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

A 200 mum thick Fe-40 at.%Al sheet, produced by powder metallurgy and hot extruding, was corroded at 1273 K for up to 360 ks in N-2-11.2 vol.%O-2-7.4 voI-%CO2 atmospheres containing 100, 500, or 2000 ppmSO(2). The alloy oxidized rapidly at the very initial stage of corrosion, forming sulfides in addition to both theta- and alpha-Al2O3 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 alpha-Al2O3, and grows obeying a parabolic rate law. The parabolic rate constants are between 5.5 x 10(-12) and 7.2 x 10(-12) kg(2) 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. (C) 2003 Published by Elsevier Science Ltd.