<p> This thesis consists of studies carried out on the Nickel-Cobalt alloy system. The surface segregation behaviour has been studied over the range of composition from 14 to 90 atomic percent Nickel using Auger Electron Spectroscopy (AES). An analysis procedure has been developed that is based on computer simulation of observed spectra using pure metal standard spectra and has resulted in excellent matches. Nickel has been observed to segregate over the entire range of compositions studied and the driving force for segregation has been investigated by monitoring the equilibrium surface composition over a range of temperatures from 813 to 1100 K. The enthalpy and entropy of segregation has been determined on single grains of orientations (111) and (210) in a sample of composition 56.0 atomic percent Nickel as well as on the (111), (100) and (110) faces of a 50.0 atomic percent Nickel single crystal.</p> <p> The initial stage of oxidation has also been studied here using Scanning Auger Mapping and digital image processing. The initial stage of oxidation carried out in-situ has been shown to proceed via an island nucleation and growth mechanism which has been confirmed by imaging islands based on the oxygen Auger signal. A preliminary study of the effects of temperature and pressure on the island growth stage of oxidation has been completed and results are reported.</p> / Thesis / Doctor of Philosophy (PhD)

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En los últimos años, las técnicas de modelado y simulación a escala cuántica han alcanzado logros inimaginables gracias a los avances tecnológicos y como respuesta a la necesidad de correlacionar un sistema de partículas interactuantes con comportamientos observados experimentalmente. Los actuales métodos ab-initio conducen a una mayor diversidad y exactitud de resultados predictivos aunque son computacionalmente más costosos. En la presente tesis doctoral, se propuso como objetivo estudiar la hidrogenación de aceites comestibles sobre catalizadores metálicos modelo usando métodos de primeros principios y empleando un modelo periódico para representar mejor al sistema; todo motivado a partir del interés suscitado por la hidrogenación catalítica de los ácidos grasos para obtener productos 0% trans con el fin de mejorar la selectividad y especificidad de los catalizadores empleados. En particular se ha utilizado al 1,3-butadieno (13BD) como modelo de un ácido graso, por ser el alqueno más simple con dos dobles enlaces conjugados, y a superficies bimetálicas multilaminares de Pd-Ni, como catalizadores. Estas superficies resultan ser modelos de catalizadores modificados a los de Pd y Ni puros, conocidos por sus actividades catalíticas en el estudio de la hidrogenación parcial, así como por sus desventajas asociadas al alto costo y/o limitada actividad en la formación de isómeros cis. La incorporación de pequeñas cantidades de otro metal de transición, como por ejemplo Pd en una superficie de Ni, mejora la actividad y la selectividad hacia los isómeros butenos. Las superficies evaluadas PdnNim(111), donde n corresponde al número de capas de Pd (n = 0 - 4) depositadas sobre m capas de Ni (n + m = 4), fueron caracterizadas mediante sus propiedades estructurales, electrónicas y magnéticas. A partir de una correcta descripción de las mismas se seleccionaron dos de ellas: PdNi3(111) y Pd3Ni(111), sobre las cuales se adsorbieron el 13BD, los intermediarios y los productos de reacción. Mediante el análisis de las geometrías, las energías de adsorción y las densidades de estados se pudieron identificar las geometrías más estables que fueron empleadas en el posterior análisis de la reacción. La hidrogenación parcial del 13BD se evaluó de acuerdo al mecanismo de Horiuti-Polanyi. El proceso resultó ser exotérmico en la superficie modelo de PdNi3(111) con barreras de activación más bajas y endotérmico en la de Pd3Ni(111). Sobre la superficie PdNi3(111) se obtuvieron como productos de la reacción exclusivamente butenos, con cierta selectividad hacia el isómero 2-buteno. El trans-2- buteno es el isómero geométrico más esperable del 2-buteno, debido a la geometría de adsorción más estable del 13BD. Al evaluar la isomerización del trans al cis-2-buteno y la formación del cis-2-buteno, a partir de la hidrogenación del dieno adsorbido en el modo apropiado para esta geometría, se descubrió que el cis-2-buteno sólo se formaría a partir de la hidrogenación del 13BD adsorbido en el sitio de igual geometría. Mediante la extrapolación de los resultados obtenidos en esta tesis sería de esperar que un catalizador con las características del modelo PdNi3(111) mejore la actividad y aumente la selectividad de los productos hacia los isómeros cis al hidrogenar aceites comestibles. / In recent years, modeling techniques and