Technische Universität Bergakademie Freiberg

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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: CHARACTERIZATION OF COMMERCIAL MgO-C REFRACTORY BRICKS BASED ON MgO-C RECYCLATE WITH VARYING TOTAL CARBON CONTENTS
(Technische Universität Bergakademie Freiberg, 2025-11-26) Schramm, Alexander; Weidner, Anja; Biermann, Horst; Aneziris, Christos G.; Schemmel, Thomas
In light of the increasing focus on the recycling of refractories, the properties of commercial MgO-C refractory bricks containing MgO C recyclate are of significant economic and ecological importance. It is essential to consider that incorporating MgO-C recyclate can lead to increased variation in the material composition and, consequently, in the properties of MgO-C grades. In the present study, two commercially available grades of MgO-C bricks containing 47.5 wt.% MgO-C recyclate were characterized. The MgO-C recyclates of both grades were taken from different sources and differed particularly in their carbon content, which resulted in different total carbon contents of both MgO-C brick grades. In addition to determining fundamental properties of both MgO-C brick grades (e. g., total carbon content, bulk density, open porosity, and cold crushing strength), XRD analysis, refractoriness under load (RUL) tests, and four-point bending tests at 1000 °C in an argon atmosphere were conducted. A lower total carbon content resulted in an increased bulk density, higher thermal expansion and increased strength. Compared to a commercial MgO-C grade made from entirely fresh raw materials, the results of the RUL and bending tests revealed no detrimental effects through the incorporation of MgO-C recyclate. Despite different total carbon contents, both MgO-C grades with recyclate exhibited improved refractoriness in the RUL tests compared to the material containing only fresh raw materials.
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GRK 2802: Characterization of MgO-C recyclate and commercial MgO-C refractory bricks with and without Recyclate
(Technische Universität Bergakademie Freiberg, 2025-11-13) Schramm, Alexander; Stadtmüller, Till M. J.; Hubálková, Jana; Schimpf, Christian; Wüstefeld, Christina; Schemmel, Thomas; Aneziris, Christos G.; Weidner, Anja; Biermann, Horst
In light of the increasing focus on the recycling of refractories, the properties of commercial MgO-C refractory bricks containing MgO-C recyclate are of significant economic and ecological importance. In the present study, MgO-C recyclate and two commercially available MgO-C bricks – one grade consisting exclusively of fresh raw materials while the other containing 47.5 wt.% MgO-C recyclate – were comprehensively characterized. This involved the use of X-ray computed tomography, scanning electron microscopy, X ray fluorescence analysis, X-ray diffraction, as well as density and porosity measurements. The MgO C recyclate exhibited a heterogeneous composition consisting of MgO aggregates and contained an increased content of impurities compared to fresh MgO raw materials. The incorporation of MgO C recyclate as a raw material for commercial MgO-C bricks resulted in a decrease of the average MgO aggregate size, a higher porosity with a decrease in the median pore size and a reduced CaO/SiO2 ratio of the corresponding MgO-C brick grade. Furthermore, the MgO-C grade with 47.5 wt.% MgO-C recyclate exhibited a higher cold crushing strength, but a reduced oxidation resistance.
