Oxidation/sulfidation of iron-aluminium alloys

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Abstract
A principal reason for the interest in iron aluminides is their potential to resist corrosion in aggressive high-temperature environments. Accordingly, the development programme for this class of alloys has included an investigation of the corrosion properties in mixed oxidant (H2S-H2− H20) environments. Corrosion studies were initially directed at Fe3A1 and FeA1, including effects of third element additions such as Cr, Nb, Mo, Zr and Y. Iron-aluminium alloys with lower aluminium concentrations (between 16 and 22 atom%) were next investigated to establish the minimum aluminium concentration needed to resist sulfidation and oxidation. The results have shown that alloys containing ≥18% A1 are uniquely resistant to H2S-containing environments at 800°C. Chromium adversely affected the corrosion resistance in this mixed gas environment, although this effect was partially offset by the addition of molybdenum. Zirconium and yttrium had no significant effect on the corrosion rate under the same temperature and environmental conditions. Metallographic and chemical analyses of the corrosion product scales and underlying alloy were performed to determine the roles of the respective metallic elements in the corrosion process in H2S-H2−H20. These results, together with weight change determinations, are discussed in terms of the apparent corrosion mechanisms and optimization of alloy composition for exposure to gasifier environments.

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