IDENTIFICATION OF GREEN RUST COMPOUNDS IN THE AQUEOUS CORROSION PROCESSES OF STEELS ; THE CASE OF MICROBIALLY INDUCED CORROSION AND USE OF 78 K CEMS

Abstract

Fe(II)-Fe(III) hydroxy-sulphate Green Rust 2, GR2(SO4–), is obtained by microbially induced corrosion of steel. Transmission Mossbauer spectroscopy (TMS) was used to characterise the corrosion products of steel sheet piles under the biofilm at low sea-water level in a harbour. To understand the process, iron coupons maintained in aqueous solutions of 4 M NaCl and 0.1 M NaHCO3 of pH 7.4 were studied by X ray diffraction and conversion electron Mossbauer spectroscopy (CEMS) at 78 K. The Fe(II)-Fe(III) hydroxy-carbonate, GR1(CO3–), covers the surface, as predicted by the Eh-pH diagram.