Browsing by Issue Date, starting with "2022-11"
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- Insights about the Sines massif: a reinterpretation of geophysical data to the assessment of the potential for CO2 storage through mineral carbonationPublication . Marques, Fábio; Pedro, J.; Araujo, A.; Moita, Patrícia; Carneiro, Júlio; Sousa, Pedro; Carvalho, João; Correia, AntonioABSTRACT: The InCarbon project aims to evaluate the potential for storage of captured CO2 using in-situ mineral carbonation in mafic and ultramafic plutonic rocks in Alentejo, Portugal. The Sines massif appears to be the most promising massif for mineral carbonation and its geochemistry, petrography, mineralogy, volume and extension are characterized. Its offshore volume and extension are evaluated through reinterpretation of previous geophysical data which confirms the occurrence of two well defined magnetic anomalies. The Sines magnetic anomaly is directly related with the outcropping area of the Sines massif to the continental shelf; three-dimensional modelling (3D) of apparent magnetic susceptibility correlates with a volume of 217 km3.The offshore magnetic anomaly presents an estimated volume of 226 km3 and is located about 10 km from the Sines anomaly to the Southwest. If both anomalies result from a single igneous body, the area of the Sines massif could as be large as 300 km2. However, the possibility of these that those two anomalies correspond distinct mafic igneous structures in the continental shelf cannot be discarded and should be further investigated.
- Corrosion behaviour in artificial saliva of medical grade SS316L sputter-coated with DLC films: the effect of adhesion layersPublication . Frois, António; Faia, Pedro; Santos, Luis; Santos, Ana; Louro, C.ABSTRACT: Hydrogenated amorphous carbon (a-C:H) top layer was deposited onto 316L medical grade stainless steel by reactive magnetron sputtering with two types of interlayers, based on Cr and Ti. The goal was to evaluate the effect of the adhesion-promoting layers on the overall coating/substrate system. After the immersion test in acidic artificial saliva, no surface signs of corrosion were detected. However, the Cr-based interlayer enhanced the metallic ions release, whereas the Ti-based one seems to improve the corrosion resistance. Electrochemical Impedance Spectroscopy was also used to evaluate galvanic corrosion evolution at the adhesion interfaces.
- A multistage stochastic approach for the optimal bidding of variable renewable energy in the day-ahead, intraday and balancing marketsPublication . Silva, Ana Rita; Pousinho, H. M. I.; Estanqueiro, AnaABSTRACT: Market agents with renewable resources face amplified uncertainty when forecasting energy production to securely place bids in electricity markets. To deal with uncertainties, stochastic modelling has been applied to optimize the bidding strategy of these market agents. However, studies found in the literature usually focus on day-ahead and balancing markets, leaving aside intraday markets that could be used to correct bidding positions as uncertainty gets resolved. This paper proposes a multistage stochastic decision-aid algorithm based on linear programming to optimize the bidding strategy of market agents in three different electricity markets -day-ahead, intraday, and balance markets. The market agent represents a Virtual Power Plant with wind, solar PV, and storage technologies, and its participation in three electricity markets was compared to the participation in DA and BM markets only. Results show that participating in all three markets increased the profit achieved by the VPP agent by 10.1% while also decreasing the incurred imbalances by 63.8%. The results demonstrate that having accurate tools to deal with the multi-settlement framework of electricity markets while considering the uncertainties of daily operations is key to a successful integration of renewable energy resources into electricity markets and power systems.
- Electrochemical assessment of corrosion-fatigue degradation stagesPublication . Simões, Alda Maria Pereira; Canut, Felipe; Reis, Luis; Napoleão Bastos, Ivan; Mamiya, EdgarABSTRACT: The study is focussed on the joint effect of corrosion and mechanical cyclic stresses observed on mooring chains of Floating Production Storage and Offloading (FPSO) units. The tests were performed using grade R4 steel in artificial sea water, under stress-controlled and fully reversed loading. The corrosion-fatigue degradation was monitored using open circuit potential measurements simultaneously with the cyclic mechanical load. The open circuit potential response varies during the corrosion-fatigue test, depending on the stage of degradation of the material. This technique has proven to be capable of identifying important phenomena, such as crack initiation and crack propagation, on the material under corrosion-fatigue loading condition.
