Pitting corrosion inhibition of 316 stainless steel in phosphoric acid-chloride solutions Part II AES investigation

The application of Auger Electron Spectroscopy (AES) to the study of the composition and thickness of the passive film formed on the surface of 316 Stainless steel in H3PO4-Cl– solutions containing nitrate, dichromate, molybdate and tungstate as inhibitors is discussed. Data are presented which explain the effectiveness of the additives on the properties of the passive films of the alloy. It is concluded that much higher corrosion resistance of the alloy is observed in nitrate additives due to marked nitrogen enrichment underneath the passive film which enhances the repassivation ability of this alloy. The results could also explain the effectiveness of the dichromate, molybdate and tungstate anions due to improved film repair conditions.