In situ Raman spectroscopy, surface enhanced Raman spectroscopy, scanning electron microscopy and measurements of corrosion potential were used to investigate the films formed on iron in 288°C water with dissolved oxygen concentrations that ranged from 0 to 208 ppb. A double layer film of Fe304 that consists of an inner, conformal layer and an outer layer of faceted, loosely packed particles forms in water containing 0 to 22 ppb oxygen. Passivation of the iron surface begins at dissolved oxygen concentrations of = 8 ppb and is a two step process: first, between 8 and 22 ppb oxygen, there is an increase in protectiveness of the Fe304 and second, between 22 and 53 ppb the outer surface of Fe304 transforms to ~-Fe203, which completes passivation.
Keyword: Oxidation, Raman Spectroscopy, SERS, Iron, Passive Film