The electrochemical and corrosion behavior of metals in aqueous environments has received substantial attention. However, relatively little work has been devoted to the electrochemistry and corrosion of metals in non-aqueous environments. Now, with greater pressures to increase fuel efficiencies and decrease exhaust emissions, alternatives and additives to gasoline (including methanol and ethanol) are receiving increased attention from government agencies and automobile manufacturers. Unfortunately, fundamental studies of the corrosion behavior of metals in these solutions are scarce.
The objective of the present work is to investigate the electrochemical and corrosion behavior of iron in methanolic solutions containing Cl, H+, SO42-, and H2O. To accomplish this, a full factorial design test matrix was developed to systematically evaluate the effects of these impurities on the corrosion behavior of iron. This test matrix enabled the determination of effects due to the impurities alone, as well as synergistic effects.
Corrosion testing of pure iron samples was performed using cyclic polarization measurements. Post-test surface morphology was evaluated with optical microscopy. Four main types of polarization behavior for iron in stagnant methanol were found, each dependent upon the nature of the aggressive species present (i.e. H+, Cl, or both). It was also found that the pitting potential is decreased by 700 mV when 10-3M chloride was present. By increasing the acidity of the solution to 10-3M, the corrosion rate of iron increased by over 15 mpy. When the water content was increased, the corrosion rate tended to decrease. Pitting was the predominant form of corrosion attack observed in all tests.