scale quantum simulation have reached unimaginable achievements through technological progress and as response to the need to correlate a system of interacting particles with experimentally observed behaviour. Current ab-initio methods lead to greater diversity and accuracy of predictable results, but are computationally expensive. This thesis mainly studies hydrogenation of edible oils on model metallic catalysts using first principle methods and a periodic model to better represent the system, all motivated from the interest generated by fatty acid catalyst hydrogenation to obtain 0% trans products in order to improve selectivity and specificity of the catalysts employed. In particular, 1,3-butadiene (13BD) has been used as a fatty acid model since it is the simplest alkene with two conjugated double bonds, and the two bi-metallic Pd-Ni surfaces multilayers have been used as catalysts. These surfaces are modified catalysts models of Pd and Ni, known for their catalytic activity in the study of the partial hydrogenation catalysts, but presenting some disadvantages associated with high cost and/or limited activity in the formation of cis isomers. The incorporation of small amounts of other transition metal such as Pd in a surface of Ni greatly improves the activity and selectivity towards butenes isomers. The evaluated PdnNim(111) surfaces, where n is the number of Pd layers (n = 0- 4) deposited on m Ni layers (n + m = 4), were characterized by studying their structural, electronic and magnetic properties. From a correct description of these surfaces, two of them PdNi3(111) and Pd3Ni(111) were selected to adsorb 13BD, intermediaries and reaction products. Analyzing geometries, adsorption energies and densities of states the most stable geometries could be identified and later employed in the subsequent analysis of the reaction. Partial hydrogenation of 13BD was evaluated according to Horiuti-Polanyi mechanism. It was found that the process was exothermic on PdNi3(111) surface model with lower barriers and endothermic on Pd3Ni(111). On PdNi3(111) surface, butenes are the exclusive reaction products, with some selectivity to 2-butene isomer. The trans-2- butene is the most expected geometric isomer of 2-butene, due to the geometry of the most stable adsorption mode of 13BD. Evaluating the isomerization reaction from trans to cis-2-butene and the cis-2-butene formation, from diene hydrogenation adsorbed in the appropriate mode for this geometry, it was found that the cis-2-butene is formed only from the 13BD hydrogenation adsorbed on the mode with the same geometry. By extrapolation of the results obtained in this thesis would be expected that a catalyst with the characteristics of the PdNi3(111) model enhance the activity and increase the selectivity of the products to the cis isomers by hydrogenating edible oils.

Ce mémoire décrit les résultats d'une étude conçue pour tester l'efficacité d'une approche particulière visant à étudier le mécanisme de la fonctionnalisation des hétéroatomes C dans les liaisons C-H catalysée par les composés des métaux de transition. L'approche en question consiste à examiner les réactivités d'une famille de complexes nickelacycliques sélectionnés pour servir de système modèle pour les intermédiaires postulés être générés in situ lors de protocoles de fonctionnalisation C−H appelés « one-pot » (en une seule étape). Ainsi, les complexes nickelacycliques susmentionnés, y compris les complexes dimériques κC, κP-{2-OPR2,4-R’-C6H4}2Ni2(μ-Br)2 et leurs adduits acétonitrile monomères κC, κP-{2-OPR2,4-R’-C6H4}Ni(Br)(NCMe), obtenus par nickelation C−H des arylphosphinites, R2P(OAr), ont été traités avec des substrats appropriés possédant une liaison faible/labile telle que des liaisons simples N–O et N–N pour déterminer si la rupture des liaisons cibles mènerait à une coupure C–O ou C–N. En tant que substrats pour les couplages C–O, nous avons testé les réactivités des hydroxylamines (PhCH2)2NOH et (CH3CH2)2NOH, en plus du substrat protégé par le benzyle PhCH2ONH2. Les réactivités observées entre ces substrats et les complexes nickelacycliques modèles susmentionnés ont révélé trois schémas distincts influencés par la nature du complexe de nickel, le solvant utilisé dans la réaction et le substrat spécifique utilisé. Premièrement, pour le substrat protégé par le benzyle PhCH2ONH2, le résultat implique la formation directe d'adduits liés à l'azote avec tous les complexes de nickel testés. Deuxièmement, le complexe dimérique non-substitué (R’ = H) réagit avec (CH3CH2)2NOH et (PhCH2)2NOH dans CH2Cl2, produisant l'amine oxyde zwitterionique κC, κP-{2-OPR2-C6H5}Ni{κO-ONH(CH3CH2)2}Br et l'aminooxyde bidente (i-R2POPh)Ni{κO,κN-ON(CH2Ph)2}Br, respectivement. Enfin, la réaction parallèle de complexes de nickel substitués (R’ = Cl, OMe, NMe2) avec