Academic literature on the topic 'Titanium compound'

This paper presents the results of an investigation of the features of phase and structure formation of a ternary compound during thermal sintering use of compacted TiH2-Al-C powder blends. The thermal sintering was carried out in a vacuum furnace at temperature 1150, 1300, and 1400 0С. The x-ray diffraction pattern and structural analysis show that the main phase after synthesis at 1150 0С is titanium carbide. The ternary Ti2AlC and intermetallic Ti3Al compound were also identified in the phase composition of the alloy. Increasing the sintering temperature to 1300 °C leads to significant increases in the content of Ti2AlC ternary compounds and accordingly decreases the content of titanium carbide TiC. Is propose a modified model thermal synthesis of ternary compounds of the Ti-Al-C system, which includes the melting of aluminum and its interaction with titanium at low-temperature stages of the process, the formation of the Ti3Al intermetallic compound, formation titanium carbide grains as a result of the interaction of the Al4C3 intermediate metastable phase with titanium or Ti3Al intermetallic compound and the synthesis of ternary Ti2AlC and Ti3AlC2 compounds as a result of the interaction of the Ti3Al intermetallic compound with carbon and Ti2AlC with titanium carbide TiC.

AbstractAlumina and 304 stainless steel were brazed with silver‐copper‐titanium filler+copper foil. The effect of adding copper foil to the filler on the microstructure of the alumina/304 joint was studied, and the reasons for the effect of adding copper foil with different thicknesses on the joint performance were also analyzed. The standard microstructure of alumina/304 joint with silver‐copper‐titanium+copper foil filler is alumina ceramic/copper compound with titanium and oxygen (3 : 3 : 1) (Cu3Ti3O) continuous layer+copper titanide (TiCu)/silver solid solution+copper solid solution/titanium compound with iron (1 : 2) (TiFe2)+iron‐chromium compound/304 stainless steel. The added copper foil inhibits the diffusion of titanium elements, thereby reducing the formation of the brittle copper compound with titanium and oxygen (3 : 3 : 1) (Cu3Ti3O) and alleviating the residual stress. In addition, after adding copper foil, the copper solid solution is distributed in blocks in the joint, which also improves the plastic deformation ability of the joint. Under the synergistic effect of these two effects after adding copper foil, the joint strength is improved. When the copper foil was 200 μm, the shear strength is 198.10 MPa.

The main objective of this paper is to offer ion-plasma technology for production of Ti (titanium) and titanium nitride (TiN) erosion-resistant nanocoatings for the machine building products, which ensures the coatings with optimum and stable properties. As a result of experiments and processing experimental data the optimum composition of ion-plasma titanium and titanium nitride nanocoatings was obtained and offered.The approbation of the developed technology on the existing machine building products (compressor blade of the helicopter gas turbine; base material: Incoloy 800) was carried out. The comparative study on the influence of the coating on the surface quality, coefficient of friction, adhesion strength and erosion resistance was done. For evaluation of the obtained nanocoating surface’s quality 2D and 3D surface description approaches were applied. Achieved results prove the effectiveness of offered ion-plasma technology for production of titanium and titanium nitride erosion-resistant nanocoatings with appropriate and stable properties.

Due to the rapid mutation of pathogenic microorganisms, drug-resistant superbugs have evolved. Antimicrobial-resistant germs may share their resistance genes with other germs, making them untreatable. The search for more combative antibiotic compounds has led researchers to explore metal-based strategies centered on perturbing the bioavailability of essential metals in microbes and examining the therapeutic potential of metal complexes. Given the limited knowledge on the application of titanium(IV), in this work, eight Ti(IV) complexes and some of their corresponding ligands were screened by the Community for Open Antimicrobial Drug Discovery for antimicrobial activity. The compounds were selected for evaluation because of their low cytotoxic/antiproliferative behavior against a human non-cancer cell line. At pH 7.4, these compounds vary in terms of their solution stability and ligand exchange lability; therefore, an assessment of their solution behavior provides some insight regarding the importance of the identity of the metal compound to the antimicrobial therapeutic potential. Only one compound, Ti(deferasirox)2, exhibited promising inhibitory activity against the Gram-positive bacteria methicillin-resistant Staphylococcus aureus and minimal toxicity against human cells. The ability of this compound to undergo transmetalation with labile Fe(III) sources and, as a consequence, inhibit Fe bioavailability and ribonucleotide reductase is evaluated as a possible mechanism for its antibiotic effect.

Electrochemical synthesis of binary and ternary compounds in the system Ti-Si-B from chloridefluoride melts has been investigated by voltammetry and electrolysis. Electrochemical syntheses of titanium diboride, four titanium silicides (TiSi2, TiSi, Ti5Si4, Ti5Si3), silicon tetraboride and a new ternary compound, Ti5Si3B3, have been found to be one-step processes. The stoichiometry of the deposited compounds has been found to correlate with the bulk concentration of Ti, Si and B ions in the melt.

The titanium amidate compound bis(N-tert-butylacetamido)(dimethylamido)(chloro)titanium was synthesized by the protonolysis of tris(dimethylamido)(chloro)titanium and structurally characterized by 1H and 13C NMR spectroscopy as well as X-ray diffraction. The compound does not appear to react cleanly nor readily with routine alkylating agents such as sec-butyllithium, benzyl potassium, or trimethylsilyl methyllithium.

