De två kemiskt nära besläktade metallerna niob (Nb) och tantal (Ta) räknas av Europakommissionen som kritiska råmaterial. Detta på grund av en kraftigt ökad efterfrågan och en geografiskt koncentrerad global produktion av dem. Det här arbetet utgör en del av ett större projekt som bedrivs av EuroGeoSurveys (EGS); GeoERA FRAME, som har till syfte att kartlägga förekomsten av kritiska råmaterial inom EU. Två granitpegmatitiska prov från Kolsva fältspatgruva har undersökts med avseende på deras kemi och mineralogi; dels sådana som tentativt identifierats som kolumbitmineral och dels sådana som innehåller ett samarskitliknande mineral. I arbetet har tre huvudsakliga analysmetoder använts: 1) optisk mikroskopi, 2) svepelektronmikroskopi (SEM) med energidispersiv mikrokemisk analys (EDS), samt 3) pulverröntgendiffraktionsanalys (XRD). De kemiska analyserna som genomfördes på ”kolumbit-proven” visade att de bestod av kolumbit-(Fe), med generell formel AB2O6 och med en järndominans i A-katjonposition och niobdominans i B-katjonposition. Analyserna visad även på förekomst av mineral tillhörande pyroklorsupergruppen. De samarskitartade mineralen uppvisade en partiell likhet med samarskitgruppmineral (generell formel ABO4), men med hög grad av metamiktisering, dåliga stökiometrier, låga REE-halter, samt med varierande järn- och kalciumdominans i tentativ A-katjonposition och niobdominans i B-katjonpositionen. Även aluminiumsilikater, mineral från spinellgruppen samt hematit påvisades. Uppsprickning av de metamikta och spröda samarskitartade mineralen har möjliggjort en fluidmedierad omvandling, vilket bl.a. lett till bildning av sekundär radiogen blyglans. Resultaten av undersökningarna bekräftar att Kolsvapegmatiten representerar ett lokalt niob-tantalmineraliserat system. / The two chemically related metals niobium (Nb) and tantalum (Ta) are classified by the European Commission as critical raw materials. This is due to a highly increased demand and a limited global supply situation for these metals. This work is a part of a larger project run by EuroGeoSurveys (EGS); the GeoERA FRAME, which aims to map the distribution of critical raw materials in the EU. Two granitic pegmatite samples from the Kolsva feldspar mine were studied with regards to their chemistry and mineralogy. They had been tentatively identified as consisting of a columbite mineral and a samarskite-like mineral, respectively. In the project, three main analytical methods have been used: 1) optical microscopy, 2) scanning electron microscopy (SEM) with energy-dispersive spectroscopy (EDS), and 3) powder X-ray diffraction analysis (XRD). The analyses performed on the “columbite samples” indicated that most of them were columbite-(Fe), general formula AB2O6, with an iron dominance in the A-cation position and niobium dominance in the B-cation position. The analyses also indicated the presence of minerals belonging to the pyrochlore supergroup. The analyses of the samarskite-like minerals yielded results showing a partial resemblance to the samarskite group minerals (general formula ABO4), but with a high degree of metamictisation, poor stoichiometries, low to very low REE contents, variable iron and calcium-dominance in a tentative A-cation position and niobium-dominance in the B-cation position. Aluminium silicates, minerals from the spinel group and hematite were also observed in this assemblage. Fracturing of the brittle, metamict samarskite-like minerals have enabled a fluid-mediated alteration, which a.o. led to the formation of secondary radiogenic galena. The study confirms that the Kolsva pegmatite represents a locally Nb-Ta mineralised system.

Hochfeste Leitermaterialien werden für gepulste Hochfeld-Magnetspulen benötigt, um damit die sehr hohen Magnetfelder mit einer magnetischen Flussdichte von bis zu 100 T zerstörungsfrei erzeugen zu können. Cu-Nb-Legierungen besitzen ein hohes Potential, um die widersprüchlichen Anforderungen an das Leitermaterial, wie hohe Festigkeit, hohe Leitfähigkeit und gute Verformbarkeit, zu erfüllen. Die Herstellung von Cu-Nb-Legierungen ist jedoch auf dem konventionellen Weg der Schmelzmetallurgie aufgrund der vernachlässigbar kleinen gegenseitigen Randlöslichkeit der beiden Komponenten sehr kompliziert. Die hier vorliegende Arbeit befasst sich mit Untersuchengen zur Technologie für die Herstellung von hochfesten Cu-Nb-Leitermaterialien auf der Basis der Pulvermetallurgie. Gleichermaßen ist die Entwicklung der Legierung Kerninhalt der vorliegenden Arbeit. Hierfür wurden während der einzelnen Prozessschritte sowohl die Entwicklung des Gefüges als auch die für die Anwendung relevanten Eigenschaften der Legierung untersucht und die Beziehungen zwischen Gefüge und mechanischen wie auch elektrischen Eigenschaften ermittelt.