des hydroxylamines fournit des adduits à base d'imines résultant de la déshydratation de (CH3CH2)2NOH et (PhCH2)2NOH. Cette dernière réactivité atteint des résultats optimaux en acétonitrile, bien qu'elle se manifeste également dans une moindre mesure en C6D6 si la réaction se poursuit pendant plus de 24 heures. Divers scénarios mécanistiques ont été explorés pour élucider la transformation observée des hydroxylamines en imines, tous indiquant deux voies mécanistiques possibles. Le mécanisme le plus en évidence est l'attaque nucléophile sur l'acétonitrile coordonné, résultant en une déshydratation nette de l'hydroxylamine avec l'élimination de la molécule d'acétamide. Dans l'ensemble, cette étude a montré que cette réaction peut également se produire par des voies radicalaires pour lesquelles la coordination de l'acétonitrile au nickel n'est pas nécessaire. S'appuyant sur les résultats décrits ci-dessus, nous avons réalisé une autre étude de réactivité entre les complexes nickelacycliques susmentionnés et les hydroxylamines en conjonction avec des oxydants, en utilisant spécifiquement le TEMPO (2,2,6,6-tétraméthyl-1-pipéridinyl-N-oxyde). Cette investigation a donné naissance à une série de nouveaux complexes Ni-TEMPOH, où TEMPOH représente le 2,2,6,6-tétraméthyl-1-pipéridinyl-N-hydroxyde. Ces composés intrigants nous ont offert l'occasion unique d'explorer leur chimie de coordination avec divers nucléophiles, comme expliqué dans le chapitre 4. Cette étude a montré que le complexe Ni-TEMPOH peut être obtenu par deux voies distinctes : 1) en convertissant le TEMPO en TEMPOH avant de réagir avec le précurseur dimérique, et 2) en formant un complexe zwitterionique par réaction du dimère avec l'hydroxylamine, suivi du traitement avec le TEMPO. Les investigations de réactivité mettent en évidence que le MeCN déplace efficacement la fraction TEMPOH des complexes Ni(II)-TEMPOH, tandis que des ligands plus volumineux tels que le PPh3 et le DMSO échouent à montrer une réactivité similaire. Cela souligne le rôle crucial des considérations stériques dans la détermination de la réaction de substitution de ce complexe spécifique. De plus, l'étude révèle qu'en réagissant ces complexes avec d'autres nucléophiles tels que la morpholine et l'imidazole, des produits correspondants sont générés, notamment un adduit de morpholine et un complexe bis-imidazole, respectivement. L'analyse RMN du complexe bis-imidazole montre qu'en solution, il existe sous forme de complexes mono-imidazole, ce qui indique qu'un processus d'échange pourrait avoir lieu en solution. Fait intéressant, un aspect supplémentaire de cette recherche implique des tentatives d'oxydation du complexe Ni(II)-TEMPOH en utilisant l'AgOCOCF3. Ce processus conduit au remplacement du Br par l'OCOCF3, donnant ainsi un complexe acétate. En plus des enquêtes précédentes concernant les hydroxylamines, nous avons examiné le potentiel de couplage C–N du 4-amino-4H-1,2,4-triazole comportant des liaisons N–N simples lorsqu'il est réagi avec nos complexes nickelacycliques. Bien que nous ayons détecté des indications d'une voie de décomposition qui pourrait impliquer la rupture de la liaison N–N, cette réactivité est un élément mineur dans le panorama de réactivité observé, la voie principale conduisant à la formation de simples adduits du substrat triazole. En conséquence, nous avons réussi à isoler à la fois des adduits mononucléaires, à savoir {κP,κC-(i-Pr)2PO-Ar}Ni(Br)(κN-4-amino-4H-1,2,4-triazole), et des adduits dinucléaires à pont triazole, spécifiquement [{κP,κC-(i-Pr)2PO-Ar}Ni(Br)}2(μ,κN,κN-4-amino-4H-1,2,4-triazole). En utilisant la surveillance par RMN à température variable des réactions impliquant les précurseurs de nickel et le substrat triazole, nous avons révélé que les nouveaux adduits triazoles s'engagent dans un processus d'échange dynamique. L'analyse des données de RMN a révélé que les adduits triazoles mononucléaires et dinucléaires sont impliqués dans des équilibres dynamiques avec leurs adduits correspondants d'acétonitrile. Une observation intéressante émerge : les espèces cristallines récupérées dans la solution sont systématiquement soit les adduits triazoles mononucléaires, soit les adduits triazoles dinucléaires, jamais les deux simultanément. De plus, il semble que le choix de l'adduit optimal pour la cristallisation dépend du précurseur spécifique utilisé. Les précurseurs [{κP,κC-(i-Pr)2PO-C6H4}Ni(μ-Br)]2 et [{κP,κC-(i-Pr)2PO-(4-MeO-C10H5)}Ni(μ-Br)]2 produisent exclusivement des produits mononucléaires, tandis que [{κP,κC-(i-Pr)2PO-(5-OMe-C6H3)}Ni(μ-Br)]2, [{κP,κC-(i-Pr)2PO-(5-Cl-C6H3)}Ni(μ-Br)]2, et [{κP,κC-(i-Pr)2PO-(C10H6)}Ni(μ-Br)]2 produisent exclusivement les produits dinucléaires. / This thesis describes the results of a study designed to test the effectiveness of a