Electrochemical Screening of Organic and Inorganic Inhibitors for the Corrosion of ASTM A-470 Steel in Concentrated Sodium Hydroxide Solution

The corrosion of ASTM A-470 turbine disk steel in concentrated sodium hydroxide solution (10 mol/kg) containing sodium silicate, sodium dihydrogen phosphate, sodium chromate, aniline and some of its derivatives, tannic acid, L-(-)-phenylalanine (aminopropionic acid) and octa-decylamine as potential inhibitors has been studied using the potentiodynamic, AC impedance, and Tafel extrapolation techniques. All tests were performed at 115 ± 2 C. The anodic and cathodic polarization data show that aniline and its derivatives, L-(-)-phenylalanine, NaH₂PO₄, Na₂SiO₃, and Na₂CrO₄ inhibit the anodic process, whereas tannic acid inhibits the cathodic reaction. Octadecylamine was found to inhibit both the anodic and cathodic processes. The mechanisms of inhibition for some of these compounds have been inferred from the wide band width frequency dispersions of the interfacial impedance.