Electrochemical behavior of Cu-9%Al-5%Ni-2%Mn alloy in chloride media

Abstract

O comportamento eletroquímico da liga Cu-9%Al-5%Ni-2%Mn em diferentes concentrações de NaCl e valores de pH foi estudado por potencial em circuito aberto (E CA ), voltametria cíclica e curvas de polarização. As curvas E CA mostraram uma considerável influência da concentração de NaCl e do pH da solução nos valores de potencial de estado estacionário. Foi observado pelos perfis I/E que a variação da velocidade de varredura indicou a formação de um filme poroso de baixa condutividade o qual foi o responsável pelo aumento linear de corrente, devido à resistência da solução contida nos poros do filme. Com o intuito de investigar os produtos formados durante a varredura de potencial, o potencial foi mantido em diferentes valores de potencial aplicado dos voltamogramas cíclicos e analisado por MO, MEV e EDX. Em geral, foi observada a presença de precipitados de CuCl em potenciais aplicados iguais a 0,20; 0,85 e 0,00 V (vs. Ag/AgCl/KCl (3 mol L -1 ) ) e somente Cu em -0,70; -1,00 e -1,35 V. Nestes últimos, uma camada de Cu foi observada na superfície da liga devido à redução de cloreto cuproso. Este filme bloqueou o aparecimento dos picos de EDX relacionados aos outros metais presentes na liga. As curvas de polarização para a liga Cu-9%Al-5%Ni-2%Mn mostraram que E CA variou conforme o pH da solução e a concentração de NaCl. Conforme a concentração de NaCl aumentou, E CA tornou-se mais negativo para os três valores de pH estudados. Os coeficientes de Tafel foram calculados das curvas de polarização e os valores foram de 60 e 120 mV década -1 , para a região anódica e catódica, respectivamente.The electrochemical behavior of Cu-9%Al-5%Ni-2%Mn alloy in different NaCl concentrantions and pHs was studied by means of open-circuit potential (E OC ), cyclic voltammetry and polarization curves. The E OC curves showed a considerable influence of NaCl concentration and solution pH in the steady-state potential values. It was observed by the I/E profiles that the scan rate variation indicated the formation of a porous film of low conductivity which was the responsible by the linear increase of current due to the solution resistance contained in the film pores. In order to investigate the products formed during the potential scan, the potential was held at different values of applied potential of the cyclic voltammogram and analyzed by OM, SEM and EDS. In general, it was noticed the presence of CuCl precipitates in applied potentials equals to 0.20, 0.85 and 0.00 V (vs. Ag/AgCl/KCl (3 mol L -1 ) ) and only Cu in -0.70, -1.00 and -1.35 V. In the latter cases, a Cu layer was observed on the alloy surface due to the cuprous chloride reduction. This film blocked the EDS peaks appearance related to the other metals present in the alloy. The polarization curves for Cu-9%Al-5%Ni-2%Mn showed that E OC varied according to the solution pH and NaCl concentration. As the NaCl concentrantion increased the E OC became more negative for the three pHs studied. The Tafel coefficients were calculated from the polarization curves and the values were ...

Corrosion behavior of Cu–Al–Be shape memory alloys with different compositions and microstructures

“…According to Chun et al [21], the CuCl salt layer formed on Cu-Al alloys may be incorporated with the Al salt films such as AlCl and Al(OH) 2 Cl. Apparent Tafel slopes in the range of 0.058-0.076 V/decade have been obtained by other authors for Cu-Al alloys in chloride media [13,19,22,23], suggesting that the same rate-determining step as in pure copper is operating in Cu-Al alloys. The samples with single b Table 2 EDX analysis of (b + c 2 ) sample before and after the anodic polarization test in 3.5% NaCl.…”

Comparison of corrosion behaviour of copper and copper alloys in aqueous chloride solution

“…Determined values of anodic Tafel slopes were close to the 60 mV/decade for Cu and Cu alloys. This implies that anodic behaviour of these Cu alloys in chloride solutions is dominated by the diffusion rate of soluble cuprous chloride ion complexes (CuCl2 -), formed during the dissolution of copper and its alloys and confirmed in the literature [18,37,42]. When Al is present on the electrode surface, one corrosion product will be aluminium chloride salt, which can be dissolved as aluminium chloride ions, in addition to the dissolution of copper as a copper chloride complex ion [43].…”

“…When Al is present on the electrode surface, one corrosion product will be aluminium chloride salt, which can be dissolved as aluminium chloride ions, in addition to the dissolution of copper as a copper chloride complex ion [43]. In spite of Al dissolution, the apparent Tafel slopes of Cu-Al and other investigated alloys have similar values to pure copper, suggesting that the same rate-determining step is operating for both pure copper and copper-based alloys [37,42]. This means that the alloying elements did not notably modify the copper dissolution mechanism in anodic Tafel region.…”

Influence of the microstructure on the corrosion behaviour of a shape memory Cu–Al–Be alloy in a marine environment

“…The single phase microstructure reached a value of Rp ∼1500 cm 2 from 3 h of immersion onwards. Using the Tafel slopes reported for Cu-Al alloys in the range 8-13 wt.% Al for both regions, anodic (60 mV decade −1 ) and cathodic (120 mV decade −1 ) [8,21], a corrosion current of 12 A/cm 2 (0.12 mm/year) could be estimated. The corrosion current was lower for the sample with precipitates for short periods of exposure (∼2.3 A/cm 2 or 0.02 mm/year), and increased with the immersion time, reaching a similar value to that of the single phase microstructure after 24 h of immersion.…”