Bergslagen är känt för sin mångfald av mineraliseringar liksom sällsynta element och mineral. Speciellt pegmatiter och vissa skarnförekomster har förhöjda koncentrationer av sällsynta jordartsmetaller (REE på engelska) och REE-förande mineral. Pegmatitprover från Flintgruvan, som ligger i norra Bergslagen (Dalarna), karakteriserades i den här studien. Proven som studerades innehöll flera REE-förande mineral; (Y,REE,U,Th)-(Nb,Ta,Ti)-oxider av AB2O6-typ, xenotim-(Y) och (Y,Yb)-förande thorit. Pegmatiten klassificerades som varandes av NYF-(Niob-Yttrium-Fluor) typ på grund av de förhöjda koncentrationerna av niob (Nb), yttrium (Y) och titan (Ti) i de undersökta faserna. Förutom yttrium så innehöll pegmatiten små koncentrationer av andra HREE (tunga sällsynta jordartsmetaller) som ytterbium (Yb) och dysprosium (Dy). (Y,REE,U,Th)-(Nb,Ta,Ti)-oxiderna innehöll även relativt höga halter av kisel (Si). På basis av de kemiska analyserna representerar dessa strakt omvandlade faser antingen aeschynit eller polykras som ursprungsmineral. Undersöknings- och analysmetoderna som användes i studien var polarisationsmikroskopi och svepelektronmikroskopi med energidispersiv spektroskopi (SEM-EDS). / Bergslagen is known for its diversity of rare elements and minerals. Especially granitic pegmatites and some uncommon types of skarn deposits have shown higher concentrations of rare earth elements (REE) and REE-bearing minerals. Samples of a granitic pegmatite from Flintgruvan, which is located in northern Bergslagen (Dalarna), were characterized in this study. The samples that were studied were found to contain several REE-rich minerals such as (Y,REE,U,Th)-(Nb,Ta,Ti) oxides of AB2O6 type, xenotime-(Y) and an Y+Yb-bearing thorite. The most abundant AB2O6 type oxides were found to represent strongly altered minerals, either belonging to the aeschynite or polycrase group. Based on mineral chemical studies, the pegmatite was classified as being of the NYF (Niobium-Yttrium-Fluorine) type due to the predominance of yttrium (Y) and niobium (Nb) as well as notable titanium (Ti) concentrations. Other than yttrium the samples contained small concentrations of other HREE (heavy rare earth elements) such as ytterbium (Yb) and dysprosium (Dy). The (Y,REE,U,Th)-(Nb,Ta,Ti) oxides also contained a relatively high content of silicon (Si). The mineralogical characterization was done by means of reflected polarized light microscopy and scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS).

