Ferrous Hydroxide Formation

Near the mild steel surface, ferrous ions from the anode combine with hydroxide ions from the cathode to form ferrous hydroxide, the corrosion byproduct that forms in intimate contact with the metal. In the presence of oxygen it oxidizes further into the iron oxides and oxyhydroxides we call rust. The appearance of this product marks a completed electrical loop.

$${\text{Fe}}^{2+}+2{\text{OH}}^{-}\to {\text{Fe(OH)}}_2$$

Variables

Symbol	Meaning	Unit
$F{e}^{2+}$	Ferrous ion produced at the anode	aqueous
$O{H}^{-}$	Hydroxide ion produced at the cathode	aqueous
$Fe(OH{)}_2$	Ferrous hydroxide corrosion byproduct	solid

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Part of The Blueprint of Water