Corrosion Mechanism for Stainless Steel

Corrosion degrades materials, which is a source of significant expense. This Demonstration explains how steel corrodes. A steel plate (whose main component is iron) is corroded in an acid solution. This plate plays the role of a working electrode in an electrochemical cell, for which the current and potential can be measured.

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DETAILS

When the metal is dissolved in a corrosive environment, the anodic reaction takes place at the interface.
In the activity domain, the anodic current increases and the overall reaction is .
In the prepassivity domain, the formation of the oxide film protects the metal from the corrosive environment. The anodic current decreases according to the reaction
.
In the passivity domain, the protective layer totally separates the metal from the environment. The anodic current is stable and at a minimum.
In the transpassivity domain, the layer ruptures. The metal continues to corrode and the anodic current again increases via
.
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