particular approach for probing the mechanism of transition metal-catalyzed C-heteroatom functionalization of C–H bonds. The approach in question involves examining the reactivities of a family of nickelacyclic complexes selected to serve as a model system for intermediates postulated to be generated in-situ during so-called one-pot C–H functionalization protocols. Thus, the said nickelacyclic complexes, including the dimeric complexes κC,κP-{2-OPR2,4-R’-C6H4}2Ni2(μ-Br)2 and their monomeric acetonitrile adducts κC,κP-{2-OPR2,4-R’-C6H4}Ni(Br)(NCMe), which were obtained via the C–H nickelation of arylphosphinites, were treated with suitable substrates possessing a weak/labile bond such as N–O and N–N single bonds to see if rupture of the target bonds would lead to C–O or C–N coupling. As substrates for studying C–O coupling reactions, we tested the reactivities of the hydroxylamines (PhCH2)2NOH and (CH3CH2)2NOH in addition to the benzyl protected substrate PhCH2ONH2. The reactivities observed between these substrates and the above-mentioned model nickelacyclic complexes revealed three distinct patterns influenced by the nature of the Ni complex, the solvent employed in the reaction, and the specific substrate used. Firstly, for the benzyl-protected substrate PhCH2ONH2, the outcome involves straightforward formation of N-bound adducts with all Ni complexes tested. Secondly, the unsubstituted dimeric complex (R’ = H) reacts with (CH3CH2)2NOH and (PhCH2)2NOH in CH2Cl2 to give the zwitterionic amine oxide κC,κP-{2-OPR2-C6H5}Ni{κO-ONH(CH3CH2)2}Br and the bidentate aminoxide (i-R2POPh)Ni{κO,κN-ON(CH2Ph)2}Br, respectively. Lastly, the parallel reaction of substituted Ni complexes (R’ = Cl, OMe, NMe2) with hydroxylamines furnishes imine-based adducts originating from the dehydration of (CH3CH2)2NOH and (PhCH2)2NOH. This latter reactivity attains optimal results in acetonitrile, although it also manifests to a lesser extent in C6D6 if the reaction proceeds for over 24 hours. Various mechanistic scenarios have been explored to elucidate the observed transformation from hydroxylamines to imines, all of which indicate two possible mechanistic pathways. The most prominent mechanism is the nucleophilic attack on coordinated acetonitrile resulting in net dehydration of hydroxyl amine with elimination of acetamide molecule. Overall, this study showed that this reaction can also proceed through radical pathways for which coordination of acetonitrile to nickel is not necessary. Building upon the findings described above, we carried out another reactivity study between the nickellacyclic complexes mentioned above and hydroxylamines in conjunction with oxidants, specifically employing TEMPO (2,2,6,6-tetramethyl-1-piperidinyl-N-oxyl). This investigation yielded a series of new Ni-TEMPOH complexes, where TEMPOH stands for 2,2,6,6-tetramethyl-1-piperidinyl-N-hydroxy. These intriguing compounds have afforded us a unique opportunity to delve into their coordination chemistry with diverse nucleophiles, as elucidated in chapter 4. This study showed that the Ni-TEMPOH complex can be accessed through two distinct pathways: 1) converting TEMPO to TEMPOH prior to reacting with the dimeric precursor, and 2) forming a zwitterionic complex through the reaction of the dimer with hydroxylamine, subsequently treated with TEMPO. Reactivity investigations highlight that MeCN effectively displaces the TEMPOH moiety from the Ni(II)-TEMPOH complexes, while bulkier ligands such as PPh3 and DMSO fail to exhibit similar reactivity. This underscores the pivotal role of steric considerations in determining the substitution reaction of this specific complex. Furthermore, the study reveals that treating these complexes with other nucleophiles such as morpholine and imidazole, the corresponding charge-neutral mono(morpholine) adduct and cationic bis-imidazole adduct. NMR analysis of the latter complex indicates that in solution it exists as a mono-imidazole adduct undergoing exchange processes in solution. Interestingly, an additional facet of this research involves attempts to oxidize the Ni(II)-TEMPOH complex using AgOCOCF3. This process leads to the replacement of Br with OCOCF3, yielding an acetate complex. In addition to the above investigations involving hdroxylamines, we have examined the C–N coupling potential of 4-Amino-4H-1,2,4-triazole featuring N–N single bonds when reacted with our nickelacyclic complexes. Although we have detected indications of a decomposition pathway that could involve N–N bond cleavage, this reactivity is a minor element within the broader reactivity landscape observed, the primary route leading to the formation of simple adducts of the triazole substrate. As a result, we have isolated both mononuclear adducts, namely {κP,κC-(i-Pr)2PO-Ar}Ni(Br)(κN-4-amino-4H-1,2,4-triazole), and