FCT: DCM - Artigos em revista internacional com arbitragem científica
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- Coupling effect of dynamic power and oscillation path on butt weld formation and melt flow behavior during aluminum alloysPublication . Cui, Jiangmei; Oliveira, J. P.; Pang, Bowen; Shen, Jiajia; Zeng, Zhi; DCM - Departamento de Ciência dos Materiais; CENIMAT-i3N - Centro de Investigação de Materiais (Lab. Associado I3N); Elsevier Science B.V., Amsterdam.The influence of the coupling effect between dynamic power and oscillation path on the formation of weld seams and the fluid behavior of the molten pool during laser welding of 5A06 aluminum alloy was investigated through numerical simulation and experimentation. Three power modes were compared in the experiments: equal power (EP), delayed dynamic power (D-DP), and non-delayed dynamic power (ND-DP). The experimental results show that both D-DP and ND-DP modes are favorable to improve the mechanical properties. Among them, the joints formed under the D-DP mode exhibit the best mechanical properties, with an average tensile strength reaching ≈ 99.1% of the base material, which is an increase of ≈ 35.3% and ≈ 5.6% compared to the EP and ND-DP modes, respectively. Numerical simulation results indicate that the D-DP mode effectively mitigates the average flow velocity of the molten pool, reduces the collision effects between liquid flows, suppresses the impact of fluid on the keyhole walls, and improves the stability of the keyhole and the welding process, thereby enhancing the mechanical properties of the joints.
- Photonic-Enhanced Perovskite Solar CellsPublication . Almeida, Eva; Alexandre, Miguel; Santos, Ivan M.; Martins, Rodrigo; Águas, Hugo; Mendes, Manuel J.; CENIMAT-i3N - Centro de Investigação de Materiais (Lab. Associado I3N); DCM - Departamento de Ciência dos Materiais; UNINOVA-Instituto de Desenvolvimento de Novas Tecnologias; ACS - American Chemical SocietyThe current exponential growth of solar electricity technologies toward consumer-oriented applications, as in building- or vehicle-integrated photovoltaics (B/VIPV), is calling for improved solar cells, not only in cost-effectiveness, but also with better adaptability and aesthetics. Here, using perovskite solar cells (PSCs) as test bed, we demonstrate an unprecedented photonic method to generate any color on a cell layout, while also increasing PV efficiency. To this end, photonic surface features were designed for PSCs, which filled the dual purpose of light-trapping (LT) and modulation of reflected light interference. A variety of geometries, from simple gratings to complex semispheroids, were optically optimized for two of the most challenging colors, magenta and green, while assuring the generation of their maximum feasible photocurrent. The best results corresponded to a current density of 22.07 mA/cm2, obtained for the magenta solar cell with top domes, exhibiting an increase of 6.68%, relative to an optimized planar reference cell. In turn, the same type of geometry was able to generate the leading green cell, with up to 21.40 mA/cm2 (a relative increase of 3.44%). Additionally, the uniformity of the optical output of the optimal solar cells was tested under a range of incident light angles, between 0◦ and 60◦, where the current density suffered relative losses only down to 6.65%.
- Cellulose Acetate and Polycaprolactone Fibre Coatings on Medical-Grade Metal Substrates for Controlled Drug ReleasePublication . Cidade do Carmo, Catarina; Brito, Miguel; Oliveira, J. P.; Marques, Ana; Ferreira, Isabel; Baptista, Ana Catarina; DCM - Departamento de Ciência dos Materiais; CENIMAT-i3N - Centro de Investigação de Materiais (Lab. Associado I3N); MDPI - Multidisciplinary Digital Publishing InstituteThis study explores a method that has the potential to be cost effective in inhibiting biofilm formation on metallic prostheses, thereby preventing rejection or the requirement for replacement. A cost-effective metal alloy used in biomedical implants was chosen as the substrate, and ibuprofen (Ibu), a well-known anti-inflammatory drug, was selected for drug release tests for its widespread availability and accessibility. Multilayer coatings consisting of cellulose acetate (CA), polycaprolactone (PCL), and chitosan (CHI), with or without ibuprofen (Ibu) content, were applied onto medical-grade stainless steel (SS-316 type) through electrospinning, electrospray, or blow spinning. The adhesion of the CA, PCL, and layered CA/PCL membranes, with thicknesses ranging from 20 to 100 μm, to SS substrates varied between 0.15 N and 0.22 N without CHI, which increased to 0.21 and 0.74 N, respectively, when a CHI interlayer was introduced by electrospraying between the SS and the coatings. Although drug release in a simulated body fluid (SBF) medium is predominantly governed by diffusion-driven mechanisms in all single- and multilayer coatings, a delayed release was noted in CA coatings containing Ibu when overlaid with a PCL coating produced by blow spinning. This suggests avenues for further investigations into combinations of multilayer coatings, both with and without drug-imbued layers.
