensadores eletrolíticos sólidos à base de óxidos de nióbio. Estudaram-se vários parâmetros de processamento abrindo caminho para a criação de um protótipo. Avançou-se também para um estudo preliminar da síntese e caracterização de outros sistemas óxidos à base de nióbio, nomeadamente ortoniobatos de terras-raras (RENbO4), cujo interesse tem sido manifestado relativamente às suas propriedades óticas e de condutividade protónica. Assim, amostras mono e policristalinas de RENbO4 foram sintetizadas e caracterizadas estrutural, ótica e eletricamente, deixando em aberto um interessante trabalho futuro.
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Silva, Bruno Henrique Sacoman Torquato da [UNESP]. "Estudo sobre o uso de compostos de nióbio em reações multicomponentes de aza-Diels-Alder." Universidade Estadual Paulista (UNESP), 2014. http://hdl.handle.net/11449/99703.
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000735770.pdf: 6911008 bytes, checksum: 035b59e52ef67d125d48e4550db4516a (MD5)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)
As reações multicomponentes (RMCs) são geralmente definidas como um processo em que três ou mais reagentes combinam-se, em um mesmo pot reacional, para formar um produto que tenha características estruturais de cada reagente utilizado, gerando produtos com uma boa complexidade estrutural em apenas uma etapa. Com base nisto este trabalho tem como objetivo a utilização de diferentes compostos de Nióbio como agente promotor de RMC de aza-Diels-Alder. O pentacloreto de nióbio promove a síntese de diferentes derivados de tetrahidroquinolinas através de reação de derivados de anilina e benzaldeíd e diferentes éteres enólicos cíclicos (di-hidropiano e di-hidrofurano), com baixos tempos reacionais, altos rendimentos e com ótimo excesso diastereoisométricos. Foi estudada também, a utilização do pentaetóxido de nióbio na síntese de derivados de cetoaminas bicíclicas através da RMC entre derivados de anilina, benzaldeído e 2 ciclo-hexenona. A reação foi promovida em moderados tempos reacionais, obtendo-se os produtos com altos rendimentos e com moderados excesso diastereoisoméricos, em condições reacionais brandas. Paralelamente aos estudos com os compostos de nióbio, foram realizados estudos de elucidação estrutural de alguns derivados de tetra-hidroquinolinas sintetizados, utilizando técnicas de RMN e cálculos teóricos
The multicomponent reactions (MCRs) are defined as a process wherein three or more reactants combine, in the same reaction pot to form a product that contains the structural characteristics of each reagent utilized, forming products with a good structural complexity in one steep. The aim of this work is the utilization of different niobium compounds as promoter of aza-Diels-Alder MCRs. The Niobium pentachloire promotes the synthesis of different tetrahydriquinolines derivatives through of reaction between anline derivatives, benzaldehyde and different cyclic enolic ethers (dihydropyran and dihydrofuran), with low reaction times, high yields and with great diastereoisomeric ratio. Was studied too, the utilization of niobium pentaethoxide in the synthesis of bicyclic ketamine derivatives through the MCR between anline derivatives, benzaldehyde and cyclohexenone. The reaction was promoted in moderate reaction times, obtaining the products with high yields and with moderate diastereoisomeric ratio, in mild reaction conditions. At the same time of the studies with niobium compounds, were realized studies of unequivocal structural elucidation of some tetrahydroquinoline derivatives synthetized, utilizing NMR techniques and theoretical calculations
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Bartolomeu, Aloisio de Andrade [UNESP]. "Síntese de 14-aril-14h-dibenzol[a,j]xantenos e 4-aril-3,4-di-hidrobenzo[f]cumarinas promovida pelo pentacloreto de nióbio, com potencial aplicação na preparação de corantes sensibilizadores para utilização em dispositivos de Grätzel." Universidade Estadual Paulista (UNESP), 2015. http://hdl.handle.net/11449/124057.
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000829934.pdf: 6618717 bytes, checksum: 9d57be237ed1cfb084af09729f3f7629 (MD5)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)
A síntese de diabenzoxantenos e 4-aril-3,4-di-hidrocumarinas (neoflavononas) apresenta grande interesse para a química orgânica porque ambos os núcleos são encontrados em moléculas naturais e sintéticas que possuem aplicações como agentes anti-inflamatórios, antioxidantes e antimicrobianos. As reações one-post fornecem uma estratégia interessante para a preparação desses compostos, pois são processos que mesmo envolvendo diversas etapas, ocorrem no mesmo meio reacional, sem a necessidade de realizar separações de produtos a cada etapa. Assim, essas reações reduzem tempo, economizam energia e permitem a obtenção de produtos de boa complexidade estrutural. Portanto, neste trabalho, investigamos o uso do pentacloreto de nióbio como ácido de Lewis em reações one-pot para a otenção de 14-aril-14H-diabezon[a,j]xantenos de 4-aril-3,4-di-hidro-benzol[f]cumarinas, moléculas com potencial aplicação no desenvolvimento de corantes sensibilizadores do tipo D-Л-A para utilização em dispositivos de Grãtzel. O NbCI5 promove a síntese dos derivados de 14-aril-14H-diabenzol[a,j]xanteno através da reação de condensação one-post entre 2-naftol e aldeídos aromáticos, à temperatura ambiente, em tempos reacionais aceitáveis e com excelentes rendimentos (70-98%).A utilização do NBCI5 na reação multicomponente entre 2-naftol, molonato de dimetila e aldeídos aromáticos também foi estudada. Essa RMC mostrou ser uma boa rota sintética para a obtenção dos derivados de 14-aril-14H-dibenzol[a,j]xanteno e de 4-aril-3,4-di-hidrobenzol[f]cumarina, com predominância das 4-aril-3,4-di-hidro-benzol[f]cumarinas (41-93%). A caracterização óptica dos derivados de 14-aril-14H-dibenzol[a,j]xanteno e de 4-aril-3,4-dihidro-benzol[f]cumarina revelou que esses compostos possuem bandas de absorção na região do ultravioleta, sendo assim necessário realizar modificações estruturais para que possamos utilizá-los como corantes...