triazole-bridged dinuclear adducts, specifically [{κP,κC-(i-Pr)2PO-Ar}Ni(Br)}2(μ,κN,κN-4-amino-4H-1,2,4-triazole). By employing variable temperature NMR monitoring of the reactions involving the Ni precursors and the triazole substrate, we unveiled that the newly formed triazole adducts engage in a dynamic exchange process. Analysis of the NMR data revealed that both mono- and dinuclear triazole adducts are engaged in dynamic equilibria with their corresponding acetonitrile adducts. Interestingly, a noteworthy observation emerges: the crystalline species retrieved from the solution are consistently either the mononuclear or the dinuclear triazole adduct, never both simultaneously. Moreover, it appears that the selection of the favored adduct for crystallization is contingent upon the specific precursor used. Precursors [{κP,κC-(i-Pr)2PO-C6H4}Ni(μ-Br)]2 and [{κP,κC-(i-Pr)2PO-(4-MeO-C10H5)}Ni(μ-Br)]2 exclusively yield mononuclear products, whereas [{κP,κC-(i-Pr)2PO-(5-OMe-C6H3)}Ni(μ-Br)]2, [{κP,κC-(i-Pr)2PO-(5-Cl-C6H3)}Ni(μ-Br)]2, and [{κP,κC-(i-Pr)2PO-(C10H6)}Ni(μ-Br)]2 exclusively yield the dinuclear products.

Arbetet som utförts är en material studie som inriktar sig på nickel-krom-molybdenbaserade legeringar som används i dagens våt skrubber. Eftersom kraven på mängden utsläpp av svaveldioxid är en viktig miljöfråga, skapar detta ett behov för användandet av en våt skrubber. Den här produkten befinner sig i anläggningar där förbränningsmotorer finns och förekommer i princip i alla större fartyg. Rökgasen som motorerna släpper ifrån sig är skadlig för miljön och därför absorberas flödet in till en våt skrubber där en förbränning sker. Rökgasen separeras med hjälp av ett antal sprinklers som är placerade ovanpå gas ingången i en skrubber. Med hjälp av havsvatten som samlas upp och sluts till skrubbern injiceras detta genom sprinklers sen vidare nedåt på rökgasen som separerar föroreningar ifrån den gasen som är tänkt ska kondensera genom och ut i atmosfären. Havsvatten tillsammans med föroreningarna samlas på botten av skrubbern och samlas i tankar. Denna miljö är väldigt skadlig för materialet som produkten består av, framför allt på botten där materialet riskerar att korrodera som mest. Arbetet beskriver ett antal typer av korrosion och förklarar innebörden av de olika typerna så att det enklare går att förstå sammanhanget med miljön och omständigheternas påverkan på legeringarna. Syftet i arbetet är att studera de olika legeringarna och beskriva de med hjälp av den litteraturstudie som gjorts. Med hjälp av insamlad data av tester som tidigare utförts enligt standard, har detta tolkats och bidragit till evalueringen av de olika legeringarna. De grundläggande tester som används vid evaluering av legeringarnas karaktär är tester där en bit av materialet doppas ned i en specifik lösning med olika omständigheter och villkor. Detta räcker inte för att säkerställa en hållbar livscykel för en våt skrubber och därför evalueras legeringarna även med hjälp av olika fälttester. Teoretiska studier på tester i aggressiva miljöer används för att resultera rangordningen av de olika materialen och även ett nytt material undersöks vid namnet alloy 2120. / This thesis work is a study of materials which focus on nickel-chromium-molybdenum-based alloys used in today’s wet scrubbers. Since the requirements for emissions of sulfur dioxide is a major environmental issue, this creates a need for the use of a wet scrubber. This product is in installations where combustion engines are available and are basically in all larger vessels. The flue gas that engines emit are harmful to the environment and for that reason, the flow is absorbed into a wet scrubber where combustion takes place. The flue gas is separated by a number of sprinklers placed above of the gas in a scrubber. Collected seawater is used to separate the gas through the sprinklers that injects the water on top of the flue gas where impurities is separated from the gas that will condense out to the atmosphere. The water fluid together with the contaminants is collected on the bottom of the scrubber and into the tanks. This environment is very harmful to the material that the product is made of, in particular on the bottom where the material is more susceptible for corrosion. The work describes several types of corrosion and the meaning of the different types so that the reader easily can understand the impact of the environment on the alloys. The type of corrosion that occurs primarily in scrubbers is pitting corrosion and is considerate to be a highly local type of corrosion, and the most dangerous type. Pitting occurs when the protective oxide layer does not have time to repassivate and can also lead to other types of corrosion. Due to the dangerous work environment, the risk for corrosion