956 resultados para Hierro-Metalurgia


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The nickel alloys are widely used in the production of various materials, especially those that require mechanical strength characteristics associated with resistance to corrosion, for example, the stainless steel. Another use is the production of nickel alloy sintered from powder of metallic nickel. A promising alternative for the production of sintered components of nickel with an important reduction in costs of starting material is the use of mixtures of powders of Ni-NiO. This work aimed to study in situ reduction of NiO during sintering mixtures of Ni / NiO produced by powder metallurgy. The nickel mixtures have been processed by the technique of powder metallurgy and were pre-sintered in an oven under plasma reducing atmosphere of hydrogen. Mixtures Ni +15%NiO, Ni +25%NiO and Ni +35%NiO were studied and compared with samples consisting only of metallic Ni. Dilatometric tests were performed to study the sintering conditions of the mixtures. The consolidated material was analyzed for their microstructure and microhardness. Dilatometry graphs showed that the addition of nickel oxide in all compositions the active sintering the mixtures studied. In tests of microhardness indentations were made at different points of the sample surface. All compositions showed microhardness values close to the consolidated material from metallic nickel. However, sample containing Ni+35% NiO, showed a large dispersion of the values of microhardness tests performed at different points of the sample surface. Microstructural analysis of the material showed a higher concentration of voids and the presence of oxides in the waste composition of the mixtures Ni 35% NiO. The samples containing Ni+15%NiO showed microstructural characteristics and mechanical properties similar to metallic nickel consolidated under the same conditions of the compositions studied in this work and therefore had great potential for production of sintered nickel alloys

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The Nb-Cu pseudoalloys present themselves as potential substitutes for the alloys from a well known system and already commercially applied, as the W-Cu alloys, used in applications such as heat sinks, electrical contacts and coils for the generation of high magnetic fields. Because it is an immiscible system, where there is mutual insolubility and low wettability of the liquid Cu on the Nb surface, the processing route used in this work was the Powder Metallurgy. Two Nb alloys were used, with additions of 10% and 20% in weight of Cu, and times of 20, 30 and 40 hours for the high energy milling of the starting powders. The milling evolution of the powders is presented through the characterization techniques, such as the LASER diffraction for particle size, XRD, SEM, EDS, DSC, dilatometry, TEM and chemical analysis. After the milling, portions of the loads were submitted to the annealing heat treatment. The process used for the samples consolidation was the hot pressing, which has been applied both on some milled powders samples, as on the annealed powders. Subsequent heat treatments were performed in the samples at temperatures of 1000ºC (solid phase) and 1100ºC (in the Cu liquid phase). All sets of consolidated samples, and also the two sets of the heat treated, were analyzed by XRD, SEM, EDS, density and Vickers microhardness. Moreover, other Nb powder samples with 10% and 20% in weight of Cu obtained by simple mechanical mixing, were consolidated, thermally treated and characterized with the same techniques applied to the others, and the results were compared among themselves. Despite the difficulty of consolidation and densification of the two pseudoalloys of the Nb-Cu system of this study, on the route that passes through the HEM, samples were obtained with densities around 90% of the theoretical density. And, on the processing route of which were only mixed, the values reached up to 97%. Therefore, in this work are also emphasized the processes that made possible these results.

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Ceramic materials alumina basis have been widely used in structural components, mainly because owning properties such as high hardness, chemical inertness and good wear resistance, however, the low toughness is a factor that compromises its use in many other applications, featuring the addition of nickel as a possible solution to this problem, in this context, this work aims to study the addition of nickel alumina using the route of powder metallurgy processing of the material. The percentage of nickel were added 2, 4 and 6 wt%; and each composition to high energy milling in a planetary mill was performed for 2, 4, 9 and 16h. Subsequently, the samples were compacted at 300 MPa and sintered in a vacuum oven at 1400⁰C for 2h. The samples were characterized as the physical and mechanical properties, observing, in general, an improvement in sinterability of the material with increasing grinding time and nickel content, and mixing with a decrease of porosity and increase of hardness, density values above 80% of theoretical were obtained. The milling time of 4 hours and addition of 2% nickel, particularly if achieved higher hardness (HV 1068.7 +/- 32.6) and density of about 99% theoretical density.

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Ceramic materials alumina basis have been widely used in structural components, mainly because owning properties such as high hardness, chemical inertness and good wear resistance, however, the low toughness is a factor that compromises its use in many other applications, featuring the addition of nickel as a possible solution to this problem, in this context, this work aims to study the addition of nickel alumina using the route of powder metallurgy processing of the material. The percentage of nickel were added 2, 4 and 6 wt%; and each composition to high energy milling in a planetary mill was performed for 2, 4, 9 and 16h. Subsequently, the samples were compacted at 300 MPa and sintered in a vacuum oven at 1400⁰C for 2h. The samples were characterized as the physical and mechanical properties, observing, in general, an improvement in sinterability of the material with increasing grinding time and nickel content, and mixing with a decrease of porosity and increase of hardness, density values above 80% of theoretical were obtained. The milling time of 4 hours and addition of 2% nickel, particularly if achieved higher hardness (HV 1068.7 +/- 32.6) and density of about 99% theoretical density.

