Depth Analysis of Passive Films on Iron in Neutral Borate Solution

Publisher Website
Google Scholar
Abstract
Composition depth profiles of passive films on iron in a borate solution atpH 8.42 have been obtained by means of cathodic reduction combined with ellipsometry and chemical analysis. Results revealed that the compositional profile varied depending primarily on the potential and to some degree on the time of film growth. The barrier layer in contact with the metal changed in composition from an iron(II–III) mixed oxide at potentials below the Flade potential to an iron(III) oxide at more noble potentials. The deposit layer next to the solution was a hydrated iron(III) oxide and absorbed iron(II) ions at less noble potentials. There was found a peak or a decrease in iron concentration at the barrier/deposit boundary. The iron‐rich boundary was gradually replaced by the iron‐depleted as the potential was shifted to more noble direction. It was the barrier layer alone that increased in thickness during the film growth at potentials above the Flade potential. In the transpassive potential region the barrier layer ceased growing with potential and tended to contain a small concentration of iron(II) ions. It is suggested that the ion transport in the layers plays a role in determining the passive film composition.
Keywords

This publication has 0 references indexed in Scilit: