In Situ Xanes Studies of the Passive Film on Fe and Fe–26Cr

In situ X-ray absorption near edge structure (XANES) has been used to study the passive film on iron and Fe–26Cr thin films under potential control in borate buffer. The technique enables information on both valence state and the amount of material lost through dissolution to be determined. The passive films on both Fe and Fe–Cr are formed with negligible dissolution. On reduction, iron is lost from both films due to reductive dissolution. In the case of Fe, it has been determined that some of the iron in the film is reduced back to the metallic state. Concurrent monitoring of the Fe and Cr edges has shown that in the case of Fe–Cr, loss of iron leads to enrichment of Cr in the film.