Characterization of surface oxides by Raman spectroscopy

Abstract

Raman spectroscopy is shown to provide direct information on the composition and structure of surface oxides formed on alloys. Previously, identification of specific compounds present in these oxides only could be inferred from conventional surface analysis methods. In our studies, backscattering spectra were obtained from thick oxide films (⪞10 μm) present on high purity and commercial stainless steels after exposure to air and coal gasifier environments at 980 °C. With as-grown oxides, data were obtained from the outer oxide regions. Spectra from inner regions also were measured using grazing-angle sectioning techniques. The presence of impurities and minor alloying constituents in the substrates are shown to have profound effect on results; for example, the addition of a few percent of titanium and manganese resulted in the formation of a duplex scale with a thin, complex, outer layer and a relatively thick α–Cr2O3 inner scale.