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- Using waste from the Barrigão abandoned mine as source of raw material for the synthesis of tetrahedrite-tennantite materials for a sustainable future [Resumo]Publication . Neves, FilipeABSTRACT: The green transition implies the use of a broad mixture of renewable energy sources where materials science-based solutions are vital for designing improved materials and devices. Despite the progress that has been achieved in the development of materials for sustainable energy technologies, current research is still facing many challenges (e.g., materials availability and processability to achieve low cost, efficiency, durability and environmental concerns).
- Structural and Optical Characterization of Mechanochemically Synthesized CuSbS2† [Abstract]Publication . Esperto, Luís; Figueira, Isabel; Mascarenhas, João; Silva, Teresa; Correia, J.B.; Neves, FilipeABSTRACT: The present work describes experimental studies related to the characterization of CuSbS2 directly synthesized after 2 h of mechanochemical synthesis (MCS) at 340 rpm, starting from mixtures of elemental powders. X-ray diffraction (XRD) and UV-VIS-NIR spectroscopy were carried out to analyze the crystal structure, degree of crystallinity, crystallite size and optical properties of the mechanochemically synthesized CuSbS2 powders. Rietveld refinement was carried out using Diffrac. TOPAS (Bruker AXS). Thermal stability of the synthesized materials was evaluated by the vacuum thermal heat treatment of the mechanochemically synthesized CuSbS2 powders at 350 °C for 24 h. Furthermore, the CuSbS2 powders were also analyzed by field-emission scanning electron microscopy (FE-SEM), laser diffraction, and differential thermal analysis.
- Microwave versus Conventional Sintering of NiTi Alloys Processed by Mechanical AlloyingPublication . Teixeira, Rodolfo da Silva; Oliveira, R. V.; Rodrigues, Patricia Freitas; Mascarenhas, João; Neves, Filipe; Paula, Andersan dos SantosABSTRACT: The present study shows a comparison between two sintering processes, microwave and conventional sintering, for the manufacture of NiTi porous specimens starting from powder mixtures of nickel and titanium hydrogenation-dehydrogenation (HDH) milled by mechanical alloying for a short time (25 min). The samples were sintered at 850 degrees C for 15 min and 120 min, respectively. Both samples exhibited porosity, and the pore size results are within the range of the human bone. The NiTi intermetallic compound (B2, R-phase, and B19 ') was detected in both sintered samples through X-ray diffraction (XRD) and electron backscattering diffraction (EBSD) on scanning electron microscopic (SEM). Two-step phase transformation occurred in both sintering processes with cooling and heating, the latter occurring with an overlap of the peaks, according to the differential scanning calorimetry (DSC) results. From scanning electron microscopy/electron backscatter diffraction, the R-phase and B2/B19 ' were detected in microwave and conventional sintering, respectively. The instrumented ultramicrohardness results show the highest elastic work values for the conventionally sintered sample. It was observed throughout this investigation that using mechanical alloying (MA) powders enabled, in both sintering processes, good results, such as intermetallic formation and densification in the range for biomedical applications.
- Processamento de materiais termoelétricos baseados na tetraedrite usando minério de tetraedrite-tenantitePublication . Esperto, Luís; Figueira, Isabel; Mascarenhas, João; Salgueiro, Rute; Silva, Teresa; Lopes, E.B.; Gonçalves, António Pereira; Correia, J.B.; de Oliveira, Daniel Pipa Soares; Almeida, P.; Neves, FilipeRESUMO: O desenvolvimento e implementação de tecnologias com baixo potencial de aquecimento global e energeticamente eficientes requer uma contínua inovação na área dos materiais para a energia. Nesta estratégia insere-se a pesquisa sobre o processamento de materiais termoelétricos baseados na tetraedrite. No presente trabalho procede-se à avaliação da viabilidade da incorporação direta, sem qualquer pré-tratamento, de minério da série tetraedrite-tenantite no processamento de materiais à base de tetraedrite por síntese mecanoquímica. Para tal prepararam-se misturas de pós contendo diferentes rácios de amostras de tetraedrite sintética, também obtida por síntese mecanoquímica, e de amostras de minério, recolhidas na mina de Neves-Corvo e na escombreira da mina do Barrigão. A caraterização estrutural e microestrutural dos materiais processados após 1 h e 2 h de síntese mecanoquímica permitiu verificar a formação de um composto constituído por tetraedrite-tenantite-(Fe) como fase principal, independentemente do minério de origem. Estes resultados são uma indicação do sucesso da abordagem seguida.
