Browsing by Author "Richter, Julia"

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Application of Raman and Photoluminescence Spectroscopy to MgO-C Refractories
(Technische Universität Bergakademie Freiberg, 2026-10-06) Richter, Julia; Drechsler, Felix; Stadtmüller, Till M. J.; Himcinschi, Cameliu; Aneziris, Christos G.; Kortus, Jens
Magnesia-carbon (MgO-C) bricks partially made of recycled magnesia (MgO) are examined in hardened and coked state using Raman and photoluminescence (PL) spectroscopy, focusing on the MgO grains compared with nominally pure MgO powder for reference. Raman and PL signals in the visible to near infrared range are distinguished and interpreted by varying the excitation wavelength between 532, 633, and 785 nm. Besides a broad PL band centered at 565 nm characteristic of the brick-derived MgO, the origin of two sharp high-intensity PL signals (699, 871 nm) surrounded by symmetrical sidebands is clarified. The 699 nm luminescence reveals the presence of trivalent chromium (Cr3+) impurities in the MgO lattice of MgO-C bricks as well as MgO powder, while the latter, V2+-related PL signal is only observed for the brick-derived MgO. The nature of the symmetrical sidebands is investigated by temperature-dependent spectroscopic measurements between 100 and 295 K. The temperature dependence of the intensity ratio between higher energy (anti-Stokes) and lower energy (Stokes) sidebands confirms the phonon involvement in both the MgO:Cr3+ and MgO:V2+ signals. This study enhances the spectroscopic methods to apply to industrial refractory materials, while it reveals impurities on a defect level that is not accessible by any well-established analysis.
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GRK 2802: Application of Raman and Photoluminescence Spectroscopy to MgO-C Refractories
(Technische Universität Bergakademie Freiberg, 2026-10-15) Richter, Julia; Drechsler, Felix; Stadtmüller, Till M. J.; Himcinschi, Cameliu; Aneziris, Christos G.; Kortus, Jens
Magnesia-carbon (MgO-C) bricks partially made of recycled magnesia (MgO) are examined in hardened and coked state using Raman and photoluminescence (PL) spectroscopy, focusing on the MgO grains compared with nominally pure MgO powder for reference. Raman and PL signals in the visible to near infrared range are distinguished and interpreted by varying the excitation wavelength between 532, 633, and 785 nm. Besides a broad PL band centered at 565 nm characteristic of the brick-derived MgO, the origin of two sharp high-intensity PL signals (699, 871 nm) surrounded by symmetrical sidebands is clarified. The 699 nm luminescence reveals the presence of trivalent chromium (Cr3+) impurities in the MgO lattice of MgO-C bricks as well as MgO powder, while the latter, V2+-related PL signal is only observed for the brick-derived MgO. The nature of the symmetrical sidebands is investigated by temperature-dependent spectroscopic measurements between 100 and 295 K. The temperature dependence of the intensity ratio between higher energy (anti-Stokes) and lower energy (Stokes) sidebands confirms the phonon involvement in both the MgO:Cr3+ and MgO:V2+ signals. This study enhances the spectroscopic methods to apply to industrial refractory materials, while it reveals impurities on a defect level that is not accessible by any well-established analysis.
