Raman spectroscopy and XPS investigations of anodic corrosion films formed on FeMo alloys in alkaline solutions

Raman spectroscopy and X-ray photo-electron spectroscopy have been used to study anodic films formed on iron-molybdenum (FeMo) alloys. It is shown that the composition of the passive film formed after oxidation/reduction cycles (ORC) in 1 M KOH depends upon the anodic reversal potential and the sweep rate of the ORC. Finally it is concluded that the growth of the ferric outer layer (amorphous a-FeOOH able to crystallize in α-FeOOH or γ-FeOOH after a certain number of cycles) is related to the reduction of the magnetite (Fe3O4) inner layer that provides a source of iron ions.