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Optical Characterization of Thin Film Oxides Grown on Ferrous and Non-Ferrous Metals
Metallic alloys used in various industrial applications can encounter high operating temperatures for varying periods of time. Under these conditions, metals are susceptible to oxidation, ultimately leading to the failure of that component or even complete system failure. Traditional methods of evaluating the extent of oxide growth, such as cross-sectional scanning electron microscopy, are destructive in nature and cannot be used to monitor the health of the structure while in service. Therefore, it is beneficial to have a method to determine the extent of oxidative attack on a component while in service. Optical analytical methods, which include spectral analysis and illuminance, offer an exciting non-destructive pathway to evaluate structures especially in hard to access or unsafe areas. In this study, the early onset of oxide films on UNS C11000, UNS G30400 and UNS R50400, at temperatures in the 125-900॰C range was determined. The color cycle was studied using a spectrophotometer to observe minute differences in the range of colors observed as the oxide film continues to grow. As the oxide film grows, it cycles between three colors: straw, brown and blue. The wavelength and intensity of the reflected incident light off the oxide film can indicate the state of oxidation. Results from the optical experiments were related to those obtained from scanning electron microscopy with energy dispersive spectroscopy (SEM/EDS) and optical microscopy. The oxide films were further characterized by non-contact profilometry and X-Ray diffraction (XRD).