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.Artigo IPEN-doc 25807 On the corrosion mechanism of Mg investigated by electrochemical impedance spectroscopy2019 - GOMES, MAURILIO P.; COSTA, ISOLDA; PEBERE, NADINE; ROSSI, JESUALDO L.; TRIBOLLET, BERNARD; VIVIER, VINCENTThis work reported 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 ðMgþ ads Þ which is responsible for the chemical reaction allowing the negative difference effect to be explained. From the impedance data analysis, 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 reaction.