Features of zinc passivation with octadecylphosphonic acid

• G.V. Redkina and O.Yu. Grafov

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

Abstract: This paper examines the regularities of zinc passivation in an ethanol solution of octadecylphosphonic acid (C₁₈P) for its protection against atmospheric corrosion. Specifically, the effect of passivation conditions (the concentration of the passivating solution, its temperature and stirring, and the treatment duration) on the composition, structure, hydrophobicity, and protective properties of the alkylphosphonate film was studied. It was shown that C₁₈P exhibits passivating properties with respect to zinc in ethanol solution at relatively low concentrations. C₁₈P is chemisorbed on zinc, forming a nanosized polymolecular film consisting mainly of a hardly soluble complex zinc octadecylphosphonate located on a thin lower oxide-hydroxide layer (ZnO and Zn(OH)₂). The combination of the hydrophobic properties of thin alkylphosphonate film with a strong chemical bond with the zinc surface determines its high protective properties. The film prevents localized depassivation of zinc by chloride ions in a neutral aqueous solution and increases its corrosion resistance in 100% humidity atmosphere (with moisture condensation on the metal surface) and in salt spray atmosphere. Increasing the temperature of C₁₈P solution, its concentration, the passivation duration, and stirring of the solution, as well as using the layer-by-layer method, improve the efficiency of zinc passivation. The protective film obtained on the zinc surface in stirred 2.5 mM C₁₈P solution for 2 hours at 40°C by the layer-by-layer method has the highest anticorrosion efficiency under atmospheric conditions.

Int. J. Corros. Scale Inhib., 2025, 14, no. 4, 1860-1880
doi: 10.17675/2305-6894-2025-14-4-8

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