Browsing by Author "Charitos, Alexandros"

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    GRK 2802: Characterization of a recyclate-based MgO-steel as-sintered inert anode candidate after exposure to cryolite electrolysis
    (Technische Universität Bergakademie Freiberg, 2026-02-12) Yaroshevskyi, Serhii; Adamczyk, Alexander; Brachhold, Nora; Schmidt, Gert; Hubalkova, Jana; Gumeniuk, Roman; Charitos, Alexandros; Aneziris, Christos
    The replacement of consumable carbon anodes with oxygen-evolving inert, carbon free anodes is a key technological challenge for decarbonizing primary aluminum production. While metallic, ceramic, and cermet anodes have been extensively studied, the use of recycled raw materials remains largely unexplored. In this work, composite cermet anodes consisting of 60 vol% AISI 316L stainless steel and 40 vol% recycled MgO from spent refractories were developed and tested under galvanostatic Hall-Héroult electrolysis conditions in cryolite at 1000 °C. The as-sintered composites exhibited stable cell voltage (3.2-3.3 V) over 2 h of operation. Post-mortem SEM/EDS/EBSD analyses revealed a multilayered structure with protective Fe-oxide, Al/Cr spinel formation, corroded Mg-F-rich phases, and cryolite infiltration extending beyond 2 mm depth. While the 316L steel matrix showed relative stability, the recycled MgO fraction proved chemically reactive, generating porosity and acting as the primary pathway for melt intrusion and secondary Al2O3 precipitation. Complementary static contact corrosion tests confirmed rapid fluoridation of MgO, whereas steel grains remained intact.
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    GRK 2802: Investigations on the corrosion of 316L steel composite materials with MgO/TiO2 ceramic immersed in molten cryolite
    (Technische Universität Bergakademie Freiberg, 2026-06-25) Yaroshevskyi, Serhii; Weigelt, Christian; Kerber, Florian; Brachhold, Nora; Zienert, Tilo; Adamczyk, Alexander; Vogt, Daniel; Charitos, Alexandros; Aneziris, Christos G.
    Composites based on a steel with 40 vol% magnesia or titania were produced with the ceramics-derived extrusion and pressureless sintering. The materials were tested in a laboratory-scale fused-salt electrolysis cell with a synthetic cryolite in order to identify their potential use as electrode material in the Hall-Heroult process. The highly corrosive atmosphere and salt melt initiated certain corrosion effects in both material variants. The corrosion depth was determined with 1160 μm for magnesia and 463 μm for titania, respectively, after 8 h corrosion test. The initial corrosion includes the complete penetration of the specimens with cryolite and the dissolution of the ceramic component. A pre-oxidation of the specimens containing magnesia depressed the corrosion depth by 75% due to the formation of an aluminium oxide layer in the composite material during corrosion tests. The reduction in corrosion depth by pre-oxidation was less ronounced for the TiO2 composite materials (- 15%).
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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.