An x-ray absorption near-edge spectroscopic study of the structure of passive films on amorphous Al-Fe-Ce alloys

We report on the composition and structure of passive oxide films of melt-spun ribbons of amorphous Al90Fe10-alphaCex (x = 3, 5, and 7) alloys using x-ray absorption near-edge structure (XANES) spectroscopy. The passive films were formed in an aerated solution of 0.9 weight percent (w/o) NaCl at constant potential in the passive region at -0.5 V vs. a saturated calomel electrode (SCE) for 60 min. The oxidation state of Fe in the passive films of these alloys is mainly +3, such as in alpha-Fe2O3 and/or gamma-Fe2O3. Cerium in the passive film of Al90Fe7Ce3 alloy is present mainly in the +3 oxidation state as Ce2O3 and/or Ce(OH)(3), with only a small fraction as Ce4+. In the passive film of Al90Fe5Ce5 alloy it is present in the +3 and +4 oxidation states (as Ce2O3 and/or Ce(OH)(3) and CeO2) while in Al90Fe3Ce7 alloy the passive film contains cerium in the +4 oxidation state as CeO2. The fact that the passive film may consist of mixed oxide phases containing Al, Fe, and Ce cannot be ruled out.