Effect of Biomineralized Manganese on the Corrosion Behavior of C1008 Mild Steel

The possibility that biomineralized manganese dioxide (MnO₂) might serve as an efficient cathodic reactant in mild steel corrosion was studied using stainless steel (SS) covered with microbially or electrochemically deposited MnO₂ and galvanically coupled to mild steel and mild steel covered with microbially deposited MnO₂. Biofilms of the manganese-oxidizing bacteria, Leptothrix discophora SP-6, were used to deposit biomineralized MnO₂. When MnO₂ was biologically deposited on the SS, the corrosion rate of the galvanically coupled mild steel was initially about eight times higher than that in a control experiment without depositing manganese. After a few minutes, the MnO₂ discharged and the corrosion rate of the mild steel decreased to values comparable with biofouled cathodes without manganese. When MnO₂ was electroplated on SS, a linear relation between the amount of MnO₂ and the duration of the elevated corrosion rate of mild steel was observed. However, when MnO₂ was biologically deposited directly onto the mild steel, the corrosion rate did not increase, possibly because the corrosion product buildup on the mild steel surface prevented electrical contact between the manganese oxide and the underlying metal.