- published: 04 Nov 2010
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A galvanic anode is the main component of a galvanic cathodic protection (CP) system used to protect buried or submerged metal structures from corrosion.
They are made from a metal alloy with a more "active" voltage (more negative electrochemical potential) than the metal of the structure. The difference in potential between the two metals means that the galvanic anode corrodes, so that the anode material is consumed in preference to the structure.
The loss (or sacrifice) of the anode material gives rise to the alternative name of sacrificial anode.
In brief, corrosion is a chemical reaction occurring by an electrochemical mechanism. During corrosion there are two reactions, oxidation (equation 1), where electrons leave the metal (and results in the actual loss of metal) and reduction, where the electrons are used to convert water or oxygen to hydroxides (equations 2 and 3).
In most environments, the hydroxide ions and ferrous ions combine to form ferrous hydroxide, which eventually becomes the familiar brown rust:
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