The inhibition of the corrosion of iron in alkaline solutions is due to the anodic formation of a film of a ferrous compound, which is usually ferrous hydroxide, but in the presence of anions yielding less soluble ferrous salts, e.g. carbonate, the composition may be mixed. The ferrous compounds are subsequently oxidised to anhydrous cubic oxide; consequentty the film thickens until it prevents the passage of ferrous ions into solution.
