Self healing ability of silicate conversion coatings on hot dip galvanized steels |
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Authors: | Mei-rong YuanJin-tang Lu Gang Kong Chun-shan Che |
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Affiliation: | School of Material Science and Engineering, South China University of Technology, Wushan Road, 510640 Guangzhou, China |
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Abstract: | The self-healing ability of a coating is an important aspect for evaluating its corrosion resistance. Chromate conversion coatings show excellent anti-corrosion properties because of their compact microstructure and their strong self-healing ability. Silicate conversion coatings, which are potential replacement candidates for chromate conversion coatings, have good corrosion resistance, but their self-healing abilities have not been determined. In this paper, silicate conversion coatings are prepared by immersing hot dip galvanized steel sheets in sodium silicate solutions with SiO2:Na2O molar ratio of 1.00 and 3.50. The coatings are scratched with a blunt knife edge and corroded in a neutral salt spray chamber for certain lengths of time. The corrosion products in and near the scratched area are investigated by scanning electron microscopy and energy-dispersive spectroscopy. The self-healing ability of silicate conversion coatings is discussed. The results show that silicate conversion coatings have self-healing abilities under the experimental conditions. Higher SiO2:Na2O molar ratios lead to improved self-healing abilities. During the corrosion process, the silicate anions in the coating migrate to the scratched area, where a new conversion coating composed of Zn, O, and Si is formed. This delays corrosion in the scratched area. |
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Keywords: | Corrosion Self-healing Silicate coatings Hot dip galvanizing |
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