The synthesis of dibenzoxanthenes and 4-aryl-3,4-dihydrocoumarins (neoflavonones) is of great interest in the field of organic chemistry because both moieties are found in natural and synthetic molecules which present applications as anti-inflammatory, antioxidant and antimicrobial agents. The one-pot reactions provide an interesting strategy for the preparation of these compounds since all the steps required can be carried out in the same reaction medium, without needing to separate the products at each step of the process. Therefore, these reactions reduce time, save energy and also allow us to obtain good structural complexity products. Hence, in this work, we investigate the use of niobium pentachloride as a Lewis acid in one-pot reactions to obtain 14-aryl-14H-dibenzo[a,j]xanthenes and 4-aryl-3,4-dihydro-benzo[f]coumarins, molecules with potential applications in the development of type D-Л-A dyes used in Grätzel Devices. The NbCI5 promotes the synthesis of the 14-aryl-14H-diabenzo[a,j]xanthene derivatives by a one-pot condensation reaction between 2-naphthol and aromatic aldehydes at room temperature, in acceptable reaction times and with excellent yields (70-98%). The use of NbCI5 in the multicomponent reaction between 2-naphthol, dimethyl malonate and aromatic aldehydes was also studied. This MCR proved to be a good synthetic route to obtain 14-aryl-14h-diabenzo{a,j]xanthene and 4-aryl-3,4-dyhydro-benzo[f]coumarin derivatives, with predominance of the 4-aryl-3,4-dihydro-benzo[f]coumarins (41-93%). The optical characterization of the derivatives of 14-aryl-14h-diabenzo[a,j]xanthene and 4-EYL-3,4-dihydro-benzo[f]coumarin revealed that these compounds have absorption bands in the ultraviolet region of the spectrum. For this reason, it is necessary to carry out structural changes in order to use them as dyes-sensitizers in Grätzel devices
FAPESP: 12/23821-7
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Silva, Bruno Henrique Sacoman Torquato da. "Estudo sobre o uso de compostos de nióbio em reações multicomponentes de aza-Diels-Alder /." Bauru, 2014. http://hdl.handle.net/11449/99703.
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Orientador: Luiz Carlos da Silva FilhoBanca: Paulo Marcos Donaté
Banca: Eduardo René Perez Gonzalez
O Programa da Pós Graduação em Ciência e Tecnologia de Materiais, PosMat, tem carater institucional e integra as atividades de pesquisa em materiais de diversos campi
Resumo: As reações multicomponentes (RMCs) são geralmente definidas como um processo em que três ou mais reagentes combinam-se, em um mesmo "pot" reacional, para formar um produto que tenha características estruturais de cada reagente utilizado, gerando produtos com uma boa complexidade estrutural em apenas uma etapa. Com base nisto este trabalho tem como objetivo a utilização de diferentes compostos de Nióbio como agente promotor de RMC de aza-Diels-Alder. O pentacloreto de nióbio promove a síntese de diferentes derivados de tetrahidroquinolinas através de reação de derivados de anilina e benzaldeíd e diferentes éteres enólicos cíclicos (di-hidropiano e di-hidrofurano), com baixos tempos reacionais, altos rendimentos e com ótimo excesso diastereoisométricos. Foi estudada também, a utilização do pentaetóxido de nióbio na síntese de derivados de cetoaminas bicíclicas através da RMC entre derivados de anilina, benzaldeído e 2 ciclo-hexenona. A reação foi promovida em moderados tempos reacionais, obtendo-se os produtos com altos rendimentos e com moderados excesso diastereoisoméricos, em condições reacionais brandas. Paralelamente aos estudos com os compostos de nióbio, foram realizados estudos de elucidação estrutural de alguns derivados de tetra-hidroquinolinas sintetizados, utilizando técnicas de RMN e cálculos teóricos
Abstract: The multicomponent reactions (MCRs) are defined as a process wherein three or more reactants combine, in the same reaction "pot" to form a product that contains the structural characteristics of each reagent utilized, forming products with a good structural complexity in one steep. The aim of this work is the utilization of different niobium compounds as promoter of aza-Diels-Alder MCRs. The Niobium pentachloire promotes the synthesis of different tetrahydriquinolines derivatives through of reaction between anline derivatives, benzaldehyde and different cyclic enolic ethers (dihydropyran and dihydrofuran), with low reaction times, high yields and with great diastereoisomeric ratio. Was studied too, the utilization of niobium pentaethoxide in the synthesis of bicyclic ketamine derivatives through the MCR between anline derivatives, benzaldehyde and cyclohexenone. The reaction was promoted in moderate reaction times, obtaining the products with high yields and with moderate diastereoisomeric ratio, in mild reaction conditions. At the same time of the studies with niobium compounds, were realized studies of unequivocal structural elucidation of some tetrahydroquinoline derivatives synthetized, utilizing NMR techniques and theoretical calculations
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Bartolomeu, Aloisio de Andrade. "Síntese de 14-aril-14h-dibenzol[a,j]xantenos e 4-aril-3,4-di-hidrobenzo[f]cumarinas promovida pelo pentacloreto de nióbio, com potencial aplicação na preparação de corantes sensibilizadores para utilização em dispositivos de Grätzel /." Bauru, 2015. http://hdl.handle.net/11449/124057.
