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Avaliação de aminoácidos como inibidores de corrosão para aço carbono AISI 1018 submetidos a meio contendo NaCl com e sem saturação de CO2

2024-01-01T00:00:00Z

Título: Avaliação de aminoácidos como inibidores de corrosão para aço carbono AISI 1018 submetidos a meio contendo NaCl com e sem saturação de CO2 Autor(es): Moura, Milena Jacinto da Silva Abstract: Corrosion represents one of the most significant challenges faced by industries, leading to considerable financial losses. Various compounds are used to prevent, reduce, or even halt corrosion in different materials affected by these effects. Thus, sectors such as oil and gas employ chemical compounds known as corrosion inhibitors. However, some substances, despite having inhibitory effects, may pose environmental and human health risks. In this context, natural, non-aggressive, and ecologically sustainable compounds, such as amino acids, aqueous extracts, and ionic liquids, are being investigated as alternatives to conventional corrosion inhibitors. Amino acids have been demonstrated to be corrosion inhibitors for a variety of materials, such as carbon steel, stainless steel, and metal alloys, in different corrosive environments. This study proposes an analysis of five amino acids — histidine, methionine, cysteine, serine, and phenylalanine — as potential corrosion inhibitors. These amino acids were investigated with varying inhibitor concentrations (250, 500, and 1000 ppm), medium temperature (25, 40, and 60°C), and the use of a surfactant to evaluate the synergism, based on whether or not inhibition efficiency increased, and the evaluation of the medium with carbon dioxide (CO2) saturation. To assess the effectiveness of these compounds as corrosion inhibitors, gravimetric and electrochemical techniques, such as potentiodynamic polarization (PP) and electrochemical impedance spectroscopy (EIS), were employed. UV-VIS measurements were performed to analyze the compounds in solution. A molecular modeling study complemented the analysis of the amino acids. The characterization of the amino acids was carried out using techniques such as Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). For surface analysis, images were collected using scanning electron microscopy (SEM) and atomic force microscopy (AFM). The results indicated an efficiency order of the amino acids: histidine > cysteine > phenylalanine > serine > methionine, which was confirmed by theoretical calculations. In the tests performed, the amino acids histidine, cysteine, and phenylalanine respectively showed efficiencies of 91%, 90%, and 88%, standing out as the most promising results. The amino acids showed the best inhibition response at a temperature of 25°C to 3.5 wt% NaCl. Tipo: Tese

Propriedades dielétricas da matriz Bi2Mo2O9 com adição de Al2O3 para aplicações em micro-ondas e radiofrequência (RF)

2025-01-01T00:00:00Z

Título: Propriedades dielétricas da matriz Bi2Mo2O9 com adição de Al2O3 para aplicações em micro-ondas e radiofrequência (RF) Autor(es): Oliveira, Lindemberg de Sousa Abstract: In the search for new high-performance materials for microwave and radio-frequency telecommuni- cation systems, with connectivity to various types of technologies, this work investigated the struc- tural and dielectric properties of the monoclinic Bi Mo O (BMO) ceramic matrix modified with 2 2 9 alumina (Al O ) additions at 10, 20, and 33 wt%. BMO powders were synthesized by the conventi 2 3 - onal solid-state reaction method and calcined at 600 °C. The phases present were confirmed by X- ray diffraction with Rietveld refinement. Cylindrical pressed samples were sintered at 640 °C. Die- lectric characterization was performed in the radiofrequency (RF) and microwave (MW) regimes, also considering the temperature dependence of the properties for potential application in electronic devices operating within these bands. The main objective was the development of ceramic dielectric components with low relative permittivity, effective porosity control, low dielectric loss, thermal stability, and optimized performance in key parameters such as bandwidth, gain, and efficiency. Using the Hakki–Coleman method, the relative permittivity (εr) showed a maximum value of 33.45 for pure BMO with a relative density of 89%, decreasing systematically with the increase in Al O2 3 mass fraction, down to 12.02 for 33% addition. The dielectric loss tangent (tan δ) increased from 7.14×10-4 to 2.35×10-3 with higher Al O content. Thermal stability was optimized in the compositi 2 3 - on with 10 wt% Al O , presenting a resonant frequency temperature coefficient (τ 2 3 f) of 3.24 ppm·°C-1. Far-field simulations were conducted using HFSS software, demonstrating good agree- ment with the experimental data. The performance of dielectric resonator antennas (DRA) based on these composites showed high efficiency (> 93%), low reflection coefficients (S11 < -30 dB), and an increase in the HE11δ mode resonant frequency with increasing Al O concentration. The (BMO) 2 3 1-X: (Al O ) 2 3 X composite showed applications in MW and RF devices at 10 and 20 wt% concentrations, due to its tunable dielectric properties, thermal stability, and thermally activated electrical conducti- on. Tipo: Tese

