Technische Universität Bergakademie Freiberg

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

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    DFG 465144480: Boron-free self-glazing Al₂O₃-C refractories
    (Technische Universität Bergakademie Freiberg, 2026-04-01) Roungos, Vasileios; Gehre, Patrick; Salpagarov, Eldar; Aneziris, Christos G.
    Al₂O₃-C refractories are extensively used as functional components in the continuous casting of steel. These high-duty products such as submerged entry nozzles, ladle shrouds, and monoblock stoppers contain up to 30 wt.-% carbon and present excellent mechanical, thermal and chemical properties, enabling the cost- and quality-effective implementation of the continuous casting process. Ceramic glazes are externally applied on Al₂O₃-C flow control refractory products to protect carbon from oxidation. These glazes typically contain boron. However, the increasing requirements for clean steel technology along with environmental- and health issues associated with boron compounds will make the utilization of boron-free glazes a necessity in the upcoming years. New boron-free self-glazing Al₂O₃-C formulations with sodium carbonate, wollastonite and magnesia additives were developed with the assistance of the FactSage software tool. These compositions presented a softening point in the range of 1000-1100 °C for self-glaze formation, which is the typical preheating temperature range for Al₂O₃-C functional refractory products. In addition, the influence of particle packing on their oxidation resistance was investigated, based on established particle size distribution models.
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    DFG 465144480: Impact of cyclic CIP on the oxidation resistance and physical properties of a newly developed boron-free self-glazing Al2O3-C refractory
    (Technische Universität Bergakademie Freiberg, 2026-03-31) Roungos, Vasileios; Gehre, Patrick; Brachhold, Nora; Fischer, Undine; Aneziris, Christos G.
    The impact of cyclic cold isostatic pressing (C-CIP) on the oxidation resistance and physical properties of a boron-free self-glazing Al2O3-C refractory for steel casting applications was investigated. Pulsations with amplitudes of 20, 40 and 65 MPa were thereby applied either at maximum isostatic pressure or at increasing pressure. The maximum isostatic pressures applied were 80, 100 and 150 MPa, respectively. Both cycling pressurizations improved the oxidation resistance and physical properties. Higher densities were obtained at higher cycling amplitudes, in particular when the pulsations were applied at maximum isostatic pressure. In addition, the evolution of a broader pore size distribution with peaks at pores larger than 4 μm was found. The pore size distributions of the samples pressed by C-CIP at increasing pressure were narrower, with higher peaks at smaller pore sizes in the area of 2.5 μm. It was shown that utilizing cycling pressurization enables tailoring of pore sizes in carbon-bonded refractories as well, providing a powerful tool for the material design of refractories.
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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: 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: 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: Interactions between Molten High-Silicon Electrical Steels and Carbon-Bonded MgO Refractories Based on Recyclates
    (Technische Universität Bergakademie Freiberg, 2026-05-29) Neubert, Lukas; Bellé, Matheus Roberto; Yehorov, Anton; Mospan, Anhelina; Stadtmüller, Till M. J.; Sridhar, Seetharaman; Aneziris, Christos G.; Volkova, Olena
    In the present study a comprehensive investigation of the interactions between different molten high-silicon electrical steels (3 to 6 mass-% silicon) in aluminum killed condition with conventional and recycled MgO–C refractories is conducted. Immersion tests are carried out in accordance with the standards for testing and assessment of corrosion of refractories by liquids (DIN CEN/TS 15 418). Various mechanisms are defined and described which determine the corrosion of the refractory material in addition to infiltration. Scanning electron microscopy including energy dispersive X-ray spectroscopy (EDX analysis) is conducted to identify wear reactions, material transfers and reaction products at the contact zones and in the infiltration layers. The theoretically possible infiltration length is calculated and the limited applicability of the equations known from the literature is discussed. The formation of calcium sulfides and on other crucible reactions that take place are considered. These provide information and at the same time they influence the interactions between refractory materials and liquid steel.
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    GRK 2802: Population of Nonmetallic Inclusions in Liquid High-Silicon Electrical Steel in Contact With MgO–C Refractories Based on Recyclates and Environmentally Friendly Binders
    (Technische Universität Bergakademie Freiberg, 2026-05-29) Neubert, Lukas; Bellé, Matheus Roberto; Kerber, Florian; Gunasekar, Dinesh Kumar; Weddige, Hans-Jörn; Aneziris, Christos G.; Volkova, Olena
    Nonmetallic inclusions (NMIs) are integral constituents of ferrous materials, but almost always have a negative impact on their properties. Therefore, it is best to implement strategies during production to avoid NMIs as much as possible or at least control their formation. To gain a better understanding of these mechanisms, this study investigated the population of nonmetallic inclusions in liquid high-silicon electrical steel (Si 3 mass-%) depending on the contact with different MgO–C refractories. Both conventional refractory materials and those containing MgO–C recyclate and environmentally friendly binder systems, such as collagen, fructose, and lignin, were considered. Immersion tests were carried out for 30min at a temperature of 1600°C in accordance with DIN CEN/TS 15418. Surface phenomena, diffusions reactions, and corrosion mechanisms occurring in the refractory materials were characterized after the tests using SEM and EDX analyses. The change in the chemical composition of the steels was determined using spark spectroscopy, and the NMI population was evaluated after the tests using an automated feature analysis (AFA).
