Browsing by Author "Schramm, Alexander"

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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: 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: 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.