DSpace Communidade:http://repositorio.ufc.br/handle/riufc/4922026-06-12T04:47:32Z2026-06-12T04:47:32ZSynthesis and characterization of multi-spectral luminescent nanocrystals based on NaYF4 and NaGdF4Resquin, Lucas Santiago Medinahttp://repositorio.ufc.br/handle/riufc/865962026-06-03T17:25:34Z2026-01-01T00:00:00ZTítulo: Synthesis and characterization of multi-spectral luminescent nanocrystals based on NaYF4 and NaGdF4
Autor(es): Resquin, Lucas Santiago Medina
Abstract: Multispectral luminescent nanoparticles based on hexagonal-phase (β-) NaYF4 and NaGdF4 ma-
trices, doped with rare-earth (RE) ions (Yb3+
/Er3+
/Tm3+
/Eu3+
) and transition metals (Fe3+
/Mn2+
),
were successfully synthesized via the thermal decomposition method. The structural characteri-
zation by X-ray diffraction (XRD) confirmed the formation of highly crystalline, single-phase
hexagonal structures with lattice parameters consistent with the reference ICSD patterns. Fourier-
transform infrared (FTIR) spectroscopy verified the effective surface capping of the nanoparticles
with oleic acid (OA) ligands. The optical properties were evaluated using ultraviolet-visible
(UV-Vis) absorption and photoluminescence (PL) spectroscopy. Under near-infrared (976 nm)
excitation, efficient upconversion (UC) emission was observed, mediated by Yb3+
sensitization
and energy transfer to Er3+
/Tm3+
activators. Core@shell architectures exhibited a significant
enhancement in UC intensity compared to core-only structures, demonstrating the effectiveness
of the inert shell in suppressing surface-related quenching. Under ultraviolet (365 nm) excitation,
downconversion (DC) luminescence was dominated by characteristic emissions from Eu3+
, Er3+
,
and Tm3+
, with OA acting simultaneously as a surface ligand, sensitizer, and blue emitter. The
introduction of transition metals (5% Fe3+ or Mn2+
) into the core of NaGdF4-based nanoparticles
induced distinct modifications: Mn2+ doping enhanced the relative intensity of the (110) diffrac-
tion peak and promoted resonant energy transfer that intensified red emission from Er3+
. The
core@shell design effectively mitigated the non-radiative quenching typically associated with
Mn2+ doping in core-only systems. These findings demonstrate that transition-metal codoping,
combined with core@shell engineering, provides a viable route to tune energy-transfer pathways
and emission profiles in RE-doped nanostructures.
Tipo: Dissertação2026-01-01T00:00:00ZPrevisão computacional do teor de silício no ferro-gusaXavier, João Victor Barrosohttp://repositorio.ufc.br/handle/riufc/864092026-05-21T17:40:06Z2026-01-01T00:00:00ZTítulo: Previsão computacional do teor de silício no ferro-gusa
Autor(es): Xavier, João Victor Barroso
Abstract: The silicon content of pig iron is one of the main indicators of its quality and the thermal state of
the blast furnace. Furthermore, a high silicon content can damage industrial equipment, leading
to the need for maintenance and, consequently, a loss of process efficiency. For these reasons,
several studies have been developed over decades to predict and monitor the silicon content
in pig iron, suggesting the use of data-driven models. In this context, this work tested models
such as the logistic perceptron, multilayer perceptron artificial neural networks with up to two
hidden layers, and different versions of support vector machines adapted for regression (SVR,
TSVR, LSSVR) to predict the silicon content in pig iron. A technique for estimating the number
of hidden neurons in neural networks based on singular value decomposition (SVD) was also
investigated to reduce tuning time and computational cost. Among the neuron-based models,
the neural network with one hidden layer presented the best balance between performance and
computational cost, while the SVD-based technique provided a smaller hyperparameter testing
window, therefore, it was used in a sensitivity analysis to study the influence of each input
variable on the silicon content in pig iron.
Tipo: Dissertação2026-01-01T00:00:00ZAvaliação de aminoácidos como inibidores de corrosão para aço carbono AISI 1018 submetidos a meio contendo NaCl com e sem saturação de CO2Moura, Milena Jacinto da Silvahttp://repositorio.ufc.br/handle/riufc/863852026-05-19T20:14:34Z2024-01-01T00:00:00ZTítulo: 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: Tese2024-01-01T00:00:00ZDesenvolvimento do fio-máquina com o aço 1010 para produção de vergalhão CA60 em laminadores a frioGondim Júnior, Irannildo Walterhttp://repositorio.ufc.br/handle/riufc/859852026-04-24T02:19:52Z2025-01-01T00:00:00ZTítulo: Desenvolvimento do fio-máquina com o aço 1010 para produção de vergalhão CA60 em laminadores a frio
Autor(es): Gondim Júnior, Irannildo Walter
Abstract: Today's steel market is increasingly competitive, where every extra minute of production is a
huge gain in financial results. In 2022, a steel mill in Ceará used 5.5mm 1008 steel wire rod to
produce 3.40mm CA60 rebars and 5.5mm 1012 steel wire rod to produce 4.20mm CA60 rebars,
two different raw materials for two different products, However, these materials presented
opportunities, such as difficulties in meeting the property requirements of the Brazilian standard
ABNT NBR 7480, which sets out the minimum requirements for rebar, so there was a need to
develop a new technology for producing this material. The aim of this work is to develop a wire
rod in 1010 steel so that it is suitable for the hot rolling process and then the cold rolling process,
so that during the hardening process it achieves the desired properties, significantly reducing
the generation of non-conforming products, as well as having a single steel that would produce
both 3.40mm and 4.20mm CA60 rebar. This development was carried out by producing a pilot
batch of 30 tonnes of SAE 1010 steel, where three temperature values were tested during hot
rolling and then subjected to the hardening process (cold rolling), reducing its section to
4.20mm and 3.40mm. This material was validated by means of tensile tests carried out on a
calibrated machine using an extensometer, as well as characterising the material for each
temperature parameter by measuring its grain size, which is a determining factor for
characteristics such as the yield strength. The results showed that the higher the hot rolling
temperature, the larger the grain size, which consequently improves the values of the material's
elastic ratio, which is the breaking limit divided by the yield limit, a parameter that is normative
and which is very difficult to achieve using different steels, especially 1012, thus showing that
the hot rolling temperature is a determining factor for the cold rolling process, favouring the
achievement of the appropriate elastic ratio for the product
Tipo: Dissertação2025-01-01T00:00:00Z