The influence of trace SO2 in simulated automotive exhaust gases at 400 °C on the oxidation and subsequent condensate corrosion of 409 stainless steel was investigated by means of mass gain, SEM, Raman spectroscopy, GDOES, Mott-Schottky and polarisation curves. SO2 suppresses the growth of oxide films, especially nodular oxides rich in magnetite and maghemite, due to forming sulphates on the oxide surfaces. The initial oxidation kinetics of type 409 SS follows approximately the parabolic law in the synthetic exhaust gases with or without trace SO2 at 400 °C. The oxide films formed in both atmospheres show similar bi-layer structure, i.e., the outer layer of Fe oxides with small amount of Si oxides and the inner layer of Cr-rich oxides. Weak depletion of chromium takes place underlying the oxide films. Oxide nodules grow continuously with the increase of Fe3O4 and γ-Fe2O3 in quantity. In the absence of SO2, the mass gain deviates from the parabolic behaviour since about 400 h of oxidation because of the fast growth of nodular oxides. The presence of SO2 suppresses the growth of oxide films, especially nodular oxides, due to forming sulphates on the oxide surfaces. The oxidised 409 SS shows typical passive corrosion in the simulated condensate solution for mufflers, which is dominated by the dissolution of iron oxide layers on the surface. Compared with the absence of SO2, the presence of SO2 in the exhaust environments may reduce the defect density, especially Fe(2+) ions, in the thermal oxide films. As a result, the passive current density for 409 SS oxidised in SO2-containing exhaust gas is much lower than that in the non-SO2 case. It is apparent that trace SO2 will not deteriorate the corrosion resistance of stainless steel mufflers through the thermal oxidation process of automotive exhaust gas. In addition, because the oxide nodules are susceptible to acidic dissolution, a further investigation of nodular effect on localised corrosion of oxidised stainless steels is necessary to elucidate the perforation of mufflers in condensate solutions.


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    Titel :

    Effect of SO2 on oxidation of type 409 stainless steel and its implication on condensate corrosion in automotive mufflers


    Weitere Titelangaben:

    Einfluss von SO2 auf die Oxidation des nichtrostenden Stahles 409 und seine Folgerungen für die Kondensatkorrosion in Automobil-Auspuffdämpfer


    Beteiligte:
    Li, M.C. (Autor:in) / Zhang, H. (Autor:in) / Huang, R.F. (Autor:in) / Wang, S.D. (Autor:in) / Bi, H.Y. (Autor:in)

    Erschienen in:

    Corrosion Science ; 80 ; 96-103


    Erscheinungsdatum :

    2014


    Format / Umfang :

    8 Seiten, 9 Bilder, 4 Tabellen, 64 Quellen




    Medientyp :

    Aufsatz (Zeitschrift)


    Format :

    Print


    Sprache :

    Englisch







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