- Photon shifting and trapping in perovskite solar cells for improved efficiency and stabilityPublication . Haque, Sirazul; Alexandre, Miguel; Vicente, António T.; Li, Kezheng; Schuster, Christian S.; Yang, Sui; Águas, Hugo; Martins, Rodrigo; Ferreira, Rute A. S.; Mendes, Manuel J.; UNINOVA-Instituto de Desenvolvimento de Novas Tecnologias; CENIMAT-i3N - Centro de Investigação de Materiais (Lab. Associado I3N); DCM - Departamento de Ciência dos Materiais; Springer NatureAdvanced light management techniques can enhance the sunlight absorption of perovskite solar cells (PSCs). When located at the front, they may act as a UV barrier, which is paramount for protecting the perovskite layer against UV-enabled degradation. Although it was recently shown that photonic structures such as Escher-like patterns could approach the theoretical Lambertian-limit of light trapping, it remains challenging to also implement UV protection properties for these diffractive structures while maintaining broadband absorption gains. Here, we propose a checkerboard (CB) tile pattern with designated UV photon conversion capability. Through a combined optical and electrical modeling approach, this photonic structure can increase photocurrent and power conversion efficiency in ultrathin PSCs by 25.9% and 28.2%, respectively. We further introduce a luminescent down-shifting encapsulant that converts the UV irradiation into Visible photons matching the solar cell absorption spectrum. To this end, experimentally obtained absorption and emission profiles of state-of-the-art down-shifting materials (i.e., lanthanide-based organic-inorganic hybrids) are used to predict potential gains from harnessing the UV energy. We demonstrate that at least 94% of the impinging UV radiation can be effectively converted into the Visible spectral range. Photonic protection from high-energy photons contributes to the market deployment of perovskite solar cell technology, and may become crucial for Space applications under AM0 illumination. By combining light trapping with luminescent downshifting layers, this work unravels a potential photonic solution to overcome UV degradation in PSCs while circumventing optical losses in ultrathin cells, thus improving both performance and stability.
- Time-resolved evolution of the deformation mechanisms in a TRIP/TWIP Fe50Mn30Co10Cr10 high entropy during tensile loading probed with synchrotron X-ray diffractionPublication . Lopes, J. G.; Shen, J.; Maawad, E.; Agrawal, P.; Schell, N.; Mishra, R. S.; Oliveira, J. P.; DEMI - Departamento de Engenharia Mecânica e Industrial; UNIDEMI - Unidade de Investigação e Desenvolvimento em Engenharia Mecânica e Industrial; CENIMAT-i3N - Centro de Investigação de Materiais (Lab. Associado I3N); DCM - Departamento de Ciência dos Materiais; ElsevierThe present research focuses on analyzing the deformation mechanisms associated with tensile loading of the Fe50Mn30Co10Cr10 high entropy alloy (HEA) using synchrotron x-ray diffraction (SXRD). This novel material is comprised by two major phases: γ-FCC and ε-HCP, where transformation induced plasticity (TRIP) effectively transforms the first into the latter, upon the application of an external stress. However, the presence of thermally stable ε-HCP prior to loading will also influence the deformation mechanism of the material during mechanical solicitation. As such, here we investigate the activation of different strain accommodation mechanisms and the consequent microstructural evolution. Four stages were identified in the mechanical response of this novel HEA, where the TRIP and the twinning induced plasticity (TWIP) deformation modes are the main events granting this HEA its outstanding properties. Such sequence of events allows to evidence the effectiveness of the collaboration between the transformative capability of the γ-FCC phase and the work hardening potential of the ε-HCP phase. This analysis is performed via quantitative and qualitative analysis of the SXRD data, allowing also to investigate the response behavior of specific crystallographic planes to the increasing stress throughout the experiment.