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GRK 2802: Densities, Surface Tensions, and Viscosities of Molten High-Silicon Electrical Steels with Different Silicon Contents
(Technische Universität Bergakademie Freiberg, 2025-10-24) Neubert, Lukas; Bellé, Matheus Roberto; Yamamoto, Taisei; Nishi, Tsuyoshi; Yamano, Hidemasa; Ahrenhold, Frank; Volkova, Olena
Density, surface tension, and viscosity of various liquid electrical steels are measured at different temperatures, varying in their silicon content between 3 and 6mass%. Density and surface tension are determined using the maximum bubble pressure method, while viscosity is investigated comparatively using a vibrating finger viscometer and an oscillating crucible viscometer. The results are compared with models known from the literature. Based on this, the density of the steel [ρ] = kgm 3 and the surface tension [σ] =Nm 1 can be described as a function of temperature [θ] = °C and silicon content [Si] =mass% using the equations: ρðθ, SiÞ ¼ 1.28 θ 104.18 Si þ 9081.8, σðθ, SiÞ ¼ 10 4 ½ 0.00903 θ2 1.21494 Si2 þ 29.268 θ 1.987 Si 22334 . There is a lack of experimental data in the literature for high-temperature thermophysical properties for electrical steels. This underlines once again the novelty and significance of this study, as the determined thermophysical properties are essential for a wide range of applications. For instance, they are crucial in the production of metallic powders for additive manufacturing by atomization to adjust the properties of the powders precisely. The findings are also important for steelmaking itself, as the corrosion behavior of refractory material can be better determined.
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GRK 2802: Effect of Oxygen on Thermophysical Properties of Molten High-Silicon Electrical Steels and Its Impact on Bubble Formation Behavior
(Technische Universität Bergakademie Freiberg, 2025-10-24) Neubert, Lukas; Bellé, Matheus Roberto; Seetharaman, Sridhar; Volkova, Olena
The presence of oxygen in liquid steels has a considerable influence on their properties. Higher oxygen concentrations are typical for unkilled melts, after tapping from the basic oxygen furnace (BOF) or during secondary metallurgy. This influences thermophysical properties, for instance, surface tension, due to the surface activity of dissolved oxygen. Processes in secondary metallurgy or the interaction of the melt with the refractory material will be different. In this study, density and surface tension of molten high-silicon electrical steels are analyzed dependent of different oxygen contents, which are comparable to industrial melts during secondary metallurgy. The maximum bubble pressure method was used, and total oxygen contents between 77 and 300 ppm were taken into consideration. The silicon content of the steels is varied between 3 and 6 mass-pct. The effect of oxygen on the bubble formation behavior during decarburization in a liquid steel melt is also discussed. The results make it possible to calculate the size of bubbles that form in a melt. These findings are transferred to the processing of electrical steels, to vacuum treatments like the RH or VOD process. Reactions such as decarburization and the dissolution behavior of alloying agents are described more precisely based on these insights.
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GRK 2802: Extraction of Vanadium from CaO–SiO2–MgO–Al2O3 Slags Based on Vaporization of Vanadium Pentoxide
(Technische Universität Bergakademie Freiberg, 2025-10-24) Neubert, Lukas; Shyrokykh, Tetiana; Tinkova, Nataliia; Seetharaman, Sridhar; Volkova, Olena
Vanadium is an important micro-alloying element for various steel grades. Consequently, it is also present in the slags used in the production of those grades. During steelmaking, the vanadium vaporization from the slag is not desirable, as it increases vanadium consumption and at the same time releases toxic vapors of its higher oxides. However, the recovery of vanadium from the slag after the processing is worthwhile. In oxidic form as vanadium pentoxide (V2O5), vanadium can be extracted from the slag. In this research, the vaporization behavior of vanadium from CaO–SiO2–MgO–Al2O3 industrial slag is investigated at 1873 K. The effect of different process parameters, e.g., the pressure in the furnace chamber, the duration of the oxygen treatment of the slag, and the oxygen flow rate, is considered. The effect of P2O5 and Fe2O3 addition on the extraction of vanadium is studied. It is possible to induce formation of V2O5 gas bubbles in the slag due to the oxidation of vanadium. Thus, vanadium respectively V2O5 is extracted from the slag.
