In-situ construction of RE conversion coating on Mn surface and comparison of chain corrosion blocking mechanism

Abstract

Different from the simple first-order oxidation behavior of other metal, Mn is prone to complex chain corrosion reaction due to its own polyvalence and Mn 2+ instability. In this paper, it is found that rare earth salts can be constructed in situ on the electrolytic manganese surface to obtain a composite RE conversion coating with RE 3+ and Mn 2+ coexisting. The coating can improve the stability of Mn 2+ , effectively inhibit the bad transformation of Mn 2+ to higher valence Mn 3+ /Mn 4+ , thereby blocking the chain corrosion reaction. Both La and Y conversion coating have good corrosion resistance, stability, corrosion resistance strength and durability, and their i corr are 1.638 × 10 −6 A/cm 2 and 2.750 × 10 −6 A/cm 2 , which are reduced by two orders of magnitude. Although the coating performance is not much different, the formation and corrosion process are quite different due to the differences in the RE properties. The comparison of chain corrosion blocking mechanism of electrolytic manganese is of great significance not only to the passivation technology, but also to the application of RE salts in metal passivation. • Emphasize the importance of chain corrosion blocking to electrolytic manganese. • Form a composite coating with RE 3+ and Mn 2+ coexisting in the form of in-situ construction. • The differences and reasons between different RE conversion coatings were analyzed. • RE conversion coating has good corrosion resistance, stability and durability. • RE conversion coating can improve the stability of Mn 2+ and inhibit its further oxidation.