This paper considers the possibility of obtaining a high-quality titanium-platinum compound. Difficulties in joining dissimilar metals lie in the fact that during their interaction, brittle intermetallic compounds are formed, which cause the destruction of the product during the operation. Hard-phase welding methods are used to control the thicknesses and dimensions of intermetallic inclusions. Vacuum diffusion welding was chosen as the technology. To determine the formation of phases in the diffuse zone, the phase diagram of Ti-Pt was analyzed. The possible types of interactions between the components were determined. It is determined that the formation of a welded joint occurs due to the formation and growth of a diffusion zone in platinum and titanium. During welding, the growth of intermetallic phases Ti3Pt, TiPt, TiPt3, as well as solid solution zones, is observed. Microsections were made, on which the microstructure of the platinum-titanium compound was studied and microhardness measurements were carried out. The total width of the transitional diffusion layer is determined. The studies carried out made it possible to establish the sequence of the phase components of the diffusion zone. The use of the DRON 1.5 diffractometer made it possible to identify the phases. X-ray diffraction maxima and calculation of line identification established the presence of intermetallic compounds and their mixtures with solid solutions. The following methods were used in the work: microstructural analysis, microhardness measurement, the determination of the phase composition. A special technique was used to obtain high-quality microsections. During long-term grinding in the diffusion zone, a degree is formed due to the different properties of titanium and platinum. The phase composition of the platinum-titanium compound and the extent of each zone were established. The experiments carried out indicate that pressure, temperature and exposure time affect the quality of the joint. By changing these welding parameters, it is possible to change the microstructure of the diffusion zone. To determine the mechanical properties, a tear test was performed. For this, special three-metal samples were made. Determination of the mechanical properties made it possible to establish by what parameters the platinum-titanium compound meets the requirements of operation.

Nanostructured titanium compounds have recently been applied in the design of gas sensors. Among titanium compounds, titanium oxides (TiO2) are the most frequently used in gas sensing devices. Therefore, in this review, we are paying significant attention to the variety of allotropic modifications of titanium oxides, which include anatase, rutile, brukite. Very recently, the applicability of non-stoichiometric titanium oxide (TiO2−x)-based layers for the design of gas sensors was demonstrated. For this reason, in this review, we are addressing some research related to the formation of non-stoichiometric titanium oxide (TiO2−x) and Magnéli phase (TinO2n−1)-based layers suitable for sensor design. The most promising titanium compounds and hetero- and nano-structures based on these compounds are discussed. It is also outlined that during the past decade, many new strategies for the synthesis of TiO2 and conducting polymer-based composite materials were developed, which have found some specific application areas. Therefore, in this review, we are highlighting how specific formation methods, which can be used for the formation of TiO2 and conducting polymer composites, can be applied to tune composite characteristics that are leading towards advanced applications in these specific technological fields. The possibility to tune the sensitivity and selectivity of titanium compound-based sensing layers is addressed. In this review, some other recent reviews related to the development of sensors based on titanium oxides are overviewed. Some designs of titanium-based nanomaterials used for the development of sensors are outlined.

The reaction of tetra([Formula: see text]-tolyl)porphyrinato titanium (IV) oxide (2) with 4,7-diethyl-5,6-dimercaptobenzo[1,2,3] trithiole (3a) produced the corresponding titanium (IV) complex, tetra([Formula: see text]-tolyl)porphyrinato titanium (IV) trithiolobenzenedithiolate (4a), fused with a trithiole ring. Related compounds 4b and 4c were prepared by a similar reaction of 2 with 5,8-diethyl-6,7-dimercaptobenzo[1,4]dithiin (3b) and 3,6-diethyl-4,5-dimercapto-1,2-bis(2-cyanoethylthio)benzene (3c). The structure of 4b was determined by X-ray crystallography. Compound 4c was further treated with cesium hydroxide to produce the corresponding dithiolate anion 4c2S, which was deposited on the gold electrode. The electrochemical property of the gold electrode was determined by cyclic voltammetry. The structure of simplified model compound 4b[Formula: see text] was optimized using the DFT method with the Gaussian 09 program. The optimized structure was utilized to calculate the NMR chemical shifts, the HOMO and LUMO energy levels, and the electronic transition in the absorption spectrum.

Today, Hygroscopic swelling is one of the biggest challenging problem of Epoxy mold compound (EMC) in packaging with Microelectromechanical system (MEMS) devices. To overcome this hygroscopic swelling problem of EMC and guard the devices, MEMS devices are molded in this paper with different Mold Compound (MC) i.e. titanium and ceramic etc. during their interconnection with the board. Also, a comparatively performance analysis of this various mold compound with MEMS pressure sensor has been studied in this paper at 60% humidity, 140 mol/m3 saturation concentration and 25 oC. It was observed that hygroscopic swelling does not take place in the titanium mold compound. But, titanium is very costly so we have to consider something cheaper material i.e. ceramic in this paper. The Hygroscopic swelling in Ceramic Mold Compound after 1 year is nearly 0.05 mm, which is very less than epoxy.

