Efficiency of a Cadmium Complex of Nitril-trismethylenephosphonic Acid As a Corrosion Inhibitor of Low-Carbon Steel in Neutral Iodide-Containing Aqueous Media and Features of Formation of Passivating Films under These Conditions

A potentiodynamic study is performed of the effect the cadmium complex of nitrile-trismethylenephosphonic acid Na₄[Cd(H₂O)N(CH₂PO₃)₃]⋅7H₂O has on the corrosion-electrochemical behavior of low-carbon steel in neutral iodide-containing aqueous media. The composition and structure of passivating films, spatial localization of inhibitor interaction with iron ions, and accompanying processes and products of these interactions, are studied via X-ray photoelectron spectroscopy with layer-by-layer etching. With 1.4 mmol/dm³ of I⁻ ions, Na₄[Cd(H₂O)N(CH₂PO₃)₃]⋅7H₂O at a concentration of 0.05–0.5 g/dm³ reduces the current density of anodic dissolution of metal. It stimulates corrosion at concentrations of 1.0 g/dm³ and above. The optimum concentration of inhibitor is 0.2–0.5 g/dm³.