Corrosion Rate and Anodic Dissolution Behavior of a B2-Iron Aluminide Alloy in Sulfuric Acid

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Abstract
An electrochemical investigation was conducted to evaluate the corrosion behavior of an iron aluminide (B2-FeAl) alloy (with 24 wt% Al) in sulfuric acid (H2SO4) under potentiodynamic polarization conditions. Corrosion rates were determined using the polarization resistance (Rp) technique, in which simultaneous computations of the Tafel slopes were obtained by a curve-fitting procedure. The corrosion rate of B2-FeAl was comparable to high-purity iron at the beginning of immersion but increased noticeably with time, showing significantly diminished corrosion resistance after several hours of immersion. At small anodic overpotentials, the polarization curve showed an active dissolution region, with the anodic current dependent upon potential and pH, which suggested an anodic process under iron dissolution control. Active corrosion of B2-FeAl was believed to follow an initial selective dissolution of the aluminum constituent. The rate-determining step of the process was the charge-transfer reaction of iron, similar to that for iron-chromium alloys. However, a significant difference between aluminum and chromium existed in the poorer performance of aluminum as an alloying element in inhibiting active dissolution of iron-based alloys.

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