Orientador: Edson Tomaz<br>Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química<br>Made available in DSpace on 2018-08-26T01:40:52Z (GMT). No. of bitstreams: 1 Ponczek_Milena_M.pdf: 3719180 bytes, checksum: efe8192ba2f868976819b64f089b973c (MD5) Previous issue date: 2014<br>Resumo: Compostos orgânicos voláteis, ou COV, são uma importante classe de poluentes do ar comumente encontrados na atmosfera ao nível do solo, nos centros urbanos e industriais. O tratamento de COV provenientes de fontes industriais através da fotocatálise heterogênea é uma técnica eficiente para a degradação de baixas concentrações de uma grande gama de compostos orgânicos diferentes (hidrocarbonetos, aromáticos, alcóois, cetonas, etc) operando em condições ambientes. Um dos problemas que ainda impede sua aplicação industrial é a desativação do catalisador e por isso muitos grupos de pesquisa têm se dedicado ao estudo desta técnica na tentativa de melhorá-la e solucionar estes entraves. A atividade fotocatalítica do TiO2 pode ser melhorada pela adição de metais na sua superfície. Neste trabalho, preparou-se catalisadores de TiO2 por impregnação de Pt (1% m/m). A platina foi reduzida com NaBH4, fazendo-se posteriormente caracterização por DRX, XPS, UV ¿Vis, BET, Quimissorção de H2 e MEV/EDS para a validação do método de síntese. Todas as técnicas confirmaram que o método de redução com NaBH4 não modifica estruturalmente o TiO2, mantendo a sua cristalinidade e a razão de anatase/rutilo. A técnica de XPS indicou a presença de metal em estado de oxidação reduzido. Para o estudo da influência da impregnação de Pt no óxido titânio, foram realizados experimentos de fotocatálise em um reator recoberto com TiO2puro, e em um reator recoberto com TiO2/Pt variando-se a concentração de entrada (de 50 à 500 ppmv) ou o tempo de residência (de 10 à 50 s) para os COV n-octano, iso-octano, n-hexano e ciclohexano. Utilizou-se reatores tubulares com volume interno de 1160 ml com os catalisadores, dióxido de titânio puro ou modificado, imobilizados na parede interna dos reatores. A fonte de radiação UV foi uma lâmpada do tipo germicida de 100W de potência, caracterizada por comprimentos de onda de 254 nm (banda de emissão UV-C). As concentrações na entrada e na saída do reator foram analisadas através de um monitor contínuo de hidrocarbonetos do tipo FID. A adição de platina ao TiO2 gera uma melhoria na eficiência fotocatalítica nas reações de oxidação de COV; a conversão dos COV utilizando o catalisador impregnado com platina atingiu 99 % de conversão, enquanto que TiO2 puro atingiu, no máximo 93%<br>Abstract: Volatile organic compounds, or VOC, are an important class of air pollutants commonly found in the atmosphere at ground level in urban and industrial centers. The treatment of VOC from industrial sources by oxidative photodegradation is presented as a good alternative. These systems are promising as pollution control technology, since they can decompose low concentrations of VOC efficiently and in ambient conditions. The recombination of electrons and holes formed on the surface of TiO2 is a factor that limits the photocatalytic efficiency. For this reason, many efforts have been made to maximize the separation of charges, in order to improve the photocatalytic efficiency. A proposed alternative is to add noble metals to TiO2 structure. This work aims to study the degradation of volatile organic compounds by heterogeneous photocatalytic oxidation using ultraviolet light, bare TiO2 and TiO2 impregnated with 1% w/w platinum as catalysts. TiO2 catalysts were prepared by impregnating Pt on TiO2 structure by reduction method with NaBH4. The photocatalysts were characterized using analytical techniques like XRD, XPS, UV-Vis Diffuse Reflectance, BET, H2 Chemisorption and SEM/EDS to validate the method of synthesis. All analysis confirmed that the reduction method with NaBH4 do not structurally modify TiO2, keeping its crystallinity and the ratio of anatase/rutile. XPS indicates the presence of metal in reduced oxidation state. To study the influence of the impregnation of platinum on titania, after synthesis and characterization, the study of gas-solid heterogeneous photocatalytic oxidation of some VOC was carried out at room temperature with annular plug flow reactors (1160 ml), one coated with pure TiO2 and another coated with TiO2/Pt, the catalysts were immobilized on reactor¿s internal walls. The photocatalystic tests were performed for n-octane , iso-octane, n-hexane and ciclohexane varying the inlet concentration (from 50 to 500 ppm) or residence time (from 10 to 50 s). The light source was an UV lamp (100 W, wavelengths with a maximum intensity at 254 nm. Reactants and products concentrations were analyzed using a continuous monitoring with a total hydrocarbon analyzer with flame ionization detector (FID). The addition of platinum to TiO2 improves photocatalytic efficiency of oxidation of VOC; conversion of the VOC using impregnated catalyst reached 99%, whereas pure TiO2 was at most 93%. No título do trabalho, a fórmula TiO2 deve vir com o "2" em subscrito, pois trata-se da fómula química da substância<br>Mestrado<br>Processos em Tecnologia Química<br>Mestra em Engenharia Química

<p>An electrolytic cell was designed and constructed for the preparation of TiO2 nanotubes. Conditions of anodic oxidation were established to reproducibly prepare TiO2 nanotubes of average length 35-50 &mu<br>m vertically orientated relative to the plain of a pure titanium metal sheet. A non-aqueous solution of ethylene glycol containing small percentage of ammonium fluoride was used as the electrolyte with an applied voltage of 60 V. The morphology and dimensions of the nanotube arrays were studied by scanning (SEM) and transmission (TEM) electron microscopy. The effect of calcination under different conditions of temperature and atmosphere (nitrogen, argon and air) were assessed by both X-ray diffraction (XRD) and cyclic voltammetry (CV). Cyclic voltammetry studies were made possible by construction of a specially designed titanium electrode upon which the nanotubes were prepared. CV studies established a positive correlation between crystallinity and conductivity of the nanotubes. Doping of the nanotubes with nitrogen and carbon was established by elemental analysis, X-ray photoelectron spectroscopy (XPS) and Rutherford back scattering (RBS). The effect of nonmetal doping on the band gap of the TiO2 nanotubes was investigated by diffuse reflectance spectroscopy (DRS).</p>

This Thesis describes the synthesis and characterisation of titanium imido compounds supported by pendant arm functionalised amidinate ligands. Reactivity studies of cyclopentadienyl amidinate-imido compounds with CO2 are presented. Chapter 1 introduces transition metal imido chemistry, with a particular emphasis on imido complexes of titanium. Chapter 2 describes recent developments in the chemistry of functionalised amidinate ligands. The synthesis and characterisation of new titanium imido compounds with pendant amine functionalised amidinate ligands is described. The preparation of an amidinate ligand with a pendant propyl arm is reported. Reactions of a selection of these complexes with small molecules are presented. Chapter 3 reviews recent developments in the chemistry of cyclopentadienyl amidinate-imido compounds. The preparation of cyclopentadienyl-supported titanium imido compounds bearing pendant arm amidinate ligands is described andthereactionsofthesecompoundswithCC>2arediscussed. Kineticanddensity functional theory studies of these reactions are presented. Chapter 4 describes the synthesis and characterisation of alkyl and aryloxide titanium amidinate-imido compounds. The preparation of cationic derivatives is also described and reactions of these cationic derivatives with small molecules are discussed. Chapter 5 presents full experimental procedures for all of the syntheses and reactivity studies outlined in Chapters 2 to 4. Chapter 6 contains characterising data for all of the new compounds reported. Appendices A - K contain tables of selected crystallographic data for all new crystallographically characterised complexes described in this Thesis. Appendices L - O contain kinetics data relating to work discussed in Chapter 3.

