Journal of South China University of Technology(Natural Science Edition) ›› 2012, Vol. 40 ›› Issue (1): 107-113.

• Materials Science & Technology • Previous Articles     Next Articles

Effect of Citric Acid on Corrosion Resistance and Self-Healing Ability of Lanthanum Conversion Coating

Kong Gang1  Huang Wei1  Lin De-xin2  Wang Xia2  Li Han-chang2  Lu Jin-tang1  Liu Ling-yan1   

  1. 1.School of Materials Science and Engineering,South China University of Technology,Guangzhou 510640,Guangdong,China; 2.Guangdong Anthen Iron Tower and Steel Structure Co. ,Ltd. ,Foshan 528000,Guangdong,China
  • Received:2011-06-10 Revised:2011-08-31 Online:2012-01-25 Published:2011-12-01
  • Contact: 孔纲(1971-) ，男，博士，副研究员，主要从事热镀锌及金属表面处理研究． E-mail:konggang@scut.edu.cn
  • About author:孔纲(1971-) ，男，博士，副研究员，主要从事热镀锌及金属表面处理研究．
  • Supported by:

    国际铅锌研究组织项目( ILZRO/IZA/2009023) ; 华南理工大学中央高校基本科研业务费专项资金资助项目( 2009ZM0072)

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Abstract:

In this paper,first,hot-dip galvanized steels were immersed into passivation lanthanum solutions with or without citric acid to respectively obtain an improved lanthanum conversion coating or a traditional lanthanum conversion
coating on the steel surface. Next,the corrosion resistances of the two kinds of coatings were investigated via the neutral salt spray ( NSS) test,the Tafel polarization and the electrochemical impedance spectroscopy. Then,the coatings scratched with a knife edge were corroded in a NSS chamber. Finally,the microstructure and chemical composition of the scratch surface during the corrosion were analyzed by means of SEM and EDS. The results
show that the addition of citric acid in the passivation solution remarkably improves the corrosion resistance and the self-healing ability of the coating,and that,during the corrosion,lanthanum ions and citric acid anions produced by the dissolution of LaCit3 at the scratch migrate from the coating to the scratch to form a new passive coating containing Zn,O,La and C,thus effectively suppressing the corrosion of zinc at the scratch.

Key words: hot-dip galvanizing, lanthanum conversion coating, citric acid, corrosion resistance, self-healing ability

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