Study of the Relation between Modified Structure and Chemical Stability of Zinc Phosphate Crystal Film
1987 Volume 38 Issue 12 Pages 571-575
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1987 Volume 38 Issue 12 Pages 571-575
The shift in the Mn content of zinc phosphate crystal films on cold rolled and galvannealed steels and the changes in anti-alkaline properties were investigated at varying concentrations of Mn2+ ion in zinc phosphate solutions. At Mn2+ ion concentrations from 0 to 2500ppm, the changes in the Mn content of the zinc phosphate crystal films formed were confirmed to be in accordance with the Mn2+ ion concentration, with Mn content reaching 6wt.% of Hopeite crystal film on galvannealed steel and 8wt.% of Phosphophyllite crystal film on cold rolled steel.
It has previously been clarified that the Mn2+ in the solution acts to modify the chemical structure of zinc phosphate crystal films, and that the modified structures were Zn3-xMnx(PO4)2⋅4H2O for Hopeite and Zn2(Fe1-xMnx)(PO4)2⋅4H2O for Phosphophyllite. As it was predicted that the anti-alkaline properties of these films would change accordingly, the loss in weight of zinc phosphate crystal films through the action of NaOH solutions adjusted to pH 10.5, 12.0 and 13.0 was discussed. At all values of pH, the weight loss of Hopeite crystal film exceeded that of Phosphophyllite, but the absolute values of weight loss decreased in accordance with Mn2+ ion concentration, i.e., with the Mn content in the zinc phosphate crystal films. The decrease in weight loss, i.e., the improvement in anti-alkaline properties was remarkable in the high alkaline region around pH 13.0.