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GRK 2802: Four-Point Bending Tests at High Temperatures on Commercial MgO-C Refractory Bricks with and Without Recyclate Considering Different Carbon Contents
(Technische Universität Bergakademie Freiberg, 2026-02-02) Schramm, Alexander; Knöchel, Lukas; Schemmel, Thomas; Aneziris, Christos G.; Weidner, Anja; Biermann, Horst
Given the growing emphasis on refractory recycling, the performance characteristics of commercial MgO-C bricks incorporating MgO-C recyclates are of considerable economic and environmental relevance. In the present study, four-point bending tests are conducted in an argon atmosphere on three commercial MgO-C brick grades over a temperature range from room temperature to 1300 °C. One MgO-C brick grade is produced exclusively from virgin raw materials, whereas the other two grades incorporate MgO-C recyclate at a high mass fraction of 47.5 wt.%. Due to the different sources of the recyclates, their carbon contents vary, resulting in different total carbon contents in the two MgO-C brick grades containing recyclate. Post-mortem SEM investigations show predominantly transgranular fracture through the MgO-C recyclates. The evaluation of the four-point bending tests reveals no detrimental effect of the MgO-C recyclates on bending strength. Instead, a decisive influence of the total carbon content is observed, with lower total carbon contents correlating with higher bending strength values. Furthermore, the heterogeneous structure of the MgO-C recyclates contributes to enhanced stress dissipation caused by anelastic deformation processes in the respective MgO-C brick grades, despite the accompanying decrease in virgin flake graphite content.
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GRK 2802: Fracture mechanics behavior of coarse-grained MgO-C at room and high temperature
(Technische Universität Bergakademie Freiberg, 2025-11-13) Solarek, Johannes; Schramm, Alexander; Henkel, Sebastian; Weidner, Anja; Aneziris, Christos G.; Biermann, Horst
The fracture mechanical properties of coarse-grained MgO-C were investigated in four-point bending tests at single-edge V-notched beams (SEVNB) at room and high temperature. For measurement of the crack mouth opening displacement (CMOD) an optical system was used. Room temperature tests were accompanied with microstructural observations of the crack path with the use of digital image correlation to investigate the mechanisms of crack propagation and to determine the crack length. MgO-C showed stable crack propagation at room temperature as well as up to 1500°C. Increased fracture toughness KIc and work of fracture were observed in the temperature range from 700°C to 1200°C. This behavior was correlated with crack closure, quasi-plastic deformation as well as the activation of visco-plastic creep mechanisms above 1200°C. Additionally, the results were discussed in terms of Hasselman’s thermal shock parameters.
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GRK 2802: HIGH-TEMPERATURE COMPRESSION TESTS AND ACCOMPANYING SEM INVESTIGATIONS OF MgO-C REFRACTORIES BASED ON FRESH MgO AND RECYCLATE
(Technische Universität Bergakademie Freiberg, 2025-08-27) Schramm, Alexander; Weidner, Anja; Biermann, Horst; Stadtmüller, Till M. J.; Aneziris, Christos G.; Schemmel, Thomas
With regard to the increasingly desired recycling of refractories, the properties of MgO-C containing recyclate are of high economic and ecological relevance. Two commercially available grades were studied to evaluate the influence of recyclate in MgO-C materials: MgO-C consisting only of fresh MgO as well as MgO-C with 50 wt.% recyclate. In this study, compression tests on these MgO-C materials were performed at room temperature, 1000°C and 1300°C. In order to investigate the microstructure and to identify the occurring damage mechanisms, scanning electron microscopy (SEM) investigations were carried out. The compression tests provided higher strengths at room temperature and at 1000°C for the MgO-C grade with recyclate compared to the grade with only fresh MgO and comparable strengths at 1300°C. Thus, the use of recycled agglomerates had no negative effect on the compressive strength.
