ME - Artigos em revistas internacionais
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- Comparison of the corrosion of ferritic and austenitic stainless steel (AISI 430 and AISI 316L) with LiNaK carbonate salts for thermal energy storage in CSP/CST applicationsPublication . Gil, Mafalda; Pedrosa, Fátima; Paiva Luís, Teresa; Figueira Vasques, Isabel; Oliveira, Fernando; Cunha Diamantino, TeresaABSTRACT: This study focuses on the corrosion rates and mechanisms of two stainless steels, austenitic AISI 316L and ferritic AISI 430, in contact with a eutectic mixture of LiNaK carbonates in long-term tests at 650 degrees C. The selection of these two stainless steels was based on their differences, both in their intrinsic characteristics and in the cost associated with each one. The research also underscores the importance of optimizing the descaling methods used to evaluate the corrosion rate. Corrosion rates were measured gravimetrically according to ISO 17245:2015, revealing an asymptotic behavior for both steels, with AISI 430 with a corrosion rate of 237 f 21 mu m and AISI 316L of 151 f 13 mu m after 2000 h of testing. Corrosion mechanisms were analyzed using SEM/EDS, GDOES, and XRD techniques, which identified well-defined oxide layers with varying compositions. Given the observed corrosion mechanisms and its lower cost, AISI 430 steel seems to have great applicability in CSP/CST plants, provided it is paired with an appropriate protective coating.
- Evolution of atomically dispersed co-catalysts during solar or UV photocatalysis for efficient and sustained H2 productionPublication . Capelo, Anabela; Fattoruso, Domenico; Valencia-Valero, Laura; Esteves, M. Alexandra; Rangel, Carmen M.; Puga, AlbertoABSTRACT: The evolution of metal/titania photocatalysts during photocatalytic H-2 evolution is herein studied. Samples containing atomically dispersed Pt co-catalysts (single atoms, clusters and sub-nanoparticles) formed after calcination were compared to pre-reduced analogues mostly having metallic nanoparticles (diameters >1 nm) during ethanol photoreforming under either UV-rich irradiation or natural sunlight. Aggregation of ultra-dispersed oxidised platinum entities (Pt delta+) with concomitant reduction into Pt-0 nanoparticles (1-2 nm) was observed after UV irradiation by transmission electron microscopy (TEM), and diffuse reflectance UV-visible (DRUV-vis) and X-ray photoelectron (XPS) spectroscopies. A parallel, albeit slower, evolution trend was evidenced during solar photocatalysis. Conversely, atomically dispersed Cu co-catalyst species did not grow and became in-situ reduced into sub-nanometric Cu-0 under irradiation. Hydrogen production rates were remarkably high during initial stages of UV irradiation, and then declined to a sustained regime (approximate to 50 and 8 mmol g(-1) h(-1) for Pt/TiO2 or Cu/TiO2, respectively, for up to 24 h of irradiation). Steadier solar photoreforming was observed in experiments performed in a compound parabolic collector tubular reactor (approximate to 7.6 and 1.7 mmol g(-1) h(-1) for Pt/TiO2 or Cu/TiO2, respectively). Despite the non-negligible effect of co-catalyst rearrangement on activity rationalised herein, attenuated total reflectance Fourier-transform infrared (ATR-FTIR) spectroscopy measurements pre- and post-photocatalysis suggest that accumulation of strongly adsorbed degradation intermediates, chiefly acetate, is a major cause for rate decreases. Notwithstanding, this phenomenon did not result in total deactivation, so that sustained hydrogen production upon long-term irradiation was not compromised.
- Exploring Marine Biomineralization on the Al-Mg Alloy as a Natural Process for In Situ LDH Growth to Improve Corrosion ResistancePublication . Marques, Maria João; Mercier, Dimitri; Seyeux, Antoine; Zanna, Sandrine; Tenailleau, Christophe; Duployer, Benjamin; Jeannin, Marc; Marcus, Philippe; Basséguy; BASSEGUY, RegineABSTRACT: This study provides a detailed characterization of the AA5083 aluminum alloy, surface, and interface over 6 months of immersion in seawater, employing techniques such as SEM/EDX, GIXRD, mu-Raman and XPS. The purpose was to evaluate the evolution of the biomineralization process that occurs on the Al-Mg alloy. By investigating the specific conditions that favor the in situ growth of layered double hydroxide (LDH) during seawater immersion as a result of biomineralization, this research provides insights into marine biomineralization, highlighting its potential as an innovative and sustainable strategy for corrosion protection.
