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

Orientador: Luiz Carlos da Silva Filho / Banca: 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) / Mestre

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<p> The partitioning of niobium to slag and gaseous niobium oxide vapourizing from metal/slag may cause niobium losses and erratic recovery rates in steelmaking practices. Knowledge of the volatility and activities of niobium oxides in slag melts are of great value for both theoretical evaluation and practical applications in niobium microalloyed steels. Because of the multi-valence state of niobium ions in slags, the behaviour of niobium in metallurgical slags is complicated. So far, little systematic attempts have been made and activity data of niobium oxides in slags are extremely scarce. The aim of this study is to determine precise data on the vapour pressures of niobium oxides, and consequently, to obtain information on thermodynamic quantities of niobium oxides in slag melts.</p> <p> The thermodynamic properties of niobium oxide in CaO-SiO2-NbOx and CaOSiO2-Al2O3-NbOx slag melts were determined by employing the transpiration method from 1800-1873K under a controlled atmosphere. To confirm the validity of the transpiration method for the measurement of thermodynamic properties, the binary alloy system silver-gold was chosen for a comparison with the same property which has been measured by other recognized procedures. The agreement with literature results confirmed that the measurement yields reliable results for thermodynamic activity data by the transpiration method.</p> <p> The vapourization of liquid Nb2O5 was studied as a function of partial pressure of oxygen in the system and this confirms that atmosphere control is the essential condition for the vapourization study. The gaseous niobium oxide species was verified to be NbO2; hence, Nb2O5 vapourizes by the reaction Nb2O5(1) = 2NbO2(g)+1/2O2(g). Heat of vapourization was estimated by applying the second law method and comparison with the literature showed a fairly good agreement.</p> <p> The thermodynamic properties of niobium oxide in the slag system of CaO-SiO2-NbOx and CaO-SiO2-Al2O3-NbOx were measured by varying the experimental conditions of slag basicities, slag compositions, temperature and oxygen partial pressures. From the basicity dependency of the activity coefficient for each oxide in this study, it is proposed that niobium oxide behaves as an amphoteric oxide and niobium pentoxide as an acidic oxide. On the other hand, it was observed in the redox equilibrium experiment that NbO2.5 becomes predominant as the slag basicity increases. However, insufficient interaction parameters as well as parameter conversions prevent the application of the regular solution model. The co-relationship between the ionic diameter and ionic energy was discovered and shows good agreement with calcium oxide and silicon oxide. With the interaction parameter and converting parameter attained, the regular solution model shows good agreement for the activity coefficients between measurement and calculation.</p> / Thesis / Doctor of Philosophy (PhD)

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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 NbN_xO_y 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.

Les aciers avancés à haute résistance (AHSS) de 3ème génération ont l’avantage de combiner résistance et ductilité. Ces aciers multi-phasés sont appréciés pour les applications dans l’industrie automobile pour leurs propriétés mécaniques, dues notamment à la présence d’austénite métastable permettant une transformation induite par la plasticité (effet TRIP- Transformation Induced Plasticity).L’objectif de ce travail a été d’étudier l’effet du microalliage sur les transformations de phases et la précipitation dans de tels aciers. Trois nuances ont été étudiées : une référence sans microalliage, une avec ajout de niobium et une avec ajout de vanadium. Elles ont été caractérisées au fil de la route métallurgique composée d’un recuit intermédiaire et d’un recuit final caractéristique des aciers bainitiques à effet TRIP.Des méthodes ex-situ et in-situ ont été mises en oeuvre. Les caractérisations in-situ pendant les traitements thermiques incluent une étude des transformations de phases par diffraction de rayons X à haute énergie (HEXRD) et une étude de la précipitation par diffusion de rayons X à petits angles (SAXS), utilisant le rayonnement synchrotron.La morphologie des grains a été observée par microscopie optique et diffraction d'électrons rétrodiffusés (EBSD) au Microscope Electronique à Balayage (MEB). L’imagerie des précipités a été effectuée par Microscopie Electronique en Transmission (MET) en imagerie en champ sombre, leur composition a été précisée par analyse dispersive en énergie (EDS) et leur localisation étudiée grâce à l’outil de nano-diffraction ACOM/ASTAR.L’ensemble de ces expériences a permis de mettre en évidence l’effet du traitement thermique et de la composition chimique sur la quantité d’austénite présente ainsi que sur sa teneur en carbone, qui sont les principaux paramètres contrôlant l’effet TRIP. La présence du microalliage se traduit par des variations de ces paramètres, liés à la fois à la présence de précipités contenant ces éléments et à leur présence en solution solide. / 3rd generation Advanced High Strength Steels (AHSS) have the advantage of combining strength and ductility. These multi-phase steels are appreciated for applications in the automotive industry for their mechanical properties, notably due to the presence of metastable austenite allowing Tranformation Induced Plasticity (TRIP effect).The objective of this work was to study the effect of microalloying on phase transformations and precipitation in such steels. Three grades have been studied: a reference without microalloying, one with niobium addition, and one with vanadium addition. They have been characterised through the metallurgical route composed of an intermediate annealing, following by a final annealing characteristic of TRIP-assisted bainitic steels.Both ex-situ and in-situ methods have been applied. In-situ characterisation during thermal treatments includes phase transformation study by High-Energy X-ray Diffraction (HEXRD) and precipitation study by Small Angle X-ray Scattering (SAXS), both performed with synchrotron radiation.Grain morphology has been observed by optical microscopy and Electron Back-Scatter Diffraction (EBSD) in a Scanning Electron Microscope (SEM). Imaging of precipitates has been made in Transmission Electron Microscopy (TEM) via dark-field imaging, their composition has been evauated by Energy Dispersive Spectroscopy (EDS) and their localization studied thanks to the nano-diffraction tool ACOM/ASTAR.All these experiments made it possible to highlight the effect of heat treatment and chemical composition on the amount of austenite present and on its carbon content, which are the main parameters controlling the TRIP effect. The presence of the microalloying results in variations in these parameters, related both to the presence of precipitates containing these elements and to their presence in solid solution.

Thesis (M.S.)--University of Texas at El Paso, 2008. / Title from title screen. Vita. CD-ROM. Includes bibliographical references. Also available online.

Thesis (M.S.)--University of Texas at El Paso, 2008. / Title from title screen. Vita. CD-ROM. Includes bibliographical references. Also available online.