Under zinc phosphating condition of Zn
2+: 800ppm, Ni
2+: 800ppm, Mn
2+: 600ppm, and F
-: 500ppm, zinc phosphate crystals were formed on the various types of steel sheets. The chemical properties of these crystals were first determined by X-ray diffraction and atomic absorption. The morphology and the chemical properties of the crystals differed according to the kind of steel.
The chemical component distribution of Hopeite crystal formed on galvannealed (GA) and electrogalvanized (EG) steels, and that of the Phosphophyllite crystal formed on cold rolled (CR) steel were analyzed by XPS and IMA. XPS showed that there was no Mn and Ni in the surface region of Hopeite, and that there was no Ni in the surface region of the Phosphophyllite. Comparing IMA intensity ratio patterns for Mn/Zn, Ni/Zn, Fe/Zn and P/Zn, the ratios for GA and EG were similar, but that for CR was different.
Correlating XPS with IMA, Mn was found to be present in the surface region of the Phosphophyllite crystal, and the crystal structure was considered as Zn
3-x(Fe, Mn)
x (PO
4)
2, 4H
2O. Mn and Ni were not present in the surface region of Hopeite crystals, but only in the bulk of the crystal. Therefore, the crystal structure of the surface region of Hopeite was considered as Zn
3(PO
4)
2⋅4H
2O, and that of the bulk was considered as Zn
3-xMn
x(PO
4)
2⋅4H
2O.
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