- START Newsletter: Recover-Reform-Reuse for a Sustainable Future, Issue 4Publication . Neves, Filipe; Vicenzi, BrunoABSTRACT: We are almost halfway through the project activities and what a journey this has been! The advances we have made together are nothing short of remarkable. This edition of our Newsletter is a testament to our collective dedication and the exciting progress we’ve achieved. The completion of our first Periodic Report marks a significant milestone, and the advancements in tetrahedrite mineral-based thermoelectric materials are not just promising—they’re a leap towards a sustainable future. We’re excited to share updates on our ongoing activities, our synergistic collaborations with the EHRASE cluster and THERMOS project, and insightful technical information on thermoelectric generators. But that’s not all, join us on the Consortium Tour, where this time SGUDS and IGME-CSIC take centre stage. Plus, don’t miss the insightful interview with Doug Crane from our Scientific Advisory Board, whose expertise enriches our understanding of thermoelectrics. This edition also features the fascinating adventures of Starty, exploring the practical uses of thermoelectric devices in a narrative that’s both educational and engaging. Looking ahead, we eagerly anticipate your visit to the START booth at the upcoming 40th International and 20th European Thermoelectric Conference, ICT/ECT 2024, in Krakow. We hope this Newsletter serves not only as a source of information but also as an inspiration for continued excellence. Stay connected with us for more exciting updates from START on our website and social media channels.
- Characterization of smart MARFOS NiTi shape memory alloysPublication . Neves, Filipe; Fernandes, F. M. Braz; Martins, J.; Correia, J.B.; Oliveira, M.; Gaffet, E.; Wang, T. Y.; Lattemann, M.; Suffner, J.; Hahn, H.In the present study, structural characterization of NiTi smart shape memory al-loys (SMAs), produced by an alternative powder metallurgy approach named mechanically ac-tivated reactive forging (MARFOS), was carried out by means of transmission electron micros-copy (TEM), scanning electron microscopy (SEM) and X-ray diffraction (XRD). It was observed that MARFOS materials had a multiphase nanocrystalline structure. In addition, the transformation behaviour associated with the shape memory effect of the MARFOS aged mate-rials was studied with differential scanning calorimetry (DSC). Multiple-step martensitic trans-formations could be observed in aged materials.
- Investigation of the Effect of Milling Time on Elemental Powders of Oxi-Reduction Nickel and Hydrogenation : Dehydrogenation TitaniumPublication . Teixeira, Rodolfo da Silva; Gurgel, Mônica Aline Magalhães; Rodrigues, Patricia Freitas; Freitas, Bruno Xavier de; Le Sénéchal, Naiara; Oliveira, R. V.; Neves, Filipe; Paula, Andersan dos SantosABSTRACT: Mechanical alloying (MA) is widely applied in the synthesis of blended elemental or prealloyed powders. This work evaluates the effect of milling time on elemental nickel and titanium powders produced by oxi-reduction and the hydrogenation-dehydrogenation process, respectively. The powders are characterized by scanning electron microscopy, X-ray diffraction, particle size, powder yield, and differential scanning calorimetry. It is observed that increasing the milling time promotes the formation of a structure composed of thin lamellae of nickel and titanium, which results in the beneficial effect of lowering the temperature for the formation of the intermetallic of the Ni-Ti system and in the powder yield achieved. The reduction of milling time in the MA process of NiTi alloys enhances technological efficiency by decreasing their overall processing time.
- Structural and optical characterization of mechanochemically synthesized CuSbS2 compoundsPublication . Esperto, Luís; Figueira, Isabel; Mascarenhas, João; Silva, Teresa; Correia, J.B.; Neves, FilipeABSTRACT: One of the areas of research on materials for thin-film solar cells focuses on replacing In and Ga with more earth-abundant elements. In that respect, chalcostibite (CuSbS2) is being considered as a promising environmentally friendly and cost-effective photovoltaic absorber material. In the present work, single CuSbS2 phase was synthesized directly by a short-duration (2 h) mechanochemical-synthesis step starting from mixtures of elemental powders. X-ray diffraction analysis of the synthesized CuSbS2 powders revealed a good agreement with the orthorhombic chalcostibite phase, space group Pnma, and a crystallite size of 26 nm. Particle-size characterization revealed a multimodal distribution with a median diameter ranging from of 2.93 mu m to 3.10 mu m. The thermal stability of the synthesized CuSbS2 powders was evaluated by thermogravimetry and differential thermal analysis. No phase change was observed by heat-treating the mechanochemically synthesized powders at 350 degrees C for 24 h. By UV-VIS-NIR spectroscopy the optical band gap was determined to be 1.41 eV, suggesting that the mechanochemically synthesized CuSbS2 can be considered suitable to be used as absorber materials. Overall, the results show that the mechanochemical process is a viable route for the synthesis of materials for photovoltaic applications.
- 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.