- Looking into historical cracks analysing repaired silver objects by electron microscopyPublication . Tissot, Isabel; Barreiros, M. Alexandra; Lemos, Manuel; Tissot, MatthiasABSTRACT: The identification of structural alterations of silver alloy objects of cultural interest is essential to assess their state of conservation and define maintenance programmes. Alterations induced by previous repair and cleaning actions strongly affect the conservation condition, influencing the type and extension of conservation procedures. The detailed analysis of ancient repairs is a subject to be investigated. In this work, we show the potentialities of scanning electron microscopy in the characterisation of structural repairs and their influence on the conservation state of silver objects. The study of distinct silver objects dated to the 16th and 18th centuries allowed us to show, among others, the non-intentional dealloying of copper due to the use of acid solutions in surface cleanings and cracks resulting from incorrect handling. The data collected by microscopic examination contributed to the definition of preservation and maintenance methodologies applied to those silver objects.
- Avaliação da resistência à exposição atmosférica de madeiras termo-modificadasPublication . Godinho, Delfina; Araújo, Solange; Paiva Luís, Teresa; Ferreira, Cristina; Quilhó, Teresa; Gominho, Jorge; Cunha Diamantino, TeresaRESUMO: Em sentido lato pode-se afirmar que a madeira sofre biocorrosão, o que constitui um fator limitante para a sua aplicação no exterior, caso não haja uma proteção adequada. A termo-modifcação é um dos métodos utilizados para aumentar a durabilidade da madeira. Uma das vantagens deste processo é que não requer qualquer tipo de adição de químicos. A temperatura utilizada no processo induz a alterações químicas dos constituintes da matriz celular que promovem o aumento da durabilidade aos agentes bióticos e abióticos, mas também provoca alterações nas propriedades mecânicas, nomeadamente a diminuição do módulo de elasticidade (MOE) e de rotura (MOR). O presente trabalho teve como objetivo a avaliação da durabilidade da madeira termo-modificada de 3 espécies: o pinheiro-bravo (Pinus pinaster), a principal espécie utilizada pela indústria portuguesa de madeira sólida, a acácia (Acacia melanoxylon) e o freixo (Fraxinus excelsior). Amostras destas madeiras termomodificadas foram depois, expostas durante 2 anos em duas estações de ensaio representativas de dois ambientes diferentes, no Lumiar (ambiente urbano) e em Sines (ambiente marítimo/industrial). A avaliação da resistência da madeira à exposição atmosférica, incluiu a recolha de amostras ao longo de 24 meses de exposição e a análise das superfícies das amostras por espetroscopia de infravermelho com transformada de Fourier (FTIR) com acessório de refletância total atenuada (ATR) e por microscopia eletrónica de varrimento (SEM) com um espectrómetro de raios X de energia dispersiva (EDS) associado. Os resultados preliminares indicam um comportamento semelhante para todas as madeiras expostas em ambas as estações. Verificou-se, contudo, que embora se tivesse observado o aparecimento de fendas e de inúmeras partículas na superfície de todas as madeiras, houve uma maior incidência nas expostas em Sines (zona com maiores variações de humidade e temperatura), nomeadamente nas amostras de 9 meses, onde se observaram na superfície cristais de NaCl, devido à proximidade desta estação da orla marítima. Os espetros de FTIR-ATR indicam ter ocorrido diminuição do teor em hemiceluloses e de lenhina na superfície das amostras principalmente nas amostras recolhidas após os 24 meses de exposição, tanto em Sines como no Lumiar.
- Técnicas avançadas no estudo da corrosãoPublication . Silva, Tiago J. L.; Cascalheira, JoãoRESUMO: A M.T. Brandão, constituída em 1984, atua no setor tecnológico tendo como principais clientes as indústrias petrolíferas, alimentares e químicas, entre outras empresas industriais e tecnológicas, bem como instituições de ensino e investigação científica, institutos e organismos públicos. Com uma linha completa de produtos e soluções dedicadas à caraterização de materiais, a MT Brandão tem como missão responder às necessidades dos nossos clientes de forma a impulsionar os seus negócios, através da inovação e da melhoria contínua. Esta apresentação pretende assim dar a conhecer os equipamentos que a MT Brandão comercializa que permitem não só o estudo do processo de corrosão como o estudo de revestimentos protetivos e sua caracterização, em particular através de técnicas de Tribocorrosão e Espectroscopia de Raman.
