Abstract
Several metallic materials form spontaneously an oxide film at the surface when is exposed in a corrosive environment. It is well known that the type of corrosive media may develop different results at the material corrosion resistance. The aim of the present paper is to investigate the influence of immersion periods and different solutions upon the corrosion resistance of pure Zn and Al specimens presenting different grain morphologies. The specimens were monitored for several periods in a 3 % NaCl solution at room temperature. Tests were also performed with variations of the 3 % NaCl solution modified by additions of acid and alkaline components. Both the electrochemical impedance spectroscopy (EIS) and polarization methods were applied.
Highlights
The corrosion mechanism and corrosion behaviour for some metallic materials may be changed through active to the passive state when immersed in aggressive environment due to spontaneous oxide and/or hydroxide film formation
The material corrosion behaviour considering both phenomena of oxide film formation and dissolution will present different performances depending on the characteristics of the solutions" \ It was suggested that the role of the corrosion behaviour in passive metals is strongly dependent on the oxide film formation and dissolution as well on its composition, morphological formation and thickness^
A comparison is shown in figure 1 among the samples immersed for 20 min and those immersed for 7 d (168 h) and 15 d (320 h) both presenting oxide film formation: (a) and (b) show the comparison between different immersion times for the zinc equiaxed structure (ZES) and (c) and (d) for the zinc columnar structure (ZCE)
Summary
The corrosion mechanism and corrosion behaviour for some metallic materials may be changed through active to the passive state when immersed in aggressive environment due to spontaneous oxide and/or hydroxide film formation. The material corrosion behaviour considering both phenomena of oxide film formation and dissolution will present different performances depending on the characteristics of the solutions" \ It was suggested that the role of the corrosion behaviour in passive metals is strongly dependent on the oxide film formation and dissolution as well on its composition, morphological formation and thickness^. As reported in previous papers, the electrolyte characteristic may affect the corrosion mechanism and corrosion behaviour^^ ^"""^ ^ ^"""^ ^l Obviously, there exist several other parameters affecting the materials corrosion behaviour'[942].
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