REJANE MARIA PEREIRA DA SILVA

REJANE MARIA PEREIRA DA SILVA

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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.
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.
Influence of chloride ions concentration on the development of severe localised corrosion and its effects on the electrochemical response of the 2198-T8 alloy
2021 - MACHADO, CARULINE de S.C.; SILVA, REJANE M.P. da; ARAUJO, JOAO V. de S.; MILAGRE, MARIANA X.; DONATUS, UYIME; VIVEIROS, BARBARA V.G. de; KLUMPP, RAFAEL E.; COSTA, ISOLDA
The development of severe localised corrosion (SLC) on the 2198-T8 alloy was investigated in solutions of various NaCl concentrations (0.001, 0.005 and 0.01 mol L−1). Immersion tests, optical profilometry, conventional and local electrochemical analyses were performed to evaluate the corrosion behaviour of the alloy. Immersion tests showed that the alloy is susceptible to SLC in all conditions, although the pits sizes were dependent on the solution concentration. The largest anodic areas, corresponding to SLC sites, were observed for the sample immersed in 0.001 mol L−1 NaCl, whereas pits with similar sizes were observed for the samples immersed in solutions with 0.005 and 0.01 mol L−1 of NaCl. Moreover, the maximum depth of attack was observed for the sample immersed in 0.001 mol L−1 NaCl. These results were in agreement with the scanning ionselective electrode technique (SIET) maps which showed stronger acidification on the sample exposed to 0.001 mol L−1 NaCl solution.
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 coupling effects on the corrosion behavior of the 6061 aluminum alloy used in research nuclear reactors
2020 - MILAGRE, MARIANA X.; DONATUS, UYIME; SILVA, REJANE M.P.; BETANCOR-ABREU, ABENCHARA M.; RAMIREZ, OSCAR M.P.; MACHADO, CARULINE S.C.; ARAUJO, JOAO V.S.; SOUTO, RICARDO M.; COSTA, ISOLDA
The 6061 alloy is used in different thermomechanical conditions in research nuclear reactors. Nuclear fuel plates are manufactured by the picture frame technique (PFT) and the 6061 alloy is used as cladding for the nuclear fuel “sandwiches”. After the PFT process, these nuclear plates are placed in a case made of 6061-T6 alloy. In this work, the galvanic effects of coupling the 6061 alloy in the T6 and PFT temper conditions were investigated in different chloride-containing solutions. The results showed that galvanic coupling was favored between the PFT and 6061-T6 alloy. A potential difference of about 50 mV was observed between the temper conditions. This was attributed to differences in β’’ phase density between the two conditions (T6 and PFT) which was indicated by microhardness results. The 6061 alloy in the PFT condition was cathodic in relation to the T6 one. Results from conventional electrochemical techniques were in agreement with the local measurements. Local electrochemical techniques such as the SVET, SECM and LEIS were useful in characterizing the electrochemical behavior of the galvanically coupled alloys.
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.