In situ Mossbauer study of the passive layer formed on the iron anode in alkaline electrolyte

In situ Mossbauer spectra of the iron electrode at anodic potential were measured in sodium hydroxide solution over a wide range of concentrations (0.1-14 mol l(-1)). It was found that the in situ Mossbauer spectra exhibit generally one sextet and one doublet corresponding to the oxide layer on the anode surface. Parameters of these spectra show only minor variations within the electrolyte concentration range of 0.1-7 M NaOH. A pronounced change in the spectra was observed in 14 M NaOH. The major processes taking place in the anode surface layer are based on the break-down of protective properties of the passive layer, incipient intense metal dissolution and subsequent oxidation. important differences were also found between in situ and ex situ spectra measurements.