Applications of Synchrotron Infrared Microspectroscopy (SIRMS) to Corrosion, Contamination and Coatings

摘要

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, beam splitters and detectors allows for application to challenges presented by complex or rough surfaces, thick and non-conducting corrosion product layers, and thin layers with complicated chemistry. Recent development of FTIR microscopy has enabled chemical maps to be formed of bonding configurations associated with very small features and thus has allowed the simultaneous optical and chemical exploration of catalysis, contamination and corrosion on surfaces. An obstacle to the application of FTIR microspectroscopy in some cases has been the long data collection times necessitated by relatively weak thermal globar type IR sources, the noise inherent in the broad spectrum associated with these sources, and the spatial resolution limit of around ten microns associated with commercial FTIR microscopes. In order to overcome these limitations, the infrared, part of the synchrotron radiation spectrum provided by vacuum ultraviolet (VUV) beam-lines has been utilized as a source for FTIR mierospee-troscppy. The extremely bright, coherent nature of the synchrotron IR source has allowed for orders, of magnitude improvement in'source intensity and signal-to- noise ratio (hence greatly reducing collection times for mapping of weak signals from dilute chemistry) and reduction in. spot size to five micrqnsor less (increasing spatial resolution). A new free electron laser source for IR that may provide even greater benefit has very recently been developed at Thomas Jefferson National Accelerator Laboratory. The free electron laser (FEL) at Jefferson Laboratory generates tunable, coherent, high power radiation, currently spanning wavelengths from 3 to 6.6 microns, which could be suitable for analysis of vibrational frequencies for many functional groups of interest to materials research, in general and corrosion protective coatings in particular. The FEL has the optical properties characteristic of conventional lasers such as high spatial coherence and a near diffraction limited radiation beam, and hence its potential as a source for optical spectroscopy is apparent.