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Orientador: Luiz Carlos da Silva FilhoBanca: Kleber Thiago de Oliveira
Banca: Timothy John Brocksom
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: A síntese de diabenzoxantenos e 4-aril-3,4-di-hidrocumarinas (neoflavononas) apresenta grande interesse para a química orgânica porque ambos os núcleos são encontrados em moléculas naturais e sintéticas que possuem aplicações como agentes anti-inflamatórios, antioxidantes e antimicrobianos. As reações one-post fornecem uma estratégia interessante para a preparação desses compostos, pois são processos que mesmo envolvendo diversas etapas, ocorrem no mesmo meio reacional, sem a necessidade de realizar separações de produtos a cada etapa. Assim, essas reações reduzem tempo, economizam energia e permitem a obtenção de produtos de boa complexidade estrutural. Portanto, neste trabalho, investigamos o uso do pentacloreto de nióbio como ácido de Lewis em reações one-pot para a otenção de 14-aril-14H-diabezon[a,j]xantenos de 4-aril-3,4-di-hidro-benzol[f]cumarinas, moléculas com potencial aplicação no desenvolvimento de corantes sensibilizadores do tipo D-Л-A para utilização em dispositivos de Grãtzel. O NbCI5 promove a síntese dos derivados de 14-aril-14H-diabenzol[a,j]xanteno através da reação de condensação one-post entre 2-naftol e aldeídos aromáticos, à temperatura ambiente, em tempos reacionais aceitáveis e com excelentes rendimentos (70-98%).A utilização do NBCI5 na reação multicomponente entre 2-naftol, molonato de dimetila e aldeídos aromáticos também foi estudada. Essa RMC mostrou ser uma boa rota sintética para a obtenção dos derivados de 14-aril-14H-dibenzol[a,j]xanteno e de 4-aril-3,4-di-hidrobenzol[f]cumarina, com predominância das 4-aril-3,4-di-hidro-benzol[f]cumarinas (41-93%). A caracterização óptica dos derivados de 14-aril-14H-dibenzol[a,j]xanteno e de 4-aril-3,4-dihidro-benzol[f]cumarina revelou que esses compostos possuem bandas de absorção na região do ultravioleta, sendo assim necessário realizar modificações estruturais para que possamos utilizá-los como corantes...
Abstract: The synthesis of dibenzoxanthenes and 4-aryl-3,4-dihydrocoumarins (neoflavonones) is of great interest in the field of organic chemistry because both moieties are found in natural and synthetic molecules which present applications as anti-inflammatory, antioxidant and antimicrobial agents. The one-pot reactions provide an interesting strategy for the preparation of these compounds since all the steps required can be carried out in the same reaction medium, without needing to separate the products at each step of the process. Therefore, these reactions reduce time, save energy and also allow us to obtain good structural complexity products. Hence, in this work, we investigate the use of niobium pentachloride as a Lewis acid in one-pot reactions to obtain 14-aryl-14H-dibenzo[a,j]xanthenes and 4-aryl-3,4-dihydro-benzo[f]coumarins, molecules with potential applications in the development of type D-Л-A dyes used in Grätzel Devices. The NbCI5 promotes the synthesis of the 14-aryl-14H-diabenzo[a,j]xanthene derivatives by a one-pot condensation reaction between 2-naphthol and aromatic aldehydes at room temperature, in acceptable reaction times and with excellent yields (70-98%). The use of NbCI5 in the multicomponent reaction between 2-naphthol, dimethyl malonate and aromatic aldehydes was also studied. This MCR proved to be a good synthetic route to obtain 14-aryl-14h-diabenzo{a,j]xanthene and 4-aryl-3,4-dyhydro-benzo[f]coumarin derivatives, with predominance of the 4-aryl-3,4-dihydro-benzo[f]coumarins (41-93%). The optical characterization of the derivatives of 14-aryl-14h-diabenzo[a,j]xanthene and 4-EYL-3,4-dihydro-benzo[f]coumarin revealed that these compounds have absorption bands in the ultraviolet region of the spectrum. For this reason, it is necessary to carry out structural changes in order to use them as dyes-sensitizers in Grätzel devices
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Moreno, Vitor Fernandes. "Síntese e aplicação de derivados quinolínicos como inibidores de corrosão em aço inoxidável AISI 430 /." Bauru, 2019. http://hdl.handle.net/11449/183375.
