Abstract
The formation and structure of passive films on steel in a borate buffer environment pH= 7.4 containing Chloride ions have been thoroughly investigated. The effect of the inhibitor Na4[ZnNTP]·13H2O with a certain molecular structure have been studied, including the mechanism of its action. The lowest anodic dissolution current is reached at the ZnNTP concentration of about 0.6 g/L. At the initial stage of its formation, the passive film is composed of iron oxides, which may further approach the structure of magnetite. Under conditions of counter-diffusion of ZnNTP and Fe2+ ions, the heteropolynuclear complex Zn1/2Fe1/2(H2O)3µ-H4NTP]n is formed. As for the character of the formed chemical bonds, steel passivation in the presence of ZnNTP differs significantly from both oxide and salt passivation, and thus should be considered as a specific case, called by “coordination passivation”.
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