MARIANA XAVIER MILAGRE
3 resultados
Resultados de Busca
Agora exibindo 1 - 3 de 3
Resumo IPEN-doc 28893 A homemade electrochemical hanging droplet cell to evaluate the corrosion resistance of friction stir weld zones of the AA2198-T8 Al-Cu-Li alloy2021 - MACHADO, CARULINE de S.C.; HERNANDEZ, JOSE W.C.; MILAGRE, MARIANA X.; ARAUJO, JOAO V. de S.; DONATUS, UYIME; COSTA, ISOLDAIn this study, the corrosion resistance of the different zones of the AA2198-T8 alloy welded using friction stir welding (FSW) was investigated by immersion and electrochemical tests during exposure to 0.005 mol L-1 NaCl solution. After immersion tests, the welding zones were classified in two groups, according to their severe localized corrosion (SLC) morphology. Zones exposed to higher temperatures during welding presented intergranular attack, whereas those exposed to lower temperatures presented intragranular attack. Electrochemical measurements performed employing a homemade hanging droplet cell revealed potential galvanic coupling between the two groups. The base metal (BM) presented the most anodic potentials. The open circuit potential (OCP) increased from BM towards the stir zone (SZ). The results obtained by the hanging droplet cell were reproducible and coherent with the classification of the zones in the two proposed groups. The homemade electrochemical hanging droplet cell proved a very reliable tool to investigate the electrochemical behavior of the FSWed zones in Al-Cu-Li alloys.Resumo IPEN-doc 28449 Microelectrochemical evaluation of severe localized corrosion sites developing on third-generation aluminium alloys2021 - IZQUIERDO, J.; SILVA, R.M.P. da; MILAGRE, M.X.; COSTA, I.; BETANCOR-ABREU, A.M.; SOUTO, R.M.Third-generation aluminium-copper-lithium alloys exhibit attractive mechanical properties, in particular light-weight and significant strength. However, the developed microstructure often results in severe localized corrosion (SLC) sites with fast in-depth pit propagation accompanied by H2 evolution.1 Such phenomena stem from a strong galvanic coupling, mainly established between Fe- and Cu-rich particles and the surrounding matrix. As a result, strong concentration and pH gradients develop throughout the aluminium surface, determining the local breakdown of the passive regime eventually provided by aluminium oxides and corrosion products. Understanding the development of such distributions is key to outline appropriate strategies for the prevention of fast degradation and materials failure. Scanning Electrochemical Microscopy (SECM) and Scanning Vibrating Electrode Technique (SVET) are capable of providing local information on the distribution of active sites and the presence of reactive chemical species. SVET has previously demonstrated the formation of gas bubbles ascribed to hydrogen evolution (i.e., electro-reduction process) at the anodically-activated sites,2,3; whereas local hydrogen production, oxygen consumption and pH changes are readily accessible using SECM, although with some limitations with regards to the detection of evolving gas.4 The present contribution reports recent advances in the investigation of local degradation phenomena occurring at the surface of Al-Cu-Li alloy AA-2098, as bare material and after friction stir welding. Oxygen consumption over nobler particles acting as cathodic sites, and SLC accompanied with strong acidification and H2 production at the local anodes were observed. The determined pH and concentration gradients allow to progress in the knowledge of the mechanistic aspects involved in the degradation processes on these materials.Resumo IPEN-doc 26824 Influence of surface finishing on the electrochemical activity of the 2098-T351 aluminum alloy2019 - SILVA, REJANE; MILAGRE, MARIANA; OLIVEIRA, LEANDRO; ANTUNES, RENATO; DONATUS, UYIME; COSTA, ISOLDAIn this work, scanning electrochemical microscopy (SECM) measurements were employed to characterize the electrochemical activities of polished and as-received surfaces of the 2098-T351 aluminum alloy (AA2098-T351). The effects of the near surface deformed layer (NSDL) and its removal by polishing on the electrochemical activities of the alloy surface were evaluated and compared by the use of different modes of SECM. Confocal Laser Scanning Microscopy (CLSM) and energy dispersive X-ray spectroscopy (EDS) were also employed to characterize the morphology of the surfaces. The surface chemistry was analyzed by X-ray Photoelectron Spectroscopy (XPS). The generation/tip collection (SG/TC) and competition modes of the SECM were used to study hydrogen gas (H2) evolution and oxygen reduction reactions, respectively. H2 evolution and oxygen reduction were more pronounced on the polished surface compared to the asreceived surface that revealed lower electrochemical activities showing that either the NSDL largely decreased the local electrochemical activities at the AA2098-T351 surface.