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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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    GRK2802: Non-metallic Inclusion Evolution in Interaction of Al-killed Mn-B Steel with Desulfurization Slag and MgO-C Refractories Containing Environmentally Friendly Binders and Recyclates
    (Technische Universität Bergakademie Freiberg, 2026-05-20) Bellé, Matheus Roberto; Neubert, Lukas; Yehorov, Anton; Kerber, Florian; Gunasekar, Dinesh Kumar; Salpagarov, Eldar; Aneziris, Christos G.; Volkova, Olena
    The high-temperature interaction between Al-killed Mn-B steel, desulfurization slag, and carbon-bonded magnesia refractories containing conventional, environmentally friendly binders and recyclate systems was systematically investigated using finger immersion testing at 1600 °C for 30 minutes. Chemical analysis of steel and slag, combined with SEM/EDX characterization of refractory/steel/slag interfaces and non-metallic inclusions (NMIs), was performed to interpret reaction mechanisms and the evolution of inclusions. Significant slag modification occurred during testing, characterized by MgO enrichment, CaO and Al2O3 depletion, and the formation of Fe- and Mn-bearing oxides. In the steel, pronounced decarburization, sulfur increase, boron depletion, and enhanced oxygen and nitrogen contents were observed, indicating reoxidation and interfacial reactions. Independent of refractory condition, MgAl2O4 spinel and Ca2SiO4 phases were detected in the infiltrated refractory zone. Refractories containing recyclates and alternative binders chemically modified the inclusion population and significantly increased NMI number density, particularly Mn-Si-Ti-based inclusions. The results demonstrate that refractory composition strongly influences slag chemistry, inclusion characteristics, and steel cleanliness. These findings provide a new understanding of refractory-slag-steel interactions during secondary metallurgy and highlight the need for optimized slag/refractory formulations to ensure inclusion control and steel quality under increasingly sustainable material strategies.
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    SPP 2419: 3D printing of alumina components via Fused Granulate Fabrication technology and solvent-free debinding of highly filled feedstocks comprising (LD)-polyethylene and cellulose
    (Technische Universität Bergakademie Freiberg, 2026-03-30) Brachhold, Nora; Heuer, Claudia; Bock-Seefeld, Benjamin; Kaiser, Patricia; Weigelt, Christian; Malczyk, Piotr; Trimis, Dimosthenis; Aneziris, Christos G.
    This study focuses on the development of components in gyroid structure based on alumina as integral part of the novel burner designed for the non-premixed combustion of ammonia. During application, the component has to withstand repeated thermal shocks of approx. 600 K or more. Due to the high geometric complexity of the gyroid structure and the need for lightweight design with both macroporous regions and microporous features only the 3D printing was suitable as manufacturing technology; in the present work Fused Granulate Fabrication was used. The manufacturing routine for the employed granules with special regard to the binder system is developed. A customized thermal debinding regime without wick or solvent debinding is presented. Challenges such as the formation of bubbles and the swelling of the samples during thermal debinding were met by adjusting the printing parameters to create porosity and cavities between the deposited strands during 3D printing. Sintered bars fabricated using optimized printing parameters had a shrinkage of 13 %, an open porosity of 41 % and a flexural strength of 50 MPa, respectively. These values are sufficient for the application of the components in the novel burners. As last part of this work sheet-gyroid structures were prepared using a 1.0 mm and 0.4 mm nozzles. These structures successfully survived 5 thermal shock cycles, each involving heating to 1100 ◦C followed by air quenching, which is an excellent result in terms of thermal shock performance.
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    SPP 2419: Investigation of the (thermo-)mechanical properties and the chemical resistance towards ammonia combustion atmosphere of alumina-based model structures manufactured via Fused Granulate Fabrication
    (Technische Universität Bergakademie Freiberg, 2026-06-17) Brachhold, Nora; Bock-Seefeld, Benjamin; Kretzler, Daniel; Heuer, Claudia; Neumann, Marc; Hubálková, Jana; Stelzner, Björn; Stein, Oliver T.; Trimis, Dimosthenis; Aneziris, Christos G.
    This study focuses on the fabrication of alumina-based model samples by fused granulate fabrication for the application in burner components for ammonia combustion. Three compositions were investigated: Two alumina systems with different initial grain size (A1-tabular alumina, A2-reactive alumina) and alumina (AZT) with MgOstabilized ZrO2- and TiO2-additions. Young’s modulus and flexural strength were determined after sintering and after up to five thermal shocks. A1 exhibited the best suitability for repeated thermal shocks, followed by A3. The high interparticle porosity of A1 limited crack propagation and resulted in a slow, gradual loss in elastic modulus (maximum loss of 8.6%) and strength (maximum loss of 35.7%) with increasing number of thermal shocks. Microstructural features due to the additive manufacturing process could enhance thermal shock performance. The materials were tested in ammonia combustion atomosphere at approx. 1500 ◦C for 1 h and showed no phase alterations. Model components with application-near geometries were successfully realized.