Browsing by Author "Roungos, Vasileios"

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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: 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: 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.