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- Corrosão de aços inoxidáveis austeníticos em sais fundidos ternários de cálcioPublication . Cunha Diamantino, Teresa; Gomes, A.; Paiva Luís, Teresa; Figueira, Isabel; Pedrosa, Fátima; Nogueira, Carlos; Guerreiro, L.; Collares-Pereira, M.RESUMO: O armazenamento de energia térmica (TES) é um fator chave para melhorar a eficiência e a despachabilidade dos diferentes sistemas energéticos, devido a um melhor ajustamento entre a procura e a oferta de energia, e ao permitir o desenvolvimento e a implementação de energias renováveis. Um exemplo claro é o TES em instalações de concentração de energia solar (CSP), onde o excesso de energia solar durante o período de luz solar é armazenado para ser utilizado durante os períodos em que a energia solar é necessária, mas não está disponível. Os sais fundidos têm sido amplamente utilizados como fluidos de transferência de calor (HTF) e para TES em instalações CSP. Uma das características fundamentais dos sais fundidos no que diz respeito à sua utilização como HTF e TES é a sua compatibilidade com os materiais de construção. Por esta razão, este trabalho apresenta a resistência à corrosão de dois aços inoxidáveis austeníticos AISI 316L e AISI 321H em contacto com sal ternário fundido com cálcio. Ambos os aços inoxidáveis demonstraram ter velocidades de corrosão aceitáveis para as centrais CSP. Entre os aços austeníticos estudados, o AISI 316L apresenta a menor velocidade de corrosão.
- Dynamic corrosion testing of metals in solar salt for concentrated solar powerPublication . Sutter, Florian; Oskay, Ceyhun; Galetz, Mathias Christian; Cunha Diamantino, Teresa; Pedrosa, Fátima; Figueira, Isabel; Glumm, Stefan; Bonk, Alexander; Aguero, Alina; Rodríguez, Sergio; Reche-Navarro, Tomas Jesus; Caron, SimonABSTRACT: Potassium nitrate and sodium nitrate in mixing proportion of KNO3-NaNO3 40-60 wt% (also called solar salt) has been successfully used for over a decade as heat storage medium for concentrated solar power parabolic-trough collector plants at temperatures up to 400 degrees C. At temperatures of 560 degrees C, reached in state-of-the-art solar tower systems, corrosion of metallic components in contact with solar salt can become an issue and has caused leaks and plant shut-downs in recently built tower projects. While the corrosion rates of several materials have been determined for different temperatures in static molten salt immersion experiments, there is a lack of corrosion data for dynamic in-service conditions. In this work, a dynamic corrosion test has been conducted on 19 different material types including protective coatings, mimicking flow-rate, temperature gradient and draining of inservice operation of a receiver in a concentrated solar power tower. The measured corrosion rates are presented and compared to static corrosion tests reported in literature.
- Breve história das tintas antivegetativasPublication . Almeida, Maria Elisabete; Cunha Diamantino, Teresa; Sousa, Orlando deNeste trabalho, os autores apresentam uma panorâmica geral sobre as tintas antivegetativas. Após a conveniente localização destas tintas no esquema de protecção anticorrosiva das obras vivas dos navios e/ ou outras estruturas móveis, fazem uma síntese dos principais tipos de produtos antivegetativos usados ao longo dos tempos, até aos nossos dias. Complementarmente, sistematizam as principais tipologias dos organismos vivos que se fixam nas obras vivas das embarcações e referem alguns tipos de fauna e flora predominantes em duas regiões da Ibero-América. Abordam também, ainda que sumariamente, os principais mecanismos básicos de funcionamento dos diferentes tipos de tintas antivegetativas. Finalmente, referem algumas das principais linhas de investigação actualmente em curso, no domínio da luta contra a fixação dos organismos marinhos nos cascos dos navios
- 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.
- FTIR, a powerful technique in organic coatings failure diagnosisPublication . Costa, M. Rosário; Santos, M. Teresa; Cunha Diamantino, TeresaFTIR spectrometry (Fourier Transform Infrared) is an instrumental technique of analysis that presents significant advantages on the dispersive traditional system, such as the increase of the relation signal-noise, the capacity of getting absorption spectra of low energy and therefore, bands of absorption of weak intensity. This technique is widely used in the study of resin characterization and evaluation of polymeric materials as well as degradation when polymers and coatings are exposed to various conditions of service, or still in the analysis and diagnosis of defects that occur during the application or production process. Techniques connected to the FTIR have appeared such as the photoacoustic (PAS-FTIR), the microscopy (MCT-FTIR) and the attenuated total reflectance (ATR), which allows to analysis of weekly transparent and dark samples without removal of coatings from the substrates. The choice of the technique to use depends on the morphology of the surfaces to analyze and the type of failure (lack of adhesion, contamination, aging degradation, etc). This work illustrates the application of FTIR and associated techniques to identify causes of diverse types of defects in applied organic coatings on polymeric materials.
