Electrochemical and Corrosion Behavior of Fe-Ni Alloys in Sulfuric Acid

The anodic and cathodic polarization of pure iron and nickel, 20%, 40%, 60%, and 80% Fe-Ni alloys in de-aerated 1N H2SO4 has been investigated. The anodic Tafel slopes ranged from 41 to 50 mv. The cathodic Tafel slopes of the hydrogen evolution reaction were either 100 or 105 mv. The corrosion rates of the pure metals and alloys were determined by weight-loss, chemical analysis, and polarization methods. The corrosion rates determined by the three methods were in reasonable agreement. Weight-loss and chemical analysis methods indicated a minimum at 40% Fe. By the polarization method, a minimum was observed at 20% Fe. In addition, the differential capacitance attained a minimum at this same composition. It has been suggested that the minima at 20% Fe might be attributed to the possible existence of the ordered structure, FeNi3.