to occur is high and therefore, focus is put on this specific material group. The purpose of this work was to study the alloys and describe them with the help of a literature study. Using data collected from tests previously performed in accordance with standards, the collected data has been interpreted and contributing to the evaluation of the various alloys. The basic tests used in the evaluation of the nature of the alloy are tests in which a piece of material immersed in a specific solution with different circumstances and conditions. This is not enough to ensure a sustainable life cycle for a wet scrubber and therefore, alloys is evaluated using various field tests as well. Theoretical studies on tests in aggressive environments is used to result the ranking of the various materials and also a new material is examined by the name alloy 2120.

No presente trabalho verificou-se a precisão de um critério que prevê composições de ligas vítreas aplicado ao sistema Zr-Ni-Cu. Este critério combina o parâmetro de instabilidade topológica (\'lâmbda\'), e o parâmetro termodinâmico (\'delta\' h) entre os elementos de liga. Os dois parâmetros correlacionam quantitativamente à composição química a tendência à formação de vidros metálicos. Este critério é uma ferramenta promissora e simples para guiar e reduzir o trabalho tedioso e intensivo de encontrar composições altas tendências a vitrificação em sistemas metálicos. Para comprovar a eficiência desta ferramenta, a metodologia foi calcular o parâmetro para o sistema de interesse e preparar ligas de acordo com algumas composições fornecidas. A metodologia de preparação das ligas seguiu a fusão a arco elétrico e subsequentemente o emprego das técnicas de resfriamento rápido, melt-spinning e splat-cooling, para a produção de fitas e discos metálicos respectivamente, e o coquilhamento para a produção de amostras maciças em forma de cunha. Para as amostras confeccionadas por melt-spinning e splat-cooling, verificou-se a precisão do critério de seleção através da quantificação das porcentagens de fases vítreas a partir de análises de difratogramas de raios-X e seus comportamentos térmicos a partir dos termogramas de análises por calorimetria exploratória diferencial (DSC). Já para as ligas coquilhadas em cunha, obtiveram-se alguns resultados com indícios de estruturas vítreas que foram caracterizadas por difração de raios-X e metalografia. Desta forma chegou-se à conclusão que o critério de seleção aplicado ao sistema Zr-Ni-Cu pode ser utilizado para o desenvolvimento de composições favoráveis à formação de vidro antes da produção das ligas. Conclui-se que o critério que combina o parâmetro de instabilidade topológica (\'lâmbda\' min) e o parâmetro termodinâmico (\'delta\' h) é uma ferramenta que pode ser utilizada como guia para encontrar as composições mais fáceis de formar vidro, reduzindo assim o trabalho experimental de tentativa e erro. / In the present work it was verified the accuracy of a proposed criterion to predict compositions of glassy alloys applied in the Zr-Ni-Cu system. This criterion combines the topological instability parameter (\'lâmbda\') and a thermodynamic parameter (\'delta\' h) among the alloying elements. The two parameters correlate quantitatively the chemical composition with the glass forming ability. This criterion is a promising and simple tool to guide and reduce the tedious and intensive work of finding good compositions of glasses in metallic systems. In an attempt to prove the efficiency of such tool, the methodology was to calculate the parameter for the system of interest and prepare alloys in accordance with the compositions provided by the tool. The methodology of preparation of the alloys followed the electric arc- melting and subsequent use of fast cooling techniques, melt-spinning and splat-cooling for the production of metallic ribbons and discs, respectively, and a wedge-shaped chiller mold to produce bulk metallic samples. For samples prepared from the melt-spinning and splat-cooling, it was verified the accuracy of the selection criteria by quantifying the percentage of glassy phases from X-ray diffractograms and their thermal behaviors from thermograms produced by differential scanning calorimetry (DSC). For alloys produced from the wedge-shaped mold, some results were obtained with evidence of vitreous structures that were characterized by X-ray diffraction and metallography. Therefore the conclusion is that the selection criteria applied to the system Zr-Ni-Cu can be used to develop favorable compositions for the formation of glasses before the production of the alloys. It is concluded that the selection criterion is a good tool and can be used as a guide to find the best glass forming alloys, thus reducing the experimental procedures of trial and error.

