Materiais para a Energia - ME
URI permanente desta comunidade:
Navegar
Percorrer Materiais para a Energia - ME por Objetivos de Desenvolvimento Sustentável (ODS) "11:Cidades e Comunidades Sustentáveis"
A mostrar 1 - 3 de 3
Resultados por página
Opções de ordenação
- Inter-equipment ongoing validation of microplastic identification by micro-FTIR using optimal resourcesPublication . Fernandes, Rafaela; Miclea, Paul-Tiberiu; ROSSI, Andrea Mario; Giovannozzi, Andrea M.; Putzu, Mara; Morgado, Vanessa; Palma, Carla; Almeida, José Miguel; Pedro, Matilde São; Drago, Claudia; Quendera, Raquel Maria Pina Amaral; Pellegrino, Olivier; Bettencourt da Silva, RicardoABSTRACT: FTIR is widely used for identifying microplastics due to its performance and affordable equipment. However, there is a need for a universal method for the automatic identification of microplastics by FTIR, robust to different spectra collection conditions, and capable of adapting to the diversity of particle spectra. This research presents a method for developing a reliable and simple algorithm for inter-instrumental microplastic identification using micro-FTIR. Spectra collected from different equipments and settings across various laboratories, from microparticles previously confirmed as PET (positive cases) and non-PET (negative cases), were compared with a PET reference using multiple algorithms (match methods) based on six weighted and unweighted correlation coefficients. After excluding low signal-to-noise spectra with a newly developed universal algorithm, the 5th percentile of the match values for positive cases, estimated using a robust bootstrap method, was used as a minimum match (P5 & raquo;P) to ensure a 95% true positive rate (TP). Assuming a normal distribution of the match values for negative cases, the false positive rate (FP) was calculated. The best method identified uses an unweighted correlation of differentiated signals, resulting in a P5 & raquo;P = 0.4140 and FP = 0.0005% for spectra with a minimum signal-to-noise ratio of three. This identification performance, estimated from 117 spectra, is statistically equivalent to that observed from the identification of 405 additional particles using the validated method, at a 99% confidence level set by the Clopper-Pearson method, thereby extending the method's applicability to 522 particles. The developed method for PET identification by FTIR is robust across various acquisition conditions and instruments, was implemented in a user-friendly MS Excel spreadsheet, and can be easily tested with more particles and different instrumental settings. The validity of the identification algorithm and the defined criteria cannot be extrapolated to a different reality with respect to spectral collection conditions and the diversity of negative cases without a prior performance assessment.
- Novel fast synthesis route for α-MgAgSb thermoelectric materialsPublication . Santos, Beatriz; Sá, Ana; Luz, Paulo P. da; Neves, Filipe; de Boor, Johannes; Pereira Gonçalves, AntonioABSTRACT: Thermoelectric (TE) materials capable of waste heat recovery in the temperature range of 300-525 K remain relatively underdeveloped compared to conventional Bi2Te3-based systems, which present inherent environmental, health, and cost challenges. Recently, MgAgSb-based compounds have garnered significant research interest for applications in this temperature range owing to their intrinsically low thermal conductivity, high figure of merit and higher abundance. However, synthesis of the desired low-temperature alpha-MgAgSb phase typically requires highly controlled production processes-such as multi-step mechanical alloying, followed by extensive, week-long annealing-to mitigate the formation of or transition to undesirable phases. This study proposes an original, rapid, and scalable synthesis strategy combining induction melting for only six minutes with the subsequent classic hot-pressing method. We investigated the effect of nominal stoichiometry on thermoelectric performance by synthesising three distinct compositions: MgAg0.97Sb0.995, MgAg0.965Sb0.985, and MgAg0.955Sb0.985. The MgAg0.955Sb0.985 composition exhibited optimal performance, achieving an average power factor (PF) of 12.8 mu W K-2 cm-1 in the 300-525 K range. By considerably reducing the thermal budget and processing time, this approach significantly improves the energy payback time (EPBT) and reduces the carbon footprint of production, addressing the critical sustainability-performance trade-off that limits large-scale deployment. This result validates the capacity of the proposed fast synthesis route to yield performant MgAgSb-based samples and suggests that the optimal nominal composition is dependent on the specific production technique employed. Fundamentally, this work demonstrates the rapid and successful preparation of the desired alpha-MgAgSb phase using an easily scalable technique that does not require a perpetually inert atmosphere. This process utilises bulky precursor elements directly, significantly reducing production complexity, associated costs, and health hazards. This advancement provides a simpler and more industrially viable pathway for the transition of MgAgSb materials toward commercial availability.