Les codes correcteurs d’erreurs Non-Binaires Low Density Parity Check (NB-LDPC) sont connus pour avoir de meilleure performance que les codes LDPC binaires. Toutefois, la complexité de décodage des codes non-binaires est bien supérieure à celle des codes binaires. L’objectif de cette thèse est de proposer de nouveaux algorithmes et de nouvelles architectures matérielles de code NB-LDPC pour le décodage des NBLDPC. La première contribution de cette thèse consiste à réduire la complexité du nœud de parité en triant en amont ses messages d’entrées. Ce tri initial permet de rendre certains états très improbables et le matériel requis pour les traiter peut tout simplement être supprimé. Cette suppression se traduit directement par une réduction de la complexité du décodeur NB-LDPC, et ce, sans affecter significativement les performances de décodage. Un modèle d’architecture, appelée "architecture hybride" qui combine deux algorithmes de l’état de l’art ("l’Extended Min Sum" et le "Syndrome Based") a été proposé afin d’exploiter au maximum le pré-tri. La thèse propose aussi de nouvelles méthodes pour traiter les nœuds de variable dans le contexte d’une architecture pré-tri. Différents exemples d’implémentations sont donnés pour des codes NB-LDPC sur GF(64) et GF(256). En particulier, une architecture très efficace de décodeur pour un code de rendement 5/6 sur GF(64) est présentée. Cette architecture se caractérise par une architecture de check node nœud de parité entièrement parallèle. Enfin, une problématique récurrente dans les architectures NB-LDPC, qui est la recherche des P minimums parmi une liste de taille Ns, est abordée. La thèse propose une architecture originale appelée first-then-second minimum pour une implantation efficace de cette tâche. / The Non-Binary Low Density Parity Check (NB-LDPC) codes constitutes an interesting category of error correction codes, and are well known to outperform their binary counterparts. However, their non-binary nature makes their decoding process of higher complexity. This PhD thesis aims at proposing new decoding algorithms for NB-LDPC codes that will be shaping the resultant hardware architectures expected to be of low complexity and high throughput rate. The first contribution of this thesis is to reduce the complexity of the Check Node (CN) by minimizing the number of messages being processed. This is done thanks to a pre-sorting process that sorts the messages intending to enter the CN based on their reliability values, where the less likely messages will be omitted and consequently their dedicated hardware part will be simply removed. This reliability-based sorting enabling the processing of only the highly reliable messages induces a high reduction of the hardware complexity of the NB-LDPC decoder. Clearly, this hardware reduction must come at no significant performance degradation. A new Hybrid architectural CN model (H-CN) combining two state-of-the-art algorithms - Forward-Backward CN (FB-CN) and Syndrome Based CN (SB-CN) - has been proposed. This hybrid model permits to effectively exploit the advantages of pre-sorting. This thesis proposes also new methods to perform the Variable Node (VN) processing in the context of pre-sorting-based architecture. Different examples of implementation of NB-LDPC codes defined over GF(64) and GF(256) are presented. For decoder to run faster, it must become parallel. From this perspective, we have proposed a new efficient parallel decoder architecture for a 5/6 rate NB-LDPC code defined over GF(64). This architecture is characterized by its fully parallel CN architecture receiving all the input messages in only one clock cycle. The proposed new methodology of parallel implementation of NB-LDPC decoders constitutes a new vein in the hardware conception of ultra-high throughput rate decoders. Finally, since the NB-LDPC decoders requires the implementation of a sorting function to extract P minimum values among a list of size Ns, a chapter is dedicated to this problematic where an original architecture called First-Then-Second-Extrema-Selection (FTSES) has been proposed.

Industrial production of hydrogen from the syngas, generated from steam reformation of natural gas or coal gasification, sets conditions for hydrogen separation membranes in terms of operating conditions. An alternative source for hydrogen is a syngas generated by gasification of municipal solid wastes which are likely to set more stringent conditions for the separation membranes. There is therefore, a growing demand for separation membranes with improved permeability and particularly of low cost. Among various alternatives, metallic membranes are particularly attractive due to their high selectivity and permeability for hydrogen, exemplified by palladium (Pd). However, due to high cost of Pd there is still a demand to develop alternative metallic membranes that are of low cost and have improved durability. Efforts have therefore concentrated on either alloying Pd so as to reduce its cost or on alternative membrane compositions of particularly b.c.c. structure. The current study deals with hydrogen separation membranes and aims to develop infrastructure for rapid identification of membrane compositions with improved permeability. The study is made up of three parts / i) development of sputter deposition system that would allow deposition of multiple compositions in a single experiment, ii) development of substrate material that would support the thin film membranes and would allow permeability measurement and iii) development of a set-up to measure the permeability of the thin film membranes. In the present thesis, a sputter deposition system incorporating three targets was successfully constructed. The system as tested with palladium-niobium-titanium (Pd-Nb-Ti) ternary system after necessary adjustment would yield thin films of homogenous thickness (&le / 7%) over a sample area of &asymp / 150 mm diameter. A total of 21 substrates each in 19 mm diameter arranged in triangular form in the substrate holder could successfully be deposited where composition distributions covered a greater portion of Pd-Nb-Ti ternary phase diagram. The structure of the deposited thin films can successfully be controlled by substrate temperature as well as by the pressure of plasma gas (argon). With the help of these parameters, structural diversity can also be produced beside the compositional variation. As for substrates, two materials were investigated. These were titanium dioxide (TiO2) modified porous stainless steel (PSS) and anodic porous alumina (AAO). TiO2 modified PSS due to its associated surface roughness leads to the deposition of films with defected structure which as a result is not gas tight. AAO produced via anodization of aluminum foil had a regular (40-60 nm) pore structure that provides a suitable surface for thin film depositions which could be defect free. However, AAO is very delicate and fragile which makes it difficult to adapt it as a support material for permeability measurement/hydrogen separation purposes. Finally, a set-up was developed for measurement of hydrogen permeability which is capable of measurement over a wide pressure and temperature conditions, i.e. hydrogen pressures up to 10 bar and temperature as high as 450 &deg / C. It is recommended that so as to identify compositions with improved permeability, Nb or a similar metal which has extremely high permeability could be used as a support material. This would tolerate the evaluation of the films which are not totally defect free.

