Browsing by Author "Rafaja, David"

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    GRK 2802: Raman Spectroscopic Identi cation of Oxide Phases in a Cor- roded MgO-Steel Composite Anode Used in Aluminum Molten Salt Electrolysis
    (Technische Universität Bergakademie Freiberg, 2026-03-04) Drechsler, Felix; Yaroshevskyi, Serhii; Adamczyk, Alexander; Mehdizadehlima, Mahnaz; Richter, Julia; Himcinschi, Cameliu; Rafaja, David; Charitos, Alexandros; Aneziris, Christos G.; Kortus, Jens
    This study presents the post-mortem phase characterization of a metal ceramic composite anode composed of 316L stainless steel and recycled MgO, sourced from spent refractory lining bricks, employed in aluminium molten salt electrolysis. The analysis focused on the immersed section of the anode, where direct exposure to the molten Na-cryolite melt promotes the formation of corrosion products. Raman spectroscopy was applied as a structural characterization technique, providing phase information that complements the morphological and elemental analyses obtained from SEM EDX measurements. Due to its high spatial resolution, micro-Raman spectroscopy enabled the identi cation of local phases within the corrosion layer and the determination of their depth-dependent distribution. The local chemical analysis revealed an outer Fe O-rich layer penetrating several tens of micrometers into the material, followed by a Fe Al O-containing zone. Raman spectroscopy identi ed the Fe O layer as magnetite (Fe3O4) and the inner layer as hercynite (FeAl2O4), with a transition region consisting of Al-doped Fe3O4. The results demonstrate the applicability of Raman spectroscopy for identifying corrosion products to provide contributions to the corrosion mechanisms of MgO-steel anodes under electrolytic conditions.
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    GRK 2802: Spinel coatings produced via oxidation of an AISI 316L-MgO composite
    (Technische Universität Bergakademie Freiberg, 2026-02-03) Mehdizadehlima, Mahnaz; Schimpf, Christian; Martin, Stefan; Fabrichnaya , Olga; Rafaja, David
    The possibilities of producing protective spinel coatings on the surface of an AISI 316L-MgO composite via hightemperature oxidation at 800 ◦C, 900 ◦C and 1000 ◦C were explored using a combination of structure and microstructure analyses, and thermodynamic calculations. The structure and microstructure of the coatings were analyzed in situ and ex situ using high-temperature and conventional X-ray diffraction, scanning electron microscopy, electron backscatter diffraction and X-ray spectroscopy. The ex situ analyses identified the oxidation and reaction products and revealed their spatial distribution within the surface coating. The in situ analyses helped to describe the oxidation and reaction kinetics. It was found that Cr2O3, which forms on the surface of oxidized austenite grains, reacts quickly to the MgCr2O4 spinel, when it comes in contact with MgO. Longer oxidation times and higher oxidation temperatures facilitate the formation of Fe2O3 and MgFe2O4, which partially intermix with Cr2O3 and MgCr2O4. As the spinel phases are formed via interdiffusion and as their molar volume is larger than the molar volume of the original phases (MgO, Cr2O3/Fe2O3), they overgrow the surface of the MgO grains. This mechanism provides a basis for controlled growth of protective spinel coatings on the surface of the AISI 316L-MgO composites.