OLANDIR VERCINO CORREA

OLANDIR VERCINO CORREA

Página do item completo

Resultados de Busca

Agora exibindo 1 - 10 de 24

Avaliação eletroquímica da liga Ti6Al4V produzida por manufatura aditiva
2023 - PIERETTI, E.F.; CORREA, O.V.; SILVA, L.C.E. da; PILLIS, M.F.; RIBEIRO, M.S.; ROSSI, W. de; NEVES, M.D.M.
O aprimoramento de propriedades de superfície é uma exigência para osbiomateriais. O objetivo deste trabalho foi investigar a resistência à corrosãode amostras da liga Ti6Al4V produzidas por manufatura aditiva, em solução deRinger, que simula os fluidos corpóreos. As amostras foram produzidas alterando-se alguns parâmetros do processo. A resistência à corrosão foi avaliadautilizando-se métodos eletroquímicos como: monitoramento de potencial decircuito aberto, medições de espectroscopia de impedância eletroquímica epolarização cíclica e análises de superfície por MEV. Algumas amostras forammais susceptíveis à corrosão, pois a alternância de parâmetros do processo defabricação produz superfícies distintas com acabamento superficialdiversificado, resultando em comportamentos diversos.
Síntese de alumina anódica nanoporosa em liga de Alumínio AA 1050
2019 - OLIVEIRA, L.S.; CORREA, O.V.; BENTO, R.T.; PILLIS, M.F.
Nos últimos anos, alumina anódica porosa tem atraído interesse devido ao arranjo regular dos nanoporos, à possibilidade de controle de seu diâmetro, e grande área de superfície específica. Neste trabalho foram obtidas estruturas de alumina anódica porosa por meio da anodização em duas etapas de uma liga de alumínio AA 1050 em eletrólito de H2SO4. As amostras foram anodizadas durante 4 e 8 h. A técnica de microscopia eletrônica de varredura com canhão de emissão de elétrons foi utilizada para a avaliação morfológica da superfície. Os nanoporos formados após 4h de anodização apresentaram distribuição homogênea na superfície da liga e diâmetro médio de 25 nm, enquanto que após 8h de anodização os nanoporos apresentaram-se com formato irregular e distribuição não homogênea.
Hydrotalcite coatings to protect spent sluminum-clad nuclear fuels during long term wet storage
2015 - FERNANDES, S.M.C.; CORREA, O.V.; SOUZA, J.A. de; ANTUNES, R.A.; OLIVEIRA, M.C.L. de; RAMANATHAN, L.V.
Pitting corrosion of the aluminium cladding of spent research reactor (RR) fuels in wet storage has been reported and attributed to synergistic influence of certain water parameters. Hence, use of conversion coatings to protect spent Al-clad RR fuel during long term wet storage was proposed. The objective was to develop a coating using a conventional chemical process as opposed to an electrochemical process due to constraints related to the shape of the fuel and its high radioactivity. In this context hydrotalcite (HTC) and boehmite were considered. This paper presents: (a) preparation of boehmite and hydrotalcite (HTC) coatings from different baths followed by post-coating treatments; (b) corrosion behavior of coated AA 6061 alloy; (c) results of field studies in which uncoated and coated AA 6061 alloy coupons and plates, the latter assembled as a dummy fuel element, were exposed to the IEA-R1 reactor spent fuel basin for periods of up to 14 months. The laboratory tests revealed marked increase in corrosion resistance of HTC coated specimens. In field tests the HTC coated coupons and plates did not reveal any pits. The mechanism of corrosion protection is presented.
Preparation and characterization of hydrotalcite coatings to protect aluminium alloys
2016 - FERNANDES, S.M.C.; CORREA, O.V.; SOUZA, J.A.; ANTUNES, R.A.; LIMA, N.B. de; RAMANATHAN, L.V.
Pitting corrosion of the aluminium alloy cladding of spent research reactor fuels during wet storage is the main form of degradation. To prevent this, hydrotalcite (HTC) based coatings were proposed. This paper presents the effect of chemical bath parameters on the microstructure of HTC coatings and the corrosion behavior of HTC coated AA 6061 specimens. The HTC coating formed at 98 °C from nitrate baths and referred to as HT-HTC was homogeneous and consisted of intersecting blade-like crystallites. Electrochemical tests revealed that HT-HTC coated specimens that were treated in a cerium salt solution were the most resistant to corrosion. Field tests in which un-coated and HTC coated AA 6061 alloy coupons as well as full-size plates were exposed to the IEA-R1 reactor’s spent fuel basin for 23 months corroborated the high corrosion resistance imparted by the HT-HTC + Ce coating. The mechanism by which the HTC coating and cerium protect the Al alloy is discussed.
