Persona: Agüero, Alina
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Instituto Nacional de Técnica Aeroespacial
El Instituto Nacional de Técnica Aeroespacial es el Organismo Público de Investigación (OPI) dependiente del Ministerio de Defensa. Además de realizar actividades de investigación científica y de desarrollo de sistemas y prototipos en su ámbito de conocimiento, presta servicios tecnológicos a empresas, universidades e instituciones.
El INTA está especializado en la investigación y el desarrollo tecnológico, de carácter dual, en los ámbitos de la Aeronáutica, Espacio, Hidrodinámica, Seguridad y Defensa.
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Agüero
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Alina
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Publicación Acceso Abierto Robust anti-icing superhydrophobic aluminum alloy surfaces by grafting fluorocarbon molecular chains(Elsevier, 2020-12) Rico, V.; Mora, Julio; García, Paloma; Agüero, Alina; Borrás, A.; González Elipe, A.R.; López-Santos, C.; Universidad de Sevilla; European Comission (EC); Unidad de Excelencia Científica María de Maeztu Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737Infusion of low surface tension liquids in nanostructured surfaces is currently used to promote an anti-icing response, although the long term stability of these systems is often jeopardized by losses of the infused liquid. In this work, we propose an alternative to the infusion procedure to induce a more effective and long lasting anti-icing capacity. The method consists of a combination of surface nanostructuration with the chemical grafting of fluorocarbon molecules. Al6061 substrates have been subjected to laser roughening and further modified with a nanostructured Al2O3 thin film to achieve a dual roughness and porous surface state. These surfaces have been subjected to a grafting treatment with perfluorooctyltriethoxysilane (PFOTES) vapor or, for comparative purposes, infused with a low surface tension liquid. A comparative analysis of the wetting, water condensation and anti-icing properties of these two systems showed an outstandingly better performance for the grafted surfaces with respect to the infused ones. Grafted surfaces were markedly superhydrophobic and required higher water vapor pressures to induce condensation. When looking for their anti-icing capacity, they presented quite long freezing delay times for supercooled water droplets (i.e. almost four hours) and exhibited a notably low ice accretion in a wind tunnel test. The high aging resistance and durability of these grafted surfaces and the reproducibility of the results obtained when subjected to successive ice accretion cycles show that molecular grafting is an efficient anti-icing methodology that, in aggressive media, may outperform the classical infusion procedures. The role of the fluorocarbon chains anchored on the surface in inducing an anti-icing functionality is discussed.Publicación Restringido Comparison of descaling methods to study the corrosion kinetics of ferritic steels after dynamic exposure to molten carbonates(Elsevier, 2022-12-24) Audigié, Pauline; Rodríguez Catela, Sergio; Agüero, Alina; Pedrosa, Fátima; Paiva, Teresa; Diamantino, Teresa C.T91 ferritic-martensitic steel was exposed to Li, Na and K molten carbonates at 650ºC under dynamic conditions up to 1000 h. After testing, three descaling methods, two from the ISO8407 and one from the ISO17245 standards were applied to remove the corrosion products and determine the corrosion rates. The two ISO8407 methods were more appropriate although the procedure required several steps to fully remove the corrosion products. The ISO17245 method led to a higher mass loss affecting probably the base material. Oxides identification was performed by XRD following step by step layers removal. Li-, Na-, K-containing oxides and chromates/chromites were detected.Publicación Acceso Abierto Estudio del Tratamiento Térmico de Difusión de Recubrimientos de Al sobre aceros ferrítico(Arrola, 2014-01-04) Agüero, Alina; Gutiérrez del Olmo, Marcos; González, VanessaPublicación Restringido Cyclic oxidation and mechanical behaviour of slurry aluminide coatings for steam turbine components(Elsevier, 2007-04-02) Agüero, Alina; Muelas Gamo, Raúl; Gutiérrez del Olmo, Marcos; Van Vulpen, R.; Osgerby, Steve; Banks, J. P.The excellent steam oxidation resistance of iron aluminide coatings on ferritic steels at 650 °C has been demonstrated both by laboratory tests and field exposure. These coatings are formed by the application of an Al slurry followed by diffusion heat treatment at 700 °C for 10 h. The resulting microstructure is mostly composed of Fe2Al5 on top of a much thinner FeAl layer. This coating exhibits perpendicular cracks due to thermal expansion mismatch between coating and substrate. However, these stress relieving cracks do not seem to have an effect on the mechanical properties of the substrate. Cyclic oxidation, creep resistance and TMF testing of these coatings at 650 °C indicate excellent performance.Publicación Restringido HVOF coatings for steam oxidation protection(Wiley online library, 2008-05-29) Agüero, Alina; Muelas