Browsing by Issue Date, starting with "2022-10"
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- Copper-Arsenic-Sulfide Thin-Films from Local Raw Materials Deposited via RF Co-Sputtering for PhotovoltaicsPublication . Centeno, Pedro; Alexandre, Miguel; Neves, Filipe; Fortunato, Elvira; Martins, Rodrigo; Águas, Hugo; Mendes, Manuel JoaoABSTRACT: he inexorable increase of energy demand and the efficiency bottleneck of monocrystalline silicon solar cell technology is promoting the research and development of alternative photovoltaic materials. Copper-arsenic-sulfide (CAS) compounds are still rather unexplored in the literature, yet they have been regarded as promising candidates for use as p-type absorber in solar cells, owing to their broad raw material availability, suitable bandgap and high absorption coefficient. Here, a comprehensive study is presented on the structural and optoelectronic properties of CAS thin-films deposited via radio-frequency magnetron co-sputtering, using a commercial Cu target together with a Cu-As-S target with material obtained from local resources, specifically from mines in the Portuguese region of the Iberian Pyrite Belt. Raman and X-ray diffraction analysis confirm that the use of two targets results in films with pronounced stoichiometry gradients, suggesting a transition from amorphous CAS compounds to crystalline djurleite (Cu31S16), with the increasing proximity to the Cu target. Resistivity values from 4.7 m ohm center dot cm to 17.4 ohm center dot cm are obtained, being the lowest resistive films, those with pronounced sub-bandgap free-carrier absorption. The bandgap values range from 2.20 to 2.65 eV, indicating promising application as wide-bandgap semiconductors in third-generation (e.g., multi-junction) photovoltaic devices.
- 3D reflection seismic imaging of volcanogenic massive sulphides at Neves-Corvo, PortugalPublication . Donoso, George; MALEHMIR, Alireza; Carvalho, João; Araújo, VítorABSTRACT: Three-dimensional reflection seismic data from the Neves-Corvo area, southern Portugal, were reprocessed with the main objective of improving the seismic signature of the Lombador and Semblana volcanogenic massive sulphide deposits. The sensitivity for choosing adequate parameters for targeted imaging, even during the pre-processing stage, such as common-depth point binning size, was studied in detail before the main processing work began helping to optimize bin size parameters; preliminary stacking results from this analysis presented severe acquisition footprint, and seismic targets were not clearly identifiable. Processing results using pre-stack dip move-out and post-stack migration methods show strong moderate to steeply dipping reflections. Several of the observed reflections can be correlated with known lithological contacts, some of which are interpreted to originate from the Semblana and Lombador deposits. Despite the mixed signal-to-noise ratio, the seismic cube reveals both shallow and deep three-dimensional structures, allowing to account for the deposits' lateral extension beyond the capabilities of two-dimensional seismic imaging alone. Given the data processing approach taken it was possible to distinguish strong diffraction patterns, interpreted as originating from faults and edges of the Lombador deposit, illustrating the usefulness of diffraction patterns for better interpretation of geological features in hard-rock environments.
- Long-term coastline evolution of Figueira da Foz - Nazaré sector (Portugal)Publication . Nave, Silvia; Rebêlo, LuísABSTRACT: ome sectors of the west Portuguese coast are particularly endangered by erosion and flooding. Regional to local scale information, on coastline evolutionary trend, is particularly valuable in sectors that includes areas with relevant erosion. A continuous, high-resolution, dataset on coastal evolution, from 1947 and 2015, between Figueira da Foz and Nazaré, was achieved within the Programme “Geological and Coastal Hazard Mapping at a 1:3000 resolution scale” at the National Laboratory of Energy and Geology (LNEG). This work, due to the detailed scale of analysis in a wide geographic context, allows to have both, a general overview of the coastal evolution and, at the same time, when zooming in up to 1:3000 scale, to observe the local behaviour and to quantify the occurred changes. Also, the well time-spaced aerial photograph dataset allows to compare the resultant coastline movement between the oldest and the youngest coastline (NSM index), with the total coastline oscillation (SCE index), bringing new insights on the coastline stability at a local scale. The evolution trend shows an overall erosional behaviour, if considering the entire sector. Erosion occurs predominantly in the north, as the south shows more stability and progradation. Quantification of the land-lost and land-gain due to the coastline shift in a 68-year period shows that 1 164 888 m2 of land were lost along 30 470 m of the coastal fringe, and 462 330 m2 were gained along an extension of 21 010 m.
