Raman spectra of passive films of iron in neutral borate solution

Abstract

The Raman spectra of the passive films formed on iron in a neutral borate solution at various potentials were measured for evaluating its composition without any enhancement technique. The ex-situ spectrum measured in air after removal from the aqueous solution corresponds to the composition of disordered Fe3O4, i.e., Fe3-δO4. The passive film in the aqueous solution, which could not be measured in this paper due to a large background scattering light intensity from surrounding water around the iron electrode, may be a compositional framework same as the ex-situ passive film, although it is expected to be hydrated under the in-situ condition. For the in-situ measurement of the passive film, it is speculated that much accumulation will be required to decrease the noise level of the background light scattering relative to the signal from the thin film.