Abstract
The electrochemical behaviour and the passive film microstructure of aluminum during its exposure to 3.5 wt% NaCl solution in the absence and presence of S2− ions are investigated using potentiodynamic polarization curves, electrochemical impedance spectroscopy measurements, XRD, XRF, SEM and AFM. Electrochemical measurements show that the presence of S2− ions enhances the uniform corrosion of aluminum in NaCl solution, but delay its susceptibility to the pitting corrosion. In addition, EIS analysis illustrate that the formation of more compact and protective passive layer in the presence of S2− ions compared to its rough surface in the absence of S2− ions as evidenced by the lower value of constant phase element (CPE) and higher value of phase shift (N). Cracks, non- homogenous and open large pits with high degree of roughness are clearly observed on the aluminum surface in the absence of S2− ions, compared to oriented grooves, elongated ridges with the accumulation of the corrosion products inside the pits in the presence of S2− ions. The inhibitory effect of S2− ions for the pitting corrosion of aluminum is interpreted on the basis of the change in its microstructure of the passive film in the absence and presence of S2−ions.
Highlights
Aluminum and its alloys are widely used in industrial applications, because of their good mechanical and industrial properties as well as, their highly corrosion protection[1,2,3,4]
It was determined that the corrosion rate of aluminum in the alkaline solution was occurred more seriousness in the presence of these additives, as concluded from the positive shift in the frequency to more highly frequency region
Sherar et al.[10], studied the effect of the sulphide ions on the aerobic corrosion of steel in near neutral saline solution using scanning electron microscopy, energy dispersive X-ray analysis and Raman spectroscopy. They found that the addition of the sulphide ions to the aerobically-exposed surface doubles the corrosion rate compared to its value in the sulphide free solution
Summary
Aluminum and its alloys are widely used in industrial applications, because of their good mechanical and industrial properties as well as, their highly corrosion protection[1,2,3,4]. Corrosion behaviour of Cu-Al-5Ni alloy in 3.5 wt% NaCl solution containing different concentrations of sulphide ions was studied using electrochemical impedance spectroscopy measurements[8]. Sherar et al.[10], studied the effect of the sulphide ions on the aerobic corrosion of steel in near neutral saline solution using scanning electron microscopy, energy dispersive X-ray analysis and Raman spectroscopy. They found that the addition of the sulphide ions to the aerobically-exposed surface doubles the corrosion rate compared to its value in the sulphide free solution. The corrosion protection of Al6Cu alloy was enhanced in the presence of PEO coating compared to as-cast alloy due to the change in its microstructure
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