A SERS INVESTIGATION OF THE PASSIVE FILMS FORMED ON IRON IN MILDLY ALKALINE SOLUTIONS OF CARBONATE/BICARBONATE AND NITRATE

摘要

In-situ surface enhanced Raman spectra were obtained for the passive films formed on iron in two different aqueous solutions: 0.3 M NaNO_3 (unbuffered pH = 10) and 0.15 M Na_2CO_3 + 0.15 M NaHCO_3 (buffered pH = 10). The results indicate that the films formed in the nitrate and carbonate solutions are somewhat alike, independent of potential (over the range of -400mV-+ 100mV), and consist of a mixture of species similar to microcrystalline/amorphous Fe(OH)_2 + Fe_3O_4/γ-Fe_2O_3. The results of the present and earlier studies indicate that the oxidation rate of iron is a strong function of the identity of the anion but that the passive film formed on iron in a mildly alkaline solution is nearly independent of the anion.