Passivation of mild steel in an ethanolic dodecylphosphonic acid solution for protection against atmospheric corrosion

• G.V. Redkina and A.S. Anatolyeva

Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, 31-4, Leninsky prospect, 119071 Moscow, Russia

Abstract: In this work, the efficiency of the passivation of mild steel in an ethanolic solution of dodecylphosphonic acid (C₁₂P) for protection against atmospheric corrosion was investigated. Specifically, the influence of passivation conditions on the protective ability of the forming alkylphosphonate film was studied. The anticorrosion and hydrophobic properties of the film were assessed by corrosion tests (in an atmosphere of 100% relative humidity with moisture condensation, droplet tests according to GOST 9.302-88 and ISO 4536-1985), static contact angle (Θc) measurements, and potentiodynamic voltammetry in chloride-containing borate buffer. It has been shown that treating mild steel in an ethanolic C₁₂P solution results in the formation of a hydrophobic (Θc=98±1°) passive film that significantly improves the corrosion resistance of steel in both a chloride environment (PE=89.83%) and in an atmosphere of 100% humidity with moisture condensation (by a factor of 207). The optimal conditions of steel passivation with C₁₂P were determined: exposure to a 10.0 mM stirred solution at 60℃ for 120 min, followed by drying at 100℃. This film not only satisfies the GOST 9.302-88 requirements established for thicker conversion phosphate coatings, but also significantly exceeds them. Using ethanol as a solvent significantly enhances the efficiency of steel passivation with C₁₂P, since it allows the use of a higher inhibitor concentration without degrading the surface appearance, in contrast to an aqueous solution.

Keywords: low-carbon steel, corrosion inhibitor, dodecylphosphonic acid, passivation, atmospheric corrosion, self-assembled layer

Int. J. Corros. Scale Inhib., 2026, 15, no. 3, 385-402
doi: 10.17675/2305-6894-2026-15-3-17

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