Technische Universität Bergakademie Freiberg

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Browsing Technische Universität Bergakademie Freiberg by Author "Aneziris, Christos"

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  • ItemOpen Access
    GRK 2802: Anodes based on MgO-C Recyclates and 316L Steel for Prospective Aluminium Fused-Salt Electrolysis Application
    (Technische Universität Bergakademie Freiberg, 2026-09-25) Gehre, Patrick; Yaroshevskyi, Serhii; Kaiser, Patricia; Brachhold, Nora; Hubálková, Jana; Aneziris, Christos
    Every year, approx. 28 million tons of used refractories accumulate worldwide. The majority of them are used as aggregates for road construction (downcycling) or are deposited in landfills. For ecological and economic reasons, an increased research potential was identified in recent years, dedicated to increasing the recycling rate and finding new markets and application fields with a higher value of the refractory recyclates. The study presents the current findings of the development of inert electrodes for the aluminum fused-salt electrolysis composed of steel and MgO gained from MgO-C recyclates. To withstand the chemical attack of molten aluminum and cryolitic melts, the metal-ceramic composites were preoxidized (PO) at 800 °C, 900 °C, and 1000 °C. The microstructure after each PO thermal treatment was analyzed. After PO at 800 °C, a (Cr,Fe)3O4 spinel-like phase and Fe-O Mg-O solid solution form. After PO at 900 °C, a larger amount of the Fe-O Mg-O solid solution and a (Cr,Fe)2O3 solid solution around the steel grains was identified. Furthermore, the electrical conductivity of the metal-ceramic-composites preoxidized at 900 °C amounts to 1.49·102 S·cm-1 and hence is in the range of carbon, which exhibits a value of 1.54·102 S·cm-1. Additionally, the impact of different preoxidation treatments at 900 °C by applying furnaces equipped with electrical heating, natural gas burner, and microwave plasma burner on the microstructure was investigated.
  • ItemPublic Metadata
    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.
  • ItemOpen Access
    GRK 2802: MgO-C Ladle Bricks based on Recyclates and Lignin-Collagen-Fructose Binder System
    (Technische Universität Bergakademie Freiberg, 2026-09-25) Gehre, Patrick; Gunasekar, Dinesh Kumar; Hubálková, Jana; Aneziris, Christos
    Every year, approx. 28 million tons of used refractories accrue worldwide. After their break out, the majority of them are used in subordinate application fields such as aggregates for road construction (downcycling) or deposited in landfills. Their recycling in the field of refractory materials played an underpart so far. For ecological and economic reasons, an increased research potential was identified in the last years consecrated to increasing the recycling rate of refractories and finding new markets and application fields with higher value for them. The study presents current findings of a long-term research training group addressing (amongst others) the development of MgO-C ladle bricks containing MgO-C recyclates and being bonded with pitch- and resin-free environmentally friendly binders. So far, the favored batches contained an oxidic grain fraction composed of 40.5 wt.-% fused MgO raw material, 40.5 wt.-% MgO-C recyclates, 14 wt.-% sintered magnesia (DBM) raw material together with 5 wt.-% graphite and optional antioxidants (TiO2, Al, SiO2). A binder system composed of a mixture of lignin, collagen, and polyethylene glycol (PEG) was developed. The latter served as a pressing aid and was necessary due to the absence of liquid resin in the batch. Even after a considerable and auspicious optimization during previous studies, this basic batch containing recyclates and no pitch or resin does not meet the physical and mechanical properties of standard industrial bricks. Hence, in the present study, the binder system was enhanced by using varying amounts of lignin, collagen, and tannin together with polyethylene glycol, fructose, and citric acid addition. The new developed MgO-C mixtures were pressed uniaxially, dried, cured, and carbonized at 1000 °C. It has been found that polyethylene glycol, which impairs the material properties, can be omitted using sufficient amounts of fructose. The addition of citric acid leads to a further increase in CCS. Consequently, actual optimized environmentally friendly MgO-C batches show a CCS of 85 % of the value of industrial pitch- and resin-bonded bricks without recyclates.