Sytnhese de natinbo5 qui par intercalation donne une serie de composes h2-2xax(tinbo5)::(2). Nh::(2)o et des composes (h::(3)nc::(n)h::(2n)nh::(3))::(0,5)tanbo::(5). On synthetise l'oxyde h::(3)ti::(5)nbo::(14). H::(2)o. Structure et proprietes magnetiques

Introduction Titanium-45, a candidate PET isotope, is under-employed largely because of the challenging aqueous chemistry of Ti(IV). The propensity for hydrolysis of Ti(IV) compounds makes radio-labeling difficult and excludes 45Ti from use in bio-conjugate chemistry. This is unfortunate because the physical characteristics are extremely desirable: 45Ti has a 3 hour half-life, a positron branching ratio of 85 %, a low Eβmax of 1.04 MeV, and negligible secondary gamma emission. In terms of isotope production, 45Ti is transmuted from naturally mono-isotopic 45Sc by low energy proton irradiation. The high cross-section and production rates on an unenriched metal foil target contribute to make 45Ti an ideal PET radionuclide. In order to bring 45Ti to even a preclinical plat-form, the hydrolytic instability of aqueous Ti(IV) needs to be addressed. Recently, the groups of Edit Tshuva (Hebrew University of Jerusalem) and Thomas Huhn (University of Konstanz) have synthesized several stable Ti(IV) compounds based upon the salan ligand [1,2]. Additionally, these compounds have shown heightened cyto-toxicity against HT-29 (human colorectal cancer) cells, amongst others, as compared to traditional metal-based chemotherapeutics such as cisplatin. The aim of our work has been to produce the radioactive analogue of one of these Ti(IV)-salan compounds, Ti-salan-dipic [2], which has hydro-lytic stability on the order of weeks. Not only will this allow us to shed some light on the still un-known mechanism of antiproliferative action of titanium-based chemotherapeutics, but it will also make progress toward bioconjugate 45Ti PET tracers. In the current abstract, we present some of the methods we are using to separate 45Ti from irradiated Sc, and subsequent labeling conditions. Material and Methods 45Ti was produced by proton irradiation of 250μm scandium foils at currents ranging from 10-20μA on a GE PETTrace. In order to increase production rate in the thin foil, an 800μm aluminum degrader was used to take the proton energy down from the nominal 16 MeV. The scandium was cooled by contact to a water-cooled silver plate. The activated foil was dissolved in 4M HCl, dried under argon at 120 oC, and taken back up in 12M HCl. Here, four (i-iv below) different approaches to removing the Ti from the Sc and labeling were taken with varying success. Briefly: i. 45Ti was separated on hydroxamate resin, as presented by K. Gagnon [3], only at 12M acid concentration followed by on-column radiolabeling. ii. 45Ti was extracted into 1-octanol [4], stripped with 12M HCl, and used directly for labeling from the organic phase. iii. 45Ti was trapped on a C-18 cartridge that had been pre-loaded with 1-octanol, similar to ion-pairing, and eluted with isopropanol. iv. 45Ti was extracted onto a polystyrene based 1,3 diol resin (RAPP polymers) and labeling commenced on the column. Radiolabeling was slightly different in each condition, but in general the salan and dipic ligands were added to the 45Ti in pyridine and reacted at elevated temperature (60–100 oC) for several (10–30) minutes. Reaction progression and radiochemical purity were assessed with silica TLC in chloroform : ethyl acetate (1 : 1). Results and Conclusion The trap, release, and yields for the four methods listed above are shown in TABLE 1. The best result was with the 1,3 diol resin which had the added advantage of reacting on-column. Further optimization is underway including a test of a solid supported 1,2 diol, and preclinical imaging with HT-29 xenografts. We conclude that hydrolytically stable 45Ti com-pounds can be synthesized in high yield, and hope that this advances the radiochemistry and use of 45Ti toward more widespread applications.