A new generation of compact and highly efficient power production and propulsion technologies are critically needed in enabling NASAs long-term goals. Nuclear fission power technologies as part of project Prometheus are in development to meet this need. Proposed reactor concepts utilize a combination of refractory metals and stainless steels. One such refractory alloy, Niobium 1% Zirconium (Nb-1Zr), will be used because of its strength at high temperatures, neutron absorption properties, and resistance to corrosion by liquid alkali metals. One potential problem in using Nb-1Zr is that it undergoes rapid high temperature oxidation, even in low oxygen concentrations. Long-term oxidation of the niobium matrix can significantly deteriorate the mechanical properties of the alloy. This thesis reports on experimental studies of the high temperature interaction of 316 stainless steel (316 SS) and Nb-1Zr under prototypic space fission reactor operating conditions. Specifically, how the high temperature oxidation rate of Nb-1Zr changes when in contact with 316 SS at low external oxygen concentrations. The objective of the project is to determine if transport of gaseous contaminants, such as oxygen, will occur when Nb-1Zr is in contact with 316 SS, thereby increasing the oxidation rate and degrading material properties. Experiments were preformed in a realistic non-nuclear environment at the appropriate operating conditions. Thermal Gravimetric Analysis techniques were used to quantify results. Coupons of Nb-1Zr and Nb-1Zr in contact with 316 SS foil are subjected to flowing argon with oxygen concentrations between 4-15ppm and heated to a temperature of 500, 750, and 1000oC for 2 to 10 hours. Experiments were conducted at the Early Flight Fission Test Facility at NASA Marshall Space Flight Center. The experimental results indicate that a complex oxidation process, which depends greatly on temperature and oxygen concentration, occurs at the expected operating conditions. Non-linear regression techniques were applied to experimental data in order to derive correlations for the approximate oxidation rate of Nb-1Zr and Nb-1Zr in contact with 316 SS as a function of time, temperature, and oxygen concentration.

Zr-2.5Nb is currently used for pressure tubes in the CANDU (CANada Deuterium Uranium) reactor. A complete understanding of the deformation mechanism of Zr-2.5Nb is important if we are to accurately predict the in-reactor performance of pressure tubes and guarantee normal operation of the reactors. This thesis is a first step in gaining such an understanding; the deformation mechanism of ZrNb alloys at room temperature has been evaluated through studying the effect of texture and microstructure on deformation. In-situ neutron diffraction was used to monitor the evolution of the lattice strain of individual grain families along both the loading and Poisson’s directions and to track the development of interphase and intergranular strains during deformation. The following experiments were carried out with data interpreted using elasto-plastic modeling techniques: 1) Compression tests of a 100%Zr material at room temperature. 2) Tension and compression tests of hot rolled Zr-2.5Nb plate material. 3) Compression of annealed Zr-2.5Nb. 4) Cyclic loading of the hot rolled Zr-2.5Nb. 5) Compression tests of ZrNb alloys with different Nb and oxygen contents. The experimental results were interpreted using a combination of finite element (FE) and elasto-plastic self-consistent (EPSC) models. The phase properties and phase interactions well represented by the FE model, the EPSC model successfully captured the evolution of intergranular constraint during deformation and provided reasonable estimates of the critical resolved shear stress and hardening parameters of different slip systems under different conditions. The consistency of the material parameters obtained by the EPSC model allows the deformation mechanism at room temperature and the effect of textures and microstructures of ZrNb alloys to be understood. This work provides useful information towards manufacturing of Zr-2.5Nb components and helps in producing ideal microstructures and material properties for pressure tubes. Also it is helpful in guiding the development of new materials for the next generation of nuclear reactors. Furthermore, the large data set obtained from this study can be used in evaluation and improving current and future polycrystalline deformation models. / Thesis (Ph.D, Mechanical and Materials Engineering) -- Queen's University, 2008-09-05 13:51:30.42

