MARIANA XAVIER MILAGRE
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Artigo IPEN-doc 27829 Use of amperometric and potentiometric probes in scanning electrochemical microscopy for the spatially-resolved monitoring of severe localized corrosion sites on aluminum alloy 2098-T3512021 - SILVA, REJANE M.P. da; IZQUIERDO, JAVIER; MILAGRE, MARIANA X.; BETANCOR-ABREU, ABENCHARA M.; COSTA, ISOLDA; SOUTO, RICARDO M.Amperometric and potentiometric probes were employed for the detection and characterization of reactive sites on the 2098-T351 Al-alloy (AA2098-T351) using scanning electrochemical microscopy (SECM). Firstly, the probe of concept was performed on a model Mg-Al galvanic pair system using SECM in the amperometric and potentiometric operation modes, in order to address the responsiveness of the probes for the characterization of this galvanic pair system. Next, these sensing probes were employed to characterize the 2098-T351 alloy surface immersed in a saline aqueous solution at ambient temperature. The distribution of reactive sites and the local pH changes associated with severe localized corrosion (SLC) on the alloy surface were imaged and subsequently studied. Higher hydrogen evolution, lower oxygen depletion and acidification occurred at the SLC sites developed on the 2098-T351 Al-alloy.Artigo IPEN-doc 27391 Galvanic coupling effects on the corrosion behavior of the 6061 aluminum alloy used in research nuclear reactors2020 - 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, ISOLDAThe 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.Artigo IPEN-doc 27390 Effects of Picture Frame Technique (PFT) on the corrosion behavior of 6061 aluminum alloy2020 - MILAGRE, MARIANA X.; DONATUS, UYIME; MOGILI, NAGA V.; MACHADO, CARULINE S.C.; ARAUJO, JOAO V.S.; KLUMPP, RAFAEL E.; FERNANDES, STELA M.C.; SOUZA, JOSE A.B. de; COSTA, ISOLDAThe 6061 Al–Mg–Si alloy is used in nuclear fuel plates of nuclear research reactors which are fed with fuel in plate shapes. The production of these plates is based on the picture frame technique (PFT). The picture frame technique (PFT) is a manufacturing process for the fabrication of nuclear fuel plates where the nuclear fuel is encapsulated by Al alloy plates and thermomechanically processed to generate a set with reduced thickness. The effects of PFT on the corrosion resistance of the 6061 aluminum alloy were evaluated in this study by immersion and electrochemical tests in 0.005 mol L−1 NaCl solution. The results showed that the PFT fabrication process increases the corrosion resistance of the 6061 alloy in relation to the conventional 6061-T6, due phase dissolution and lower content of β’’ phase. Also, corrosion propagation gradually changes, with an increasing number of processing steps, from intergranular to intragranular corrosion attack.Artigo IPEN-doc 25203 Corrosion and anodizing behaviour of friction stir weldment of AA2198- T851 Al-Cu-Li alloy2018 - DONATUS, UYIME; FERREIRA, RAPHAEL O.; MOGILI, NAGA V.V.; VIVEIROS, BARBARA V.G. de; MILAGRE, MARIANA X.; COSTA, ISOLDAAnodizing behaviour of AA2198-T851 friction stir weldment and the corrosion behaviour of unpolished and polished weldments of the alloy have been investigated. Electrochemical and microscopic techniques were employed in the study. The results revealed that the manufacturing-process induced near-surface deformed layer significantly affected the corrosion behaviour of the weldment. Thus, the corrosion behaviour of the weldment in the polished condition (which is the common practice) was different from that of the unpolished one due to the presence of near-surface deformed layer. Anodizing as a corrosion protection method for the weldment caused the formation of pronounced non-uniform oxide layer thicknesses across the weld zones. This was because the weldment oxidized at a higher rate compared with the parent material (PM) due to an increased proportion of Li in solid solution in the stir zone of the weldment.