57Fe-DCEMS studies of thin corrosion layers

The characterization of the corrosion products formed on an 57 Fe film onto a low alloy steel disc after 4 h and 8 h exposure to an artificially SO2-polluted atmosphere has been carried out by ICEMS/DCEMS. The corrosion products found are FeSO3·3H2O, FeSO4·nH2O, a third unidentified Fe2+ species, an amorphous Fe3+ oxyhydroxide and a second Fe3+ species which could correspond to superparamagnetic α-FeOOH or ferrihydrite. Although the DCEM spectra recorded at different electron energies do not show dramatic differences in the relative concentrations with depth, the results suggest that FeSO3·3H2O is preferentially located in the inner part of the corrosion layer whilst the outer part is richer in FeSO4·nH2O and Fe3+ species