Abstract

An automated Raman microscope mapping system is described which uses single point analysis combined with a stepper-motor-driven microscope stage. Methods for one-dimensional full spectra line-scans and repetitive frequency selective line-scans providing a two-dimensional species map are reported. The technique is applied to a surface feature appearing on a sample of Fe-Cr steel oxidized at 800°C for 143 h. The results suggest that Fe<sub>3</sub>O<sub>4</sub>, FeCr<sub>2</sub>O<sub>4</sub> and Cr<sub>2</sub>O<sub>3</sub> develop fairly uniformly across much of the surface and that the formation of raised areas of more extensive corrosion is due to the absence of Cr<sub>2</sub>O<sub>3</sub> in these regions. In addition, a sample oxidized at 675°C for two hours was ball-cratered to provide a Raman depth profile. The corrosion scale was complex—the outermost layer comprising Fe<sub>2</sub>O<sub>3</sub> and some Fe<sub>3</sub>O<sub>4</sub>, while the inner layer consisted mainly of FeCr<sub>2</sub>O<sub>4</sub>, with some evidence of Cr<sub>2</sub>O<sub>3</sub>.

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