Manganese Pourbaix Diagram
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Corrosion Potentials:
The Pourbaix diagram indicates that the corrosion potential of manganese is very pH dependent. For pH values below 11 manganese can thermodynamically form a Mn(+2), which is a corrosion product of manganese. Since D.I. water typically has a pH value less then 6, manganese is very suceptible to cleaning and water based lubricants or slurries. Above a pH of 11, manganese can form both stable oxides and a manganese hydroxide ion, so passivating manganese is very dependent upon the solution chemistry.
Corrosion Rates:
The Tafel plots show that with the addition of a corrosion inhibitor, the corrosion rate of managanese can be reduced from a very high level of 124.1 angstroms/minute to a more acceptable level of 2 Angstroms/minute at even very low additions of an organic corrosion inhibitor. The corrosion value can be reduced further with higher concentrations of the organic inhibitor.
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