Analysis of Discolored Aluminum Foil by Laser Ablation Inductively Coupled Plasma Mass Spectrometry and Scanning Electron Microscopy

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) was employed for the characterization of the elemental composition of discolored areas of thin (50 μm) aluminum foil samples. The spatial distribution of the impurities, which included 11 elements present in the foil material at ppm and ppb levels, was analyzed. Elevated concentrations of almost all studied elements were found in the discolored regions with respect to the nondiscolored regions of the foil. In particular, the difference in the elemental yield observed for iron was approximately 6 to 25 times higher in the discolored regions of the foil. In addition, an elevated level of oxygen was detected in the discolored regions of the sample by the use of scanning electron microscopy with a wavelength-dispersive spectroscopy (SEM-WDS) system. Thus, the elevated levels of iron and oxygen in the same discolored regions of the foil, according to the authors' opinion, strongly indicated the development of a corrosion process within the samples. The discoloration itself was most likely a result of the formation of metal oxide compounds as products of the corrosion process, with iron oxide contributing the yellowish color in the affected areas.