Effects of Metal Cations on the Corrosion of Iron in Acids

The corrosion of iron was studied in 1N sulfuric acid, 1N hydrochloric acid, and 1N acetic acid containing oxidizing, reducing, or stable metal cations. Oxidizing cations (Fe+++, Ce++++, Cu++, and Cr2O7--) increased the corrosion rate of iron in these acids. The increased rate was found to be a linear function of the cation concentration for the concentration range studied (up to 0.1 g ions/liter). For the same oxidation-equivalent concentration the corrosion rate was proportional to the valence change which the metal cations underwent during the corrosion process. Reducing cations (As+++ and Sn++) decreased considerably the corrosion of iron in acids, whereas stable cations (Fe++, Mn++, Cr+++, and Ni++) with the exception of Ni++ showed no effect. The electrochemical action of the various cations was explained on the basis of corrosion data and electrode potential measurements. 3.8.2