The inhibition of the corrosion of iron in neutral and alkaline solutions. I

The potentials at which iron is converted into anhydrous cubic oxide in certain inhibitive solutions have been measured and it has been shown that these potentials are more negative than the potentials acquired by unpolarised specimens immersed in the solutions for 3 days. It is suggested that when iron, carrying its air-formed film, is placed in an inhibitive solution, saturated with air, the corrosion current is concentrated at the weak spots in the oxide film and at the air-formed film is thereby thickened and corrosion prevented. When the pH of the inhibitive solution exceeds 9, anhydrous cubic oxide may also be formed by the interaction of the anodic product, ferrous hydroxide, with atmospheric oxygen. This explanation of inhibition has been extended to account for the corrosive nature of pure water, the effect of the concentration of the inhibitor, the dual rǒle of oxygen and the effect of oxygen on the efficiency of non-oxidising inhibitors.