Browsing by Author "Brachhold, Nora"

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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 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: 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: 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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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.