ELECTROCHEMICAL AND CONVERSION ELECTRON MOSSBAUER STUDY OF CORROSION INDUCED BY ACID-RAIN

The passivation of low carbon steel was studied in aqueous solution of 0.5M Na2SO4 + 0.001M NaHSO3 (pH 3.5, 6.5 and 8.5) which can be consid ered as a model of acid rain. The used conversion electron Mossbauer s pectroscopy (CEMS) with the complementary electrochemical investigatio ns proved that the sulfite ions induce pitting corrosion at pH 3.5 and 6.5, while the measurements showed much weaker pitting at pH 8.5. The compositions and thicknesses of the passive films formed during the e lectrochemical treatments are determined from the CEM spectra. Only ga mma-FeOOH was found on the surface of the samples at pH 6.5 and 8.5. N evertheless, at pH 3.5 the sextet belonging to Fe3C appears in the spe ctra, and also FeSO4.H2O could be detected in low concentration.