O campo vulcânico Patagônico é composto pelo vulcanismo datado do Quaternário ao Cretáceo e está amplamente distribuído no ambiente geotectônico de extra back-arc continental. Onze vulcões associados à ocorrência de xenólitos mantélicos estão situados dos 36°13’S aos 44°52’S. Estes vulcões são dominantemente compostos por basanitos e a basaltos alcalinos, que são divididos em dois grupos com base em aspectos petrográficos, geoquímicos e isotópicos. (Grupos I e II). Estes Grupos estão relacionados a fontes mantélicas similares, mas foram submetidos a diferentes processos metassomáticos. Os Grupos I e I foram gerados a partir de baixas taxas de fusão a partir de uma fonte mantélica do tipo OIB na zona de estabilidade da granada, mas o Grupo II tem características de manto enriquecido (EMII) possivelmente herdadas de um agente metassomático relacionado à zona de subducção, enquanto que o Grupo I demonstra assinatura geoquímica de magmas tipo OIB relacionados a fontes mantélicas ricas em flogopita. Os basaltos alcalinos do vulcão Agua Poca (37º01’S - 68º07’W) pertencem ao Grupo II e são traquibasaltos. O vulcão Agua Poca é definido é piroclástico monogenético, é composto por intercalações de camadas de spatter e cinder, hospeda xenólitos mantélicos e está localizado a oeste da Província de La Pampa, no extremo norte da Argentina. As amostras de xenólitos mostram textura protogranular, protogranular a porfiroclástica, porfiroclástica e porfiroclástica a equigranular e são compostos por olivina (fosterita), ortopiroxênio (enstatita), clinopiroxênio (diopsídio) e espinélio (sp). Os xenólitos estudados são peridotitos da fácies espinélio e piroxenitos anidros em basaltos alcalinos do Pleistoceno com #Mg em rocha total de 89 a 91. As assinaturas geoquímicas desses xenólitos mostram correlação negativa entre os principais óxidos quando dispostos contra o #Mg e estão empobrecidos em elementos incompatíveis em relação ao manto primitivo (MP). Os xenólitos do vulcão Agua Poca são caracterizados pelo empobrecimento de ETRP e ETRM normalizados para o MP e pelo fracionamento de ETRL em relação aos ETRP (CeN/YbN = 0,15-0,5), com exceção da amostra HAP10 (1,46). Esse comportamento indica que os xenólitos do terreno Cuyania são o resultado de 1 a 10% de fusão do DMM (Manto Depletado) ou de 8 a 17% do MP (Manto Primitivo). Em geral, os peridotitos mostram anomalias positivas de Ba, U, Ta, Pb, Zr e Ti; e anomalias negativas de Rb, Th, Nb, La e Y, enquanto que os piroxenitos mostram anomalias positivas de Ba, U, Ta e Pb; e anomalias negativas de Th, Nb, La, Zr, Hf, Ti e Y. Curvas de mistura calculadas para o resíduo de fusão do MP/DMM com a composição de fluídos/sedimentos derivados de ambientes de subducção indicam interação do manto com até 3% de fluídos/sedimentos. As razões 87Sr/86Sr (0,702874 - 0,704999, com média de 0,704035) são muito similares àquelas definidas para peridotitos com fonte tipo OIB. Agua Poca tem razões 87Sr/86Sr, que estão abaixo daquelas definidas para peridotitos metassomatizados (usualmente >0,705). As razões de Nb/Ta sugerem a presença de um reservatório eclogítico refratário subductado fusão parcial gerando líquidos alcalinos com razões Nb/Ta supercondríticas. / The Patagonian Volcanic Field composed of late Cretaceous to Quaternary volcanism is widely distributed in a continental extra back-arc geotectonic environment. Eleven monogenetic volcanoes accompanied with ultramafic xenoliths are situated from 36°13′S to 44°52′S. These volcanoes are dominantly composed of basanite to alkaline basalt, which are divided into two groups, based on mineralogy, geochemical and isotope compositions (Groups I and II). These Groups are originated from the similar subcontinental mantle sources, but were undergone to different metasomatism processes. Groups I and II were generated from low melting degrees of an OIB-like garnet peridotite, but the Group II has enriched mantle (EMII) characteristics possibly inherited from on-going subduction related metasomatism, while Group I demonstrates the OIB-like