Corrosion Behavior of Nickel and Inconel in Acidic Chloride Solutions

The corrosion behavior of nickel and Inconel in acidic solutions has been investigated by polarization methods. The cathodic Tafel slope for the h.e.r. of nickel in de-aerated 1N H₂SO₄ and the corresponding exchange current density were 135 mv and 3.4 μa/cm². Two cathodic Tafel slopes and exchange currents for the h.e.r. were obtained for Inconel in the same solution: 50 mv and 0.22 μa/cm²; 115 mv and 7.2 μa/cm². With increase in concentration of chloride ions, the corrosion potential of nickel decreased and the open circuit differential capacitance increased. Each parameter approached a constant value at the higher chloride ion concentrations. Anodic polarization of both metals showed that the primary passivation potential, the critical and passive current densities increased with increase in chloride ion concentration. The passivity of Inconel was shown to be superior to that of nickel in acidic solutions in the absence and presence of chloride ions.