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Este artículo analiza las estatuas-menhir noroccidentales que se distribuyen en el área comprendida entre los valles del río Duero y el río Miño, pero que descubrimientos recientes han extendido a regiones fuera de este área nuclear. Partiendo de tres aspectos claves para su interpretación (la cronología, su relación con el paisaje y su sentido iconográfico), se examinan las relaciones entre estas formas materiales y un paisaje socio-material de acción específico (las formas socio-materiales de interacción propias del Bronce final atlántico). Para ello, se tiene en cuenta diferentes conexiones materiales (presencia, encuentro, coexistencia, hibridación, etc.) que permiten contextualizar las estatuasmenhir dentro de un proceso histórico particular: la integración del noroeste de la península Ibérica en un contexto de relaciones mediterráneo-atlánticas, en la segunda mitad del II milenio a.C.

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The occurrence of hand grindstones at the Cogotas I archaeological sites is considered to be a common feature. Given that a distant-provenance raw material is frequently involved, determination of its source is a basic factor in the search for a better understanding of resource management and for any Political Economy approach. To progress in these directions an overall study should be planned, using selected grindstones with a view to covering diverse sub-zones of the Cogotas I dispersal area, especially because of its considerable distance from the granite basement source. Such a study may today includes diverse analytical procedures combining successive geographic, petrographic, mineralogical and geochemical criteria. To check the plausibility of the proposed methodology, a preliminary test has been carried out on two granite grindstones, obtained at the archaeological excavation at the Castronuño (Valladolid) Cogotian site, which is fifty km away from an inferred source area that was presumably located at Peñausende (Zamora). The result obtained validates the proposed operational process, yielding a generalizable knowledge to other similar situations.

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Research surrounding the transition from II to I millennium cal BC in Eastern Iberian Peninsula has a large and extensive tradition of investigation. However, the chances to do research on this historical process have been limited by the lack of a well contextualized and dated stratigraphic sequence. For this reason, recent studies in this topic have followed the periodic proposals which were developed in closer regions and areas, especially in the South East and North East of the Peninsula. The investigation perspective about the Late Bronze in Eastern Iberian has however now improved, with the development of several archaeological investigations, the increase in the number of sites being dated and more recent studies into the region helping to bring about this change. As such, it is now in the correct state to be able to propose a new periodization and delve into the changes which occurred in the transition between 1500 and 725 cal BC.

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The recent archaeological works in Hinojosa, allowed us to discover a camp from Roman republic period. It is located in the center of the Celtiberian area and its study could open interesting perspectives to study this historical period. This paper shows the results of its preliminary studies.

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[ES] En la bibliografía reciente sobre los lacértidos de El Hierro se sugiere la coexistencia hasta tiempos relativamente recientes de tres especies en la isla: Gallotia caesaris, G. simonyi y G. goliath. Según esta bibliografía las diferencias específicas estarían basadas en la morfología dentaria, en el número de dientes, en el número de series de dientes en el pterigoides, en la morfología general del cráneo (estimada a partir de la longitud relativa de los procesos parietales) y en el tamaño de los individuos. El análisis comparativo de los numerosos restos subfósiles de lacértidos encontrados en El Hierro ha permitido concluir que si bien algunos de estos caracteres permiten distinguir a G. caesaris de otros lagartos de mayor tamaño, ninguno de ellos sirve para diferenciar a las otras dos especies propuestas.

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[ES] La distribución de 39 yacimientos paleontológicos y arqueológicos en los que se han encontrado restos de Gallotia simonyi en El Hierro muestra que su área primitiva de distribución estaba ligada a los ecosistemas xerófilos y termófilos de la isla. Lamentablemente, este paisaje ha sido fuertemente alterado por el hombre. La datación con 14C de restos procedentes de varios yacimientos ha puesto de manifiesto que en la zona llamada La Dehesa, en la que actualmente estos ecosistemas están bien conservados, todavía podían encontrarse lagartos gigantes en la segunda mitad del siglo XIX, y que éstos podían ser muy longevos y alcanzar grandes tamaños.

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[ES] En el marco del proyecto titulado «Plan de Recuperación del Lagarto Gigante de El Hierro, Gallotia simonyi (Programa Life 84-3200/94/743)» se ha contemplado, en un futuro próximo, la posibilidad de ampliación del área actual de distribución de dicho lagarto. La zona escogida (La Dehesa) es un sabinar sometido actualmente a poca intervención humana. Aunque el lagarto gigante de El Hierro (Gallotia simonyi) es una especie eminentemente herbívora complementa su dieta con el consumo de presas de origen animal, fundamentalmente artrópodos. Con el fin de evaluar los recursos tróficos disponibles en el área de reintroducción se ha realizado un seguimiento a lo largo de un ciclo anual. La evolución de los recursos tróficos animales se determinó mediante biocenómetros mensuales.