Raman imaging for surface characterisation of annealed electrical steel surfaces

Raman spectroscopy is a powerful tool in the determination of biological and polymeric samples. However, also the use of Raman spectroscopy for inorganic applications like for the determination of different iron oxides after specific corrosion experiments or meteorite compositions is common. In this work, the method of Raman imaging has been used for surface characterisation of high temperature long-term annealed steel samples as a function of the dew point of the annealing atmosphere. The investigation revealed that at a high dew point, oxides (Al2O3, SiO2), silicates (Fe2SiO4) and spinel phases (Fe2SiO4-spinel) could be identified by Raman imaging whereas at a low dew point the reactivity of aluminium with nitrogen and oxygen was preferred and the phase of aluminium nitride (AlN) as well as some aluminium oxide (Al2O3) could be detected. The Raman imaging was supported by EDX mapping to obtain the elemental composition of the surface and by XPS measurements to get an insight into the bonding states of the elements which both confirmed the results obtained via Raman imaging.