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GRK 2802: Hochtemperatur-Biegefestigkeit von kohlenstoffgebundenem Magnesiumoxid (MgO-C) unter Einbindung von DIC
(Technische Universität Bergakademie Freiberg, 2025-09-16) Schramm, Alexander; Knöchel, Lukas; Biermann, Horst; Weidner, Anja
Kohlenstoffgebundenes Magnesiumoxid (MgO-C) als Vertreter der Feuerfestwerkstoffe ist als Zustellungsmaterial in Konvertern, Stahlgießpfannen und Elektrolichtbogenöfen unverzichtbar. Der Werkstoff ist in der Anwendung komplexen thermischen, mechanischen und korrosiven Beanspruchungen ausgesetzt. Die Bewertung der quasi-statischen Hochtemperaturfestigkeit ist daher von zentralem Interesse und Gegenstand der vorliegenden Studie. Vier-Punkt-Biegeversuche an kommerziellem MgO-C Feuerfestmaterial wurden in einer Hochtemperaturprüfmaschine unter Schutzgas bis 1300°C durchgeführt. Mittels digitaler Bildkorrelation (DIC) bei Raumtemperatur wurden Aussagen zu ablaufenden Schädigungsmechanismen gemacht. Die in dieser Studie durchgeführten Versuche lieferten bei erhöhten Temperaturen höhere Biegefestigkeiten als bei Raumtemperatur, was auf das Schließen von Rissen entlang der Grenzfläche zwischen MgO und kohlenstoffhaltiger Matrix zurückgeführt wird.
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GRK 2802: IMPROVEMENT OF THE PROCESSABILITY AND THE PROPERTIES OF LIGNIN AND COLLAGEN BONDED MGO-C REFRATORY MATERIALS BY ETHYLENE GLYCOL ADJUSTMENT
(Technische Universität Bergakademie Freiberg, 2026-02-16) Stadtmüller, Till Manon Jannis
This study systematically investigates the influence of the ethylene glycol content on the physical properties of lignin- and collagenbonded MgO-C refractory materials, particularly the compressibility, density, and porosity. The results show that an ethylene glycol content of 1.5 wt.% results optimal material properties, achieving the highest geometric bulk density, lowest open porosity, and maximum cold crushing strength of the experimental series. This work highlights the crucial role of the moisture content on the processability and its impact on the mechanical properties of the final product. The findings provide valuable insights into optimizing the binder systems of MgO-C materials, leading to improved production processes and enhanced performance in hightemperature applications.
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GRK 2802: Influence of MgO-C recyclate on the thermo-mechanical compression behavior of commercial MgO-C refractory bricks
(Technische Universität Bergakademie Freiberg, 2026-02-02) Schramm, Alexander; Hubálková, Jana; Roungos, Vasileios; Schemmel, Thomas; Aneziris, Christos G.; Weidner, Anja; Biermann, Horst
In the present study, various thermo-mechanical tests under compressive load were performed on commercial MgO-C refractory brick grades over a wide temperature range up to 1600 °C in an argon atmosphere. The focus of the present study was the assessment of the influence of the incorporation of MgO-C recyclate on the thermo-mechanical behavior. Therefore, one MgO-C brick grade contained only fresh raw materials, while the other grade included MgO-C recyclate with a high mass fraction of 47.5 wt.%. Subsequent investigations, including scanning electron microscopy and porosity analyses, provided insights into the mechanisms occurring within the material during the thermo-mechanical tests. The incorporation of MgO-C recyclate led to an improvement in the thermo-mechanical properties, as increased compressive strength values were observed within the tested temperature range, along with enhanced creep resistance and improved behavior in the refractoriness under load tests.
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GRK 2802: Mechanische Hochtemperatur-Eigenschaften von Stahl-Keramik Verbundwerkstoffen auf der Basis von Cr-Ni Stahl und grobkörnigem MgO
(Technische Universität Bergakademie Freiberg, 2026-02-05) Müller, Moritz; Compart, Amaya; Biermann, Horst; Weidner, Anja
In dieser Studie wurden potenzielle Materialien für den Einsatz als kohlenstofffreie Elektroden in der Schmelzflusselektrolyse von Primäraluminium untersucht. Dabei wurden Metall-Keramik Verbundwerkstoffe auf Basis von Stahl AISI 316L und grobkörnigem MgO hinsichtlich ihrer Kriechbeständigkeit bei 900°C über eine maximale Dauer von 10 h charakterisiert. Verglichen wurden Verbundwerkstoffe, die entweder mit frischem Schmelzmagnesia oder mit recyceltem MgO verstärkt wurden. Beide Materialien zeigten lediglich eine minimale Kriechrate, ohne dass ein stationärer Kriechbereich erreicht wurde. Die deutlich bessere Kriechbeständigkeit der Variante mit recyceltem MgO ist auf die feinkörnigere und homogenere Partikelgrößenverteilung zurückzuführen. Als dominanter Schädigungsmechanismus wurde die Dekohäsion und Hohlraumbildung an den Grenzflächen zwischen Stahl und Keramik identifiziert.