- Influence of Cr on the quaternary FeTaTiW medium entropy alloyPublication . Martins, Ricardo; Monteiro, Bernardo; Pereira Gonçalves, Antonio; Correia, Jose B.; Galatanu, Andrei; Alves, Eduardo; Tejado, Elena; Pastor, Jose Ygnacio; Dias, MartaABSTRACT: The search for advanced materials has been growing, and high entropy alloys (HEAs) are emerging as promising candidates for application in the fusion domain. This work investigates the effect of Cr on the FeTaTiW medium entropy alloy to form (CrFeTaTi)70W30 high entropy alloy, comparing the experimental production and characterization with the simulation (molecular dynamics and hybrid molecular dynamics-Monte Carlo) of the phases formed. The alloys were produced by mechanical alloying and sintered by spark plasma sintering. Both simulations have shown that a body-centered cubic structure is formed for both compositions. Monte Carlo simulation provides a more precise prediction of microstructural formation and element segregation. Microstructural examination of the consolidated material revealed the presence of a W-rich phase and a Ti-rich phase, consistent with the phase separation observed in the MC simulations. Moreover, X-ray diffraction analysis of the milled powder for FeTaTiW and (CrFeTaTi)70W30 confirmed the formation of a bcc (body-centered cubic)-type structure with a low fraction of intermetallic phases. Mechanical testing showed ductile behavior at 1000 degrees C where (CrFeTaTi)70W30 showed a stress magnitude almost double that of FeTaTiW. Additionally, the thermal diffusivity between 20 and 1000 degrees C of both alloys increases as the temperature rises. (CrFeTaTi)70W30 exhibits an increase from 3 to 5 mm2/s, while FeTaTiW increases from 4 to 9 mm2/s. Still, both system's thermal diffusivity values are lower than those of CuCrZr and pure tungsten. Despite this, the study underscores the promising attributes of HEAs and highlights areas for further optimization to enhance its suitability for extreme conditions.
- Mechanical Performance of Ceria-Coated 3D-Printed Black Zirconia Cellular Structures After Solar Thermochemical CO/H2 Fuel Production CyclesPublication . Oliveira, Fernando; Sardinha, Manuel; Justino Netto, Joaquim Manoel; Leite, Marco; Farinha, Miguel; Barreiros, Maria Alexandra; Abanades, Stéphane; Fernandes, JorgeABSTRACT: Solar fuels production requires developing redox active materials with porous structures able to withstand thermochemical cycles with enhanced thermal stability under concentrated solar irradiation conditions. The mechanical performance of 3D-printed, macroporous black zirconia gyroid structures, coated with redox-active ceria, was assessed for their suitability in solar thermochemical cycles for CO2 and H2O splitting. Experiments were conducted using a 1.5 kW solar furnace to supply the high-temperature concentrated heat to a windowed reaction chamber to carry out thermal redox cycling under realistic on-sun conditions. The ceria coating on ceramic structures improved the thermal stability and redox efficiency while minimizing the quantity of the redox material involved. Crushing strength measurements showed that samples not directly exposed to the concentrated solar flux retained their mechanical performance after thermal cycling (similar to 10 MPa), while those near the concentrated solar beam focus exhibited significant degradation due to thermal stresses and the formation of CexZr1-xO2 solid solutions (similar to 1.5 MPa). A Weibull modulus of 8.5 was estimated, marking the first report of such a parameter for fused filament fabrication (FFF)-manufactured black zirconia with gyroid architecture. Failure occurred via a damage accumulation mechanism at both micro- and macro-scales. These findings support the viability of ceria-coated cellular ceramics for scalable solar fuel production and highlight the need for optimized reactor designs.
- New Modified SPEEK-Based Proton Exchange MembranesPublication . Teixeira, Fatima; Teixeira, António Paulo Silva; Rangel, Carmen M.ABSTRACT: A decarbonized society demands cleaner and sustainable energy sources based on well-established or emerging technologies with the potential to make a significant contribution to energy storage and conversion, such as batteries, fuel cells and water and/or CO2 electrolyzers. The performance of these electrochemical devices relies on key components such as their separators/ion-exchange membranes. The most common commercial membrane, Nafion (R), has several technological limitations. In this study, it is proposed the incorporation of bisphosphonic acid (BP) dopants into membrane matrices to improve their properties. Following this strategy, we prepared new membranes based on sulfonated poly(etheretherketone) (SPEEK) polymer, a reliable and effective alternative membrane polymer, through the incorporation of the BP dopants, to obtain low-cost membranes with improved properties. These membranes were structural, thermal and morphological, characterized by AT-FTIR, TGA and SEM. Their proton conductivity was evaluated over a temperature range between 30 degrees C and 60 degrees C, using Electrochemical Impedance Spectroscopy, and their stability during this process was also observed. The best proton conductivity was observed for the SPEEK membrane doped with BP1 at 2.0 wt% load at 60 degrees C, with a proton conduction of 226 mS cm-1.
