Programa de Pós-Graduação em Química - PPGQ/ICEN
URI Permanente desta comunidadehttps://repositorio.ufpa.br/handle/2011/4046
O Programa de Pós-Graduação em Química (PPGQ) do Instituto de Ciências Exatas e Naturais (ICEN) da Universidade Federal do Pará (UFPA). Oferece oportunidade para a formação de Mestres e Doutores nas áreas de Química Orgânica, Físico-Química, Inorgânica e Analítica.
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Item Acesso aberto (Open Access) Influência do ph do banho e da densidade de corrente no comportamento capacitivo de eletrodos de mno2 obtidos por eletrodeposição anódica(Universidade Federal do Pará, 2025-01-30) RENTE, Arthur de Farias Silva; NOCE, Rodrigo Della; http://lattes.cnpq.br/3734170057844016MnO₂ electrodes are obtained by anodic electrodeposition on stainless steel substrate at room temperature from a 0.1 M manganese sulfate bath, under different current densities, ranging from 200 µA·cm⁻² to 5 mA·cm⁻² (galvanostatic mode), and pH values from 2 to 6. The material morphology is analyzed by scanning electron microscopy, revealing compact, homogeneous, and two-dimensional film deposition, with the presence of microcracks that provide active sites for the incorporation of sodium sulfate (Na₂SO₄) electrolyte ions, enhancing the material's specific capacitance. At low current densities, such as 200 and 500 µA·cm⁻², the formed film is homogeneous, while increasing the current density to 2 mA·cm⁻² results in cracks on the material's surface. Morphological changes are also identified as a function of pH: near neutrality (pH 6), cracks become evident, whereas in more acidic pH levels, such as 2 and 3, the structure remains uniform. At pH 4, an irregular structure is observed. The structure of the formed films, analyzed by by X-ray diffraction, reveals the presence of the alpha (α) phase under all studied conditions, regardless of the applied current density and bath pH. Electrochemical characterization of the films, carried out using cyclic voltammetry and charge-discharge curves (chronopotentiometry), indicates a working potential window of 1.1 V and specific capacitance values ranging from 13 to 371.8 F·g⁻¹, depending on the applied current density and bath pH. The highest specific capacitance value is obtained at a current density of 2 mA·cm⁻² and pH 4.Item Acesso aberto (Open Access) Obtenção de filmes finos de ligas de alta entropia à base de CoFeNi por eletrodeposição em meio aquoso(Universidade Federal do Pará, 2025-04-25) FREITAS, Gregório Felipe do Nascimento; NOCE, Rodrigo Della; http://lattes.cnpq.br/3734170057844016High-entropy alloys, also called multicomponent alloys, are alloys that have five or more elements whose composition is formed between 5% and 35% in terms of atomic composition of the elements. These alloys have gained prominence recently because they present very distinct and attractive properties in relation to conventional alloys composed of a single major element. In this context, the alloys have been produced by different physical and chemical methods. The present work addresses the subject of obtaining thin films of high-entropy alloys based on CoFeNi by the electrodeposition technique in aqueous medium, with additions of elements such as Mo, Mn, Sn and W. A simple and low-cost technique in relation to other methods proposed in the literature. By using the direct current (galvanostatic) method at room temperature and by varying the current density to obtain thin films in a range of 5 to 100 mA/cm2, the high entropy alloy CoFeNiMoW and the possibility of obtaining the CoFeNiMnSn alloy on a brass substrate (CuZn) are demonstrated. The electrodeposited films are characterized by Energy Dispersive Spectroscopy (EDS), Scanning Electron Microscopy (SEM), X-ray Diffractometry (XRD) and Mossbauer Spectroscopy techniques. EDS analyses reveal that the composition of the alloys is strongly influenced by the applied current density. In the high entropy alloy with five elements CoFeNiMoW formed from applied current density of 50 mA cm-2, the atomic proportion obtained is Co 30%, Fe 21%, Ni 19%, Mo 25%, W 5%. For the CoFeNiMnSn alloy, its composition formed by means of a current density equal to 50 mA cm-2 is Co 26.2%, Fe 33.8%, Ni 5.5%, Mn 1.8%, Sn 32.6%, thus evidencing the formation of alloys with five elements by the proposed method.