signature, which might result from phlogopite-bearing in the subcontinental lithosphere. The alkaline basalts from Agua Poca volcano (37º01’S - 68º07’W) belong to the Group II and are trachybasalts. The Agua Poca volcano is a monogenetic pyroclastic volcano composed by intercalation of spatter and cinder layers, host ultramafic mantle xenoliths and is located in the West of the La Pampa Province, Northernmost of Argentine Patagonia. The xenoliths show protogranular, protogranular to porphyroclastic, porphyroclastic and porphyroclastic to equigranular textures, and are composed of olivine (fosterite), orthopyroxene (enstatite), clinopyroxene (diopside) and spinel (sp). The studied xenoliths are anhydrous spinel-bearing peridotite and pyroxenite xenoliths in Pleistocene alkali basalts with whole rock Mg# from 88 to 91. Geochemical signatures of the mantle xenoliths show negative correlation between main oxides against Mg# and depletion in incompatible elements compared to primitive mantle (PM). Agua Poca mantle xenoliths are characterized by flat Sun & McDonough (1989) primitive mantle (PM) normalized HREE and MREE patterns, and depletion of LREE compared to HREE (CeN/YbN = 0.15-0.5), with exception of the HAP10 (1.46) sample. These characteristics suggest that partial melting event is the main process responsible for the generation of these xenoliths. Model calculations suggest that the xenoliths are the result of 1 to 10% of DMM (Depleted Mantle MORB) or 8 to 17% of PM partial melting. Peridotite samples show positive anomalies of Ba, U, Ta, Pb, Zr and Ti; and negative anomalies of Rb, Th, Nb, La and Y, while the pyroxenite samples show positive anomalies of Ba, U, Ta and Pb; and negative anomalies of Th, Nb, La, Zr, Hf, Ti and Y. Mixing curves calculated to mixtures of melting residue of PM/DMM and fluid or sediment compositions related to subduction tectonic setting end members suggest up to 3% of interaction of the fluid sediment on the depleted mantle residue. 87Sr/86Sr ratios (0.702874 - 0.704999, with average of 0.704035) are similar to those defined to peridotites with OIB source (87Sr/86Sr = 0.70244 to 0.70502), being close to Depleted Mantle (DM; 87Sr/86Sr = 0.7023 to 0.7032) values. Nb/Ta ratios suggest that Agua Poca xenoliths were undergone to partial melting processes that generated alkaline magmas with superchondritic Nb/Ta ratios.

São realizados estudos termodinâmicos de nitretos, carbonetos e carbonitretos dos microelementos V, Nb, Al e Ti, utilizando bancos de dados computacionais do programa FactSage, com finalidade de verificar seus potenciais como inibidores do crescimento do grão na faixa de temperatura do processo de forjamento a quente dos aços. Um procedimento para verificação da solubilidade dos compostos dos microelementos por meio do FactSage foi desenvolvido e foram estudadas situações mais complexas e menos abordadas na literatura, tais como o efeito combinado de dois microelementos no aço e o estudo do comportamento dos carbonitretos em altas temperaturas com variantes do porcentual de carbono e nitrogênio. Os estudos demonstraram que os nitretos com presença de titânio possuem elevada estabilidade em altas temperaturas e, por isso, são potencialmente muito efetivos no controle do crescimento do grão. Alguns carbonetos com presença de nióbio apresentam também uma boa estabilidade em altas temperaturas, assim como os carbonitretos desses dois elementos. Foi verificada uma boa correlação dos produtos de solubilidade obtidos tanto por métodos experimentais como por cálculos termodinâmicos apresentados pela literatura, bem como a valiosa contribuição do software para estudos de precipitação e dissolução de carbonetos, nitretos e carbonitretos na austenita, permitindo auxiliar na seleção de aços e/ou modificação da composição de aços convencionais por meio da adição de microelementos juntamente com uma escolha apropriada de porcentuais de nitrogênio e/ou carbono, quando se busca controlar o crescimento do grão em altas temperaturas. Os resultados obtidos podem auxiliar de forma indireta nos estudos de eliminação de tratamentos térmicos convencionais, seja pelo uso de aços microligados com resfriamento controlado, seja pelo uso de aços convencionais de baixa liga temperados logo após forjamento, permitindo, assim, uma redução