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Orientador: Luiz Carlos da Silva FilhoBanca: Marco Antônio Barbosa Ferreira
Banca: Fenelon Martinho Lima Pontes
Resumo: A corrosão é um processo espontâneo de transformação química que degrada os materiais, principalmente os metais, condenando as propriedades físico-químicas que lhes dão emprego. Dessa forma, torna-se necessária a substituição das peças afetadas pela corrosão tanto nas indústrias como nas obras públicas. Estudos da Organização Mundial da Corrosão (OMC) estimam que os gastos com a manutenção dos materiais afetados chegam em média a 2,8 % do Produto Interno Bruto (PIB) mundial. Buscando soluções economicamente viáveis, o desenvolvimento de eficientes inibidores de corrosão aparece como alternativa para diminuir o custo da manutenção dos metais. Os inibidores funcionam como películas protetoras que interferem na ação eletroquímica, prevenindo ou diminuindo os efeitos da corrosão. Algumas substâncias orgânicas polares que possuem elétrons deslocalizados despertam interesse de grupos científicos devido a sua potencialidade de ação como inibidores de corrosão. Dentre estes compostos as quinolinas vêm recebendo atenção principalmente por se tratar de uma classe de moléculas extremamente versátil devido a sua estrutura π-conjugada que permite atuação destes derivados em diversas áreas de aplicação. Neste trabalho foi realizada a síntese de derivados quinolínicos por meio de reações multicomponentes promovidas por pentacloreto de nióbio, além de desenvolver uma nova rota para produção de derivados aminoquinolínicos. As substâncias sintetizadas foram avaliadas como inibidores/retardador... (Resumo completo, clicar acesso eletrônico abaixo)
Abstract: Corrosion is a spontaneous process of chemical transformation that degrades materials, especially metals, condemning their physicochemical properties. Thus, it is necessary to replace the parts affected by corrosion in both industries and public works. Studies by the World Corrosion Organization (WTO) estimate that spending on the maintenance of affected materials averages 2.8% of world gross domestic product (GDP). Seeking economically viable solutions, the development of efficient corrosion inhibitors appears as an alternative to lowering the cost of metal maintenance. Inhibitors act as protective films that interfere with electrochemical action, preventing or decreasing the effects of corrosion. Some polar organic substances that have delocalized electrons arouse interest of scientific groups due to their potential action as corrosion inhibitors. Among these compounds, quinolines have been receiving attention mainly because they are an extremely versatile class of molecules due to their π-conjugated structure that allows these derivatives to act in several application areas. In this work, the synthesis of quinolinic derivatives was performed by means of multicomponent reactions promoted by niobium pentachloride, besides developing a new route for the production of aminoquinolinic derivatives. The synthesized substances have been evaluated as corrosive process inhibitors / retarders for AISI 430 steel in 1M HCl. For the characterization and verification of the anticorrosive... (Complete abstract click electronic access below)
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Visani, Piero. "Superconducting proximity effect between silver and niobium /." [S.l.] : [s.n.], 1990. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=9046.
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Hanna, Ivil. "Mechanical Properties of Niobium Alloyed Gray Iron." Thesis, KTH, Fordonsdynamik, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-39691.
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The influence of adding an amount of 0.1% and 0.3% niobium to the gray iron alloy used for brake discs, these disc materials are called disc 16 respective 17, have been investigated at RT (room temperature). That is together with two other alloys, the reference disc which contains 0.32% molybdenum but lacks niobium and another one with neither niobium nor molybdenum in it, this is called disc material 15. Focus in this thesis work is on the mechanical properties of the studied materials and for this purpose the low cycle fatigue (LCF) properties of the mentioned alloys are investigated. The strain controlled LCF were done at strain amplitudes varying from 0.05 to 0.43%. According to the results, all the materials become survivors when the applied strain was 0.05%. For the other applied strain ranges the reference disc material shows the shortest life-span, while it is difficult to distinguish the other three materials. However, on average material 16 and 17 show a slightly better performance compared to material 15. This means that niobium can be used to replace molybdenum in this application. However, an obvious difference between disc material 16 and 17 cannot be observed when material disc 16 showed to be the superior at some applied strains and material disc 17 at the others. For this reason, it is more profitable to replace the 0.32% molybdenum with 0.1% niobium. The results also show that if the loading is mainly in the elastic region the life increases dramatically. It is also obvious that the static properties of gray iron increases with increasing niobium content and the fracture stress increases with about 30 MPa when the niobium contents go from 0.1% to 0.3%.
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Scott, Peter. "Cycloheptatri-ene and -enyl derivatives of niobium." Thesis, University of Oxford, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.293470.
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Rios, P. R. "Some effects of niobium in alloy steels." Thesis, University of Cambridge, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.373698.
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Rueffer, Mareike. "Collinear laser spectroscopy of neutron-rich niobium." Thesis, University of Birmingham, 2010. http://etheses.bham.ac.uk//id/eprint/802/.
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Hyperfine structure spectra and isotope shifts of the neutron-rich nuclei \(^{99}\)Nb, \(^{101}\)Nb, \(^{102}\)Nb and \(^{103}\)Nb were obtained at the IGISOL (Ion Guide Isotope Separator On-Line) facility at the accelerator laboratory of the University of Jyväskylä. The data were taken using collinear laser spectroscopy of bunched beams. Optical pumping from the ground state to populate metastable atomic states in the ion beam cooler allowed efficient spectroscopy of the ionic system that would otherwise be inaccessible due to a lack of suitable ground state resonance lines. The measurements of the hyperfine structure and the isotope shifts contribute valuable nuclear information to the understanding of the \(A\) ~ 100 region which displays a sudden onset of deformation that cannot be explained by the single particle shell model. It was possible to confirm the spin assignments for \(^{99}\)Nb, \(^{101}\)Nb and \(^{103}\)Nb as \(I\) = 9/2, \(I\) = 5/2 and \(I\) = 5/2 respectively. The extracted information on the mean square charge radii, \(\delta\big
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Cossairt, Brandi M. (Brandi Michelle). "Niobium-mediated synthesis of phosphorus-rich molecules." Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/57702.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2010.Vita. Page 224 blank. Cataloged from PDF version of thesis.
Includes bibliographical references.
