Chemical composition, electrochemical, and morphological properties of iron phosphate conversion coatings
- Calgon Corp., Pittsburgh, PA (United States)
- ECC International Ltd., Cornwall (United Kingdom). R and D Dept.
- Katz Analytical Services, Chanhassen, MN (United States)
- Applied Redox Technology, Moon Township, PA (United States)
Iron phosphate conversion coatings are used widely in the pretreatment industry to enhance paint adherence to metal substrates and therefore improve corrosion resistance. However, very limited nonproprietary literature describing the properties of iron phosphate coating is available, as compared to volumes dedicated to zinc phosphate coating. The present study described chemical, electrochemical, and morphological characterizations of iron phosphate coating using x-ray photoelectron spectroscopy (XPS), potentiodynamic scans, and scanning electron microscopy (SEM). For the samples under investigation, the mode of operation of iron phosphate coating was to promote paint adhesion, and the coating itself did not impart significant corrosion protection to the metal substrate. It also was shown that the Fe/P ratio in the phosphate coating ranged from 1:2 to 1:1. When tested in pH 7 buffered phosphate solution, the phosphate coating displayed a passivation region, which also possessed the highest impedance value. The phosphate coating was found to comprise two layers: a dense, adherent layer and a loose, granular top layer. For samples with coating weights of 20 mg/ft{sup 2} to 30 mg/ft{sup 2} (0.22 g/m{sup 2} to 0.32 g/m{sup 2}), the corresponding coating thickness was {approximately} 0.1 {micro}m to 0.3 {micro}m.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 684448
- Journal Information:
- Corrosion, Vol. 55, Issue 9; Other Information: PBD: Sep 1999
- Country of Publication:
- United States
- Language:
- English
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