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Effect of zinc phosphate chemical conversion coating on corrosion behaviour of mild steel in alkaline medium: protection of rebars in reinforced concrete

Science and Technology of Advanced Materials. 2008;9(4):045009


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Journal Title: Science and Technology of Advanced Materials

ISSN: 1468-6996 (Print); 1878-5514 (Online)

Publisher: Taylor & Francis Group

Society/Institution: National Institute for Materials Science

LCC Subject Category: Technology: Electrical engineering. Electronics. Nuclear engineering: Materials of engineering and construction. Mechanics of materials | Technology: Chemical technology: Biotechnology

Country of publisher: United Kingdom

Language of fulltext: English

Full-text formats available: PDF, HTML



Florica Simescu and Hassane Idrissi


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Time From Submission to Publication: 15 weeks


Abstract | Full Text

We outline the ability of zinc phosphate coatings, obtained by chemical conversion, to protect mild steel rebars against localized corrosion, generated by chloride ions in alkaline media. The corrosion resistance of coated steel, in comparison with uncoated rebars and coated and uncoated steel rebars embedded in mortar, were evaluated by open-circuit potential, potentiodynamic polarization, cronoamperometry and electrochemical impedance spectroscopy. The coated surfaces were characterized by x-ray diffraction and scanning electron microscopy. First, coated mild steel rebars were studied in an alkaline solution with and without chloride simulating a concrete pore solution. The results showed that the slow dissolution of the coating generates hydroxyapatite Ca10(PO4)6(OH)2. After a long immersion, the coating became dense and provided an effective corrosion resistance compared with the mild steel rebar. Secondly, the coated and uncoated steel rebars embedded in mortar and immersed in chloride solution showed no corrosion or deterioration of the coated steel. Corrosion rate is considerably lowered by this phosphate coating.