Electrochemical reduction of thermally prepared oxides of iron and iron-chromium alloys studied by in situ Raman spectroscopy

Abstract

Pure Fe and Fe/Cr alloys (3% and 12% Cr) were oxidized at 250–260°C and subsequently electrochemically reduced in borate buffer, pH 8.4. The reduction was followed by in situ Raman spectroscopy as well as chronopotentiometric and chronoamperometric measurements. At several time intervals ex situ Raman control investigations and ESCA analyses were undertaken. Although at −0.7 V vs sce partial reduction of the oxide film was observed, α-Fe 2O 3 remained unchanged and reduced at −0.9 V. A mixture of spinel structured oxide, possibly Fe 3O 4, and a ferrous deposit were observed when the oxide film was galvanostatically reduced at 100 μA cm −2; after prolonged reduction the bare metal resulted. The thermally created oxide of the Cr alloy possessed an inner Cr rich layer which during the galvanostatic reduction of the oxide film at 50 μA cm −2 is most likely responsible for an increase in the overpotential of more than 80 mV.