The use of a sterically demanding enolate ligand -OC[2Ad]Mes supported by niobium has allowed for the synthesis of (Mes[2Ad]CO) 3Nb=PP7Nb(OC [2Ad]Mes)3 through P4 coupling by a low-valent niobium intermediate. This asymmetric phosphorus-rich cluster harbors a niobium phosphinidene unit bound to a niobium-supported P7 cluster. The phosphinidene terminus was found to react with a range of ketones to give phosphaalkene complexes R2C=PP7Nb(OC[2Ad]Mes) 3. These phosphaalkenes are unstable towards intramolecular rearrangement to give R2CP8Nb(OC[ 2Ad]Mes)3 in which the carbene unit has been internalized into the P8 cage. This rearrangement was studied through both Eyring and Hammett analyses. Structrually the new R2CPsNb(OC[2Ad]Mes)3 are viewed as coordinated-diphosphenes and it was found that the diphosphene unit could be liberated and trapped by reaction with pyridine-N-oxide in the presence of excess 1,3-cyclohexadiene, generating niobium oxo and R2CP8(C 6H8). Searching for new platforms to investigate niobium-phosphorus chemistry led to the synthesis of [Na(THF) 3][P3Nb(ODipp) 3], an anionic cyclo-P3 complex that is accessible in two steps from commercially available reagents. It was discovered that [Na(THF) 3] [P3Nb(ODipp) 3] could function as a source of P3 3-, which has allowed for the synthesis of the tetraatomic molecule AsP 3 as a pure substance for the first time. AsP 3 has been studied by gas-phase electron diffraction, photoelectron spectroscopy, solid-state NMR spectroscopy, raman spectroscopy, as well as high resolution mass spectrometry, and a variety of quantum chemical calculations. Further, a wide array of AsP3 reaction chemistry has been probed including the synthesis and structural characterization of two metal complexes with a coordinated, intact AsP3 ligand. Motivated to explore the chemistry of [Na(THF)3][P3Nb(ODipp) 3] further, a series of investigations were carried out to generate substituted triphosphirene ligands complexed to niobium. In particular Ph3SnP3Nb(ODipp) 3 was prepared and was found to react cleanly and efficiently with pyridine-N-oxide in the presence of an excess of 1,3-cyclohexadiene to generate the niobium oxo complex and Ph3SnP3(C6H8), the product of a Diels-Alder reaction between the liberated triphosphirene and 1,3-cyclohexadiene. This unusual phosphorus-rich molecule was exploited in a number of transformations. One reaction of particular interest was the synthesis of P3Rh(PPh 3)3 from Ph3SnP3(C6Hg) and Wilkinson's catalyst (ClRh(PPh3)3) with loss of 1,3-cyclohexadiene and ClSnPh3- This transformation is an illustrative example of the ability of Ph3SnP 3(C6H8) to act as a P3 transfer agent.
Brandi M. Cossairt.
Ph.D.
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Harris, Donald Carl. "Percolation in proximity coupled gold/niobium arrays /." The Ohio State University, 1989. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487668215806717.
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Nikonova, Olesya A. "Alkoxide complexes of rhenium, niobium and tantalum /." Uppsala : Deptartment of Chemistry, Swedish University of Agricultural Sciences, 2009. http://epsilon.slu.se/11446279.pdf.
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Bonnet, Gilles. "Synthèse de dérivés phosphorés du niobiocène : accès à des systèmes bimétalliques avec pont phosphido." Dijon, 1990. http://www.theses.fr/1990DIJOS015.
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Ce mémoire décrit la réactivité des complexes trihydruro et monohydruro du niobiocène vis-à-vis de dérivés chlorophosphorés. Le trihydrure de niobiocène permet d'accéder à des complexes monohydruro porteurs d'un ligand fonctionnalise PRR'H. Les monohydrures conduisent à des métallophosphines, des métallophosphinites et des métallophosphonyles, composés dans lesquels le niobium et l'atome de phosphore sont liés par une liaison covalente. Ces complexes permettent, par réaction avec des fragments métallés insatures, d'obtenir de nombreux composés binucléaires mono ou bi pontés (pont phosphido, pont hydrogène, pont carbonyle). L'ensemble de ces complexes a été caractérisé par leurs données analytiques et spectroscopiques. Certains d'entre eux ont fait l'objet d'une analyse cristallographique. La dernière partie de ce mémoire traite de problèmes de stéréochimie dans des complexes porteurs d'un groupe phosphore chiral, et en particulier de la stéréostabilité de l'atome de phosphore asymétrique
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Arurault, Laurent. "Contribution à l'étude de l'élaboration électrolytique du niobium à partir de solutions de K2NbF7 dans l'eutectique NaCl-KCl fondu à 750°C." Grenoble INPG, 1992. http://www.theses.fr/1992INPG0148.
