REJANE MARIA PEREIRA DA SILVA

REJANE MARIA PEREIRA DA SILVA

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S-doped ZnO photoelectrode modified with silver and platinum nanoparticles and their photocatalytic activity for progesterone degradation
2024 - LUIS, JAILSON S.; EDUARDO, SAMUEL S.; COSTA, MARIA J.S.; BRANDAO-LIMA, LUCIANO C.; ANTUNES, RENATO A.; FERREIRA, RAPHAEL O.; SILVA, REJANE M.P.; SANTOS, REGINALDO S.
Zinc oxide doped with sulfur (ZnO-S) has presented improved photocatalytic activity under visible irradiation. In this work, ZnO-S film was efficiently prepared by thermal decomposition from zinc sulfide (ZnS) in an oxidizing atmosphere. X-ray diffraction analysis (XRD) showed ZnS phase transformation occurred from cubic sphalerite to ZnO hexagonal wurtzite at temperatures between 500 and 600 °C. ZnO-S electrodes prepared onto a transparent conductive substrate were modified by silver (Ag0) or platinum (Pt0) nanoparticles (NPs). X-ray photoelectron spectroscopy (XPS) confirmed that sulfur was incorporated into ZnO structure. Field Emission Gun-Scanning Electron Microscope (FEG-SEM) images showed that occur a drastic modification in the particle morphology of the films treated at distinct temperatures. Photoelectrochemical investigation displayed a negative photopotential (∆E<0) for all photoelectrode investigated as well as superior photocurrents for samples modified with metallic Ag0 and Pt0 NPs. In order to investigate the photoelectroactivity, ZnO-S6, Ag0/ZnO-S6, Pt0/ZnO-S6 and commercial ZnO electrodes were used to degrade progesterone solution under polychromatic irradiation. The superior performances were observed for ZnO-S films functionalized with Ag0 or Pt0. Therefore, the results showed advances in the degradation of organic contaminants in the water treatment process and possible contributions to a better use of solar radiation.
Crystalline S-doped TiO2 photoanodes from amorphous titanium oxysulfide (TiOxSy) for photo-oxidation reactions
2023 - PITOMBEIRA, DANIEL R.S.; COSTA, MARIA J.S.; ANTUNES, RENATO A.; FERREIRA, RAPHAEL O.; SILVA, REJANE M.P.; SANTOS, REGINALDO S.
S-doped TiO2 films were prepared by oxidation annealing of amorphous titanium oxysulfide (TiOxSy) at different temperatures. According to the X-ray diffraction patterns, the films calcined at temperatures of 300–600 ◦C showed only anatase phase, while the uncalcined sample was amorphous. The chemical composition of synthesized TiOxSy was estimated by X-ray photoelectron spectroscopy (XPS). High-resolution S 2p spectra showed S􀀀 2 bonds at 163.47 eV for the amorphous sample. The intensity of this signal decreased after heat treatment. Raman spectroscopy indicated an organization of the material structure with heat treatment of the material. Furthermore, optical characterization revealed that sulfur as dopant into the anatase TiO2 structure, shifted light absorption from ultraviolet to the visible region. Photoeletrochemical studies developed under polychromatic irradiation revealed superior photocurrents for samples calcined at 600 ◦C, with n-type behavior, adequate for photo-oxidation reactions.
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.
Investigação da atividade eletroquímica de liga Al-Cu-Li após processo de soldagem por fricção e mistura
2023 - SILVA, REJANE M.P. da; MILAGRE, MARIANA X.; ARAUJO, JOAO V. de S.; RAMIREZ, OSCAR M.P.; MACHADO, CARULINE de S.C.; ANTUNES, RENATO A.; COSTA, ISOLDA
In this work, the local electrochemical activity of the zones coupled by Friction Stir Welding (FSW) of an Al-Cu-Li alloy was studied and the results were correlated to the microstructural characteristics of each zone. Electrochemical studies were carried out in the zones affected by welding using cyclic voltammetry (CV) and scanning electrochemical techniques (namely, SECM - Scanning Electrochemical Microscopy and LEIS – Local electrochemical impedance spectroscopy). The results showed that the welding joint (WJ) is predominantly cathodic relatively to the heat affected zones (HAZ). The HAZ was always anodic and showed the highest electrochemical activities among the tested ones. The high electrochemical activity of the HAZ was associated with the effect of galvanic coupling between the cathodic region (WJ) and the anodic region (HAZ). In addition, the advancing side (AS) presented increased electrochemical activity compared to the retreating one (RS).
Naphthenic corrosion using electrochemical and analytical techniques
2022 - SIMOES, A.M.P.; SILVA, R.M.P.; SUFFREDINI, H.B.; SANTOS, L.F.; BASTOS, I.N.
Naphthenic acid corrosion of steel was studied in a stagnant, biphasic oil/aqueous phase system, by means of electrochemical measurements and surface analysis. Corrosion was restricted to 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. In-situ electrochemical impedance spectroscopy (EIS) reveals the processes occurring at the aqueous phase, which nevertheless increase with the fraction of oil phase and with degree of acidity of the oil.
A new methodology in scanning electrochemical microscopy
2022 - BOLSANELLO, M.F.; PEREZ, J.I.; SILVA, R.M.; SOUTO, R.M.; ROSSI, J.L.
Among the electrochemical tests under development, scanning electrochemical microscopy (SECM) stands out for allowing the investigation of corrosive processes in situ, since it is capable of providing information with high spatial resolution on a small scale, in addition to allowing the direct identification of electrochemical species involved in the ongoing corrosive processes. In the study of automotive steel sheets coated with metallic alloys, a crucial region under the action of corrosive agents is the cross-sectional area. In this work, a new methodology for measures in spatial resolution at the SECM is presented. The applicability of this technique was demonstrated considering the corrosion behavior of a steel sheet coated with zinc, aluminum and magnesium alloy. Samples of this material were prepared according to this new methodology. Maps of pH variation, hydrogen evolution and oxygen distribution were obtained in the cross section area, in different electrolytes. With the acquisition of these results, it was possible to certify the applicability of this method in the study of coated metallic materials, as well as its potential to generate valuable contributions regarding the influence of the coating / substrate ratio on the electrochemical response of these materials.
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.
Corrosion behaviour of the 2098-T351 Al–Cu–Li alloy after different surface treatments
2022 - BARBOZA, WANESSA das G.; MILAGRE, MARIANA X.; DONATUS, UYIME; MACHADO, CARULINE de S.C.; RAMIREZ, OSCAR M.P.; ARAUJO, JOAO V. de S.; SILVA, REJANE M.P. da; COSTA, ISOLDA
The effect of different surface treatments on the corrosion resistance of the AA2098 Al–Cu–Li alloy has been investigated. Surface characterization was performed using 3D optical profilometry, energy dispersive X-ray spectroscopy and scanning electron microscopy. The corrosion resistance of the 2098 alloy after the surface treatments was investigated in 0.1 mol L−1 NaCl solution by electrochemical techniques and microscopy. Corrosion results showed that the untreated and the chemically etched surfaces were more active than the mechanically abraded and mechanically polished surfaces owing to differences in the nature of the native oxides formed after the surface treatments. Corrosion rate and mode were also affected by how close the exposed surface was to the mid-thickness region of the AA2098-T351 plate relative to the actual top surface (before polishing). This is associated with the variation in the volume fraction and distribution of the T1 phase as the mid-thickness region of the AA2098-T351 plate is approached.