dos custos globais das peças. Além dessas considerações, os resultados apresentados e a técnica desenvolvida podem também ser úteis em outras áreas em que seja importante o controle do crescimento do grão, tais como laminação a quente e cementação em alta temperatura. / Thermodynamics studies of nitrides, carbides and carbonitrides of the micro elements V, Nb, Al and Ti were performed using the FactSage program databases, in order to verify their potential for grain growth inhibition in a range of temperatures of hot forged steels. A procedure to verify the solubility of compounds of the micro elements was developed by means of FactSage, and it was studied complex states less discussed in literature, such as the combined effect of two micro elements in steel and the behavior of carbonitrides at high temperatures, varying carbon and nitrogen contents. The studies demonstrate that the nitrides with Titanium have high stability in austenite at elevated temperatures: therefore they are potentially highly effective in grain size control. Carbides with Niobium also present effective stability at high temperatures, as well as the carbonitrides of these two elements. A good correlation was verified between the solubility product obtained either by experimental methods, or by thermodynamics calculation presented by literature. Also, a valuable contribution is made by the software in the studies of precipitation and dissolution of nitrides, carbides and carbonitrides in austenite; thus aiding the selection of steels, and/or modification of the chemical composition of standardized steels, by means of adding micro elements; and providing a suitable choice of carbon and nitrogen content when one seeks to control the grain growth at elevated temperatures. Such results can help indirectly in the studies eliminating conventional heat treatment methods, by using micro alloyed steels with controlled cooling and low alloy steels quenched after forging, with overall reducing costs. Besides these considerations, the results presented and the developed procedure can be useful in other areas where grain growth is an important factor, such as in hot rolling and carburizing at high temperature.

O campo vulcânico Patagônico é composto pelo vulcanismo datado do Quaternário ao Cretáceo e está amplamente distribuído no ambiente geotectônico de extra back-arc continental. Onze vulcões associados à ocorrência de xenólitos mantélicos estão situados dos 36°13’S aos 44°52’S. Estes vulcões são dominantemente compostos por basanitos e a basaltos alcalinos, que são divididos em dois grupos com base em aspectos petrográficos, geoquímicos e isotópicos. (Grupos I e II). Estes Grupos estão relacionados a fontes mantélicas similares, mas foram submetidos a diferentes processos metassomáticos. Os Grupos I e I foram gerados a partir de baixas taxas de fusão a partir de uma fonte mantélica do tipo OIB na zona de estabilidade da granada, mas o Grupo II tem características de manto enriquecido (EMII) possivelmente herdadas de um agente metassomático relacionado à zona de subducção, enquanto que o Grupo I demonstra assinatura geoquímica de magmas tipo OIB relacionados a fontes mantélicas ricas em flogopita. Os basaltos alcalinos do vulcão Agua Poca (37º01’S - 68º07’W) pertencem ao Grupo II e são traquibasaltos. O vulcão Agua Poca é definido é piroclástico monogenético, é composto por intercalações de camadas de spatter e cinder, hospeda xenólitos mantélicos e está localizado a oeste da Província de La Pampa, no extremo norte da Argentina. As amostras de xenólitos mostram textura protogranular, protogranular a porfiroclástica, porfiroclástica e porfiroclástica a equigranular e são compostos por olivina (fosterita), ortopiroxênio (enstatita), clinopiroxênio (diopsídio) e espinélio (sp). Os xenólitos estudados são peridotitos da fácies espinélio e piroxenitos anidros em basaltos alcalinos do Pleistoceno com #Mg em rocha total de 89 a 91. As assinaturas geoquímicas desses xenólitos mostram correlação negativa entre os principais óxidos quando dispostos contra o #Mg e estão empobrecidos em elementos incompatíveis em relação ao manto primitivo (MP). Os xenólitos do vulcão Agua Poca são caracterizados pelo empobrecimento de ETRP e ETRM normalizados para o MP e pelo fracionamento de ETRL em relação aos