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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.
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GRK 2802: Phosphorus Partition Between Liquid Crude Steel and High-Basicity Basic Oxygen Furnace Slags Containing V2O5
(Technische Universität Bergakademie Freiberg, 2025-10-24) Neubert, Lukas; Kovtun, Oleksandr; Kreschel, Thilo; Volkova, Olena
The influence of V2O5 on the phosphorus partition between liquid crude steel and heterogenous basic oxygen furnace (BOF) slag with CaO/SiO2 = 4.2 was investigated at a temperature of 1600 C in a middle frequency induction furnace. Thereby the phosphorus transfer from ‘‘steel to slag’’ as well as from ‘‘slag to steel’’ was studied over a holding time of 60 minutes. The measured results were shown as phosphorus partition and phosphorus capacity and compared with the experimental values from the literature. It was found that V2O5 in highly basic BOF slags decreases phosphorus partition and phosphorus capacity. In addition, the resulting slags were investigated using a scanning electron microscope (SEM).
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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.
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GRK 2802: Recycled magnesia particles in steel-based composites: Impact on thermo-mechanical behaviour
(Technische Universität Bergakademie Freiberg, 2026-02-02) Müller, Moritz; Mehdizadehlima, Mahnaz; Yaroshevskyi, Serhii; Aneziris, Christos G.; Biermann, Horst; Weidner, Anja
This study investigates the thermo-mechanical behaviour of steel-ceramic composites based on a matrix of austenitic stainless steel and coarse-grained magnesia particles. Composites reinforced with fresh-fused magnesia particles were compared to those reinforced with recycled magnesia sourced from spent MgO-C refractory lining bricks. The volume fraction of recycled magnesia varied from 20 vol% to 40 vol%. Quasi-static compression tests were performed at room temperature and within a temperature range of 800 ◦C–1100 ◦C. Results showed that incorporating coarse-grained ceramic reinforcements into the steel matrix increased the compressive strength at all temperatures. The composite reinforced with recycled magnesia demonstrated superior mechanical properties over the variant with fresh-fused magnesia due to a smaller and more uniform particle size distribution resulting from crushing steps in the recycling process. Although non-metallic inclusions from contaminated zones of the refractory bricks were present in the recycled powder, they did not affect the overall damage mechanisms.
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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.
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GRK 2802: Vaporization of Vanadium Pentoxide from Iron and Steel-Making Slags
(Technische Universität Bergakademie Freiberg, 2025-10-24) Neubert, Lukas; Volkova, Olena
Vanadium is present in increased amounts in slag because of the production of certain steel grades and manufacturing technologies. In terms of circular economy, vanadium should be recovered from the slag, to use it again as an alloying element. Only a few studies on the extraction of vanadium have been carried out with synthetic slags. The core of this study is the characterisation of the extraction behaviour of vanadium by evaporation of its oxides from real iron and steel-making slags. The effect of various influencing factors on the evaporation behaviour of the slags should be demonstrated. The evaluation of the results should also take crucible wear into account. In addition, the phases formed in the slag are to be analysed. For this purpose, several melting tests are carried out with different blast furnace slags. To determine the vaporised components, the slags are analysed by an X-ray fluorescence spectrometer.

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