Raman spectroscopy of surface oxides at elevated temperatures

Backscattering Raman spectroscopy is demonstrated to be a useful technique for in situ characterization of oxide films on metals at high temperatures. Data obtained during oxidation at temperatures between 300 and 850 °C are presented for two different iron-based alloys. The sensitivity and specificity of the technique were sufficient to detect the formation of iron oxide films (Fe2O3 and Fe3O4) less than 150 Å in thickness at temperatures below 350 °C. Above 600 °C, the predominant oxide was Cr2O3; however, the presence of a few weight percent Mn in a commercial alloy produced a mixed spinel oxide in addition to Cr2O3.