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Research Project
Solar Facilities for the European Research Area - Third Phase
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Publications
Análise do comportamento de lentes em vidro de sílica perante a utilização de radiação solar concentrada
Publication . De Almeida, G.; Guerra Rosa, L.; Pereira, J.C.G.; Bravo Gonzalo, I.; Franco, P.; Fernandes, J.C.; González-Aguilar, J.
RESUMO: Este trabalho descreve os ensaios realizados com um simulador laboratorial de radiação solar concentrada com o objectivo de avaliar o comportamento de lentes em vidro de sílica quando sujeitas a elevados fluxos de radiação, e permitiu comparar o seu comportamento com o que foi demonstrado por lentes idênticas, mas fabricadas em vidro de borossilicato (BK-7) cujo preço é muito inferior. Os ensaios de irradiação das lentes atingiram durações de 60 minutos, durante os quais se procedeu à monitorização contínua da potência da radiação aplicada sobre cada lente e da temperatura nela gerada. Todas as lentes em vidro de sílica se comportaram bem, mas o mesmo não ocorreu com as lentes em vidro de borossilicato. No trabalho é aventada a hipótese de o comportamento negativo registado nas lentes em borossilicato ser provocado pelo facto de se ter usado a radiação emitida por uma lâmpada de arco de xénon que pode conter comprimentos de onda que estão ausentes na radiação solar, pelo que é proposto que nos futuros testes não se use um simulador de radiação solar.
A direct comparative study of the corrosion behaviour of Si-free and Si-rich slurry aluminide coatings in molten carbonate melts
Publication . Audigié, Pauline; Rodríguez Catela, Sergio; Agüero, Alina; Pedrosa, Fátima; Paiva Luís, Teresa; Cunha Diamantino, Teresa
ABSTRACT: This study is focused on the evaluation of the hot corrosion behaviour of two low-cost slurry aluminide coatings with and without Si addition deposited on ferritic-martensitic steels, comparing them with uncoated steel, after 1000-h of exposure to Li, K, Na molten carbonates at 650ºC, under static and dynamic conditions with a high linear velocity (1.3 m/s). Both coatings evidenced a high performance increase in comparison with uncoated substrates after exposure in both conditions. Both coatings behaved in a similar way according to the gravimetric results. However, after dynamic exposure, the Si-free aluminide maintained its morphology and composition after 1000 h with α-LiAlO2 as the only corrosion product while the Si-rich coating showed a higher attack extent in the outer part and developed a large quantity of voids at the coating/substrate
interface, leading to substrate corrosion.
TiO2-reduced graphene oxide-Pt nanocomposites for the photogeneration of hydrogen from ethanol liquid and gas phases
Publication . Esteves, M. Alexandra; Fresno, Fernando; Fernandes, Vitor; Oropeza, Freddy E.; O'Shea, Victor A. de la Peña; Rangel, C. M.
ABSTRACT: The production of hydrogen by photocatalysis presents attractive features but also stringent requirements of materials properties. A series of TiO2-based photocatalysts containing reduced graphene oxide (rGO) and plat-inum, TiO2-rGO(x)-Pt(y) (x=0-5 wt%; y=1.5, 2.5, 3.8 wt%), were synthesized by a simple two-step procedure. The ternary composites exhibited promising performance for hydrogen generation, in both liquid and gas phase photocatalysis, using ethanol as hole scavenger, under UV light. The effect of the concentration of ethanol, graphene oxide, and Pt, as well as photocatalyst loading and solution pH were assessed. The photocatalyst TiO2-rGO3%-Pt3.8%, in the liquid phase, produced gases containing over 95% hydrogen at very high initial pro-duction rates, similar to 560 mmolh(-1)g(cat)(-1). The gas production vs irradiation time (6 h) showed linear dependence in a two-slope graph, with a drastic decrease of the rate due to Pt poisoning. Solution pH reached values of 3.5, regardless of the initial value. In the liquid phase, partial oxidation of ethanol took place with the dehydroge-nation of ethanol to acetaldehyde. In the gas phase photocatalysis, TiO2-rGO3%-Pt3.8% showed capability for photo-reforming as indicated by produced gases with a molar ratio H-2/CO2 of 3. rGO reinforces the effect of Pt as a suppressor of charge recombination.
Synthesis of Non-Cubic Nitride Phases of Va-Group Metals (V, Nb, and Ta) from Metal Powders in Stream of NH3 Gas under Concentrated Solar Radiation
Publication . Shohoji, Nobumitsu; Oliveira, Fernando Almeida Costa; Galindo, José; Rodriguez, Jose; Cañadas, Inmaculada; Fernandes, Jorge Cruz; Rosa, Luís Guerra
ABSTRACT: Using a high-flux solar furnace, loosely compacted powders of Va-group transition metal (V, Nb, and Ta) were reacted with stream of NH3 gas (uncracked NH3 gas) being heated by concentrated solar beam to a temperature (T) range between 600 and 1000 degrees C. From V, sub-nitride V2N (gamma phase) and hypo-stoichiometric mono-nitride VN possessing fcc (face-centered cubic) crystal lattice structure (delta phase) were synthesized. On the other hand, in the reaction product from Nb and Ta, hexagonal mono-nitride phase with N/M atom ratio close to 1 (epsilon phase) was detected. The reaction duration was normalized to be 60 min. In a conventional industrial or laboratory electric furnace, the synthesis of mono-nitride phase with high degree of crystallinity that yield sharp XRD peaks for Va-group metal might take a quite long duration even at T exceeding 1000 degrees C. In contrast, mono-nitride phase MN of Va-group metal was synthesized for a relatively short duration of 60 min at T lower than 1000 degrees C being co-existed with lower nitride phases.
High-temperatures corrosion of AISI 316L and AISI 430 steels in dynamic conditions with molten solar salt
Publication . Pedrosa, Fátima; Paiva Luís, Teresa; Figueira Vasques, Isabel; Cunha Diamantino, Teresa
ABSTRACT: 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 a heat storage medium for concentrated solar power plants. At temperatures of 550 ºC, 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 inservice conditions. Fluid dynamics and scale-up are two factors that can influence the corrosion phenomena.
In this work, corrosion studies were carried out on austenitic stainless steel (SS) (AISI 316L) and ferritic steel
(AISI 430) under dynamic conditions, with long-term immersion in solar salt, on a pilot scale. It was found that
AISI 316L steel forming more adherent oxides, presented a significantly lower corrosion rate than the AISI 430
steel, due to the formation of a protective FeCr2O4 layer, making it less susceptible to corrosion. The measured corrosion rates are presented and compared to static corrosion tests.
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Funding agency
European Commission
Funding programme
H2020
Funding Award Number
823802