The Formation of Oxide Scale on FeCrAl at 900°C in dry O2 and O2 + 40% H2O

Polished Kanthal AF samples were oxidized isothermally at 900°C in O2 and in O2+40% H2O for between 1 and 168 hours. The samples were analysed gravimetrically, by Grazing-Incidence X-ray diffraction, Scanning Electron Microscopy, Energy Dispersive X-ray analysis and Auger Electron Spectroscopy profiling. Much of the surface is covered by a thin and smooth base oxide with Mg-rich nodules on top. In addition, patches of thick uneven oxide and RE-oxide protrusions are present on the surface. Exposure to O2+40% H2O results in significantly higher initial oxidation rate than dry O2. The presence of water vapour also influences oxide morphology. The thick oxide patches exhibit needle-like crystals in dry O2 while rounded oxide agglomerates dominate in O2/H2O. The chemical composition of the oxide was the same in O2 and in O2+40% H2O. α-Al 2O3, γ-Al2O3 and MgAl 2O4 form in both environments