A eletrodeposição de ligas magnéticas de ferro, níquel e cobalto, além de permitir um maior controle sobre a composição e geometria dos filmes obtidas apresenta um fenômeno curioso: o filme apresenta uma maior quantidade do metal menos nobre do que a concentração do íon metálico no banho, o que contradiz o esperado termodinamicamente. A esse fenômeno deu-se o nome de codeposição anômala. A codeposição anômala já foi bastante estudada e muitos mecanismos foram propostos, mas não há um consenso na comunidade científica sobre eles. Os aditivos são usados nesses banhos para diversos fins, mas fora o seu efeito na composição dos filmes pouco é conhecido sobre seu papel no processo. Essa tese apresenta estudos realizados na tentativa de compreender o mecanismo da codeposição anômala da liga CoNi e a influência de glicina, o aditivo escolhido, no fenômeno. Várias técnicas de análise acopladas às técnicas eletroquímicas são empregadas, como a microbalança eletroquímica de cristal de quartzo, a espectroscopia no infravermelho por reflexão externa e medidas de stress no crescimento do filme. A presença do aditivo no banho da liga altera a composição da mesma, aumentando a quantidade do metal menos nobre, cobalto. A análise gravimétrica sugere que o aditivo mantém o pH superficial por meio do efeito tamponante ao mesmo tempo em que complexa com os íons metálicos, o que ocorre mesmo em meio ácido onde a concentração do agente complexante, glicinato, é baixa. A diferença entre suas constantes de complexação com os íons metálicos explica seu papel na composição do filme. A glicina torna o mecanismo de redução do níquel semelhante ao do cobalto além de indicar a ocorrência de fenômenos de oxidação na superfície do mesmo. A glicina pouco se adsorve sobre o eletrodo, mas há indícios através do stress de haver uma adsorção inicial sobre o Au. Há evidências da ocorrência de adsorção de hidrogênio na superfície do eletrodo, o que, acoplado com os altos valores de calor de adsorção, sugerem que o fenômeno da codeposição anômala pode estar atrelado à adsorção de H sobre os diferentes metais / Magnetic alloys, mainly the ones made of Fe, Ni or Co, have great technological importance, being used in many parts of our daily life, such as in magnetic recording devices. The electrodeposition of those alloys, which enables a greater control over the process, presents a curious phenomenon: the film has a greater amount of the less noble metal than the bath, something not expected thermodynamically. This phenomenon is called anomalous codeposition and it has been widely studied and although many mechanisms are available none is unanimous amongst the scientific community. Additives have been used to various extents in this baths but outside of controlling the composition of the film little is known. This thesis presents studies attempting to comprehend the anomalous codeposition mechanism of CoNi alloy and to understand the influence of glycine, the additive chosen, on the phenomenon. Many analytical techniques, coupled with electrochemical ones, have been used, such as quartz crystal electrochemical microbalance, external reflection FTIR spectroscopy and stress measurements during the film growth. The presence of glycine in the bath alters the film composition by increasing the quantity of the least noble metal, cobalt. The analysis through gravimetry suggests that glycine keeps the pH values at the surface by acting as a buffer and at the same time it forms complexes with the metallic ions. The different values of complexation constants with different metals explains its role in the film composition. Glycine changes the nickel reduction mechanism to one similar to that of cobalt. Besides that, its presence indicates that oxidation phenomena are happening at the surface of nickel films. The additive shows no signs of adsorption on the electrode, but stress measurements indicates that perhaps an initial adsorption on gold may happen. There are evidences that hydrogen adsorption may be happening in the electrodes surface which, coupled with the high values of heat of adsorption, suggests that the anomalous codeposition phenomenon may be linked to the effect of this species on different metals.

