Plasma nitriding of AA2011 alloy and surface characterization by NDT techniques

Al-Cu alloys are widely used in the aerospace and automotive industries due to their high specific strength in some tempered conditions. However, due to poor corrosion and wear resistance, they are often anodized and/or painted. Plasma nitriding has been proposed as an alternative, though the developments in this technique are still in a recent stage for Al alloys. Electrical characterization techniques are well implemented NDTs in the industry because of good accuracy associated with lower cost, compared to other methods. Some, like eddy currents and 4-point probe techniques, are often used in coating inspection. The objective of this study was to perform Al nitriding at low temperatures to minimize the tempering initial condition damage and to assess the feasibility of eddy currents technique as a method for evaluating surface properties. The work developed can be divided in two stages. The first one was the process tuning, done at the Shibaura Institute of Technology, in Tokyo; and the second was the electrical characterization done in Faculdade de Ciências e Tecnologia, UNL. Low temperature nitriding of AA2011 alloy specimens was successfully achieved. Electrical conductivity results show that lift-off measurements by eddy currents testing can be related to surface properties.

In-situ X-ray diffraction studies during growth of Ni-Ti shape memory alloy films and their complementary ex-situ characterization

Shape Memory Alloy (SMA) Ni-Ti films have attracted much interest as functional and smart materials due to their unique properties. However, there are still important issues unresolved like formation of film texture and its control as well as substrate effects. Thus, the main challenge is not only the control of the microstructure, including stoichiometry and precipitates, but also the identification and control of the preferential orientation since it is a crucial factor in determining the shape memory behaviour. The aim of this PhD thesis is to study the optimisation of the deposition conditions of films of Ni-Ti in order to obtain the material fully crystallized at the end of the deposition, and to establish a clear relationship between the substrates and texture development. In order to achieve this objective, a two-magnetron sputter deposition chamber has been used allowing to heat and to apply a bias voltage to the substrate. It can be mounted into the six-circle diffractometer of the Rossendorf Beamline (ROBL) at the European Synchrotron Radiation Facility (ESRF), Grenoble, France, enabling an in-situ characterization by X-ray diffraction(XRD) of the films during their growth and annealing. The in-situ studies enable us to identify the different steps of the structural evolution during deposition with a set of parameters as well as to evaluate the effect of changing parameters on the structural characteristics of the deposited film. Besides the in-situ studies, other complementary ex-situ characterization techniques such as XRD at a laboratory source, Rutherford backscattering spectroscopy(RBS), Auger electron spectroscopy (AES), cross-sectional transmission electron microscopy (X-TEM), scanning electron microscopy (SEM), and electrical resistivity (ER) measurements during temperature cycling have been used for a fine structural characterization. In this study, mainly naturally and thermally oxidized Si(100) substrates, TiN buffer layers with different thicknesses (i.e. the TiN topmost layer crystallographic orientation is thickness dependent) and MgO(100) single crystals were used as substrates. The chosen experimental procedure led to a controlled composition and preferential orientation of the films. The type of substrate plays an important role for the texture of the sputtered Ni-Ti films and according to the ER results, the distinct crystallographic orientations of the Ni-Ti films influence their phase transformation characteristics.

À la búsqueda de la ciência política tomasiana. En torno al libro IV del "de regimine principum"

pp. 73-85

A presença meso-assíria no Médio Eufrates: o contributo da cerâmica de Tall Qabr Abū al-'Atīq (Deir ez-Zor, Síria)

Dissertação apresentada para cumprimento dos requisitos necessários à obtenção do grau de Mestre em Arqueologia.

O radicalisno islamista na Península Ibérica. A reconquista do Al Andalus

Dissertação apresentada para cumprimento dos requisitos necessários à obtenção do grau de Mestre em Ciência Política e RelaçõesInternacionais.