La síntesis y el estudio de complejos polinucleares de metales de transición constituyen un área de gran interés en la Química Inorgánica. La presencia de varios centros metálicos en una misma molécula puede modificar la reactividad que cabría esperar en compuestos metálicos. Por otra parte, estos sistemas polinucleares sirven como modelos a escala molecular para el estudio de ciertos procesos catalíticos como los que tienen lugar sobre superficies metálicas u óxidos metálicos.<br/><br/>El estudio teórico de dos familias de compuestos metálicos bien diferenciadas constituye el núcleo de esta tesis. En ambos casos el objetivo principal es ayudar a racionalizar las características químicas de las especies analizadas. El tratamiento se basará en cálculos teóricos mediante la teoría del funcional de la densidad, que han demostrado ser apropiados a la hora de estudiar agregados metálicos.<br/> <br/>Una primera parte, consta del estudio de la nueva familia de compuestos cubánicos de titanio que han sido recientemente sintetizados por el grupo del profesor Mena de la universidad de Alcalá de Henares. Un estudio teórico de dichos compuestos en colaboración conjunta con el trabajo en el laboratorio se ha venido realizando. Fruto de esta colaboración, nuevas pautas de investigación se han tratado de proponer por ambas partes. Como ejemplo, el análisis teórico para la obtención de espectros de resonancia magnética nuclear por métodos ab initio, que se expone en el segundo capitulo de la tesis, es fruto de un esfuerzo por parte de nuestro grupo por entender y racionalizar los datos de RMN obtenidos en el laboratorio para la caracterización de los compuestos. Además, fruto de los excelentes resultados obtenidos en este estudio, los conocimientos han sido aplicados a otros campos de interés dentro del grupo. Un estudio de la viabilidad para el análisis teórico del espectro de los núcleos de 183W en compuestos de Keggin forma un apartado importante en esta memoria.<br/><br/>Fruto de una estancia de seis meses en el grupo del doctor McGrady de la universidad de York surge un segundo apartado basado en el estudio de las importantes capacidades catalizadoras de los compuestos binucleares de molibdeno con azufres puente. La gran importancia industrial de procesos de hidrogenación catalizados por este tipo de compuestos ha despertado un gran interés, no obstante algunos aspectos del mecanismo de estas reacciones permanecen sin aclarar. El estudio teórico de esta reacciones puede proporcionar un poco de luz a estos aspectos. <br/><br/>Dentro del estudio de los compuestos cubánicos de titanio, los resultados principales se refieren a los asuntos siguientes:<br/><br/>- Descripción de las características estructurales y electrónicas de las especies implicadas. La disposición de los ligandos tridentados, (precubanos) de fórmula general [{TiCp*(&#61549;-O)}3(&#61549;3-CR)] y [{TiCp*}(&#61549;-NH)}3(&#61549;3-N)], para actuar como ligandos macrocíclicos donores de seis-electrones proporciona una ruta eficaz para la obtención de estructuras cúbicas con esqueleto [MTi3(&#61549;3-Y)(&#61549;-X)3]. <br/><br/><br/> <br/>Reacción del ligando con el fragmento metálico <br/><br/><br/>Es de esperar que fragmentos de casi todos los grupos metálicos sean capaces de interactuar con estos ligandos. Así se ha estudiado la formación de estructuras cubánicas a partir de fragmentos metálicos de los grupos 1,2, 4-6, 9, 13 y 14. Cambios en la naturaleza de la interacción, en el comportamiento del ligando, estructura molecular han sido analizados. Los resultados muestran las versatilidad de estos ligandos para actuar no sólo como donores de electrones si no también como posibles aceptores a través de los orbitales vacíos de los metales. Una mención especial en este apartado es necesaria para los isomeros acetilénicos y vilidénicos encontrados a partir de la deprotonación del compuesto [{TiCp*(&#61549;-O)}3(&#61549;3-CMe)] por la interacción con fragmentos metálicos del grupo 2. En este caso, el núcleo formado por los átomos de titanio sirve como base para la estabilización de estas especies.<br/><br/>- Estudio de la estabilidad de los compuestos y de los procesos energéticos en que están implicados (energías de la reacción, procesos de la isomerización). Un estudio de las condiciones experimentales que conducen a la obtención de estructuras cúbicas será analizado. El desplazamiento de ligandos lábiles en fragmentos metálicos por parte de los ligandos tridentados para formar los correspondientes cubanos ha sido probado, o también la activación de los enlaces nitrógeno-protón del ligando por interacción con el fragmento metálico. Estos procesos vienen caracterizados por unas condiciones energéticas favorables, estas condiciones son analizadas y estudiadas por su utilidad a la hora de proponer nuevas vías de síntesis en el laboratorio. Además, algunos compuestos presentarán evidencias del tener más que un isómero, o de experimentar un comportamiento dinámico en solución. Estas situaciones también se han descrito. Como resultado ha sido descrito el comportamiento de estas estructuras como ligandos mono- di- y tridentados, y adicionalmente como ligandos neutros o aniónicos. A su vez, respecto de la interacción con el fragmento metálico, un comportamiento como ligandos simples, que solo estabilizan el metal, o dobles, estabilizando metal y su respectivo contraión, han sido descritos.<br/><br/>- La influencia del solvente también se ha evaluado debido a la importancia que tiene su presencia en la obtención o no de ciertos compuestos. La termoquímica relacionada con la presencia del disolvente ha sido analizada desde el punto de vista teórico, debido a la imposibilidad de explicar ciertos procesos a partir de estudios en fase gas. Un modelo basado en un medio continuo de constante dieléctrica conocida se utiliza para demostrar los efectos del solvente. Para una misma familia de compuestos, solamente en algunos casos la interacción con los ligandos precubánicos conducen a la formación de los correspondientes cubanos, o en condiciones muy específicas. Por ejemplo, ha sido estudiado que los efectos del solvente son un factor decisivo en la obtención de los cubanos a partir de las sales de metales alcalinos y alcalino térreos. Este efecto permite explicar como la energía de red de las sales es fuertemente debilitada por la presencia del solvente, como factor principal en la obtención de las especies, por encima de la energía de interacción con el ligando.<br/><br/> - Descripción de algunas características químicas importantes. La contribución de los espectros de resonancia magnética nuclear resulta decisiva para la caracterización de los compuestos. Una descripción en detalle de las particularidades en el cálculo de los desplazamientos químicos para espectros de RMN es revisado en un apartado puramente teórico, especialmente para los métodos DFT. La activación del enlace C-H del carbono apical en el ligando [{TiCp*(&#61549;-O)}3(&#61549;3-CH)] durante la formación de estructuras diméricas fue seguida mediante espectroscopia RMN de 13C. Los grandes cambios experimentados en los desplazamientos químicos entre las especies protonadas y no protonadas han sido descritos y racionalizados perfectamente mediante cálculos teóricos. Los resultados obtenidos corroboran las suposiciones experimentales y proporcionan una visión muy clara de los procesos electrónicos que conducen a estos resultados. El carácter predictivo de estos estudios para con otras especies es claro, no obstante cuantitativamente hablando se encuentran dificultades a la hora de atribuir todos los desplazamientos.