- Competing water uses between agriculture and energy: Quantifying future climate change impacts for the Portuguese power sectorPublication . Fortes, Patricia; Simoes, Sofia; Brás, Teresa; Amorim, FilipaABSTRACT: Climate change may increase water needs for irrigation in southern Europe competing with other water uses, such as hydropower, which may likely be impacted by lower precipitation. Climate change will also potentially affect the variability and availability of other renewable energy resources (solar and wind) and electricity consumption patterns. This work quantifies the effect of competition for water use between irrigation and hydropower in the future 2050 Portuguese carbon-neutral power sector and under Representative Concentration Pathway 8.5 climate change projections. It uses the power system eTIMES_PT model to assess the combined effects of climate change on the cost-optimal configuration of the power sectorconsidering changes in irrigation, hydropower, wind and solar PV availability. eTIMES_PT is a linear optimisation model that satisfies electricity demand at minimal total power system cost. Results show that, by 2050, climate change can lead to an increase in annual irrigation water needs up to 12% in Tagus and 19% in Douro watersheds (from 2005 values), with substantially higher values for spring (up to 84%). Combining these increased water needs with the expected reduction in river runoff can lead to a decline in summer and spring hydropower capacity factors from half to three times below current values. By 2050, concurrent water uses under climate change can reduce hydropower generation by 26–56% less than historically observed, mainly in summer and spring. Higher solar PV, complemented with batteries’ electricity storage, can offset the lower hydropower availability, but this will lead to higher electricity prices. Adequate transboundary water management agreements and reducing water losses in irrigation systems will play a key role in mitigating climate impacts in both agriculture and power sector.
- Geofísica e sondagens no estudo tectónico e geológico da região a Oeste de EstarrejaPublication . Marques, Tiago; Moura, Rui M; Machadinho, Ana; Matias, ManuelRESUMO: A região a Oeste de Estarreja, de topografia aplanada, é geologicamente caracterizada por formações quaternárias e cretácicas que assentam discordantemente sobre um bedrock xisto-grauváquico, do Precâmbrico, de topografia pouco conhecida. Esta topografia é investigada recorrendo a dados de sondagens mecânicas e prospeção geofísica que incluem dois perfis de sondagens elétricas e um mapeamento gravimétrico sobre uma área aproximada de 30 km2, delimitada a Este pela linha do Norte e a Oeste pelo braço da ria de Aveiro que separa a Murtosa da Torreira. Os dados das sondagens mecânicas permitiram construir um modelo 3D da topografia do bedrock que conjuntamente com a inversão e modelação dos dados de prospeção geofísica propõem um modelo robusto para essa topografia. São identificados alinhamentos estruturais NW-SE, já inferidos por outros autores, propostas duas zonas delimitadas lateralmente, em que o bedrock se encontra mais profundo, que estão de acordo com modelação geofísica anterior a Sul desta região.
- Trace Element Geochemistry of Alluvial TiO2 Polymorphs as a Proxy for Sn and W DepositsPublication . Gaspar, Miguel; Grácio, Nuno; Salgueiro, Rute; Costa, MafaldaABSTRACT: The Segura mining field, the easternmost segment of the Gois-Panasqueira-Segura tin-tungsten metallogenic belt (north-central Portugal), includes Sn-W quartz veins and Li-Sn aplite-pegmatites, which are believed to be genetically related to Variscan Granites. Sediment geochemistry indicates granite-related Ti-enrichments, locally disturbed by mineralization, suggesting magmatic and metamorphic/metasomatic titaniferous phases. Therefore, Segura alluvial samples and the geochemistry of their TiO2 polymorphs (rutile, anatase, and brookite) were investigated, and their potential as exploration tools for Sn and W deposits was evaluated. The heavy-mineral assemblages proved to be good proxies for bedrock geology, and TiO2 polymorph abundances were found to be suitable indicators of magmatic and/or metasomatic hydrothermal processes. The trace element geochemistry of Segura's alluvial rutile, anatase, and brookite is highly variable, implying multiple sources and a diversity of mineral-forming processes. The main compositional differences between TiO2 polymorphs are related to intrinsic (structural) factors, and to the P-T-X extrinsic parameters of their forming environments. Anomalous enrichments, up to 9% Nb, 6% Sn and W, 3% Fe, 2% Ta, and 1% V in rutile, and up to 1.8% Fe, 1.7% Ta, 1.2% Nb, 1.1% W 0.5% Sn and V in anatase, were registered. Brookite usually has low trace element content (<0.5%), except for Fe (similar to 1%). HFSE-rich and granitophile-rich rutile is most likely magmatic, forming in extremely differentiated melts, with Sn and W contents enabling the discrimination between Sn-dominant and W-dominant systems. Trace element geochemical distribution maps show pronounced negative Sn (rutile+anatase) and W (rutile) anomalies linked to hydrothermal cassiterite precipitation, as opposed to their hydrothermal alteration halos and to W-dominant cassiterite-free mineralized areas, where primary hydrothermal rutile shows enrichments similar to magmatic rutile. This contribution recognizes that trace element geochemistry of alluvial TiO2 polymorphs can be a robust, cost- and time-effective, exploration tool for Sn(W) and W(Sn) ore deposit systems.