  • ItemPublic Metadata
    GRK 2802: MgO-C REFRACTORIES BASED ON REFRACTORY RECYCLATES AND ENVIRONMENTALLY FRIENDLY BINDERS
    (Technische Universität Bergakademie Freiberg, 2026-02-16) Stadtmüller, Till Manon Jannis; Storti, Enrico; Brachhold, Nora; Lauermannová, Anna-Marie; Jankovský, Ondřej; Schemmel, Thomas; Hubálková, Jana; Gehre, Patrick; Aneziris, Christos
    This study focused on the development of an environmentally friendly binder system based on lignin and collagen for uniaxial pressed MgO-C refractories as an alternative to commonly used resin or pitch binders. Additionally, recycled MgO-C refractories from steel plants were partially utilized as raw material, investigating their influence on the resulting physical and mechanical properties. The binder system showed reliable binding properties, although the recyclate-containing MgO-C exhibited higher porosity, slightly lower density, and lower strength compared to the reference batches without recyclates. However, antioxidants significantly improved the properties of the recyclatecontaining MgO-C samples. Scanning electron microscopy analysis with energydispersive X-ray spectroscopy revealed the formation of whiskers, as well as oxidation and nitridation of aluminum particles. This research highlights the potential of environmentally friendly binders and the utilization of recycled materials in MgO-C refractories to mitigate their environmental impact and enhances the environmental performance of carbon containing refractory materials.
  • ItemPublic Metadata
    GRK 2802: Pre‐oxidized Recycled MgO–Steel Composite Material for Possible Application in Cryolitic Melts
    (Technische Universität Bergakademie Freiberg, 2026-02-16) Yaroshevskyi, Serhii; Brachhold, Nora; Malczyk, Piotr; Gehre, Patrick; Aneziris, Christos
    Recycled MgO–C lining bricks and 316L stainless steel are used to manufacture composite material for inert anode samples for aluminum electrolysis cell. The microstructure of the composite material is characterized after preoxidation thermal treatments at 800, 900, and 1000 °C as well as in its sintered state. Preoxidation (PO) process is designed to enhance the material's corrosion resistance in molten cryolite environments by developing robust Fe–Mg–O, Fe–Cr–O- containing phases. Analytical techniques including scanning electron microscopy, electron backscatter diffraction, and energy dispersive X-ray spectrometry are applied to characterize the phase formation, revealing the potential of these composites for use as inert anodes in aluminum electrolysis cells. PO at 800 °C is not sufficient to form adequate protective oxide layers. Whereas, PO at 900 and 1000 °C leads to the formation of protective oxide layers containing Mg–O Fe–O halite-like solid solutions and (Cr,Fe)3O4 spinel phase. Sample, preoxidized at 1000 °C is sealed in Mg–Fe–O spinel phase.
  • ItemPublic Metadata
    GRK 2802: Steel ceramic composite anodes based on recycled MgO–C lining bricks for applications in cryolite/aluminum melts
    (Technische Universität Bergakademie Freiberg, 2026-02-16) Yaroshevskyi, Serhii; Weigelt, Christian; Malczyk, Piotr; Roungos, Vasileios; Hubalkova, Jana; Zienert, Tilo; Kraft, Bastian; Wagner, Stefan; Aneziris, Christos
    Novel manufacturing route for composite inert anodes containing 60:40 of 316 L stainless steel and MgO powder obtained from recycled MgO-C brick material has been developed and evaluated. After burnout of residual carbon from the recycled MgO-C powder, MgO and steel were granulated and pre-sintered in order to generate agglomerates of composite material acting as coarse grains within the composite material, and thus lowering the sintering-related shrinkage. The pre-sintered granules were mixed with raw steel and MgO powder in order to achieve a high particle packing and subsequently cold isostatically pressed in the form of electrodes. All manufactured anode samples were subjected to sintering at 1350 ◦C and pre-oxidation at different temperatures – 800 °C, 900 °C, and 1000 °C. Afterwards, mechanical and electrical properties of the manufactured electrodes were characterized. The results show that upcycling of the MgO-C material enables manufacturing of sophisticated electrode products, which can be applied in the aluminum industry.