An EXAFS investigation of molybdate-based conversion coatings

Wharton, J. A.; Ross, D. H.; Treacy, G. M.; Wilcox, G. D.; Baldwin, K. R.
July 2003
Journal of Applied Electrochemistry;Jul2003, Vol. 33 Issue 7, p553
Academic Journal
The composition of molybdate-based conversion coatings on zinc–nickel alloy electrodeposits was examined by extended X-ray absorption fine structure (EXAFS). The absorption spectra from appropriate standards showed distinct differences between the Mo(IV) and Mo(VI) oxidation states. A pre-edge peak was apparent for the various molybdate species and molybdenum trioxide, with the energy and intensity dependent on the coordination of the molybdenum. A shift in the molybdenum K-edge spectra was also evident between Mo(IV) and Mo(VI) compounds. A qualitative analysis revealed that both Mo(IV) and Mo(VI) species were present within the molybdate-based conversion coating, with a significant prevalence of hexavalent molybdenum.


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