Uniformity of passive films formed on ferrite and martensite by different inorganic inhibitors

By Metroke, Tammy L.; Gandhi, Jaspreet S. & Apblett, Allen
Published in Corrosion Science NULL 2002

Abstract

A comparison of uniformity of passive films formed on ferrite and martensite by three kinds of inorganic inhibitors, chromate, bicarbonate and nitrite, has been made by anodic polarization curve and AC impedance measurements. It was found, by anodic polarization curve analyses, that there was different pitting susceptibility of passive films formed on ferrite and martensite by chromate or bicarbonate. In the solution containing chloride ions, the broken potential of the passive film formed on ferrite by chromate or bicarbonate was more negative than that on martensite. However, the passive films formed on both ferrite and martensite by nitrite had similar pitting susceptibility. Their broken potentials were almost the same. The difference in pitting susceptibility of the passive films was explained by Mott–Schottky analyses. It was found that the passive film formed on ferrite by chromate or bicarbonate had a higher donor concentration than the passive film on martensite. The passive films with higher donor concentrations were more sensitive to chloride ions. However, the passive films formed on both ferrite and martensite by nitrite had the same donor concentration. A uniform passive film can be formed on a martensite mild steel with ferrite bands by nitrite.

Read Article » Back