Dual spectral matching in perovskite solar cells via upconverting plus downshifting nanoparticles

2025-01-01T00:00:00Z

Título: Dual spectral matching in perovskite solar cells via upconverting plus downshifting nanoparticles Autor(es): Palácio, Milliane Passos da Silva Abstract: Maximizing the efficiency of solar cells is a key step toward advancing photovoltaic technologies and fully harnessing the energy conversion potential of sunlight. This study investigates the incorporation of core–shell nanoparticles (NPs) NaGdF4:Yb3+ ,Tm3+@NaGdF4:Eu3+ (TMN) and NaGdF4:Yb3+ ,Er3+@NaGdF4:Eu3+ (ERN) into perovskite solar cells (PSCs) with the aim of enhancing their power conversion efficiency. The NPs were synthesized via thermal decomposition and characterized using a set of techniques, including photoluminescence spectroscopy, quantum yield measurements, transmission electron microscopy, X-ray diffraction, solar simulator-based efficiency measurements, and external quantum efficiency evaluations. The lanthanide-doped NPs exhibited intense downshifting luminescence and weaker upconversion emission, acting as spectral converters that transform poorly absorbed regions of the solar spectrum into wavelengths usable by the device. Devices containing ERN NPs showed a relative increase of 22.19% in power conversion efficiency, whereas those with TMN NPs exhibited an improvement of 13.23%. These gains are primarily attributed to the efficient downshifting emission of Eu3+ and the superior surface passivation provided by the core–shell architecture. Together, these mechanisms suppress recombination losses and optimize charge carrier dynamics. These results highlight the potential of lanthanide-based photon-converting materials to overcome the intrinsic spectral absorption limitations of PSCs, presenting a promising strategy for the development of next-generation photovoltaic technologies. Tipo: Tese

Avaliação de trinca a quente em ligas cuproníquel e monel aplicando o ensaio trans-varestraint

2025-01-01T00:00:00Z

Título: Avaliação de trinca a quente em ligas cuproníquel e monel aplicando o ensaio trans-varestraint Autor(es): Moura Filho, Adroaldo José Silva de Abstract: Due to the challenges associated with deepwater oil extraction, technological advancements in this sector have been aimed at pushing boundaries. The development of new materials and manufacturing processes, with an emphasis on welding techniques used for joining pipelines and claddings, demands the use of advanced technologies, which contributes to the increased cost of oil extraction. Among the most commonly used materials in refinery cooling units, water intake systems, and fire-fighting systems are cupronickel and Monel alloys, which are essential due to their high corrosion resistance. In these applications, welding of piping made from these alloys is a common practice. However, the occurrence of hot cracking during welding is a critical issue, considering the high costs associated with repairs and replacements. The objective of this study is to evaluate the metallurgical phenomena related to solidification during the formation of hot cracks in CuNi and NiCu alloys, using the Trans-Varestraint (TVT) weldability test. Three factors were analyzed in relation to hot cracking formation: material, welding energy, and imposed strains. The alloys studied were UNS C70600 and AWS A5.7 ERCuNi, commercially known as CuNi 90/10 and CuNi 70/30, respectively, as well as the AWS A5.14 ERNiCu-7 alloy, corresponding to Monel 60. The tests were conducted with five levels of strain and two welding energy inputs: 1.09 and 0.74 kJ/mm. The results from the weldability tests were compared with thermodynamic simulations based on solidification curves using the Scheil model. Paradoxically, it was observed that the CuNi 90/10 alloy—despite not forming low-melting phases and having the narrowest brittle temperature range (BTR)—showed greater susceptibility to cracking. This contradiction was explained by the occurrence of different cracking mechanisms. In the CuNi 90/10 alloy, cracks were associated with both ductility loss and solidification, whereas in CuNi 70/30, cracks were exclusively related to solidification. All analyzed alloys exhibited grain boundary cracks with preferential crystallographic orientation. It was concluded that the CuNi 90/10 alloy is more susceptible to cracking due to the combined effect of solidification and ductility loss mechanisms, while the CuNi 70/30 alloy exhibited only solidification-induced cracks. Tipo: Tese