ETRP (CeN/YbN = 0,15-0,5), com exceção da amostra HAP10 (1,46). Esse comportamento indica que os xenólitos do terreno Cuyania são o resultado de 1 a 10% de fusão do DMM (Manto Depletado) ou de 8 a 17% do MP (Manto Primitivo). Em geral, os peridotitos mostram anomalias positivas de Ba, U, Ta, Pb, Zr e Ti; e anomalias negativas de Rb, Th, Nb, La e Y, enquanto que os piroxenitos mostram anomalias positivas de Ba, U, Ta e Pb; e anomalias negativas de Th, Nb, La, Zr, Hf, Ti e Y. Curvas de mistura calculadas para o resíduo de fusão do MP/DMM com a composição de fluídos/sedimentos derivados de ambientes de subducção indicam interação do manto com até 3% de fluídos/sedimentos. As razões 87Sr/86Sr (0,702874 - 0,704999, com média de 0,704035) são muito similares àquelas definidas para peridotitos com fonte tipo OIB. Agua Poca tem razões 87Sr/86Sr, que estão abaixo daquelas definidas para peridotitos metassomatizados (usualmente >0,705). As razões de Nb/Ta sugerem a presença de um reservatório eclogítico refratário subductado fusão parcial gerando líquidos alcalinos com razões Nb/Ta supercondríticas. / The Patagonian Volcanic Field composed of late Cretaceous to Quaternary volcanism is widely distributed in a continental extra back-arc geotectonic environment. Eleven monogenetic volcanoes accompanied with ultramafic xenoliths are situated from 36°13′S to 44°52′S. These volcanoes are dominantly composed of basanite to alkaline basalt, which are divided into two groups, based on mineralogy, geochemical and isotope compositions (Groups I and II). These Groups are originated from the similar subcontinental mantle sources, but were undergone to different metasomatism processes. Groups I and II were generated from low melting degrees of an OIB-like garnet peridotite, but the Group II has enriched mantle (EMII) characteristics possibly inherited from on-going subduction related metasomatism, while Group I demonstrates the OIB-like signature, which might result from phlogopite-bearing in the subcontinental lithosphere. The alkaline basalts from Agua Poca volcano (37º01’S - 68º07’W) belong to the Group II and are trachybasalts. The Agua Poca volcano is a monogenetic pyroclastic volcano composed by intercalation of spatter and cinder layers, host ultramafic mantle xenoliths and is located in the West of the La Pampa Province, Northernmost of Argentine Patagonia. The xenoliths show protogranular, protogranular to porphyroclastic, porphyroclastic and porphyroclastic to equigranular textures, and are composed of olivine (fosterite), orthopyroxene (enstatite), clinopyroxene (diopside) and spinel (sp). The studied xenoliths are anhydrous spinel-bearing peridotite and pyroxenite xenoliths in Pleistocene alkali basalts with whole rock Mg# from 88 to 91. Geochemical signatures of the mantle xenoliths show negative correlation between main oxides against Mg# and depletion in incompatible elements compared to primitive mantle (PM). Agua Poca mantle xenoliths are characterized by flat Sun & McDonough (1989) primitive mantle (PM) normalized HREE and MREE patterns, and depletion of LREE compared to HREE (CeN/YbN = 0.15-0.5), with exception of the HAP10 (1.46) sample. These characteristics suggest that partial melting event is the main process responsible for the generation of these xenoliths. Model calculations suggest that the xenoliths are the result of 1 to 10% of DMM (Depleted Mantle MORB) or 8 to 17% of PM partial melting. Peridotite samples show positive anomalies of Ba, U, Ta, Pb, Zr and Ti; and negative anomalies of Rb, Th, Nb, La and Y, while the pyroxenite samples show positive anomalies of Ba, U, Ta and Pb; and negative anomalies of Th, Nb, La, Zr, Hf, Ti and Y. Mixing curves calculated to mixtures of melting residue of PM/DMM and fluid or sediment compositions related to subduction tectonic setting end members suggest up to 3% of interaction of the fluid sediment on the depleted mantle residue. 87Sr/86Sr ratios (0.702874 - 0.704999, with average of 0.704035) are similar to those defined to peridotites with OIB source (87Sr/86Sr = 0.70244 to 0.70502), being close to Depleted Mantle (DM; 87Sr/86Sr = 0.7023 to 0.7032) values. Nb/Ta ratios suggest that Agua Poca xenoliths were undergone to partial melting processes that generated alkaline magmas with superchondritic Nb/Ta ratios.