REJANE MARIA PEREIRA DA SILVA

REJANE MARIA PEREIRA DA SILVA

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Welding and galvanic coupling effects on the electrochemical activity of dissimilar AA2050 and AA7050 aluminum alloys welded by Friction Stir Welding (FSW)
2023 - VIVEIROS, BARBARA V.G. de; SILVA, REJANE MARIA P. da; DONATUS, UYIME; COSTA, ISOLDA
In this work, the effects of friction stir welding (FSW) on the microstructure and electrochemical activities of dissimilar AA2050 and AA7050 aluminum alloys have been investigated. Local electrochemical tests supported by surface analytical characterization were used to study the local electrochemical activities developed along the weld zones of the dissimilar alloys. The investigation was carried out on the cross-section of the welded Al alloys. The results showed that the friction stir welding (FSW) of the dissimilar alloys affected the microstructure and the electrochemical behavior of the different regions (HAZ, TMAZ, SZ) formed by the welding process. Scanning vibrating electrode technique (SVET) and micropotentiometry by using an ion-selective microelectrode showed that TMAZ was the zone with the highest electrochemical activity. This zone corresponded to the transition region between the two welded alloys. The high electrochemical activity observed in this region was associated with the effect of welding on the microstructure and, also, with the galvanic coupling between the two alloys, where the alloy AA7050 acted as an anode and the AA2050 as a cathode. Preferential corrosion attack on the AA7050 alloy was also evident.
Investigating local corrosion processes of magnesium alloys with scanning probe electrochemical techniques
2022 - OLIVEIRA, MARA C.L. de; SILVA, REJANE M.P. da; SOUTO, RICARDO M.; ANTUNES, RENATO A.
The study of corrosion of magnesium and its alloys has emerged a hot topic in the applications of lightweight structural materials. The inherently high electrochemical activity of bare magnesium surfaces still lacks a convincing mechanism to describe the observed experimental characteristics, and it has prompted the development of various types of protective coatings with the aim of slowing metal dissolution. In recent years, new instruments and techniques have been developed to study with spatial resolution the local corrosion processes that occur in metallic materials in general, and for magnesium and its alloys in particular, both for bare surfaces and coated. Scanning microelectrochemical techniques, such as local electrochemical impedance spectroscopy (LEIS), scanning electrochemical microscopy (SECM), scanning vibrating electrode technique (SVET), scanning ion-selective electrode technique (SIET) and scanning Kelvin probe (SKP) can provide information about the local electrochemical activity of metallic surfaces. In the present work, the applications of these techniques in corrosion studies of magnesium and its alloys are reviewed. Assessment of corrosion mechanisms, barrier properties of conventional coatings and active corrosion behavior of self-healing coatings are examined. Limitations and future developments in this area are discussed.
Surface finishing effects on the corrosion behavior and electrochemical activity of 2098-T351 aluminum alloy investigated using scanning microelectrochemical techniques
2022 - SILVA, REJANE M.P. da; MILAGRE, MARIANA X.; IZQUIERDO, JAVIER; BETANCOR-ABREU, ABENCHARA M.; OLIVEIRA, LEANDRO A. de; ARAUJO, JOAO V. de S.; ANTUNES, RENATO A.; SOUTO, RICARDO M.; COSTA, ISOLDA
The effects of surface finishing on the corrosion behavior and electrochemical activity of AA2098-T351 (Al–Cu–Li alloy) were investigated on the basis of the correlation between surface chemistry, microstructure and electrochemical activity. The alloy was evaluated in the as-received and polished conditions. The morphology of the two types of surfaces was investigated using confocal laser scanning microscopy (CLSM), optical microscopy and optical 3D profilometry. The surface chemistry was analyzed by X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray spectroscopy (EDX). Scanning microelectrochemical techniques (namely, localized electrochemical impedance spectroscopy (LEIS), the scanning vibrating electrode technique (SVET) and scanning electrochemical microscopy (SECM) in potentiometric mode) were used to examine the electrochemical activity of the surfaces. The results showed that on the as-received surface, the near surface deformed layer (NSDL), which is composed of Mg-rich bands, influenced the corrosion activity of the alloy. Higher electrochemical activity and greater susceptibility to severe localized corrosion were related to the polished surface condition compared to the as-received one.