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Le travail consiste a rechercher les mecanismes de reduction cathodique des ions niobium en milieu nacl-kcl fondu a 750c. On a tout d'abord etudie la stabilite des solutions diluees d'heptafluoroniobate de potassium, et montre qu'elles evoluent par oxydo-reduction interne ou par reaction avec le carbone vitreux pour donner au bout de plusieurs minutes un melange contenant essentiellement des ions nb(iv). Cette evolution est demontree par analyse par diffraction des rayons x des bains refroidis, ainsi que par le suivi du potentiel d'abandon d'une electrode de tungstene immergee dans l'electrolyte. Les ions niobium v restants sont sous forme de chloro-fluorocomplexes. Les solutions se reduisent cathodiquement sur electrode de tungstene, d'argent ou de carbone vitreux en deux etapes: une premiere etape monoelectronique rapide, suivie d'une seconde lente etape a 4 electrons, avec =0,45 et k=9 10##7 cm/s. Le coefficient de diffusion des ions nb(iv) vaut 5,7 10##5 cm#2/s. Une reaction lente de dismutation des ions nb(iv): 5 nb(iv)4 nb(v)+nb provoque la formation d'une corolle metallique a la surface du bain fondu au voisinage de la cathode, ainsi que la formation de niobium metal qui peut sedimenter ou reagir sur les parois de carbone vitreux du creuset
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Deblonde, Gauthier. "Spéciation du niobium et du tantale en milieux basiques et développement d’un procédé hydrométallurgique pour la séparation niobium-tantale." Thesis, Paris 6, 2015. http://www.theses.fr/2015PA066761.
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Le niobium (Nb) et le tantale (Ta) sont deux éléments stratégiques pour les pays développés car ils sont difficilement substituables et utilisés dans de nombreux secteurs clés comme l’automobile, l’aéronautique, le nucléaire, le bâtiment, l’industrie pétrolière, l’imagerie médicale et l’électronique.La très grande similarité chimique du Nb et du Ta fait que les procédés industrialisés permettant leur séparation requièrent des milieux très complexants, comme les solutions d’acide fluorhydrique. Cependant, la toxicité et l’impact environnemental de ces solutions poussent les industriels à développer de nouveaux procédés. Les milieux alcalins peuvent être une alternative mais la chimie du Nb et du Ta à pH alcalin est encore peu connue à l’heure actuelle. Les objectifs de cette thèse étaient d’étudier la spéciation du Nb et du Ta dans les solutions aqueuses basiques et d’élaborer un procédé hydrométallurgique, sans fluor, pour la séparation niobium-tantale. Tout d’abord, de nouvelles données ont été acquises sur la spéciation du Nb et du Ta grâce à des mesures de solubilité, de spectrophotométrie UV-visible, de RMN du solide, de spectroscopie Raman et d’électrophorèse capillaire. Ensuite, les informations obtenues à partir de solutions aqueuses, synthétiques et industrielles, ont permis de développer un nouveau procédé d’extraction par solvant capable de séparer le Nb et le Ta et n’utilisant aucun réactif fluoré. Le procédé développé a également été testé et validé à l’échelle pilote (~ 1 L/h) sur des solutions industrielles. Enfin, l’étude technico-économique du procédé développé révèle que celui-ci sera rentable et compétitif par rapport aux procédés existantsNiobium (Nb) and tantalum (Ta) are two strategic elements for developed countries because of their unequalled properties and their use in several key sectors like the aerospace, fuel, building, nuclear, medical imaging or electronic industries. Due to their almost-identical chemical properties, the industrial processes currently used for the niobium-tantalum separation require strongly complexing media, like hydrofluoric acid. However, the high toxicity and the environmental footprint of these media force the industrials to develop new processes. In this regard, alkaline media represent a good alternative but the chemistry of Nb and Ta in such media is still poorly known. The objectives of this PhD thesis were to probe the speciation of Nb and Ta in alkaline aqueous solutions and to develop a new hydrometallurgical process able to perform the Nb-Ta separation. Firstly, new data were obtained on the speciation of Nb and Ta in alkaline media based on solubility measurements, UV-visible spectrophotometry, solid state NMR, Raman spectroscopy and capillary electrophoresis. Secondly, the information obtained from aqueous solutions (both synthetic and industrial) allowed us to develop an original solvent extraction process able to separate Nb and Ta without using any fluoride compound. This innovative process was tested at a pilot-scale (~ 1 L/h) on industrial solutions. The technical-economic evaluation of the developed process shows that this latter is profitable and economically competitive over the current industrial processes
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Ferrand, Laura. "Hydrofonctionnalisations de liaisons multiples carbone-carbone catalysées par des complexes à base de métaux non nobles." Thesis, Paris 6, 2017. http://www.theses.fr/2017PA066348/document.
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Ce travail de thèse est consacré au développement de nouvelles méthodologies en catalyse mettant en jeu des complexes métalliques à base de métaux non nobles, en l’occurrence le cobalt et le niobium. Ces deux métaux ont été utilisés pour catalyser des réactions d’hydrofonctionnalisation de liaisons multiples carbone‒carbone. L’objectif était de proposer des systèmes catalytiques compétitifs à base de métaux non précieux et de promouvoir leur utilisation par rapport à d’autres métaux peu abondants et onéreux. Un complexe de cobalt bien défini, HCo(PMe3)4, a été employé pour catalyser des réactions d’hydroboration régio- et stéréosélectives d’alcynes internes, ainsi que des réactions de diboration d’alcynes. D’autre part, un système catalytique au niobium(V) cationique a été mis au point et utilisé pour diverses réactions d’hydrofonctionnalisation intramoléculaires, permettant la synthèse d’une large famille d’hétérocycles. De manière à mettre encore davantage en lumière ce métal et ces bienfaits, des travaux ont été réalisés en catalyse énantiosélective. Un système catalytique chiral de niobium(V) a été utilisé pour l’hydroalkoxylation d’alcènes énantiosélective. Des résultats encourageants ont été obtenus même si ce système doit encore être optimisé et testé en présence de différents hydroxyalcènesThis PhD work has focused on the development of new methodologies in catalysis based on non-noble metals: cobalt and niobium. These two metals have been used to catalyze hydrofunctionalization reactions of carbon‒carbon multiple bonds. The aim of those projects was to propose competitive catalytic systems based on non-precious metals and to promote their use compared to other rare and expensive metals. To this end, we successfully demonstrated that a well-defined cobalt complexe HCo(PMe3)4 is an efficient catalyst for regio- and stereoselective hydroboration reactions of internal alkynes, as well as diboration reactions. Also, a new catalytic system based on cationic niobium(V) has been developed and used to catalyze intramolecular hydrofunctionalization reactions leading to the synthesis of a large family of heterocycles. In order to reveal even more the potential of niobium in catalysis, we aimed to propose a chiral system able to catalyze enantioselective hydroalkoxylation of alkenes. Despite the promising results, some more efforts on the optimization of this system still need to be done
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Pallecchi, Emiliano. "Multiwall carbon nanotube Josephson junctions with niobium contacts." kostenfrei, 2009. http://www.opus-bayern.de/uni-regensburg/volltexte/2009/1310/.
