Materiais para a Energia - ME
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- AA 5083 aluminium alloy corrosion in estuarine environmentPublication . Marques, Maria João; Alves, Isabel Nascimento; Gonçalves, Rita
- AA 5083 aluminium alloy corrosion in estuarine environment [Poster]Publication . Marques, Maria João; Alves, Isabel Nascimento; Gonçalves, Rita; Cunha Diamantino, Teresa
- Accelerated aging tests to selective solar absorber coatings for low temperature applicationsPublication . Cunha Diamantino, Teresa; Gonçalves, Rita; Páscoa, Soraia; Alves, Isabel Nascimento; Carvalho, Maria JoãoABSTRACT: The need of a higher role of solar energy within the energy mix in the coming decades obliges the collectors to increase their performance and reliability. It is demanded that the solar absorbers, as the key component of solar thermal collectors, should be low cost with high efficiency for extended lifetimes under different kinds of environments. Commercially, there are presently two main types of solutions as selective solar absorbers coatings for low temperature applications: coatings obtained by physical vapour deposition (PVD) and by paint coatings (PC). These coatings present different physical and chemical characteristics. Therefore, it is important to know how these commercial coatings degrade over time in different environments. Results obtained with two different PVD coatings and three PC, under different accelerated aging tests, are presented. The aging tests performed included different environmental stress corrosion conditions: temperature, humidity, chlorides, sulfur dioxide and nitrogen oxides. The chlorides and the gases SO2 and NO2 affect distinctly the different selective coatings. Cyclic variation of corrosion promoting gases (sulfur dioxide and nitrogen dioxide), higher humidity, salt spraying and drying seem to be an aging test that reflects the different environments where the solar thermal collectors are exposed. In addition to the contaminants, drying/wetting cycles also play an important role in degradation mechanisms of absorber coatings. So, the international standard ISO 22975-3 needs to be revised to include cyclic conditions with these contaminants.
- Advanced cyclic accelerated aging testing of solar reflector materialsPublication . Wette, Johannes; Sutter, Florian; Tu, Mai; Fernández-Garcia, Aránzazu; Buendia, Francisco; Carvalho, Maria João; Cunha Diamantino, TeresaABSTRACT: Lifetime prediction methods for the components of concentrated solar power (CSP) plants have been in the focus of interest of manufacturers and plant developers for the past years. Recently, an accelerated aging standard for solar mirrors was published by the Spanish AENOR committee [1]. This standard allows performing comparative testing but it is not suited to derive meaningful life-time estimations. Firstly, the testing defined in the standard is not aggressive enough to produce significant degradation on most of the materials and secondly, it has been shown that the passing of these tests does not guarantee a high durability during outdoor exposure [2]. These findings have proven the need for the investigation of more realistic procedures. To provoke the mechanisms that are detected during outdoor exposure, a more realistic application of environmental stresses is being investigated. In this work a series of tests is conducted in which several weathering stresses are combined and applied in a cyclic manner. Some of these cycles have shown to correlate better with real outdoor behavior.
- Advances in electrochemical reduction of CO2 in ionic liquid-based electrolytes [Resumo]Publication . Machado, Ana; Messias, Sofia; Paninho, A. B.; Nunes, A. V. M.; Rangel, C. M.; Branco, Luis CABSTRACT: Electrochemical reduction of CO2 was for the first time reported in 1870 [1], but it was only after 2010 that this field was the subject of intense research efforts. The use of renewable electricity to convert CO2 into products that are currently derived from fossil products and have high carbon footprint will certainly make this technology one pillar of a sustainable chemical industry. The scepticism towards the availability of cost effective products derived from CO2 electro-reduction that customers will be willing to buy has shifted to the belief that they can be commercially viable. Turning electrochemical CO2 reduction into a commercial technology will depend on economics, on the price of electricity, efficiency of the process and the value of the products. One way to improve the economics and improve the efficiency of the process is to integrate CO2 capture with conversion [2,3]. In this way the energy intensive regeneration step of the capture media can be eliminated and also CO2 transportation and storage. Ionic liquids are ideal media to achieve this integration, due to high CO2 adsorption capacity, high selectivity, wide electrochemical windows and nearly zero vapour pressure. The present work reports the progress of electrochemical reduction of CO2 in ionic liquids and the work of the authors in this field. It has been recognized that ionic liquids promote CO2 electro-reduction through lowering the reduction potential, the suppression of the competing hydrogen evolution reaction and by increasing the selectivity towards the target products. However, the understanding of the interactions between ionic liquids, CO2 and catalyst is still quite limited, but fundamental for synthetizing more efficient electrolytes for CO2 electro-reduction [4]. Thus, current cation and anion effects will be analysed and an overview of the current performance of heterogeneous electro-catalysts in ionic liquid- based electrolytes for CO2 electro-reduction will be provided.
