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Characteristics of Zr-base Passivation Layers of Tinplate  

Bae D.C. (Sheet Products & Process Research Group, Technical Research Laboratories, POSCO)
Kim T.Y. (Sheet Products & Process Research Group, Technical Research Laboratories, POSCO)
Cho K. (Department of Metallurgical Engineering, Pusan National University)
Publication Information
Journal of the Korean institute of surface engineering / v.36, no.3, 2003 , pp. 251-255 More about this Journal
Abstract
With increasing environmental demands in surface treatment of steel sheets, the passivation layers containing hexavalent chromium $(Cr^{+6})$ are being replaced by non-chromium or trivalent chromium compounds. After review on the various types of inorganic compounds, the zirconates was chosen as the candidate for alternative to sodium dichromate in the aspect of its barrier properties with excellent adhesion to organics. The ammonium zirconium carbonate (AZC) and sodium hexafluorozirconate (SFZ) could be reach $70-80\%$ level of CDC (cathodic dichromate) treatment by their single applications. But high porosity in the AZC layer and poor electrical conductivity of SFZ solution limit the single application of zirconate. Mixed composition of zirconates to compensate their inferiorities or incorporation of organic compounds to seal the porosity seems to be inevitable to match up the target level of Cr-free passivation of tinplate.
Keywords
Cr-free passivation; zirconate; ammonium zirconium carbonate(AZC); sodium lexafluorozirconate (SFZ); cathodic dichromate(CDC); tinplate;
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