Electrochemical characterization of alloy segregation in the near-surface deformed layer of welded zones of an Al-Cu-Li alloy using scanning electrochemical microscopy
2022 - SILVA, REJANE M.P. da; IZQUIERDO, JAVIER; MILAGRE, MARIANA X.; ARAUJO, JOAO V. de S.; ANTUNES, RENATO A.; SOUTO, RICARDO M.; COSTA, ISOLDA
The development of heterogeneous electrochemical activity in the welded zones of aluminum alloy 2098-T351 by friction stir welding (FSW) associated with the formation of a near-surface deformed layer (NSDL) upon exposure to an aqueous chloride-containing solution was characterized using scanning electrochemical microscopy (SECM) in potentiometric operation. A solid-contact Mg2+ ion-selective microelectrode allowed in situ monitoring of the corrosion reactions sites for magnesium dissolution from different zones of the FSW weld upon exposure to a chloride-containing aqueous environment. In this way, localized corrosion reactions developing in the galvanically coupled joint/heat affected zones (WJ/HAZ) of the weld were detected and imaged with spatial resolution. The most active domains for local Mg2+ concentrations were associated with the HAZ of the retreating side (RS), and these corresponded to Mg oxidation from the Mg-enriched oxide bands in NSDL.
Development of an Al3+ ion-selective microelectrode for the potentiometric microelectrochemical monitoring of corrosion sites on 2098-T351 aluminum alloy surfaces
2022 - SILVA, REJANE M.P. da; IZQUIERDO, JAVIER; MILAGRE, MARIANA X.; ANTUNES, RENATO A.; SOUTO, RICARDO M.; COSTA, ISOLDA
A novel potentiometric Al3+−ion selective microelectrode (ISME), with internal solid contact, based on the use of a neutral carrier morin as ionophore is reported. The ability of the ISME to image local ion concentration distributions was tested on aluminum alloy surfaces freely corroding in an aqueous solution containing chloride ions. The microelectrode was then used as the sensing tip for scanning electrochemical microscopy (SECM) in potentiometric operation to monitor the reactive sites associated with the dissolution of aluminum that developed in the 2098−T351 Al−Cu−Li alloy as a result of welding by the Friction Stir Welding (FSW) process. The ISME detected differences in the local concentrations of Al3+ species arising from the 2098−T351 Al−Cu−Li alloy (base material) and from the coupled weld joint/heat affected zones (WJ/HAZ) of the alloy produced by the FSW process. More active domains for Al3+ dissolution were found in the HAZ regions coupled to WJ, more specially in the HAZ of the advancing side (AS). These results demonstrate that the Al3+−ISME presented in this work can be used to monitor corrosion sites on aluminum alloys surfaces with combined chemical and spatial resolution.
Naphthenic acid corrosion of API 5L X70 steel in aqueous/oil environment using electrochemical surface-resolved and analytical techniques
2022 - SILVA, REJANE M.P.; SUFFREDINI, HUGO B.; BASTOS, IVAN N.; SANTOS, LUIS F.; SIMOES, ALDA M.P.
Naphthenic acid corrosion of steel is studied in crude oil/aqueous phase system at ambient temperature, using a biphasic stagnant liquid without emulsification, by means of electrochemical measurements and surface analysis. The in-situ electrochemical impedance is assigned to the processes occurring at the aqueous phase. Corrosion occurred only in the region of the aqueous phase, as crater-shaped pits that eventually coalesced, generating a nearly uniform attack in the vicinity of the oil phase. The impedance values, normalized to the aqueous region only, reveal corrosion rate increasing with the ratio of crude oil/water. Despite the localized character of the anodic oxidation, the iron naphthenate corrosion products became partitioned between the two phases. Surface-resolved electrochemical techniques in aqueous solution revealed enhanced activity of the regions pre-exposed to oil.
On the local corrosion behavior of coupled welded zones of the 2098-T351 Al-Cu-Li alloy produced by Friction Stir Welding (FSW)
2021 - SILVA, REJANE M.P. da; IZQUIERDO, JAVIER; MILAGRE, MARIANA X.; BETANCOR-ABREU, ABENCHARA M.; OLIVEIRA, LEANDRO A. de; ANTUNES, RENATO A.; SOUTO, RICARDO M.; COSTA, ISOLDA
Localized electrochemical methods supported by surface analytical characterizations were employed to investigate galvanic coupling effects and local electrochemical activity developed along the welded zones in Friction Stir Welded 2098-T351 Al-Cu-Li alloy. The investigation was carried out in the coupled weld joint/heat affected zones (WJ/HAZ) for both, the retreating (RS) and the advancing (AS) sides. The correlation between the surface chemistry, the microstructural characteristics and the electrochemical activity of these welded areas was studied. The results showed the development of galvanic interactions within and between the WJ and HAZ regions, which were imaged using the scanning vibrating electrode technique (SVET), and scanning electrochemical microscopy (SECM). SVET analyses showed that HAZ was more susceptible to the development of anodic sites than WJ. SECM in amperometric operation mode showed that WJ coupled to HAZ exhibited higher oxygen consumption and higher cathodic activity compared to HAZ. Furthermore, SECM in potentiometric operation showed alkalinization around WJ and increased acidity in HAZ, mainly at sites of severe localized corrosion (SLC). Based on the SVET and SECM results in combination with the surface analyses, it is proposed that the microgalvanic cells formed within these welded zones are due to the presence of secondary phases in the 2098-T351 alloy and their interactions with the adjacent matrix.
