Optical fluorescence spectroscopy for identification of minor oxide phases in alumina scales grown on high temperature alloys

In the present study laser induced fluorescence optical spectroscopy (LIFOS) has been used for characterization of alumina based surface scales formed during oxidation of high temperature alloys. Prior to the analysis of oxide scales, a set of reference data has been obtained on single crystals of α-Al2O3 and several oxide phases (Y3Al5O12, YAlO3 and MgAl2O4) frequently found as minor constituents in the alumina scales. A number of effects, which can affect the fluorescence spectra has been studied on the single crystals. Hence the analyses were carried out at different temperatures in the range of 77 to 303 K, at different laser powers and using two primary laser wavelengths. ference spectra were used as a basis for phase analyses of the oxide scales formed on FeCrAl-alloys during air oxidation at 1200 °C. The spectrometry results of the oxide scales were compared with the data obtained with SEM and XRD. Although identification of the minor alumina scale phases using LIFOS appears to be possible, care should be taken when interpreting the results. The main reason is by far stronger fluorescence from alumina, however other important effects are also discussed, which are responsible for discrepancies between the spectra obtained from “ideal” reference specimens and those from the minor phases in oxide scales.