Corrosion behavior of Fe-40Al sheet in N2–11.2O2–7.5CO2 atmospheres with various SO2 contents at 1273 K

A 200 μm thick Fe-40 at.%Al sheet, produced by powder metallurgy and hot extruding, was corroded at 1273 K for up to 360 ks in N2–11.2 vol.%O2–7.4 voI.%CO2 atmospheres containing 100, 500, or 2000 ppmSO2. The alloy oxidized rapidly at the very initial stage of corrosion, forming sulfides in addition to both θ- and α-A12O3 scales, it was suggested that sutfides may be formed by direct reaction of SO2 gas molecules with the alloy. Sulfide or dissociated sulfur at the alloy-scale interface may promote exfoliation of the external scale. With further oxidation, the oxide scale consisted solely of α-Al2O3, and grows obeying a parabolic rate law. The parabolic rate constants are between 5.5×10−12 and 7.2×10−12 kg2 m−4 s−1, independent of SO2 concentration. After 360 ks of corrosion the Al content in the alloy sheet remained at about 38 at.%Al, with an almost flat profile across the entire sheet.