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Journal of Materials Science

, Volume 30, Issue 3, pp 809–823 | Cite as

Surface modification of electrogalvanized steels by zinc phosphate conversion coatings

  • T. Sugama
  • T. Takahashi
Papers

Abstract

When electrogalvanized steel (EGS) surfaces were treated by immersing them in a phosphating solution consisting of Zn3(PO4)2-4H2O, H3PO4, Co(NO3)2·6H2O, poly(acrylic acid) (p(AA)) and water, the resulting electrochemical reaction led to the creation of short-circuited cells with cobalt acting as the cathode and the galvanized (zinc) coating as the anode. These cells accelerate the anodic dissolution of zinc, which then rapidly precipitates embryonic zinc phosphate tetrahydrate (hopeite) crystals on the EGS surfaces, resulting in their complete coverage with fully grown hopeite crystals after only 5 s immersion. The hopeite layers formed not only serve to protect the galvanized coatings against NaCl induced corrosion, but also contribute significantly to improving adhesion to the Polyurethane (PU) topcoating. The reasons for the latter improvement were due primarily to the following: (1) the interfacial chemical reaction between the p(AA) existing at the top surface of hopeite and the PU, and (2) the anchoring effects of the penetration of PU into the rough hopeite crystal layers.

Keywords

Polyurethane Acrylic Acid H3PO4 Interfacial Chemical Reaction Anodic Dissolution 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© Chapman & Hall 1995

Authors and Affiliations

  • T. Sugama
    • 1
  • T. Takahashi
    • 2
  1. 1.Energy Efficiency and Conservation Division, Department of Applied ScienceBrookhaven National LaboratoryUptonUSA
  2. 2.Department of Inorganic MaterialsHyogo Prefectural Institute of Industrial ResearchKobeJapan

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