- FTIR, a powerful technique in organic coatings failure diagnosisPublication . Costa, Maria do Rosário; Santos, M. Teresa; Cunha Diamantino, TeresaFTIR spectrometry (Fourier Transform Infrared) is an instrumental technique of analysis that presents significant advantages on the dispersive traditional system, such as the increase of the relation signalnoise, the capacity of getting absorption spectra of low energy and therefore, bands of absorption of weak intensity. This technique is widely used in study, resin characterization and evaluation of polymeric materials as well as of its degradation when exposed to the most varied conditions of service, or still in the analysis and diagnosis of defects that occur during the application or production process. Techniques connected to the FTIR had more recently appeared as the photoacoustic (PAS-FTIR), the microscopy (MCT-FTIR) and the attenuated total reflectance (ATR), which allow to analyze weekly transparent and dark samples without removal of coatings from the substrates. The choice of the technique to use depends on the morphology of the surfaces to analyze and the type of failure in cause (lack of adhesion, contamination, aging degradation, etc). In this work the application of FTIR and techniques associates to the identification of the causes that had originated diverse types of defect in applied organic coatings on polymeric materials is presented. Key words: FTIR, Organic Coatings, Failure Diagnosis
- Hot Corrosion Behavior of Slurry Sprayed Aluminide Coatings in a Simulated Dynamic Molten Carbonate Environment [Comunicação oral]Publication . Audigié, Pauline; Rodríguez Catela, Sergio; Agüero, Alina; Pedrosa, Fátima; Paiva Luís, Teresa; Cunha Diamantino, TeresaABSTRACT: One of the key challenges associated with the use of molten salts in Concentrated Solar Power (CSP) plants is to reduce or even suppress corrosion phenomena occurring at elevated temperatures. Molten nitrate mixtures are currently seen as the most viable storage medium for Thermal Energy Storage. But the upper temperature limit of the currently used “Solar Salt” is restricted by salt decomposition at ~580ºC. Prieto et al. estimated that increasing the temperature to 650ºC could increase the solar-to-electric conversion up to 18.5%, so alternative salts operating at higher temperature are required. Molten carbonates which are less corrosive and allow an operation up to 800ºC are an appealing breakthrough for future CSP plants.
- 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.
- Molten nitrate salts containing lithium as thermal energy storage media : a short reviewPublication . Pedrosa, Fátima; Marcelo, Teresa; Nogueira, Carlos; Gomes, A.; Cunha Diamantino, TeresaABSTRACT: Energy storage plays a crucial role in the development and progress of renewable energy sources. In the case of thermal energy, storage has been a step ahead since storage solutions already exist, unlike other conversion energy technologies. In this sense, the utilization of molten salts, mainly composed of mixtures of alkali/alkaline earth metals, in nitrate forms (sometimes also with nitrite), have been proposed and successfully applied. Molten salts have recognized advantages over other solutions namely in what concerns simultaneous use as heat transfer fluids and as storage media. Commercial utilization of molten salts has been tested essentially with the Na/K salt mixtures. Introduction of lithium nitrate in these formulation has been proposed, since can allow decreasing the melting point of the mixtures, thus providing safety concerning the risks of freezing in the tubes or tanks of the storage plant. This paper provides a short review on the utilization of lithium in molten salt mixtures used for thermal energy storage. Physical, chemical and thermal properties, as well as stability and decomposition issues are evaluated. Corrosion of stainless steels in contact with the salts is another crucial question that is also addressed.
- The Stability of Tio₂-rGO Self-Cleaning Photocatalytic Coatings for Outdoor ApplicationsPublication . Covei, M.; Tismanar, I.; Cunha Diamantino, TeresaABSTRACT: Self-cleaning coatings are lately being studied for different applications such as civil buildings (windows, facades, indoor walls, metallic products), the automotive industry (mirrors, windshields, the health field (surgical rooms' walls or tiles) and renewable energies, namely for solar energy (solar reflectors, photovoltaic panel). The self-cleaning occurs through two mechanisms that involve (1) (super)hydrophobic coatings, when the pollutant rolls off the surface without being degraded or (2) (super)hydrophilic coatings, when the pollutant is dissolved in the water sheet and afterwards is degraded through the photocatalytic process (Merai et al., 2019). The most-used photocatalytic material is titanium dioxide (TiO₂) because of its non-toxicity, acceptable production cost and possible anticorrosive properties. The main disadvantage of TiO₂ is related to its UV activation which leads to additional process costs. Recent studies indicate the Vis- or solar-active composite materials (such as TiO₂ - rGO composites) as a solution to overcome the activation problem (Tismanar et al., 2021; Covei et al., 2022). However, for outdoor applications, their stability under environmental conditions (high temperature and humidity or highly corrosive atmospheres) must be analyzed. This research reports on the stability of the TiO₂/TiO₂-rGO double-layered composite thin films deposited on 5x5cm² Al substrates using up-scalable and low-cost deposition methods (spray pyrolysis deposition for TiO₂ intermediate layer coupled with sol-gel spraying for the TiO₂-rGO composite second layer).