Abstract
Potentiostatic anodic polarization behavior of annealed, high purity Fe and 6 binary Fe-Al alloys containing up to 16 Wt% Al was investigated in hydrogen saturated, 1, 5, and 10N sulfuric acid solutions at 22 ± 1 C. All specimens exhibited active, passive, and transpassive behavior in all acid environments. Tafel lines for anodic dissolution in the active potential region shifted in the active potential direction with increasing aluminum content and increasing pH. Tafel lines for oxygen evolution in the transpassive potential region shifted in the noble potential direction with decreasing pH and appeared to be independent of the aluminum content. Tafel slopes for anodic dissolution and oxygen evolution varied, respectively, from 0.040 to 0.078 and 0.060 to 0.105 volt per decade of current density, and both appeared to be composition and pH independent. Corrosion potentials (Ecorr) for pure Fe and the Fe-Al alloys were linear functions of pH over the pH range −1.12 to +1.29. Slope dependency of the corrosion potential with pH (dEcorr/dpH) varied from −0.045 to −0.049, independent of composition. Critical current density for passivation decreased with decreasing pH and appeared to be composition independent. Passive current density increased with decreasing pH and exhibited a general trend to decrease with increasing aluminum content.