Gamo, Raúl; González, Vanessa; Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737In the context of the European project ‘Coatings for Supercritical Steam Cycles’ (SUPERCOAT), the use of steam oxidation resistant coatings on currently available ferritic materials with high creep strength but poor oxidation resistance was investigated in order to allow increase in the operating temperature of steam power plants from 550 to 650 °C. Among the explored coating techniques for this application, chosen on the basis of being potentially appropriate for coating steam turbine components, High Velocity Oxy Fuel (HVOF) thermal spray has resulted in one of the most successful techniques. Different alloyed materials such as FeCrAl, NiCrSiFeB, FeAl, NiCr and FeCr have been deposited, optimized and tested under flowing steam at 650 °C. Characterization of as deposited and tested samples by metallography, SEM-EDS and XRD was carried out. Some of these coatings form protective pure chromium or aluminium oxides exhibiting excellent behaviour for at least 15 000 h of exposure, whereas others form less stable complex mixed oxides which nevertheless grow at considerably slower rates than the oxides formed on uncoated P92 (9 wt% Cr ferritic steel).Publicación Acceso Abierto Laboratory intercomparison of solar absorptance and thermal emittance measurements at room temperature(Elsevier, 2022-05-14) Caron, Simon; Herding, L.; Binyamin, Yaniv; Baidossi, M.; Vinetsky, Y.; Morales, Angel; Hildebrandt, C.; Reoyo Prats, R.; Faugeroux, O.; Agüero, Alina; Rodríguez Catela, Sergio; Sutter, Florian; Röger, M.; Manzano Agugliaro, F.; European Commission (EC)Solar thermal absorber coatings play an important role in the opto-thermal efficiency of receivers in Concentrated Solar Power (CSP). Two standard figures of merit are the solar absorptance αsol and thermal emittance εth, derived from spectral directional hemispherical reflectance measurements at room temperature. These two figures of merit allow comparing coating formulations in terms of performance and durability. In this study, a black coating and a solar selective coating are optically characterized by different laboratories to compare spectral datasets, solar absorptance αsol and thermal emittance εth calculations. The comparison includes various benchtop spectrophotometers operating in the UV-VIS-NIR and Infrared spectral ranges as well as three commercial portable reflectometers/emissometers. A good agreement is found between the nine parties participating in this intercomparison campaign. The black coating αsol value is 96.6 ± 0.2%, while the solar selective coating αsol value is 94.5 ± 0.4%. For the thermal emittance, spectral data is concatenated and integrated from 0.3 to 16 μm. The black coating εth value calculated at 650 °C is 80.8 ± 3.8%, while the solar selective coating εth value calculated at 650 °C is 25.0 ± 0.5%.Publicación Restringido Performance study of slurry aluminide coated 347H immersed in Li-Na-K carbonate molten salt for 5000-h at 700 °C(Elsevier, 2025-10-06) Oger, Loïc; Agüero, Alina; Audigié, Pauline; European CommissionConcentrated Solar Power (CSP) systems coupled with thermal energy storage (TES) are increasingly considered to provide dispatchable, low-carbon energy. To further improve their performance, next-generation CSP plants are designed to operate under more severe conditions, which raises concerns regarding high-temperature corrosion of structural materials by molten salts. This study examines the corrosion behaviour of bare and slurry aluminide-coated 347H stainless steel after exposure to a Li–Na–K carbonate eutectic at 700 °C for up to 5000 h. The uncoated alloy showed rapid degradation, characterized by a brittle, multi-layered oxide scale, extensive internal oxidation, and carburization. The outer oxide layer consisted mainly of LiFeO₂ and LiMnO₂, while the internal oxidation zone contained (Fe,Cr)₃O₄ spinels, LiCrO₂, and Ni-rich metallic islands. In contrast, the aluminide-coated samples exhibited excellent corrosion resistance without spallation or mechanical failure. The coating transformed into a compact FeAl layer, overlaid by a dense oxide composed of α- and γ-LiAlO₂. The α-LiAlO₂ phase, forming at the oxide–coating interface via the reaction of Al₂O₃ with lithium oxide, acted as a continuous and chemically stable barrier. Its persistence during exposure was key to prevent molten salt ingress and ensure long-term protection. These findings demonstrate that slurry aluminide coatings effectively increase the durability of structural alloys in molten carbonate environments relevant for advanced CSP-TES applications.Publicación Restringido Corrosion Resistance of Novel Coatings on Ferritic Steels for Oxycombustion–Supercritical Steam Boilers: Preliminary Results(Springer Nature Link, 2015-07-23) Agüero, Alina; Baraibar, Ignacio; González, Vanessa; Muelas Gamo, Raúl; Plana, Daniel; European Commission; Ministerio de Economía y Competitividad (MINECO)Increasing the efficiency of coal fired steam power plants is an important contribution towards clean coal power. In fact, new ferritic steels are expected to withstand 325 bar and 650 °C. Moreover, in order