- Aerogel cathodes for electrochemical CO2 reduction [Comunicação oral]Publication . Messias, Sofia; Fialho, Maria T.; Paninho, A. B.; Branco, Luis C; Nunes, A. V. M.; Martins, Rodrigo; Mendes, Manuel Joao; Nunes, D.; Rangel, C. M.; Machado, AnaABSTRACT: Electrochemical reduction of carbon dioxide powered by renewable energy to produce fuels and chemicals is a technology with potential to contribute to an economy based on a carbon neutral cycle. The development of cost effective, highly active and stable catalysts for CO2 electroreduction is being intensively researched. This work addresses the development of aerogel supported copper-zinc bimetallic catalysts[1]. Aerogels are substances with exceptional properties with many current and potential applications [2-3]. Due to their high surface area, stability in corresponding gaseous or liquid phases, transport through large meso and macropores they are especially suited as catalysts and carrier materials for catalysis and, when electric conductive for electro-catalysis. Aerogels prepared by the sol gel method and impregnated with metallic particles will be tested as cathodes for the co-electrolysis of CO2 and water to produce syngas at temperatures near room temperature and high-pressure. In this way this process can be directly coupled to other high pressure processes, such as Fischer-Tropsch that use high pressure syngas as raw material. Productivities and faradaic efficiencies will be evaluated. The characterization of the aerogel-based cathodes will be undertaken by surface analysis techniques. BET surface areas will be determined. The catalytic cathodes will be tested in an ionic liquid-based electrolyte as a way to increase current densities, due to the high CO2 solubilities exhibited by some ionic liquid families.
- Alternative baths for the gold electrodeposition based on 1-butyl-1-methyl-pyrrolidinium dicyanamide ionic liquidPublication . Sá, A.I. De; Quaresma, S.; Eugénio, S.; Rangel, C. M.; Vilar, R.
- Aluminium en milieu marin : protection par la biocorrosion [Resumo]Publication . Jaume, Julien; Basseguy, Regine; Marques, Maria João; Délia, Marie-LineABSTRACT: Pour être utilisés en milieu marin, les matériaux doivent être particulièrement résistant à la corrosion, du fait de la composition chimique de l’eau de mer (concentration en chlorure élévée, …) mais également de la présence des microorganismes. En effet, les microorganismes sont connus pour catalyser la corrosion ou l’inhiber [1,2]. Ces phénomènes antagonistes sont regroupés sous le terme de « Microbiologically Influenced Corrosion » (MIC) et « MIC Inhibition » (MICI). Les alliages d’aluminium Al-Mg, série 5000 qui présentent une bonne résistance mécanique mais également à la corrosion, sont un matériau de choix pour les structures immergées dans l’eau de mer.
- An electrochemical process for the production of synthetic fuels at low temperatures [Resumo]Publication . Fernandes, Vitor; Furtado, Olívia; Rodrigues, J.; Rangel, C. M.Following work exploring the low temperature electrolysis in alkaline media, using graphite consumable anodes, from which syngas was obtained1, laboratory studies have been conducted in acid media pursuing higher efficiency in the production of hydrogen and synthetic fuels. Experiments were conducted in an own designed undivided planar cell with 25 cm2 geometrical area electrodes using a 0.5 M H2SO4 solution with and without Fe(II) additions. Fe2+ oxidizes to Fe3+ at the anode surface. The redox couple Fe3+/ Fe2+ acts as an oxidation mediator not only oxidizing the bulk and detached graphite but also the surface functional groups. The practical experimental potential for graphite oxidation is within the range for the electroxidation of the Fe redox couple giving as a result a 4-fold increase in the amount of produced CO2 at near room temperature, when using 0.025 M FeSO4.
- Analysis of a stand-alone residential PEMFC Power system with sodium borohydride as hydrogen sourcePublication . Pinto, P.J.R.; Fernandes, Vitor; Pinto, A. M. F. R.; Rangel, C. M.Catalytic hydrolysis of sodium borohydride (NaBH4) has been investigated as a method to generate hydrogen for fuel cell applications. The high purity of the generated hydrogen makes this process an ideal source of hydrogen for polymer electrolyte membrane fuel cells (PEMFCs). In this paper, the possibility of using a NaBH4-based hydrogen generator with a PEMFC for stand-alone residential use is examined. A complete model of the system is developed, based on models taken from literature with appropriate modifications and improvements. Supervisory control strategies are also developed to manage the hydrogen generation and storage and the power flow. The operation and performance of the integrated system over a one-week period under real loading conditions is analyzed through simulation. Finally, results of the analysis are summarized and the limitations/further scope are indicated.