In situ micro-Raman spectroscopy to investigate pitting corrosion product of 1024 mild steel in phosphate and bicarbonate solutions containing chloride and sulfate ions

The nature of the corrosion products generated by localized attack on 1024 mild steel have been investigated in the presence of chloride and/or sulfat e ions in bicarbonate and phosphate aqueous solutions. A spectroelectrochem ical cell was used for in situ measurements of the Raman spectra of the cor rosion products generated during pitting. These products were identified as the so-called green rust compounds. The assignment of the hydroxyl groups in green rust is confirmed by isotopic substitution. The composition of the green rust generated in bicarbonate or phosphate solution containing chlor ide and/or sulfate ions has been determined. A correlation between the gree n rust composition and the electrochemical behaviour after the initiation o f pitting has been noted and discussed.