<br/><br/>Fruto de los excelentes resultados obtenidos en la descripción de los valores de RMN para los compuestos cubánicos, estos estudios se han ampliado a otros campos de interés para nuestro grupo de trabajo. Una sección, en parte diferente a la estructura global de la tesis, se ha dedicado ha mostrar estos primeros pasos a la hora de examinar las capacidades de los métodos DFT para computar los desplazamientos en núcleos de 183W en compuestos de Keggin. Nos encontramos ante unas mayores dificultades a la hora de reproducir los espectros experimentales, y gran parte de nuestros esfuerzos se han centrado en tratar de buscar la forma de trabajo más adecuada en términos de precisión y de coste computacional. La investigación y el interés continúan abiertos en un campo que necesita nuevas revisiones, sobre todo a la hora de racionalizar las posibles fuentes de error.<br/><br/>Las importantes características catalíticas de los sulfuros de molibdeno son objeto de estudio en la segunda parte de la tesis. El estudio teórico intentará aclarar ciertos aspectos confusos en la mecanistica asociada con las reacciones de estos compuestos. Estos complejos dinucleares de molibdeno con ligandos puente de azufre son una de las familias que posee una gran flexibilidad estructural y electrónica. Parte de los posibles isómeros del compuesto tipo [(CpMo)-S2]2 han sido estudiados, prestando gran interés al intercambio electrónico metal ligando con el cambio de estructura. <br/><br/><br/><br/><br/><br/><br/><br/><br/><br/><br/><br/><br/><br/><br/><br/><br/><br/><br/><br/>Ejemplos de estructuras cerradas (a-b) y abiertas (c-d) para el complejo <br/><br/><br/>La capacidad de los complejos del sulfuro de activar el hidrógeno molecular y de catalizar la reducción del substrato por el hidrógeno es particularmente relevante en la química. En especial los procesos relacionados con la activación de hidrógeno y posterior reducción de un sustrato ligado a los azufre puente son analizados; y en particular aquellos relacionados con la estructura electrónica del catalizador y del substrato. En estos estudios se pone de manifiesto la importancia catalizadora del metal, sirviendo como puente para protones en la reducción. A su vez se muestra como la naturaleza del sustrato resulta decisiva a la hora de observar una eliminación de hidrógeno molecular o una obtención del substrato reducido.<br/><br/><br/>Tarragona, 2004 J. Gracia<br>The overall framework of this report aims to summarize the work we have done over the past four years. Conceptually, this thesis is divided into three parts. The nucleus is based on a joint project with prof. Mena, of the University of Alcalá, whose group is involved in the synthesis and characterization of new aza- and oxo- titanium cubanes. These families of compounds are basically obtained from preorganized titanium tridentate ligands which can incorporate almost all the metals of the periodic table and yield the corresponding heterometallic cubanes. In this respect, the theoretical study is based on and adapted from the progress in the laboratory work. Practically every section in this part starts by describing the experimental data available for the specific system studied when we began the analysis. Then we go on to describe the theoretical study and attempt to involve the reader in the problems discussed. As a consequence of the advance in the experimental work, NMR spectra are used to characterize the new compounds. This leads us to initiate studies in the computational simulation of NMR chemical shifts. The most theoretical part of this report is an assimilation of these studies. The excellent results obtained for the cubane compounds enabled us to extend the knowledge acquired to other interesting fields and our group has started a study of the NMR shielding tensors in polyoxometalate compounds. The third part of the thesis focuses on some molybdenum-sulphide clusters and their activity as catalysts.<br/><br/>Chapters 3 and 4 focuse on the electronic structure of the new titanium cubane compounds recently synthesized by Mena et al. We work parallel to an experimental group to compare and contrast the theoretical and experimental data, and so establish the base chemistry of these new compounds. In this sense, the various reaction energies were studied, and the compounds and their possible isomers were characterised by means of DFT methods. Particular emphasis is paid to the properties of incomplete Ti3 core cubane tridentate ligands (precubanes) as bases for obtaining cubanes. The electronic structure, bonding energies, electron transfer processes and reactivity in the titanium Ti3 core of the metal clusters are studied.<br/><br/>The reaction of the azatitanium compound with some titanium derivatives leads to nitrocubane formation (see Scheme 1.3). This reaction forms a cubane compound by adding the fourth vertex to a structure that becomes a precubane. <br/><br/> <br/>Scheme 1.3. Reaction of with <br/><br/><br/>Chapter 5 summarizes the work carried out during a six-month stay in Dr. John E. McGrady's group, which uses density functional theory to explore problems of structure, bonding and reactivity in inorganic compounds. The main focus of the research is metal-metal bonding in cluster compounds. Transition metals have a prominent position in catalysis, both in industrial and biological contexts, and the ultimate goal is to understand the part played by the metal and its ligand environment in facilitating a particular chemical transformation. Chapter 5 studies the electronic structure of the core catalysts and the mechanism of their, unresolved, catalytic activity. The various possible isomers with the generic formula were studied, and the energy of the electron transfer between the metallic centres and the sulphide ligands, so important in the catalytic process, was investigated in depth. Subsequently, the mechanism of the hydrogen activation reaction promoted by these bi-molybdenum compounds (Equation 1.1) was studied, and the nature of the different reaction pathways was elucidated.<br/><br/><br/>[(CpMo(&#61549;-S))2(S2CH2)] promotes the hydrogenation of alkynes to cis alkenes, allenes to alkenes, and ketenes to aldehydes and the hydrogenolysis of carbon disulphide to hydrogen sulphide and thioformaldehide. The mechanisms of hydrogen interaction with these complexes have not been established. It is apparent that the sulphide ligands play a role in hydrogen coordination, and this ligand reactivity was a dominant characteristic throughout the study of these dinuclear molybdenum systems.<br/><br/><br/> <br/>Equation 1.1