- Microstructure and mechanical properties of Al-Zn-Mg-Cu alloy fabricated by multi-wire arc-based directed energy depositionPublication . Wang, Liwei; Tan, Zhen; Chen, Shaohui; Zeng, Zhi; Teshome, F. B.; Yan, Huan; Liu, Ying; Peng, Zhenzhen; Yang, Xiao; Wang, Dianlong; Narayanaswamy, Balaji; Liang, Zhimin; Oliveira, J. P.; DCM - Departamento de Ciência dos Materiais; CENIMAT-i3N - Centro de Investigação de Materiais (Lab. Associado I3N); Elsevier BVER5356, ER2319 and Zn wires were synchronously fed using a multi-wire gas metal arc directed energy deposition (DED) system. This allowed the successfully fabrication of Al-6.0Zn-2.5Mg-1.5Cu alloy. The microstructure and mechanical properties of the fabricated parts were studied. It is shown that the main precipitated phases are η and nanoscale η'. The upper and lower parts of the deposited parts are composed by coarse equiaxed grains and columnar dendrite structures, respectively. The average microhardness of the fabricated alloy was 118.5 HV. The ultimate tensile strength and elongations in the perpendicular to the building direction (BD) and parallel to the BD were 267 MPa and 2.7 %, 238 MPa and 2.3 %, respectively. The average tensile strength is higher than that of 7075-O alloy. The fracture mode of the samples composed brittle and ductile features, although the former dominated. This multi-wire arc DED approach provides a new choice for the in-situ synthesis of Al-Zn-Mg-Cu alloys.
- Role of TiB2 inoculation particles during welding of a AlCoCrFeNi high entropy alloyPublication . Lopes, J. G.; Candeias, A.; Agrawal, P.; Shen, J.; Schell, N.; Mishra, R. S.; Oliveira, J. P.; DEMI - Departamento de Engenharia Mecânica e Industrial; UNIDEMI - Unidade de Investigação e Desenvolvimento em Engenharia Mecânica e Industrial; CENIMAT-i3N - Centro de Investigação de Materiais (Lab. Associado I3N); DCM - Departamento de Ciência dos Materiais; ElsevierHigh entropy alloys (HEAs) are a novel class of materials that represent an evolution of common engineering alloys to a wider array of compositional and properties possibilities. As such, the exploration of methodologies to achieve improved microstructure and mechanical characteristics of these materials for potential applications in industry is a requirement that is experiencing extended research efforts. One example of a processing method able to expand the potential applications of these alloys is Gas Tungsten Arc Welding (GTAW), which allows to evaluate the metallurgical evolution and corresponding mechanical performance, associated to the impact of a localized heat input on the material. However, GTAW and related fusion-based welding processes are known to generate large grain sized-structures in the fusion zone, which often is detrimental to the joint performance. Thus, the integration of high temperature inoculant particles on the fusion zone during welding is a potential way to improve this region's microstructure and, therefore, its mechanical performance. In this work, we discuss the effect that the addition of TiB2 micron-sized particles have on the microstructure of a GTAW AlCoCrFeNi-based HEA. For this, the microstructure of the welds was evaluated by means of optical and electron microscopy, synchrotron X-ray diffraction and CalPhaD-based simulations. Mechanical testing was performed using microhardness mapping and tensile testing coupled with digital image correlation. The results evidenced that successful inoculation with TiB2 proved capable of altering the microstructure of the fusion zone (FZ), refining it. Nevertheless, preferential deformation in the relatively softer heat affected zone during tensile testing resulted on premature failure of the inoculated joints, due to the concomitant higher hardness of the FZ.
