Enhancement of steel passivation by triazoles in neutral chloride solutions using copper sulphate microadditives

• N.P. Andreeva, Yu.I. Kuznetsov, M.O. Agafonkina and I.A. Kuznetsov

A.N. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Leninsky pr. 31, 119071 Moscow, Russian Federation

Abstract: The influence of microadditives of copper cations (Cu²⁺) on the adsorption and protective properties of layers formed by 1,2,3-benzotriazole (BTA) and 5-chloro-1,2,3-benzotriazole (5-chloroBTA) on mild steel in a neutral borate buffer solution with a pH of 7.4 has been studied. Introduction of an electron-withdrawing –Cl substituent into the molecule of BTA improves its adsorbability on mild steel and copper compared to unsubstituted azole. Surface modification of mild steel by adsorption of copper cations added to neutral aqueous solution in micro quantities (1.5 μmol/L) increases the free energy of adsorption of BTA and facilitates the passivation of steel. XPS analysis showed that during adsorption on the steel surface, Cu²⁺ cations reduce to Cu⁺, which replaces Fe cations in the top layer of FeOOH at a ratio of Fe/Cu=1/(0.2–0.6). This contributes to a more lasting retention of a monolayer of 5-chloro-BTA and improves its protective properties. On the surface of iron oxide, 5-chloro-BTA molecules form a monomolecular layer in which the planes of molecules are arranged vertically to the surface due to the formation of coordination bonds of metal cations with nitrogen lone pairs. Copper cations contribute to the formation of a self-organizing BTA or layer with a less defective structure.

Keywords: adsorption, passivity, 1,2,3-benzotriazole, 5-chloro-1,2,3-benzotriazole, copper cations, mild steel, ellipsometry, XPS

Int. J. Corros. Scale Inhib., 2023, 12, no. 4, 2080-2091
doi: 10.17675/2305-6894-2023-12-4-34

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