In-Situ Synchrotron Studies of the Effect of Nitrate on Iron Artificial Pits in Chloride Solutions

The effect of nitrate on the iron dissolution in artificial corrosion pits in chloride-containing solutions has been studied with in-situ synchrotron X-ray diffraction and ex-situ Raman spectroscopy. A black layer containing Fe 3 C and carbon was found in the pit in pure 1 M HCl at 0.1 V(Ag/AgCl), but at higher voltages up to 1 V(Ag/AgCl), the black layer was not observed and Fe 3 C was not detected. The dissolution of Fe 3 C at low potentials may be inhibited by a carbon layer. In the presence of nitrate, the black layer containing Fe 3 C was present at all the voltages tested, and current fluctuations were observed and found to be potential-dependent, with greater fluctuations at higher voltages. After dissolution in 1 M HCl, the metal surface appeared slightly roughened with some small cavities, but the surface became crystallographically etched after dissolution in 1 M HCl and 50 mM NaNO 3 .