Surface chemistry, film morphology, local electrochemical behavior and cytotoxic response of anodized AZ31B magnesium alloy
2020 - OLIVEIRA, LEANDRO A. de; SILVA, REJANE M.P. da; RODAS, ANDREA C.D.; SOUTO, RICARDO M.; ANTUNES, RENATO A.
This work investigates the effect of current density on the surface chemistry, film morphology, cytotoxic response, global and local electrochemical behaviors of AZ31B alloy anodized in 1.0 M NaOH + 0.5 M Na2SiO3 solution. Three different current densities, namely 5, 10 and 20 mA cm−2 were tested. The surface morphology and thickness of the anodized layers were examined by scanning electron microscopy. The surface chemical states were assessed by X-ray photoelectron spectroscopy. The corrosion resistance was evaluated in phosphate-buffered saline (PBS) based on electrochemical impedance spectroscopy and potentiodynamic polarization measurements. The use of scanning probe techniques with physicochemical resolution, the scanning electrochemical microscopy (SECM) and the scanning Kelvin probe (SKP), allowed the best corrosion behavior to be assigned to the sample anodized using a current density of 20 mA cm−2. Altogether, these methods allowed to establish that the anodizing current density imposed to the magnesium alloy had a major effect on the morphology and composition of the surface layers, and produced changes in their electrochemical behavior. In vitro cytotoxicity tests using the MTS assay demonstrated that the good biocompatibility of the AZ31B magnesium alloy was not damaged by the surface layers formed during the anodization treatment.
Galvanic and asymmetry effects on the local electrochemical behavior of the 2098-T351 alloy welded by friction stir welding
2020 - MILAGRE, MARIANA X.; DONATUS, UYIME; MOGILI, NAGA V.; SILVA, REJANE M.P.; VIVEIROS, BARBARA V.G. de; PEREIRA, VICTOR F.; ANTUNES, RENATO A.; MACHADO, CARULINE S.C.; ARAUJO, JOAO V.S.; COSTA, ISOLDA
Scanning electrochemical microscopy (SECM) and scanning vibrating electrode technique (SVET) were used to investigate the electrochemical behaviour of the top surface of the 2098-T351 alloy welded by friction stir welding (FSW). The SVET technique was efficient in identifying the cathodic and anodic weld regions. The welding joint (WJ), which comprises the thermomechanically affected zone (TMAZ) and the stir zone (SZ), was cathodic relative to the heated affected zone (HAZ) and the base metal (BM). The reactivities of the welding joint at the advancing side (AS) and the retreating side (RS) were analyzed and compared using SECM technique in the competition mode by monitoring the dissolved oxygen as a redox mediator in 0.005 mol L−1 NaCl solution. The RS was more electrochemically active than the AS, and these results were correlated with the microstructural features of the welded alloy.
Macro and microgalvanic interactions in friction stir weldment of AA2198-T851 alloy
2019 - DONATUS, UYIME; SILVA, REJANE M.P. da; ARAUJO, JOAO V. de S.; MILAGRE, MARIANA X.; ABREU, CAIO P. de; MACHADO, CARULINE de S.C.; COSTA, ISOLDA
The galvanic interactions within and between the friction stir weld zones of the AA2198-T851alloy have been investigated using electrochemical and microscopy techniques. The parentmaterial (PM) was the most anodic region and exhibited pronounced severe localized corro-sion (SLC) both when coupled and isolated. The stir zone was the most resistant to corrosionand exhibited no SLC when coupled, but exhibited SLC when isolated. Profiles associatedwith dissolved oxygen consumption and hydrogen generation currents across the weldmentwere inversely related because the anodic (PM) region produced higher hydrogen bubblesand, interestingly, consumed more dissolved oxygen compared with the other regions.