Effect of Chloride Ion Concentration on the Polarization Behavior of an Fe-25Ni Alloy

The polarization behavior of a high purity Fe-25Ni was determined as a function of the chloride ion (Cl⁻) concentration in a 1N H₂SO₄ solution. The anodic Tafel slopes were increased while the cathodic Tafel slopes were unchanged by increases in the (Cl⁻) concentration. However, a parallel shift in the cathodic curve in the noble potential direction was noted. Except for the increase in the anodic Tafel slopes, the active portion of the polarization curves were unaffected by the presence of (Cl⁻). The passive state of the alloy was greatly affected by increases in the (Cl⁻) concentration. At concentrations between 300 and 400 ppm rapid changes in the passive current density were observed. At concentrations greater than about 400 ppm, the passive state was no longer exhibited; and dissolution of the alloy occurred continuously throughout the anodic polarization test.