Production of aluminium based composites reinforced with embedded NiTi by friction stir welding

Dissertação para a obtenção do grau de Mestre em Engenharia Mecânica

Experimental Gravimetric Adsorption Equilibrium of n-Alkanes and Alkenes, Carbon Dioxide and Nitrogen in MIL-53(Al) and Zeolite 5A

Dissertação para obtenção do Grau de Mestre em Engenharia Química e Bioquímica

Gas tungsten arc welding of NiTi shape memory alloy

Shape memory alloys are characterized by the ability of recovering their initial shape after being deformed and by superelasticity. Since the discovery of these alloys, a new field of interest emerged not only for the scientific community but also to many industries. However, these alloys present poor machinability which constitute a constrain in the design of complex components for new applications. Thus, the demand for joining techniques able to join these alloys without compromising their properties became of great importance to enlarge the complexity of existing applications. Literature shows that these alloys are joined mainly using laser welding. In the present study, similar NiTi butt joints, were produced using TIG welding. The welds were performed in 1.5 mm thick plates across the rolling direction. A special fixture and gas assist device was designed and manufactured. Also a robot arm was adapted to accommodate the welding torch to assure the repeatability of the welding parameters. Welds were successfully achieved without macroscopic defects, such as pores and distortions. Very superficial oxidation was seen on the top surface due to insufficient shielding gas flow on the weld face. The welded joints were mechanically tested and structurally characterized. Testing methods were used to evaluate macro and microstructure, as well as the phase transformation temperatures, the mechanical single and cyclic behaviour and the shape recovery ability. Differential Scanning Calorimetry (DSC), Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), microhardness measurements were techniques also used to evaluate the welded joints. A depletion in Ni in the fusion zone was seen, as well as a shift in Ms temperature. For strain values of 4% the accumulated irrecoverable strain was of about 30% and increased with the strain imposed during cycling. Nevertheless, a complete recovery of initial shape was observed when testing the shape memory effect on a dedicated device that introduces a deformation of 6.7%. That is, the welding procedure does not remove the ability of the specimens to recover their initial shape.

Al-doped ZnO ceramic sputtering targets based on nanocrystalline powders produced by emulsion detonation synthesis – deposition and application as a transparent conductive oxide material

Transparent conducting oxides (TCOs) have been largely used in the optoelectronic industry due to their singular combination of low electrical resistivity and high optical transmittance. They are usually deposited by magnetron sputtering systems being applied in several devices, specifically thin film solar cells (TFSCs). Sputtering targets are crucial components of the sputtering process, with many of the sputtered films properties dependent on the targets characteristics. The present thesis focuses on the development of high quality conductive Al-doped ZnO (AZO) ceramic sputtering targets based on nanostructured powders produced by emulsion detonation synthesis method (EDSM), and their application as a TCO. In this sense, the influence of several processing parameters was investigated from the targets raw-materials synthesis to the application of sputtered films in optoelectronic devices. The optimized manufactured AZO targets present a final density above 99 % with controlled grain size, an homogeneous microstructure with a well dispersed ZnAl2O4 spinel phase, and electrical resistivities of ~4 × 10-4 Ωcm independently on the Al-doping level among 0.5 and 2.0 wt. % Al2O3. Sintering conditions proved to have a great influence on the properties of the targets and their performance as a sputtering target. It was demonstrated that both deposition process and final properties of the films are related with the targets characteristics, which in turn depends on the initial powder properties. In parallel, the influence of several deposition parameters in the film´s properties sputtered from these targets was investigated. The sputtered AZO TCOs showed electrical properties at room temperature that are superior to simple oxides and comparable to a reference TCO – indium tin oxide (ITO), namely low electrical resistivity of 5.45 × 10-4 Ωcm, high carrier mobility (29.4 cm2V-1s-1), and high charge carrier concentration (3.97 × 1020 cm-3), and also average transmittance in the visible region > 80 %. These superior properties allowed their successful application in different optoelectronic devices.