- Wind Resource Assessment in Building Environment: Benchmarking of Numerical Approaches and Validation with Wind Tunnel DataPublication . Costa, Paula Silva; Cataldo, José; Mazaira, Leorlen; González, Daniel; Costa, Alexandre; Simões, TeresaABSTRACT: In the framework of the wind energy network for distributed generation in urban environments for most South American countries, wind resource assessment studies have been carried out in activities to establish a suitable methodology to assess the wind potential in urban environments. Some methodologies are already published in research studies, and the wind tunnel is the most accurate solution to obtain insight into the wind resource when measurements are unavailable, which is the most frequent case. Nevertheless, besides its validity, one cannot disregard the high cost of producing a scaled urban model and access to a wind tunnel. In this sense, this paper compares results from a wind tunnel experiment and different numerical modeling approaches. Two commercial models (WindSim and Wasp Engineering) and one open-source CFD code (OpenFOAM) are used. The results from the modeling simulation concluded that CFD models could achieve lower deviations for the mean wind speed and turbulence intensity when compared with non-CFD models. With such results, CFD modeling is a promising tool for reliably evaluating wind potential in urban environments.
- The Biorefinery of the Marine Microalga Crypthecodinium cohnii as a Strategy to Valorize Microalgal Oil FractionsPublication . Moniz, Patricia; Martins, Daniela; Oliveira, Ana Cristina; Reis, Alberto; Silva, Teresa Lopes daABSTRACT: Chrypthecodinium cohnii lipids have been almost exclusively used as a source of Docosahexaenoic acid (DHA). Such an approach wastes the remaining microalgal lipid fraction. The present work presents a novel process to produce C. cohnii biomass, using low-cost industrial by-products (raw glycerol and corn steep liquor), in a 7L-bioreactor, under fed-batch regime. At the end of the fermentation, the biomass concentration reached 9.2 g/L and the lipid content and lipid average productivity attained 28.0% (w/w dry cell weight) and 13.6 mg/L h, respectively. Afterwards the microalgal biomass underwent a saponification reaction to produce fatty acid (FA) soaps, which were further converted into FA ethyl ester (FA EE). C. cohnii FA EE mixture was then fractionated, using the urea complexation method at different temperatures, in order to obtain a polyunsaturated fatty acid ethyl ester (PUFA EE) rich fraction, that could be used for food/pharmaceutical/cosmetic purposes, and a saturated fatty acid ethyl ester (SAT EE) rich fraction, which could be used as biodiesel. The temperature that promoted the best separation between PUFA and SAT EE, was -18 degrees C, resulting in a liquid fraction with 91.6% (w/w) DHA, and a solid phase with 88.2% of SAT and monounsaturated fatty acid ethyl ester (MONOUNSAT), which could be used for biodiesel purposes after a hydrogenation step.
- Damage threshold of CuCrFeTiV high entropy alloys for nuclear fusion reactorsPublication . Dias, Marta; Magalhães, S.; Antão, Francisco; Silva, R.C. da; Gonçalves, António Pereira; Carvalho, Patricia Almeida; Correia, J.B.; Galatanu, Andrei; Alves, E.ABSTRACT: A CuCrFeTiV high entropy alloy was prepared and irradiated with swift heavy ions in order to check its adequacy for use as a thermal barrier in future nuclear fusion reactors. The alloy was prepared from the elemental powders by ball milling, followed by consolidation by spark plasma sintering at 1178 K and 65 MPa. The samples were then irradiated at room temperature with 300 keV Ar+ ions with fluences in the 3 x 1015 to 3 x 1018 Ar+/cm2 range to mimic neutron-induced damage accumulation during a duty cycle of a fusion reactor. Structural changes were investigated by X-ray diffraction, and scanning electron microscopy and scanning transmission electron microscopy, both coupled with X-ray energy dispersive spectroscopy. Surface irradiation damage was detected for high fluences (3 x 1018 Ar+/cm2) with formation of blisters of up to 1 mu m in diameter. Cross-sectional scanning transmission electron microscopy showed the presence of intergranular cavities only in the sample irradiated with 3 x 1018 Ar+/cm2, while all irradiation experiments produced intragranular nanometric-sized bubbles with increased density for higher Ar+ fluence. The Williamson-Hall method revealed a decrease in the average crystallite size and an increase in residual strain with increasing fluence, consistent with the formation of Ar+ bubbles at the irradiated surface.
- A New Insight into the Role of Silicate-Type Binders on the Crushing Strength of Alumina FoamsPublication . Oliveira, Fernando Almeida Costa; Pommier, Stéphane; Fernandes, Jorge Cruz; Dias, DiamantinoABSTRACT: Semi-closed cell macroporous alumina foams with relative densities ranging from 0.26 to 0.35 have been produced by the well-established replication method based on the coating of a polyurethane (PU) template foam by a ceramic slurry, followed by burnout of the PU template, and sintering of the ceramic skeleton. Collapse of the three-dimensional structure upon the volatilisation of the PU sponge can only be prevented using appropriate binders. Scarce data are available on the slurry formulations of commercial alumina foams. The aim of this study was to investigate the influence of silicate-type binders, namely kaolin and bentonite additives, on the crushing strength of alumina foams. The highest crushing strength of around 10 MPa was observed at a porosity of 66 +/- 2%. The open-cell model is inadequate to fit the crushing strength data of such semi-closed cell type structures. Both microscopic and macroscopic flaws resulting from the foam processing method contribute to the wide scatter of the strength, thereby explaining the Weibull modulus ranging from 4 to 7. Both flaw populations require further improvement to maximise the crushing strength of these foams with high potential for the design of structured catalyst carriers and molten aluminium filters.