Abstract Advanced Beta-21S titanium alloy is being considered for future high speed aircraft and hypersonic propulsion system applications due to its strength at elevated temperature and formability compare with any intermetallic compounds. The objective of this investigation was to evaluate the high temperature corrosion behavior of the alloy in air, molten salt and hydrogen gaseous environments and compare it with titanium aluminides and iron aluminides intermetallic compounds. This investigation showed that Beta-21S alloy is extremely oxidation resistant below 870°C (1600°F). Above 900°C due to the formation of a volatile molybdenum oxide its oxidation rate increases sharply and in presence of any molten salt severe metal dissolution would be observed. Hydrogen environment embrittlement (HEE) susceptibility of Beta-21S was studied in 34.5 Mpa (5000 psi) hydrogen gas at elevated temperature, no susceptibility to HEE was observed below 150°C, due to the alloy high hydrogen solubility limit (Beta phase titanium alloy). However, severe HEE susceptibility was observed at above 200°C, and titanium was converted to a brittle titanium hydride phase.

Abstract Stainless steels resist corrosion through formation of an oxygen-rich passive film. Halide ions damage this film and promote localized attack. Chloride ions are the most prevalent halide ions in our environment and are involved in many stainless steel corrosion failures. Bromine compounds have many important technological uses and localized corrosion caused by bromide ions is a significant problem, but one that has been less studied. The types and uses of bromides include lithium bromide for absorption refrigeration, volatile bromine compounds concentrated during thermal desalination of seawater, zinc bromide in heavy drilling fluids, bromine compounds used as less oxidizing disinfectants in spas and pools, and bromide feeds for FGD mercury control. Titanium is very resistant to chloride containing environments. However, it can corrode via pitting in bromide containing solutions depending on conditions. In many cases the bromides are present alongside chlorides. Reliable corrosion data is needed to support materials selection and process design for such environments. Experiments were conducted to determine the critical pitting temperature of several alloys (S31603, S32003, S32205, N08367, S32760, N06110, N06022, N10276 alloys and Grade 2 titanium) in calcium bromide solutions using the ASTM G150 electrochemical critical pitting test procedures. Similar experiments were also conducted in solutions containing equal concentrations (by weight) of chlorides and bromide. Corrosion of S32003, N08367, Grade 1 titanium and other alloys in LiBr solutions was studied. The results of these experiments are described in this paper.

Abstract Corrosion increasingly is impacting performance and reliability of microelectronic devices, which may be due to a combination of the decreasing feature sizes in these devices, the expanding range of environments in which these devices operate or the evolution of materials utilized in these devices. The layered configurations of microelectronics may facilitate either interfacial or galvanic corrosion, and therefore work is needed to characterize the susceptibility to corrosion. Since transition metals and their compounds are widely used as either adhesion or barrier layers, this study focuses on understanding the corrosion of Ti and TiNx films. The 100 nm monolithic Ti and TiNx thin films were deposited onto (100) Si wafers using PVD processes. The electrochemical and semi-conductive behavior of these films was studied at room temperature in one of three electrolytes with 3 wt.% chloride ions but varying pH values ranging from 2 to 13. In addition, the performance of electrically coupled Ti and TiNx were studied. Four replicates of each test condition (sample type and electrolyte) were monitored up to 105 days. Results indicated a more negative potential for the Ti films, TiNx films and coupled Ti and TiNx films in basic electrolyte when compared to replicates within either the acidic or neutral electrolytes. Galvanic effects between the coupled Ti and TiNx films were also observed when they were placed into an acidic electrolyte.

Abstract Advanced Beta-21S titanium alloy is being considered for future high speed aircraft and hypersonic propulsion system applications due to its strength at elevated temperature and formability compare with any intermetallic compounds. The objective of this investigation was to evaluate the susceptibility of this alloy to stress corrosion cracking and corrosion fatigue in several different corrosive environments. Electrochemical studies of Beta-21S alloy in sodium chloride solution showed it was not susceptible to any localized corrosion, but addition of more than 400 ppm fluoride ions to sodium chloride solution resulted in intergranular attack. Corrosion fatigue tests performed in this solution exhibited intergranular cracking at initiation stage which changed into transgranular during the crack propagation stage. But no susceptibility to SCC was observed under any condition. The results showed this alloy to have extreme corrosion resistance and possesses better performance compare to titanium aluminides and iron aluminide intermetallic compounds. Hydrogen reaction embrittlement (HRE) was studied by cathodically hydrogen charging method (applied potential -1500 mVSCE), no susceptibility to HRE was observed because of alloy high hydrogen solubility limit.

Abstract Fasteners for top-side applications on Naval ships have historically been steel fasteners. These fasteners when exposed to marine environments suffer extensive corrosion. Alternatives such as high strength stainless steel, nickel alloy and titanium alloy fasteners are being considered. While these alternative materials offer better corrosion resistance than steel, they can suffer from thread galling when used in the uncoated and/or unlubricated condition. Solid film lubricants such as molybdenum disulfide-impregnated epoxy polyimide have shown anti-galling properties. Additionally, anti-seize compounds such as copper loaded grease have also shown anti-galling properties. In a paper on titanium as alternative fasteners1, K. Faller compares titanium fasteners to steel and high strength alternative materials. In this study, Beta-C titanium fasteners are investigated as an alternative fastener for Naval use. Galvanic interactions and thread galling are evaluated to identify candidate coatings or lubricants sothat Beta -C titanium fasteners can be utilized for top-side applications.

