A STUDY OF ELECTROCHEMICALLY-INDUCED CORROSION OF LOW-CARBON STEEL INA MEDIUM MODELING ACID-RAIN

Complementary electrochemical, spectrophotometric and electron microso pic investigations were made in addition to the conversion electron Mo ssbauer spectroscopic (CEMS) measurements to learn more about the mech anism of corrosion of low carbon steel samples in aqueous sulfate and sulfite containing sulfate solutions (pH 3.5, 6.5 and 8.5). Passivatio n of iron in pure sulfate solution was studied in detail in earlier pa pers. In the present work, we used a solution containing both sulfate and sulfite anions to obtain more information about the effect of acid rain on low carbon steel samples. The compositions and thicknesses of the passive films formed due to the electrochemical treatments were d etermined from the CEM spectra. gamma-FeOOH was found in each case on the surface of the samples; nevertheless, at pH 3.5 the sextet belongi ng to Fe3C appears in the CEM spectra, and also FeSO4.H2O was detected in low concentration after the shortest polarization time (90 min). T he results of the applied methods proved that the sulfite ions induce pitting corrosion at pH 3.5 and 6.5, while the measurements referred t o suppressed pitting at pH 8.5.