Study of the Effect of Nitrogen and Molybdenum in the Corrosion Inhibition ofAustenitic Stainless Steel (Final Report)

摘要

The synergistic effect of nitrogen and molybdenum in remarkably improving thecorrosion resistance of austenitic stainless steels in chlorine ions containing solution has been investigated. Electrochemical techniques in conjunction with X-ray photoelectron spectroscopy (XPS) were utilized to elucidate the mechanism by which N and Mo influence the passivation behavior of austenitic stainless steel. Since nitrates and nitrites are known to be powerful corrosion inhibitors, the possibility that alloyed nitrogen was capable of oxidizing to either of these species was considered. While no evidence could be found of NO3 formation by XPS, it was decided to further clarify this issue by considering the stability of NO3 ions on the surface of pure chromium and a variety of Molybdenum bearing stainless steels polarized through an extensive range of potentials. Nitrate was found to be unstable at all potentials considered provided that the metal was exposed directly to the solution. This resulted in clear evidence that alloyed nitrogen does not oxidize to NO3 or NO2. Indeed a new mechanism by which nitrates inhibit corrosion was uncovered.