Chemical imaging of iron oxides and oxyhydroxides using near infrared Raman imaging microscopy

A new method of identifying and mapping the distribution of both iron oxides and oxyhydroxides using near infrared Raman imaging microscopy (NIRIM) is reported. This technique offers an important alternative to conventional spectroscopic techniques that provide spatially averaged data. The NIRIM instrument used for these studies combines fibre bundle image compression hardware and multivariate signal processing software to identify and map different iron minerals and corrosion products. The NIRIM images clearly distinguish hematite, magnetite, wustite, goethite, and lepidocrocite microstructures. The first chemical maps of naturally occurring iron minerals and corroded steel surfaces obtained using NIRIM spectral images, classified with the aid of a library of pure compound spectra, are presented.