Effect of nanocrystalline mixed rare earth oxide coatings on the high temperature oxidation behavior of Fe20Cr5Al alloy
2014 - FERNANDES, STELA M.C.; CORREA, OLANDIR V.; RAMANATHAN, LALGUDI V.
Rare earths (RE) have been used to improve high temperature oxidation resistance of chromium dioxide and alumina forming alloys. The RE can be added to the alloy as elements or as oxide to form dispersions. It can also be applied as a RE oxide coating to the surface of the alloy. In this investigation the sol-gel technique was used to prepare sols of the RE oxides as it produces nanocrystalline oxide particles. In an effort to increase further the oxidation resistance of high temperature alloys, optimization of RE oxide additions to the alloy surface has been attempted. This paper presents the effect of nanocrystalline oxide gel coatings of CeO2, Nd2O3, Pr2O3, CeO2 + Nd2O3, CeO2 + Pr2O3 and Pr2O3 + Nd2O3 on the oxidation behavior of Fe20Cr5Al alloys at 1100 °C. The individual oxides decreased oxidation rate. However, the CeO2 + Nd2O3 mixture did not increase oxidation resistance of the alloy further, compared to those with either one of these two rare earth oxides. The Pr2O3 + CeO2 mixture increased oxidation resistance of the alloy markedly where as the mixture Nd2O3 to Pr2O3 had no significant effect. The differences in the influence of a specific rare earth oxide or a mixture are attributable to differences in the ionic radii of the RE and the morphology as well as the crystallite sizes of the RE oxides.
Influence of aging time on the corrosion behavior of 6061 Al alloy in alkaline solution
2014 - CORREA, OLANDIR V.; SOUZA, JOSE A.B. de; OLIVEIRA, MARA C.L. de; ANTUNES, RENATO A.
Al alloys of the 6XXX series (Al-Mg-Si) are employed as structural materials in a variety of industrial applications due to a combination of high mechanical strength and good corrosion resistance. The final mechanical properties are achieved after specific precipitation hardening heat treatments. The aging time during precipitation hardening is known to affect these properties and can also influence the corrosion resistance of the alloy. The susceptibility of Al alloys to corrosion in alkaline media is well-known. In this work the effect of aging time on the corrosion behavior of 6061 Al alloy was evaluated in NaOH and NaCl solutions. The material was aged at 200 ºC for times ranging from 1 to 36 h. The corrosion behavior of the aged alloy was studied using potentiodynamic polarization and electrochemical impedance spectroscopy. The results showed that the corrosion resistance was progressively lower for increasing aging times up to 8 h in NaCl and up to 24 h in NaOH. Longer aging times led to a decrease of the corrosion current density.
Protective coatings for long term wet storage of spent aluminium-clad research reactor fuel
2014 - FERNANDES, S.M.; CORREA, O.V.; SOUZA, J.A.; RAMANATHAN, L.V.; ANTUNES, R.A.; OLIVEIRA, M.C.L de
Effect of processing on microstructure and corrosion mitigating properties of hydrotalcite coatings on AA 6061 alloy
2015 - FERNANDES, STELA M. de C.; CORREA, OLANDIR V.; SOUZA, JOSE A.B. de; ANTUNES, RENATO A.; LIMA, NELSON B. de; RAMANATHAN, LALGUDI V.
Estudo do efeito de tratamentos térmicos sobre a resistência à corrosão da liga de alumínio 7075
2015 - FILGUEIRAS, DENISE R.; CORREA, OLANDIR V.; ANTUNES, RENATO A.
Lanthanide based conversion coatings for long term wet storage of aluminium-clad spent fuel
2010 - FERNANDES, S.M.C.; CORREA, O.V.; SOUZA, J.A. de; RAMANATHAN, L.V.
Spent fuels from research reactors are stored in basins with water of less than desirable quality at many facilities around the world and instances of cladding failure caused by pitting corrosion have been reported. Conversion coatings have been used in many industries to protect different metals, including aluminium alloys. This paper presents the results of an ongoing investigation in which the corrosion resistance of lanthanide (cerium, lanthanum and praseodymium) based conversion coated RR fuel cladding alloys has been studied. Electrochemical tests in the laboratory revealed higher corrosion resistance of CeO2, La2O3 and Pr2O3 coated AA 1100 and AA 6061 alloys in NaCl solutions. Uncoated and CeO2 coated coupons of these alloys exposed for 50 days to the spent fuel basin of the IEA-R1 research reactor in IPEN, Brazil, revealed marked reductions in the extent of pitting corrosion.