MAURILIO PEREIRA GOMES
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Artigo IPEN-doc 29082 Improved experimental setup to reach a broad frequency domain in local electrochemical impedance spectroscopy measurements2022 - GOMES, MAURILIO P.; GATEMAN, SAMANTHA M.; COSTA, ISOLDA; GHARBI, OUMAIMA; NGO, KIEU; ROSSI, JESUALDO L.; TURMINE, MIREILLE; VIVIER, VINCENTWe report a new experimental setup enabling local electrochemical impedance spectroscopy (LEIS) measurements over a wide frequency range, including the low frequency domain. First, an improved signal treatment was performed using a potential shifter to minimize the DC component of the measured potential, allowing for the local AC potential to be probed using an ideal electrochemical system. Then, a unique, three-electrode LEIS probe was implemented to study the influence of radial and lateral contributions on the LEIS response. The radial LEIS response is highest when the LEIS probe is positioned in the middle of the gold electrode substrate, whereas the lateral LEIS response is similar in both measured regions. Both experimental modifications were implemented to study the LEIS response over a corroding aluminum substrate, for which reliable results are obtained in the low frequencies. These tools could be used in future LEIS studies in other fields that require time-sensitive measurements.Artigo IPEN-doc 29040 A new look on the corrosion mechanism of magnesium2022 - BENBOUZID, ABDELMOHEIMAN Z.; GOMES, MAURILIO P.; COSTA, ISOLDA; GHARBI, OUMAIMA; PEBERE, NADINE; ROSSI, JESUALDO L.; TRAN, MAI T.T.; TRIBOLLET, BERNARD; TURMINE, MIREILLE; VIVIER, VINCENTThis study investigates the electrochemical impedance diagrams obtained for a Mg electrode in a sodium sulphate solution at different pHs. A comprehensive model, independent of the pH range, with the presence of two adsorbed intermediates accounting for the anodic dissolution and the cathodic reaction was proposed to explain the singular behaviour of Mg at low pH values. It was also shown that, in acidic media, the contribution of the double layer as well as the cathodic partial reaction must be considered, whereas at higher pH values the oxide/hydroxide layer plays a significant role and slows down the magnesium corrosion rate.Tese IPEN-doc 19065 Investigation on the corrosion mechanisms of pure magnesium and the effect of friction stir welding (FSW) on the corrosion resistance of aluminum alloy 2524-T32021 - GOMES, MAURILIO P.Friction stir welding (FSW) is a process that has proven to be quite efficient when it comes to joining high-strength aluminum alloys, for instance AA2524-T3. This can be justified by the fact that welding aluminum alloys by FSW technique allows (i) reduction of aircraft weight by eliminating the rivets commonly used and (ii) the use of different aluminum alloys that have low specific density and high mechanical strength. However, even though FSW allows the joining of metallic parts without their effective fusion, which theoretically would result in a defect-free weld bead, the heat resulting from the friction of the welding tool causes significant microstructural changes. In consequence, it results in variations of mechanical properties and corrosion resistance in the welded region. It was evaluated the FSW welding process influence on the corrosion resistance of the joined 2524-T3 aluminum alloy. Different tools have been used, such as: optical and scanning electron microscopy; open circuit potential and electrochemical impedance spectroscopy measurements; and corrosion tests: agar-agar test, intergranular corrosion test, and exfoliation corrosion test. It was proven by different techniques that the thermomechanically/thermal affect zone interface on the retreating side was the most susceptible to corrosion among all investigated zones. A parallel study was developed regarding the corrosion mechanism of pure magnesium. It has been the subject of a considerable amount of work, and despite its ubiquity and history, it remains controversial. This is mainly due to the presence of the negative difference effect (NDE), which increases hydrogen formation when the magnesium is biased on the anodic domain. We was performed a detailed analysis of the electrochemical impedance spectra obtained for the Mg electrode during immersion in a sodium sulfate solution. A model was proposed which took into account the presence of: (i) a thin oxide film (MgO) which progressively covered the Mg electrode surface, (ii) film-free areas where the Mg dissolution occurs in two consecutive steps, (iii) a thick layer of corrosion products (Mg(OH)2), (iv) an adsorbed intermediate Mg+ads which is responsible for the chemical reaction allowing the NDE to be explained. From the impedance data analyses, various parameters were extracted such as the thin oxide film thickness, the resistivity at the metal/oxide film interface and at the oxide film/electrolyte interface, the active surface area as a function of the exposure time to the electrolyte, the thickness of the thick Mg(OH)2 layer and the kinetic constants of the electrochemical reactions.Capítulo IPEN-doc 28006 Simulação computacional de recristalização de grãos2020 - GOMES, MAURILIO P.; REIS, LUIS A.M. dos; BETINI, EVANDRO G.Um modelo de Monte Carlo bidimensional foi desenvolvido para simular a recristalização de grãos na presença de uma partícula circular imóvel para diferentes valores de energias armazenadas. Para energias armazenadas maiores que um valor crítico (H/J = 2,01) a propagação da recristalização pôde facilmente transpor a partícula imóvel, levando a uma densidade aleatória dos grãos e a uma influência insignificante da partícula imóvel na cinética da recristalização. Para energias armazenadas mais baixas (H/J = 0,1), a partícula imóvel limita a propagação da recristalização, levando à uma recristalização incompleta.