Introduction:

A primary coating is one that is applied on the surface of the steels as a first coating layer that allows better adherence and sealing of the protective systems. However, some of its components are toxic for the environment and harmful to the health of those who use them. An alternative that has been explored in recent years, which can be environmentally friendly, is the use of oxide converters obtained from natural plant extracts. Their use can have a strong impact in the industrial field and they show promise in the conservation of metallic cultural heritage. In this work, the anticorrosive effect of an rust converter obtained from an extract of the Mimosa tenuiflora plant applied on corrosion products of a 1018 steel was evaluated. The morphological characterization of the rust converter was carried out by Scanning Electronic Microscopy (SEM). On the other hand, the anticorrosive properties were evaluated by Electrochemical Impedance Spectroscopy (EIE).

Method:

AISI 1018 steel substrates were used and two surface cleaning treatments were applied: chemical pickling and sandblasting. Subsequently, to form corrosion products, the coupons were exposed for 90 days to the urban-marine atmosphere of the city of Boca del Río, Veracruz. The extract used as a rust converter was obtained from the Mimosa tenuiflora plant and two formulations were prepared that were applied by spraying on the layer of corrosion products. The corrosion products were characterized by Raman Spectroscopy, X-Ray Diffraction (XRD) and SEM-EDX. For its part, the morphology of the converted film was characterized by SEM. The anticorrosive properties of the corrosion products and the oxide converter were evaluated by EIS during 24 hours of exposure in a 3.5 % NaCl solution.

Results:

The corrosion product layer consists mainly of goethite, lepidocrocite and hematite. By SEM, changes in the morphological characteristics of the corrosion products were observed, which change their rough and porous surface appearance to that of a compact and cracked surface due to the action of the rust converter. The results by EIE showed that the sandblasting treatment on the specimens allowed a better adherence of the corrosion products and rust converter, favoring an increase in the protective capacity compared to the surface treatment by chemical pickling.

Discussion or Conclusion:

Natural rust converter improves the protective properties of the corrosion product layer. In addition to the above, a surface preparation of the substrate with sandblasting allowed better adhesion of the rust converter. This rust converter can be used in industrial environment and metallic cultural heritage.

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