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Lyne, Michael Peter. "High resolution spectroscopy of aminoborane and niobium nitride." Thesis, University of British Columbia, 1987. http://hdl.handle.net/2429/26442.
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The infrared spectrum of aminoborane (NH₂BH₂) was recorded by a Fourier transform interferometer and the 1550-1750 cm⁻¹ region of the spectrum was rotationally analyzed by a new search/match algorithm based on ground state combination differences. Sub-bands from four separate vibrational bands were discovered in this region. The interaction scheme was deduced to be a three-way anharmonic resonance between the V₃, V₇ + VB, and 2v₆ levels with the fourth level, V₆ + V₁₂ induced by a Coriolis mechanism with the members of the triad. The first order anharmonic constants were approximated by a least squares fit of the triad intensities: W₃₇₈ = 8.4±0.1 cm⁻¹, W₃₆₆ = 15.8±0.4 cm⁻¹ with W₇₈₆₆ held fixed at zero. Perturbations from unseen interloper levels plus the fully correlated nature of the pure vibrational anharmonic interaction prevented a successful fit of the rotational structure of this system. Both the search/match and the intensity least squares algorithms were developed for this work.
Four sub-bands in the red-orange region of the laser induced fluorescence spectrum of niobium nitride (NbN) were rotationally analyzed. Analysis of three sub-bands of the ³ϕ₂ - ³Δ₁ system allowed the vibrational spacings of each electronic state to be determined: ΔG½ = 986.351 cm⁻¹, ΔG1½ = 977.855 cm⁻¹ for the ³ϕ₂ state and ΔG1½, =. 1033.739cm⁻¹ for the ³Δ₁, state. The previously unassigned ³Π₁-³Δ₂ (0-0) sub-band was discovered 970 cm⁻¹ below its expected position of 18025 cm⁻¹. The electronic state assignment of this transition was confirmed by -wavelength resolved fluorescence measurements made with a diode array detector mounted on a spectrometer. A description of how the diode array detector was interfaced into the experiment is given.Science, Faculty of
Chemistry, Department of
Graduate
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Hilborn, Monica Maria. "Production of ferro-niobium in the Plasmacan furnace." Thesis, McGill University, 1988. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=63993.
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Paritong, Hilke. "Development of corrosion resistant niobium-based PVD coatings." Thesis, Sheffield Hallam University, 2000. http://shura.shu.ac.uk/20185/.
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Niobium is well known for its excellent corrosion resistance based on the formation of a stable passive oxide layer, which protects the metal against corrosion in most aqueous media and makes it an interesting candidate for corrosion resistant coating applications. However, deposition of Nb films is restricted to few technologies and difficulties arise from the toxic nature of the electrolytes employed in electrodeposition of Nb, the high reactivity of the metal with residual gases in vacuum plasma spraying and its high melting point (Tm = 2500 0C) in PVD deposition. The present thesis describes the development of corrosion resistant Nb coatings on stainless steel and brass substrates by the combined steered arc/unbalanced magnetron sputtering technique. Evaluation of the corrosion behaviour is performed by potentiodynamic polarisation measurements in 3% NaCl. It is shown that corrosion resistant Nb coatings, with passivation characteristics similar to that of bulk Nb, can be produced on stainless steel substrates by unbalanced magnetron sputtering at a low deposition temperature (T = 250 0C) under reduced ion bombardment. However, the ion etching pre-treatment of the substrate prior to deposition has a significant influence on the corrosion resistance of the coating/substrate system. The employed polarisation measurements reveal that a fully passive and protective behaviour could only be achieved if Nb ions from the cathodic arc source are chosen as the etching species. In contrast, coatings deposited after Cr ion etching from the arc source and inert Ar ion etching, utilising a glow discharge, exhibit localised breakdown and pitting of the substrate. Cross sectional TEM imaging and STEM-EDX analyses reveal that bombardment of the stainless steel substrate by the multiply charged Nb ions generates a compositionally intermixed, very fine crystalline or "amorphised" interface layer, with a thickness of ~3-8nm, depending on the Nb ion energy. It is proposed that this layer acts as an additional barrier against corrosion due to (i) the structural homogeneity achieved by amorphisation and (ii) chemical stabilisation due to the introduction of Nb in the near surface region. The energy of the bombarding Nb ions, i.e. the substrate bias voltage during the etching stage, was found to further influence the corrosion resistance. Best results are achieved with "medium" bias voltages in the range of -600V to -800V, which is believed to be due to an optimum combination of structural and chemical protection mechanisms. The fully passive corrosion behaviour could not be observed in the case of brass substrates. However, the PVD coating systems on brass and on stainless steel are superior, in the employed polarisation measurements, to commercially produced, electroplated Cr, Ni and Ni/Cr coatings on the same substrate materials. Other coating properties investigated in the present study include microstructure, hardness, crystallographic orientation and residual film stresses.