- New proton exchange membranes based on ionic liquid doped chitosanPublication . Naffati, Naima; Teixeira, Fatima; Teixeira, António Paulo Silva; Rangel, Carmen M.ABSTRACT: The development of new proton exchange membranes (PEM) for electrochemical devices have attracted researcher's attention in the pursuit for more sustainable and cost-effective technologies for clean energy production and conversion. In this work, new doped chitosan (CS) membranes were prepared by the casting method. Chitosan is an abundant, biodegradable and non-toxic material, and as a membrane, a sustainable and cheaper alternative to those perfluorinated and commonly used, such as Nafion. Three different ionic liquids were employed as dopants, ([EMIM][OTf], [EMIM][FSI] and [MIMH][HSO4]), in various concentrations and up to 50 wt% load. The new membranes were characterized by ATR-FTIR, thermogravimetry, using TGA and DSC techniques to assess their thermal properties, and by SEM, to analyse their surface morphology. Proton conduction properties of the new membranes were assessed by Electrochemical Impedance Spectroscopy (EIS). The new doped membranes showed an increase in the proton conduction compared with pristine chitosan membranes. The incorporation of ionic liquids into chitosan membranes improved their proton conductivity and thermal properties, with [EMIM][OTf] and [MIMH][HSO4] showing the most promising results. A 2-fold increment in the proton conduction was generally observed with the increase of the temperature from 30 to 60 degrees C. The best proton conductivity was found at 60 degrees C for the membrane doped with [EMIM][OTf], with a value of 47 mS.cm(-1).
- Scale-up of a clean hydrogen production system through the hydrolysis of sodium borohydride for off-grid applicationsPublication . Silva, Diogo; Nunes, Helder Xavier; Rangel, Carmen M.; Pinto, A. M. F. R.ABSTRACT: Hydrogen is considered a promising energy vector with the potential to replace fossil fuels, and sodium borohydride serves as an effective energy carrier capable of releasing hydrogen (H2) for off-grid applications. However, the hydrolysis of sodium borohydride has only matured at laboratory-scale. Therefore, the scale-up of a laboratory reactor was designed and manufactured to study the effect of larger H2 production. For that, the effect of inhibitor NaOH concentration and water quality were studied. Experiments using 3 wt% NaOH showed overall better performance than those using 1 wt%. Additionally, experiments using tap water - scarcely reported in the literature - demonstrated performance equal to or better than that achieved with distilled water. These results are indicative of a possible significant reduction in the H2 production cost through this method.
- Tetrahedrite Nanocomposites for High Performance ThermoelectricsPublication . Coelho, Rodrigo; Moço, Duarte; Sá, Ana; Luz, Paulo P. da; Neves, Filipe; Cerqueira, Maria de Fátima; Lopes, E.B.; Brito, Francisco; Mangelis, Panagiotis; Kyratsi, Theodora; Pereira Gonçalves, AntonioABSTRACT: Thermoelectric (TE) materials offer a promising solution to reduce green gas emissions, decrease energy consumption, and improve energy management due to their ability to directly convert heat into electricity and vice versa. Despite their potential, integrating new TE materials into bulk TE devices remains a challenge. To change this paradigm, the preparation of highly efficient tetrahedrite nanocomposites is proposed. Tetrahedrites were first prepared by solid state reaction, followed by the addition of MoS2 nanoparticles (NPs) and hot-pressing at 848 K with 56 MPa for a duration of 90 min to obtain nanocomposites. The materials were characterized by XRD, SEM-EDS, and Raman spectroscopy to evaluate the composites' matrix and NP distribution. To complement the results, lattice thermal conductivity and the weighted mobility were evaluated. The NPs' addition to the tetrahedrites resulted in an increase of 36% of the maximum figure of merit (zT) comparatively with the base material. This increase is explained by the reduction of the material's lattice thermal conductivity while maintaining its mobility. Such results highlight the potential of nanocomposites to contribute to the development of a new generation of TE devices based on more affordable and efficient materials.
- Thermal Stability and Irradiation Resistance of (CrFeTiTa)70W30 and VFeTiTaW High Entropy AlloysPublication . Pereira, André; Martins, Ricardo; Monteiro, Bernardo; Correia, Jose B.; Galatanu, Andrei; Catarino, Norberto; Jenus, Petra; Dias, MartaABSTRACT: Nuclear fusion is a promising energy source. The International Thermonuclear Experimental Reactor aims to study the feasibility of tokamak-type reactors and test technologies and materials for commercial use. One major challenge is developing materials for the reactor's divertor, which supports high thermal flux. Tungsten was chosen as the plasma-facing material, while a CuCrZr alloy will be used in the cooling pipes. However, the gradient between the working temperatures of these materials requires the use of a thermal barrier interlayer between them. To this end, refractory high-entropy (CrFeTiTa)70W30 and VFeTiTaW alloys were prepared by mechanical alloying and sintering, and their thermal and irradiation resistance was evaluated. Both alloys showed phase growth after annealing at 1100 degrees C for 8 days, being more pronounced for higher temperatures (1300 degrees C and 1500 degrees C). The VFeTiTaW alloy presented greater phase growth, suggesting lower microstructural stability, however, no new phases were formed. Both (as-sintered) alloys were irradiated with Ar+ (150 keV) with a fluence of 2.4 x 1020 at/m2, as well as He+ (10 keV) and D+ (5 keV) both with a fluence of 5 x 1021 at/m2. The morphology of the surface of both samples was analyzed before and after irradiation showing no severe morphologic changes, indicating high irradiation resistance. Additionally, the VFeTiTaW alloy presented a lower deuterium retention (8.58%) when compared to (CrFeTiTa)70W30 alloy (14.41%).