Characterization of oxide scales on coatings for gas turbine blades by infrared reflection-absorption spectroscopy

The oxidation of chromia (Cr₂O₃) and alumina (Al₂O₃) forming alloys for the protection of gas turbine blades has been studied by Infrared Reflection Absorption Spectroscopy (IRAS). The Berreman-Effect (i. e. minimum of reflectivity of p-polarized light at oblique incidence) allows an unambiguous distinction between Al₂O₃ and Cr₂O₃ for thin scales (<0.1 m) as well as for thick scales (6 m). The position of interference fringes in the non-absorbing region of the spectrum results in simultaneous thickness determinations.