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Alquier-Villepelet, Cécile. "Syntheses et proprietes des gels d'oxyde de niobium." Paris 6, 1988. http://www.theses.fr/1988PA066019.
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On etudie le procede sol-gel applique au niobium v sous divers aspects. On ameliore les synthese et proprietes physiques des gels. On etudie les gels et oxydes amorphes obtenus par analyse chimique et thermique, diffraction rx, spectrocopies ir, raman et exafs. On etudie les proprietes et applications potentielles: fabrication de ceramiques linbo::(3) et pb(nb2/3 mg1/3)o::(3), avec abaissement de la temperature de frittage et obtention de grains homogenes monodisperses, mesure de la conductivite ionique dans les xerogels hydrates, proprietes optiques(photochromie)
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Wu, Genfa. "Energetic Deposition of Niobium Thin Film in Vacuum." Diss., Virginia Tech, 2002. http://hdl.handle.net/10919/28110.
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Niobium thin films are expected to be free of solid inclusions commonly seen in solid niobium. For particle accelerators, niobium thin film has the potential to replace the solid niobium in the making of the accelerating structures. In order to understand and improve the superconducting performance of niobium thin films at cryogenic temperature, an energetic vacuum deposition system has been developed to study deposition energy effects on the properties of niobium thin films on various substrates. The system directly uses microwave power to create a pure niobium plasma, which can be used to extract niobium ion flux with controllable kinetic energy for direct deposition. The ultra high vacuum avoids the gaseous inclusions in thin films. A retarding field energy analyzer is developed and used to measure the kinetic energy of niobium at the substrate location. A systematic process for thin film characterization is developed and used to analyze the niobium thin films made by this energetic condensation. The properties of niobium thin films at several deposition energies are obtained, and the results show that there exists a preferred deposition energy around 115eV.Ph. D.
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Schwartz, Viviane. "Preparation and Reactivity of Niobium-Containing Hydrotreating Catalysts." Diss., Virginia Tech, 2000. http://hdl.handle.net/10919/26368.
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A series of niobium-containing nitride and carbides were prepared by a temperature-programmed synthesis method. The catalysts synthesized comprised a monometallic niobium oxynitride and a new bimetallic oxycarbide supported system, Nb-Mo-O-C/Al₂O₃ (Mo/Nb = 1.2; 1.6; 2.0).
In the case of the niobium oxynitride, the progress of formation was analyzed by interrupting the synthesis at various stages. The effect of the heating rate on product properties was also investigated. The solid intermediates and the final niobium oxynitride were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), elemental analysis (CHNS), and gas adsorption techniques. The solid state transformation occurred directly from Nb₂O₅ to NbNxOy without any suboxide intermediates.
The bimetallic supported oxycarbide materials were also characterized by X-ray diffraction (XRD), gas adsorption techniques, X-ray photoelectron spectroscopy (XPS), and near-edge X-ray absorption fine structure (NEXAFS). It was found that the electronic properties of the oxycarbide were modified by the interaction with the Al₂O₃ support, and that most of the oxygen atoms were associated with the niobium rather than the molybdenum atom. All of the niobium-containing catalysts were tested in a three-phase trickle-bed reactor for the simultaneous hydrodenitrogenation (HDN) of quinoline and hydrodesulfurization (HDS) of dibenzothiophene. The niobium oxynitride presented low HDS activity and moderate HDN activity, whereas the supported bimetallic oxycarbide was found to be highly active for both, HDN and HDS, demonstrating higher activities than the commercial sulfided Ni-Mo/Al₂O₃ when compared on the basis of active sites.
In addition to these studies a comprehensive investigation of the HDN reaction mechanism was carried out over bulk unsupported Mo₂C, NbC, NbMo₂-O-C, and compared with the mechanism over a sulfide catalyst, MoS₂/SiO₂. For this purpose, a comparison of the HDN rate of a series of isomeric amines was performed, and the reaction occurred mainly through a β-elimination mechanism for all catalysts. Temperature programmed desorption of ethylamine was used to investigate the acid properties of the catalytic surfaces, and a good agreement between the specific rate of reaction and the number of Brønsted acid-sites was obtained. Infrared spectroscopy showed that the amines interacted with acidic centers to form adsorbed quartenary ammonium species. The deamination reaction over the carbide and sulfide catalysts probably occurs by a concerted push-pull mechanism involving basic sulfur species and Brønsted-acidic centers. In order to obtain more insight into the mechanism a study of the pyridine HDN network was carried out.All of the catalysts showed the same activity trend: the reactivity of n-pentylamine was high, while those of piperidine and pyridine were relatively low. The carbide catalysts showed higher selectivity towards HDN products than the sulfide catalyst at the same conversion levels. The higher selectivity was related to the higher ratio (r = k₂/k₁) between the rate constants of the two consecutive reactions, hydrogenation of pyridine (k₁) and ring opening of piperidine (k₂). The order of activity of the carbides and sulfide differed considerably depending on the substrate. However, for the pyridine reaction network the similarity in product distribution suggested that a similar surface composition, a carbosulfide, was attained during the reaction.Ph. D.
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Hinton, Michael J. "Superfluidity in Ultrathin Cuprates and Niobium/Ferromagnetic Heterostructures." The Ohio State University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=osu1420673882.
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