De la crisis de experiencia a la experiencia de la crisis. Una aproximación al arte público en Argentina

Siguiendo algunos desarrollos de Walter Benjamin y la lectura de su pensamiento que realiza Giorgio Agamben, este artículo explora ciertas aristas de la relación entre historia, tiempo y catástrofe como la crisis que permite comprender el vínculo del hombre con la experiencia en la modernidad. Esto implica tematizar una nueva noción de experiencia a fin de pensar modos de concebir la relación entre las prácticas artísticas y la historia, fundados en la discontinuidad, la interrupción y el shock. Dar por tierra el tiempo continuo y vacío significa asumir un tiempo “pleno, separado, indivisible y perfecto de la experiencia humana concreta”, tal como propone Agamben. A esta nueva concepción de la historia y al arte les compete posibilitar el advenimiento del tiempo pleno que supone la liberación del goce ahistórico, para acceder a una temporalidad placentera, cualitativamente transformadora del tiempo, a la vez crítica y destructiva.

Inventário da obra O Medo complementado com Luminoso Afogado do escritor Al Berto

O presente relatório tem como objectivo descrever o trabalho desenvolvido na Biblioteca Nacional de Portugal, concretamente no Arquivo de Cultura Portuguesa Contemporânea (ACPC), no sentido da conclusão do Mestrado de Edição de Texto ministrado pela Faculdade de Ciências Sociais e Humanas da Universidade Nova de Lisboa. O estágio foi acompanhado pela Drª. Fátima Lopes, responsável pelo ACPC, e realizou-se na Sala de Leitura de Reservados. No encontro anterior ao início do estágio, foi proposto pela mesma realizar o Inventário de um autor português contemporâneo e facultada a lista de «Elenco dos Acervos Existentes em setembro de 2014», para seleccionar o autor. Era importante ter em conta que só podia escolher os autores que tinham como menção na coluna de observação a informação «guia preliminar» e não os que tinham «inventário». O contacto com o espólio d’ O Medo do escritor Al Berto foi imprescindível para a realização do trabalho de inventariação. Surgiu a proposta de complementação ao inventário, a qual tinha como objectivo escolher um texto para observar as várias versões a que o mesmo foi sujeito até à sua publicação, tendo sido seleccionado Luminoso Afogado. O relatório apresenta quatro capítulos. Após a introdução do mesmo, inicia o primeiro capítulo, o qual centra-se na história da instituição onde decorreu o estágio, para além da abordagem da importância da arquivística textual. O segundo capítulo introduz o autor e as obras trabalhadas. No terceiro capítulo é exposto todo o trabalho de descrição, identificação e inventariação e a análise das versões de Luminoso Afogado. Por fim, o quarto capítulo destina-se aos resultados do trabalho efectuado. Procede em seguida com uma Conclusão, a Bibliografia e os anexos com os inventários e exemplos ilustrativos do trabalho desenvolvido.

A Presença islâmica em al-Qasr : uma análise sobre o urbanismo e o sistema defensivo

Alcácer do Sal é uma cidade que esteve desde sempre ligada ao rio Sado, permitindo essa mesma ligação, que nela se fossem fixando ao longo do tempo, distintos povos, provindos das mais diversas partes do mundo. Esta ocupação por parte das populações, só foi possível, porque o território era abundante em recursos naturais e, entre eles, possuía solos bastante férteis para a agricultura. Uma das comunidades que mais marcas deixou da sua presença naquele núcleo urbano, foi, sem dúvida, a muçulmana, tal como se pode verificar no topónimo que dá o nome à cidade, assim como pela presença dos vários vestígios materiais, como a imponente fortificação militar, que se ergue na colina mais alta da povoação, assim como pelas estruturas e espólios encontrados nas diversas intervenções arqueológicas realizadas naquela cidade. Tendo em conta estes aspetos, esta dissertação pretende fazer uma aproximação ao estudo do urbanismo da medina islâmica de al-Qasr, abarcando cronologicamente o século IX, altura em que os Banu Danis se fixam na cidade, até aos inícios do século XIII, correspondente à última fase de ocupação muçulmana da cidade.