O presente trabalho visou desenvolver ligas à base de Níquel-Cromo para prótese dentária, que confiram as melhores características metalúrgicas e químicas para posterior produção e aplicação. Para isto foram adquiridas amostras de ligas comerciais de 8 fabricantes. Os materiais foram caracterizados em termos de composição química, propriedades mecânicas, caracterização microestrutural, temperatura de fusão, coeficiente de expansão térmica, corrosão e biocompatibilidade. Para isto, utilizou-se as fluorescência de raios X (XRF-WDS), ICP-OES, ensaios de tração, ensaios de dureza, ensaios de corrosão, avaliação de citotoxicidade, microscopia eletrônica de varredura (MEV), microanálise eletrônica (EDS), difratometria de Raios X (DRX), análise térmica diferencial (DTA), dilatometria e avaliação de fluidez. A maioria dos resultados composicionais não condiz com as composições fornecidas pelos fabricantes. Os resultados mostraram claramente a presença de um eutético típico formado pelas fases Niss e NiBe nas ligas contendo Be, que pode ser considerado uma \"impressão digital\" da presença deste elemento nestas ligas. É possível verificar a formação de intermetálicos na região interdendritica para as ligas isentas de Be, sendo identificado um siliceto (Nb6Ni16Si7) em uma das ligas, que possui temperatura de inicio de fusão inferior ao eutético Niss e NiBe das ligas com Be. De uma forma geral, os resultados dos ensaios de dureza mostraram valores superiores de dureza para as ligas com Be. Foi escolhida uma das ligas comerciais para a reprodução em escala laboratorial (LAB) e industrial (IND). Estas ligas produzidas apresentaram as mesmas características microestruturais, químicas e físicas da liga comercial. Nos ensaios de fluidez, a liga LAB apresentou o mesmo comportamento da liga comercial. A liga IND apresentou limite de escoamento e módulo de elasticidade de ?e0,02%= 810MPa e E= 200 GPa, respectivamente. Os ensaios de corrosão mostraram comportamento passivo tanto para a liga comercial quanto para a liga IND em saliva artificial e enxaguante bucal. O ensaio de citotoxicidade da liga IND indicou comportamento não citotóxico em controle negativo (Chapa de Ti). Os resultados obtidos com a liga IND indicam a possibilidade de fabricação desta liga Ni-Cr para próteses dentárias em escala industrial. / This study aimed to develop nickel-chromium base alloys for dental prostheses with the best characteristics for subsequent production and application. Samples were acquired from eight manufacturers of commercial alloys. The materials were characterized in terms of chemical composition, mechanical properties, microstructure, melting temperature, coefficient of thermal expansion, corrosion and biocompatibility. For this, we have used X-ray fluorescence (XRF-WDS), ICP-OES, tensile tests, hardness testing, corrosion testing, evaluation of cytotoxicity, scanning electron microscopy (SEM), electron probe microanalysis (EDS) , X-ray diffraction (XRD), differential thermal analysis (DTA), dilatometry and evaluation of fluidity. Most of the chemical compositional determined in this study were not consistent with the compositions provided by the manufacturers. The results clearly showed the presence of a typical eutectic microstructure formed by Niss and NiBe in alloys containing Be, which can be considered a \"fingerprint\" of the presence of this element in these alloys. It was possible to verify the formation of intermetallics in the interdendritic region of the Be-free alloys. In one of the alloys this intermetallic was identified as (Nb6Ni16Si7), this alloy presenting a initial melting temperature below the eutectic melting of the Niss+NiB eutectic. Overall, the results of hardness tests showed superior hardness for alloys with Be. One of the commercial alloys was chosen for reproduction in laboratory (LAB) and industrial (IND) scales. The alloys produced showed the same microstructural characteristics, chemical and physical characteristics of the commercial alloy. In the fluidity tests, the LAB alloy showed the same behavior of the commercial alloy. The IND alloy presented yield strength and modulus of elasticity ?e0, 02% = 810MPa, E = 200 MPa, respectively. The corrosion tests showed passive behavior for both commercial and IND alloy in artificial saliva and mouthwash solutions. The cytotoxicity assay indicated that the IND alloy is not cytotoxic in the negative control (Ti plate). The results obtained with the IND alloy indicate the possibility of fabrication this alloy for dental prosthesis on an industrial scale.