- Green Fabrication of Stackable Laser-Induced Graphene Micro-Supercapacitors under Ambient ConditionsPublication . Silvestre, Sara L.; Morais, Maria; Soares, Raquel R. A.; Johnson, Zachary T.; Benson, Eric; Ainsley, Elisabeth; Pham , Veronica; Claussen, Jonathan C.; Gomes, Carmen L.; Martins, Rodrigo; Fortunato, Elvira; Pereira, Luís; Coelho, João; CENIMAT-i3N - Centro de Investigação de Materiais (Lab. Associado I3N); DCM - Departamento de Ciência dos Materiais; UNINOVA-Instituto de Desenvolvimento de Novas Tecnologias; WileyExtensive research into green technologies is driven by the worldwide push for eco-friendly materials and energy solutions. The focus is on synergies that prioritize sustainability and environmental benefits. This study explores the potential of abundant, non-toxic, and sustainable resources such as paper, lignin-enriched paper, and cork for producing laser-induced graphene (LIG) supercapacitor electrodes with improved capacitance. A single-step methodology using a CO2 laser system is developed for fabricating these electrodes under ambient conditions, providing an environmentally friendly alternative to conventional carbon sources. The resulting green micro-supercapacitors (MSCs) achieve impressive areal capacitance (≈7–10 mF cm−2) and power and energy densities (≈4 μW cm-2 and ≈0.77 µWh cm−2 at 0.01 mA cm−2). Stability tests conducted over 5000 charge–discharge cycles demonstrate a capacitance retention of ≈80–85%, highlighting the device durability. These LIG-based devices offer versatility, allowing voltage output adjustment through stacked and sandwich MSCs configurations (parallel or series), suitable for various large-scale applications. This study demonstrates that it is possible to create high-quality energy storage devices based on biodegradable materials. This development can lead to progress in renewable energy and off-grid technology, as well as a reduction in electronic waste.
- MoS2 decorated carbon fiber yarn hybrids for the development of freestanding flexible supercapacitorsPublication . Carvalho, José Tiago; Correia, Afonso; Cordeiro, Neusmar J. A.; Coelho, João; Lourenço, Sidney A.; Fortunato, Elvira; Martins, Rodrigo; Pereira, Luís; CENIMAT-i3N - Centro de Investigação de Materiais (Lab. Associado I3N); DCM - Departamento de Ciência dos Materiais; UNINOVA-Instituto de Desenvolvimento de Novas Tecnologias; Nature Publishing GroupAcademic and industrial efforts have focused on developing energy storage devices for wearable and portable electronics using low-cost, scalable, and sustainable materials and approaches. In this work, commercially available stretch-broken carbon fiber yarns (SBCFYs) were hybridized with mixed phases of 1 T and 2H MoS2 nanosheets via conventional and microwave-assisted heating (CAH, MAH) without the use of binders to fabricate symmetric freestanding 1D fiber-shaped supercapacitors (FSCs). Electrochemical characterization performed in a three-electrode configuration showed promising results with specific capacitance values of 184.41 and 180.02 F·g−1, at 1 mV·s−1 for CAH and MAH, respectively. Furthermore, after performing 3000 CV cycles at 100 mV·s−1, the capacitance retention was 79.5% and 95.7%, respectively. Using these results as a reference, symmetric 1D FSCs were fabricated by pairing hybridized SBCFYs with MoS2 by MAH. The devices exhibited specific capacitances of approximately 58.60 ± 3.06 F·g−1 at 1 mV·s−1 and 54.81 ± 7.34 F·g−1 at 0.2 A·g−1 with the highest power density achieved being 15.17 W·g−1 and energy density of 5.06×10–4Wh·g−1. In addition, five 1D FSCs were hand-stitched and connected in series onto a cotton fabric. These supercapacitors could power a temperature and humidity sensor for up to six minutes, demonstrating the practicality and versatility of the prepared 1D FSCs for powering future electronic systems.
- Understanding the Potential of Light Absorption in Dots-in-Host SemiconductorsPublication . Alexandre, Miguel; Águas, Hugo; Fortunato, Elvira; Martins, Rodrigo; Mendes, Manuel J.; CENIMAT-i3N - Centro de Investigação de Materiais (Lab. Associado I3N); DCM - Departamento de Ciência dos Materiais; UNINOVA-Instituto de Desenvolvimento de Novas Tecnologias; ACS - American Chemical SocietyThe outstanding physical properties of dots-in-host (QD@Host) hetero semiconductors demand detailed methods to fundamentally understand the best routes to optimize their potentialities for different applications. In this work, a 4-band k.p-based method was developed for rock-salt quantum dots (QDs) that describes the complete optical properties of arbitrary QD@Host systems, trailblazing the way for the full optoelectronic analysis of quantum-structured solar cells. Starting with the determination of the QD bandgap and validation against well-established literature results, the electron transition rate is then computed and analyzed against the main system parameters. This is followed by a multiparameter optimization, considering intermediate band solar cells as a promising application, where the best QD configuration was determined, together with the corresponding QD@Host absorption spectrum, in view of attaining the theoretical maximum efficiency (∼50%) of this photovoltaic technology. The results show the creation of pronounced sub-bandgap absorption due to the electronic transitions from/to the quantum-confined states, which enables a much broader exploitation of the sunlight spectrum.