![]() ![]() In the yellow part of the diagram, an active metal such as iron can be protected by a second mechanism, which is to bias it so that its potential is below the oxidation potential of the metal. The red and green regions represent conditions under which oxidation of iron produces soluble and insoluble products, respectively. This behavior can be summed up on the color-coded Pourbaix diagram below. More generally, iron (and other active metals) are passivated whenever they oxidize to produce a solid product, and corrode whenever the product is ionic and soluble. Therefore iron corrodes much more slowly in oxygenated solutions. This oxidation reaction is orders of magnitude slower because the oxide that is formed passivates the surface. Saturating the water with air or oxygen moves the system closer to the O 2 line, where the most stable species is Fe 2O 3 and the corrosion reaction is: \( \newcommand\]īut only in water that contains relatively little oxygen, i.e., in solutions where the potential is near the H 2 line. ![]()
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