- Corrosion and anticorrosive protection by painting of aluminum rolling stockPublication . Rosa, Teresa; Marques, Maria João; Gonçalves, Rita; Carvalho, Francisco; Leal, Cristóvão Francisco; Ferreira, Cristina; Cunha Diamantino, TeresaABSTRACT: Due to its characteristics, aluminum and its alloys have been widely used in the manufacture of high-speed rolling stock. The series 4000 (Alfa Pendular service), manufactured by Fiat Ferroviaria (current Alstom), have aluminum alloy case structure, highlighting the 6082 alloy due to its good formability, with applications at structure level [1]. In operation since 1999, they are subjected to reactive maintenance and planned maintenance. Regarding maintenance related to the corrosion protection of structures, it is of particular importance to develop an appropriate specification and ensure that all tasks, with particular emphasis on those associated with surface preparation and corrosion protection by painting, are performed in accordance with improved practices to ensure longer service life. In addition to the conditions inherent to the service, the vandalism to which the material is subjected, foreign bodies that cause mechanical damages, various atmospheric conditions with environments of different categories of corrosivity, as well as accumulation of water/condensates or cleaning products/graffiti removers, are factors that contribute to the degradation of the material.
- Corrosion behaviour of FE and NI-based alloys in solar salt and corrosion mitigation strategies via protective coatingsPublication . Oskay, Ceyhun; Meißner, Tobias; Grégoire, Benjamin; Burek, B.O.; Schlereth, Clara; Bonk, Alexander; Bik, Maciej; Solimani, Ali; Galetz, MathiasABSTRACT: This study investigated the corrosion behaviour of commercial and model Fe- and Ni-based alloys in solar salt at 600°C. The thermal decomposition of nitrate salts led to an increasing concentration of oxidizing agents in the salt melt and thus to a higher corrosion rate. For Fe-based alloys, the oxide scales contained a Na- and Fe-rich outer layer, followed by an inner Cr-rich layer and nitridation as well as Cr-depletion was observed at the scale/metal interface. Furthermore, higher extent of chloride impurities in solar salt, led to a significantly higher corrosion rate for ferritic-martensitic alloys. For Ni-based alloys, the formation of a duplex scale consisting of a NiO outer and Ni-Cr spinel layer showed protective character during isothermal exposure; however even for Ni-based alloys, Cr was detected in the salt melt, which showed evidence for its dissolution in the melt as toxic hexavalent Cr. Diffusion aluminide and electroless Ni-P coatings deposited on cost-efficient ferriticmartensitic alloys led to formation of protective oxide scales and hindered the Cr-dissolution into the salt melt.
- Impact of the wave/wind induced oscillations on the power performance of the WindFloat wind turbinePublication . Couto, António; Justino, Paulo Alexandre; Simões, Teresa; Estanqueiro, AnaABSTRACT: The main objective of this work is the characterization of the wave/wind induced oscillations on the power performance of the wind turbine operating on a WindFloat floating system. To assess the potential impact on the wind turbine power performance induced by these oscillations, the nacelle movements of the WindFloat wind turbine were monitored using accelerometer sensors synchronized with : 1) metocean data measured with a buoy; 2) wind turbine power data installed in the WindFloat floating system; and 3) wind speed data gathered from a nacelle-mounted LiDAR. Based on this data, a clustering analysis approach is proposed. No meaningful relationship between the ocean parameters and the nacelle movements or the wind power production could be established. The obtained results suggest that the dynamic adaptation of the drive train (mainly due to wind turbine torque control) to a fast oscillating (primary energy) moving force is the source of the largest oscillations in the nacelle of the WindFloat wind turbine. Nevertheless, results suggest that the wind/wave induced oscillations and their impact on the power performance of the WindFloat wind turbine is low considering its nominal capacity. Outcomes of this work were extremely relevant to demonstrate the stability of the WindFloat system, and, consequently, also important for the development of the floating wind offshore industry (and other technologies).