Abstract The environmental behavior of Titanium alloys UNSR50250 and UNSR50400 in seawater from the Red Sea was tested under induced applied potential in the presence of microorganism. The study was carried out in a unique apparatus composed of two separated electrolytic cells, electrically connected by the tested titanium plate as a diaphragm. During the exposure of the titanium alloys to the electrolyte the anodically polarized surface potential of the titanium plates was recorded versus an Ag/AgCl reference electrode. Potentiodynamic polarization measurements curve for both UNSR50250 and UNSR50400 did not show a clear passive-transpassive transition up to a potential of about 7V vs. Ag/AgCl. However current oscillations were observed indicating metastable local sensitivity of the surface to the environment, resulting in shallow crevice and pits. To our opinion, UNSR50250 exhibited higher sensitivity to localized attack most probably due to the influence of thiobacillus bacteria. Exposing the alloys to seawater under applied potential showed that when the anodically polarized surface of the UNSR52400 exceeded a potential of 3.5V vs. Ag/AgCl a droop in the steady potential of about 0.5V vs. Ag/AgCl was observed after 5 hours. This potential drop phenomenon is related to a potential breakdown process, as confirmed by the pits observed using SEM. In contrast, polarization curve of UNSR50250 did not show any potential drop. This lack of potential drop can be explained by the higher electrical conductivity of the surface and by the almost uniform anodic dissolution of the alloy that took place when the potential was applied.

Abstract Zirconium is resistant to many corrosive media such as acids, alkalies, organic compounds and salts. When used in applications where high corrosion resistance is required, zirconium will reduce maintenance and downtime and in many cases will increase process efficiency. Several examples of cost savings are shown. Three different sulfuric acid applications are cited. In nitric acid where austenitic stainless steels and titanium had limited corrosion resistance, the use of zirconium has led to reduced maintenance and increased process efficiency. The replacement of a brick-lined tower and the use of zirconium tower packing and internals rather than ceramics has resulted in reduced maintenance costs in a chlorinated hydrocarbon process. In an alternating hot sulfuric acid and caustic service, zirconium has replaced a combination of three construction materials for a maintenance-free operation.

Abstract Corrosion, an ever-present entity in refinery operations, is classified into low temperature &amp; high temperature corrosion. Principal materials of construction typically are carbon &amp; low alloy steels, stainless steels, copper &amp; aluminum alloys, nickel alloys &amp; titanium. Corrosion is typically caused by crude oil contaminants such as H2S, HCl, nitrogen compounds and polythionic acid and/or by process chemicals such as organic chlorides, aluminum chloride, caustics, H2SO4, HF, amines and others. High temperature corrosion occurs due to presence of sulfides, naphthenic acids, oxidation, carburization, nitriding, and fuel-ash deposits. Some of the newer alloys of superaustenitic stainless and Ni-Cr-Mo alloy family show excellent resistance against general corrosion, pitting corrosion and stress corrosion cracking whereas some others show good resistance against sulfidation, nitriding, chlorination, and carburization. This paper presents some of the laboratory data generated both in low temperature and high temperature corrosive environments.

Abstract Deposits of natural rock salt are among the leading candidates as sites for this country's first high level nuclear waste repository. Materials being considered for waste containers in this medium include the corrosion-resistant alloy ASTM Grade-12 titanium (TiCode- 12). This paper describes a series of laboratory experiments conducted to first, evaluate the probable near-field hydrochemical environment surrounding the waste packages and secondly, to evaluate the corrosion properties of Grade-12 titanium under these conditions. Natural rock salt was irradiated, using a60 Co gamma source, at a dose rate of 8 x 106 rad/h at temperatures of 40° and 125°C. After 1000 hours of irradiation, brines were made from the salt and analyzed for pH and total base in solution. It was found that the irradiated salt, containing radiation- induced free sodium, reacted with deionized water to form highly alkaline brines (pH and total base values as high as 9.6 and 35 μeq/g, respectively). Rock salt samples irradiated at 125°C produced brines whose alkalinity increased according to a power law function and, therefore, in a manner similar to sodium-colloid formation within the salt. Using these data as a basis, the corrosion properties of Grade-12 titanium immersed in simulated alkaline brines were evaluated for periods up to 56 days. It was found that corrosion rates were higher in these solutions when compared to neutral solutions; this effect may be attributable to the chemical dissolution of passive oxides formed on the surface of the metal. After testing, sample surfaces in alkaline solutions were found to be covered with black scales which are considered to be a mixture of oxide and hydrogen compounds. Samples also showed an early stage of crevice corrosion after 21-day tests at 150°C. The crevice corrosion process was slow, however, because the necessary formation of low pH conditions within the crevice was retarded by the initially high pH of the test solution. Tests for hydrogen uptake included the immersion of metal coupons for 14day periods in autoclaves containing 150°C alkaline brines and hydrogen. It was found that, relative to tests conducted in neutral brines, twice as much hydrogen was absorbed by the alloy. The enhanced hydrogen uptake is attributed to the chemical dissolution of oxides which are known to limit hydrogen uptake. The coupons from hydrogen uptake tests typically develop black scales as observed in uniform corrosion testing. A tensile test was performed after cathodic charging at room temperature to determine the mechanical degradation of Grade-12 titanium upon hydrogenation. The hydrogenated sample showed more than 30% decrease in elongation even though the change in yield strength and tensile strength were the same as those for non-hydrogenated samples, thus, verifying slow-strain-rate embrittlement upon hydrogenation. Constant extension rate tests showed the presence of cleavage zones in the fracture surfaces, indicating that Grade-12 titanium, under the conditions studied, is susceptible to internal hydrogen embrittlement rather than stress-corrosion cracking.