Characterization of Conversion-Coated Aluminum Using Fourier Transform Infrared and Raman Spectroscopies

Authors: Ahern, Angela M.; Schwartz, Paul R.; Shaffer, Lori A.

Source: Applied Spectroscopy, Volume 46, Issue 9, Pages 1327-1441 (September 1992) , pp. 1412-1419(8)

Publisher: Society for Applied Spectroscopy

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Abstract:

Fourier transform infrared and Raman spectroscopies have been employed to define the molecular composition of chromium phosphate conversion coatings on aluminum. Attenuated total reflectance at 55° can be employed to probe the structure of conversion coatings present on aluminum at relatively high coating weights (≥23 mg Cr/m2). Both reflection-absorption infrared and surface-enhanced Raman spectroscopic techniques can discern the presence of conversion coatings at coverages as low as 9 mg Cr/m2. On the basis of the vibrational spectra from these techniques, we have determined that hydrated chromium phosphate is the major component in these conversion coatings on aluminum. Reflection-absorption infrared and surface-enhanced Raman spectroscopies also provide a means to determine the molecular structure of the nascent oxide layer on aluminum as a function of processing conditions. Specular reflection, attenuated total reflectance at 35°, diffuse reflectance, and Raman spectroscopic methods, in general, lack the surface sensitivity necessary to probe thin (≤ 23 mg/m2) inorganic films on aluminum.

Keywords: Aluminum; Chromium phosphate; Conversion coating; FT-IR; Raman spectroscopy

Document Type: Research Article

DOI: http://dx.doi.org/10.1366/0003702924123764

Affiliations: Alcoa Technical Center, 100 Technical Drive, Alcoa Center, Pennsylvania 15069-0001

Publication date: September 1, 1992

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