to facilitate CO2 capture oxygen can be used instead of air for combustion (oxycombustion) so that no NOX emissions are produced. Boiler components, such as superheater tubes, are exposed to both steam and fireside corrosion and at higher temperatures, ferritic steels corrode at very fast rates under both atmospheres. A solution can be found in the use of protective coatings, a number of which, applied by techniques capable of depositing said coatings both on the inner and outer surfaces of tubes, are being studied within nationally and European funded projects. In particular, two new Ni and Cr modified aluminide coatings deposited on P92 by non-line-of-sight hybrid processes have been produced and the preliminary results of on-going laboratory testing, both under oxycombustion model atmospheres as well as under pure steam at 650 °C are promising, in particular those exhibited by the Cr enriched aluminide coating. Moreover, results obtained in a pilot oxycombustion boiler operated by CIUDEN in Leon, Spain are also shown.Publicación Restringido Comparison between field and laboratory steam oxidation testing on aluminide coatings on P92(Wiley online library, 2011-01-12) Agüero, Alina; González, V; Gutiérrez del Olmo, Marcos; Knödler, R; Straub, S; Muelas Gamo, Raúl; Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737Steam oxidation has become an important issue for steam power plants as operating temperatures increase from the current 550 to 600–650 °C. For the last 10 years several groups have been carrying out steam oxidation testing of both uncoated substrates and coatings in the laboratory. On the other hand, field testing results are very scarce. In this paper, a comparison of laboratory steam oxidation testing with field test results carried out by Alstom at the Kraftwerk Westfalen power station located in Hamm, Germany will be presented. Both slurry deposited aluminide coatings and uncoated P92 steel have been included in the study. Under steam (atmospheric pressure) and isothermal conditions in the laboratory at 650 °C, spallation of oxides formed on ferritic steels occurs after significantly longer time when compared to exposure to real operating conditions. Oxide spallation results in serious damage in steam power plants by obstructing heat exchanger tubes, erosion of valves and turbine blades, etc. Moreover, the thickness of the oxide scales formed under field testing conditions is significantly higher after similar exposure. On the other hand, aluminide coated P92, which exhibit thickness through cracks, have shown to be stable in the laboratory for up to 60 000 h at 650 °C under steam, without evidence of crack propagation. However, field test results indicate that some degree of crack propagation occurs but without causing substrate attack up to 21 700 h of exposure. Moreover, the aluminium oxide observed in both laboratory and field tested specimens is different.Publicación Restringido Overview of steam oxidation behaviour of Al protective oxide precursor coatings on P92(Taylor and Francis online, 2016-03-04) Agüero, Alina; Gutiérrez del Olmo, Marcos; Muelas Gamo, Raúl; Spiradek Hahn, K.Future designs for steam power plants are expected to operate at 625–750°C, at which the candidate ferritic/martensitic steels exhibit insufficient steam oxidation resistance. Al-based coatings constitute an alternative to prevent or reduce oxidation. For over 50 years this type of coating has been applied on blades and vanes made of Ni- and Co-based alloys used in the hot section gas of turbines which operate at temperatures higher than 900°C. For these coatings, the mechanism of protection from high-temperature oxidation, is based on the formation and maintenance of a thin layer of dense α-Al2O3. Many articles have been written about the nature, formation and failure mechanism of oxide precursor coatings, under air, at over 900°C. [1–6] However, very little is known regarding alumina scales formed under pure steam at lower temperatures, which is the expected scenario for new steam power plants. This paper covers a recapitulation of the behaviour of Al-based protective oxides formed on coatings with various compositions under steam at 650°C, including new data relative to the formation of said oxides under steam and the microstructure of samples exposed to steam for 70 000 h. It has been shown that on Al containing coatings, such as diffusion Fe aluminides and FeCrAls, alumina forms under steam at 650°C. Provided that a critical content of Al is maintained underneath the scale, Al2O3 is very stable, surpassing 70 000 h under steam at 650°C, without evidence of spallation (testing is still ongoing). The industry target for coatings in this cases is 100 000 h. In turn, the critical Al content depends on the coating's Cr content, and if the oxidation takes place at temperatures of 900°C or higher, under air. However, under steam, alumina phases formation and transformations are different: at 650°C χ-Al2O3 forms initially, and appears to slowly transform unto α-Al2O3. General considerations regarding the stability of protective oxides formed under steam as a function of the composition of the subjacent material will be provided.
