Anodic Potentiostatic Polarization of Iron In Sulfuric Acid: Effect of Chloride Ions^⋆ Available to Purchase

Anodic polarization of iron⁽¹⁾ was studied by the potentiostatic technique in both aerated and deaerated H₂SO₄ solutions at pH 1,2 and 3 and at four different chloride ion concentrations (0.001 — 0.050 M NaCl). The potential control was maintained with an electronic potentiostat. Electrode potentials were measured with respect to a saturated calomel electrode. Magnetic iron cyclinders (¼ in. diameter x ⅛ in. length) served as anodes and were rotated at 100 rpm (3.32 cm/sec) to minimize diffusion effects during the experiment. The experimental results indicated that the corrosion potential was independent of chloride ion concentration, but dependent on pH. The corrosion potential of iron was 30 to 40 mv more noble in aerated than in deaerated solutions. The anodic polarization of iron in the active region was not appreciably affected by chloride ions. In the passive region, however, passivity was greatly affected by the concentration of chloride ions at all the pH values studied in both the aerated and deaerated solutions. Passivation was achieved to almost the same extent in 0.001 M NaCl solutions as in the chloride-free solutions. There was a considerable difference, however, between the 0.001 M and 0.005 M NaCl solutions because the passive current of iron in 0.005 M was approximately two orders of magnitude larger than in 0.001 M NaCl.