Applications of synchrotron-based infrared microspectroscopy (SIRMS) corrosion, contamination and coatings

Fourier Transform Infrared (FTIR) spectroscopy is capable of characterizing both organic and inorganic bonds in surface compounds resulting from a variety of environmental interactions. In addition to the high sensitivity inherent in the technique, use of multiple combinations of sampling configurations, including the recent development of FTIR microscopy, allows for application to challenges presented by complex or rough surfaces, thick and non-conducting corrosion product layers, and thin layers with complicated chemistry. Further value has been brought to FTIR analysis of surfaces through the use of the infrared part of the synchrotron radiation spectrum provided by vacuum ultraviolet (VUV) beamlines as a source for FTIR microspectroscopy to increase signal to noise ratios and provide a bright coherent IR source. This review will present recent results from synchrotron IR studies of (1) pitting of Al aerospace alloy AA2024-T3 surfaces resulting from acetone degreasing prior to exposure to a salt mist, (2) the mechanism of corrosion protection of AA2024-T3 by chromate conversion coatings and the effect of intermetallic compounds in the alloy matrix on coating properties, and (3) the mechanism of attachment of contaminant uranium in thick corrosion product layers formed on structural carbon steel in a humid environment and the resulting complexation and removal of uranium by citric acid.