Passivation of galvanized steel in a solution based on cerium and lanthanum compounds

• E.A. Zheludkova¹, A.A. Abrashov¹, V.A. Sukhorukova¹, N.S. Grigoryan¹, A.V. Sundukova¹, O.Yu. Grafov² and T.A. Vagramyan¹

¹ Mendeleev University of Chemical Technology, Russia, Moscow, Miusskaya sq., 9, 125047 Moscow, Russian Federation
² A.N. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Leninsky pr. 31, 119071 Moscow, Russian Federation

Abstract: A technology has been developed to replace highly toxic chromate plating processes by depositing protective conversion coatings in a solution containing ions of rare-earth metals on galvanized surfaces. The compositions of the solutions were developed and optimized, and the physicochemical and mechanical properties of the protective coatings on zinc formed in these solutions as an alternative to chromate coatings were studied. A new comprehensive method for assessing the self-healing ability of conversion coatings was developed. The addition of lanthanum nitrate to a cerium-containing solution for zinc passivation was shown to increase the protective ability of the resulting coatings when the ratio of cerium to lanthanum ions in the solution is 2:1 at a total concentration of rare-earth metals in the solution of 3 g/L. It was shown that the protective ability increased due to a decrease in the number and diameter of pores in the coatings. It was found that in the course of self-healing in cerium-lanthanum containing coatings newly formed on damaged areas, the proportion of Ce³⁺ compounds increases. It has been found that addition of sodium pyrophosphate to the solution for the formation of passivating conversion cerium-containing coatings doubles the service life and increases the solution stability fivefold.

Keywords: corrosion protection, conversion coatings, surface treatment, chromate-free passivation, rare-earth metals

Int. J. Corros. Scale Inhib., 2024, 13, no. 2, 775-789
doi: 10.17675/2305-6894-2024-13-2-7

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