Corrosion rate and anodic dissolution behavior of a B2-iron aluminide alloy in sulfuric acid

An electrochemical investigation was conducted to evaluate the corrosion be havior of an iron aluminide (B2-FeAl) alloy (with 24 wt% Al) in sulfuric ac id (H2SO4) under potentiodynamic polarization conditions. Corrosion rates w ere determined using the polarization resistance (R-p) technique, in which simultaneous computations of the Tafel slopes were obtained by a curve-fitt ing procedure. The corrosion rate of B2-FeAl was comparable to high-purity iron at the beginning of immersion but increased noticeably with time, show ing significantly diminished corrosion resistance after several hours of im mersion. At small anodic overpotentials, the polarization curve showed an a ctive dissolution region, with the anodic current dependent upon potential and pH, which suggested an anodic process under iron dissolution control. A ctive corrosion of B2-FeAl was believed to follow an initial selective diss olution of the aluminum constituent. The rate-determining step of the proce ss was the charge-transfer reaction of iron, similar to that for iron-chrom ium alloys. However, a significant difference between aluminum and chromium existed in the poorer performance of aluminum as an alloying element in in hibiting active dissolution of iron-based alloys.