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GRK 2802: Extra-carbonization of biochar pellets obtained after co-torrefaction and co-pyrolysis with bituminous coal
(Technische Universität Bergakademie Freiberg, 2025-11-28) Koveria, Andrii; Zuber, Jan; Himcinschi, Cameliu; Vogt, Carla; Richter, Julia
The paper investigates the chemical and structural changes in biochar pellets resulting from the co-torrefaction and co-pyrolysis of pine wood (Pinus sylvestris) pellets with bituminous coal at a 1:1 ratio at 300, 500, and 700 °C. At 500 °C co-pyrolysis, noticeable changes occur in biochar during co-treatment with coal, as observed by Fourier-transform infrared spectroscopy (FT-IR), graphite-assisted laser desorption/ionization-Fourier transform ion cyclotron resonance mass spectrometry (GALDI-FT-ICR-MS), and Raman spectroscopy compared to individual pyrolysis. Proximate and ultimate analyses show an increase in carbon content and decreases in volatile matter, oxygen, and hydrogen in co-treated biochar pellets. FT-IR and van Krevelen plots indicate compounds with lower O/C ratios and fewer oxygen-rich functionalities. Raman spectroscopy shows that, at 300 and 500 °C, co-pyrolyzed biochar pellets have slightly more structural ordering and less disorder than biochar pellets from individual pyrolysis. This suggests that co-processing allows the creation of a more ordered aromatic carbon structure. GALDI-FT-ICR-MS indicates an increase in condensed aromatic hydrocarbons at the expense of lignin-like and oxygen-rich structures compared with individual pyrolysis. Specifically, 500 °C co-pyrolysis shifts biochar pellets composition toward lower O/C ratios (0–0.3); products are enriched in condensed aromatic hydrocarbons and occupy van Krevelen regions with low O/C (0–0.2) and H/C (0.4–0.8). The results demonstrate extra-carbonization effects in biochar pellets during co-pyrolysis with bituminous coal at 500 and 700 °C.
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GRK 2802: Raman Spectroscopic Identi cation of Oxide Phases in a Cor- roded MgO-Steel Composite Anode Used in Aluminum Molten Salt Electrolysis
(Technische Universität Bergakademie Freiberg, 2026-03-04) Drechsler, Felix; Yaroshevskyi, Serhii; Adamczyk, Alexander; Mehdizadehlima, Mahnaz; Richter, Julia; Himcinschi, Cameliu; Rafaja, David; Charitos, Alexandros; Aneziris, Christos G.; Kortus, Jens
This study presents the post-mortem phase characterization of a metal ceramic composite anode composed of 316L stainless steel and recycled MgO, sourced from spent refractory lining bricks, employed in aluminium molten salt electrolysis. The analysis focused on the immersed section of the anode, where direct exposure to the molten Na-cryolite melt promotes the formation of corrosion products. Raman spectroscopy was applied as a structural characterization technique, providing phase information that complements the morphological and elemental analyses obtained from SEM EDX measurements. Due to its high spatial resolution, micro-Raman spectroscopy enabled the identi cation of local phases within the corrosion layer and the determination of their depth-dependent distribution. The local chemical analysis revealed an outer Fe O-rich layer penetrating several tens of micrometers into the material, followed by a Fe Al O-containing zone. Raman spectroscopy identi ed the Fe O layer as magnetite (Fe3O4) and the inner layer as hercynite (FeAl2O4), with a transition region consisting of Al-doped Fe3O4. The results demonstrate the applicability of Raman spectroscopy for identifying corrosion products to provide contributions to the corrosion mechanisms of MgO-steel anodes under electrolytic conditions.
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GRK 2802: Thermophysical Properties of the Desulphurization Slags With Various CaS and CaO/Al2O3 Ratio
(Technische Universität Bergakademie Freiberg, 2026-09-25) Salpagarov, Eldar; Bellé, Matheus Roberto; Yehorov, Anton; Richter, Julia; Volkova, Olena
Low sulphur content is essential for high-quality steels and can be achieved by using desulphurization slag. During the desulphurization process the chemical composition of the slag changes leading to alteration in its thermophysical properties, such as surface tension, viscosity, and density. However, the influence of CaS on these thermophysical properties is poorly investigated nowadays. In this study, the influence of various CaS content (0-10 wt%) and CaO/Al2O3 ratio (1.87-1.36) on the viscosity, surface tension, and density of desulphurization slags is investigated. Measurements of surface tension and density are carried out using the maximum bubble pressure method, while viscosity is determined using the rotating bob method. The obtained results show that a decrease in viscosity value is observed with an increase in CaS content only up to 6 wt%, however, further addition of CaS sharply increases viscosity. In case of surface tension and density measurements, an increase in CaS content up to 10 wt% results in a reduction of both property values. Additionally, to study microstructure differences of the investigated slags, they were quenched and examined using Scanning electron microscopy (SEM) and Energy-dispersive X-ray spectroscopy (EDX).