• Herr Han Sun, M.Sc.
• Freitag, 6. Dezember 2024, 11:45 Uhr
• Hörsaal Formgebung, FOR-0270, Haus Formgebung, Bernhard-von-Cotta-Straße 4, EG

This work studies the biotransformation profiling of a battery of endocrine-disrupting chemicals (EDCs), including 22 thyroid-disrupting chemicals (TDCs) and 9 parabens in rat and fish through in vitro enzyme assays using liver S9 fractions extracted from rat and fish hepatocytes. Biotransformation profiling succeeds in determining the Michaelis-Menten kinetics for several TDCs and parabens, as well as their intrinsic clearences, in rat- and fish-S9, and identifying formed metabolites by non-target analysis employing high resolution mass spectrometry. Significant differences in the metabolic kinetics and pathways of tested EDCs between rat and fish have been elucidated. Biotransformation resulting in toxic metabolites has been evidenced. These results characterize the species-specific biotransformation of EDCs and inform about the potential relevance of ED metabolites for their endocrine disruptions.

• Herr Rahul Ganesh, M.Sc.
• Montag, 9. Dezember 2024, 13:30 Uhr
• Hörsaal Ledebur-Bau, LED-1105, Leipziger Straße 34, 1. OG

This work was carried out as part of the research project „TMF Crack Path Calculation for Turbocharger Hot Parts“ of the FVV e.V., and aimed to develop a 3D Finite Element based incremental crack growth procedure for low cycle fatigue (LCF) and thermomechanical fatigue (TMF) in engineering components. The established crack growth simulations, based on linear elastic fracture mechanics concepts, are not applicable considering significant plastic and creep deformations over extended regions around the crack tip. As such, the cyclic crack tip opening displacement (∆CTOD) is chosen to quantify crack tip loading, and a solution mapping procedure is adapted to account for the deformation history effects due to large plastic deformations. A CHABOCHE-type viscoplastic temperature dependent material model under large strain settings, specified for the austenitic cast iron Ni-Resist D-5S, is used to accurately simulate ∆CTOD. Extensive 2D and 3D numerical investigations were conducted in a Single Edge Notch Tension specimen. This revealed that the collapsed crack tip elements in a focused mesh pattern as the most suited method for ∆CTOD calculations. A software called PROCRACKPLAST is developed in this regard by extending PROCRACK, an ABAQUS-based software for linear elastic crack growth applications. Different LCF/TMF crack growth simultions were performed in PROCRACKPLAST and appropriate ranges of the numerical parameters involved are identified. Finally, PROCRACKPLAST is validated with the CG models of Ni-Resist D-5S, for LCF and TMF applications. PROCRACKPLAST shows huge potential in terms of performing complex 3D CG simulations. Furthermore, it may be used to develop CG models and augment CG experiments under large scale yielding conditions to interpret the results.

• Herr Valentin Garbe, M.Sc.
• Freitag, 13. Dezember 2024, 10:00 Uhr
• Seminarraum UBH-0209, Universitätsbibliothek/Hörsaalzentrum, Winklerstraße 3, EG

The electrification of transport, the increase in renewable energies, and the power supply for large artificial intelligence data centers represent challenges that require highly efficient power conversion. To minimize power losses, optimized electronic components are required. Nitride-based compound semiconductors with a large band-gap are very promising and on the way to market entry. However, the source and drain terminals that connect the semiconductor component to integrated circuits still pose a key challenge. These ohmic contacts contribute significantly to the power loss of the component, leading to heat generation and energy losses. In addition, the manufacturing costs for nitride power components must be reduced, which makes integrationn into the Si-CMOS process chain essential. However, CMOS requires an Au-free metallization, which represents a major challenge for the ohmic contact development, but also promises further advantages in the long term, such as a significantly im-proved surface morphology. In the framework of this thesis, the state-of-the-art Au-based as well as conventional and a newly developed Au-free ohmic contact stack were fabricated on heterostructures with normal and increased Al-content and benchmarked. For the investigations, various epitaxially grown GaN and AlGaN/GaN wafers from different manufacturers were used. The origin of the power losses of Au-free contacts was investigated by electrical and microstructural characterizations and discussed. A CMOS-compatible V/Al/Ti/TiN contact stack with extremely low contact resistance is presented an demonstrated by HEMTs on GaN-on-Si substrates, as it could be used in the CMOS process chain.

• Herr Dipl.-Ing. Oleksandr Kovtun
• Dienstag, 17. Dezember 2024, 10:30 Uhr
• Seminarraum EG.133, ZeHS, Winklerstraße 5, EG

The use of hydrogen in metallurgical processes holds significant promise for enhancing sustainability and reducing environmental impact. Based on the literature, the direct reduction of iron ore can be characterized by the reduction degree and reduction swelling index (RSI), which significantly depend on parameters such as temperature, pressure, type of reducing agent, porosity and material chemistry. This thesis enabled the assessment of the influence of temperature, reducing atmosphere and material chemistry on the reduction degree and RSI. Three types of iron ore pellets were reduced and studied for their reduction degree and RSI at different temperatures. The effect of a reducing atmosphere consisting of 80 % nitrogen and 20 % hydrogen was studied and compared with the reduction in a hydrogen atmosphere under the same conditions. The high iron-rich metallurgical dust was also studied using hydrogen-based reduction. The results showed a possibility of the use of metallurgical dust during the direct reduction process, thereby reducing waste and conserving resources.

• Herr Dipl.-Ing. Fengbo An
• Donnerstag, 19. Dezember 2024, 10:00 Uhr
• Seminarraum 318, DBI-Gebäude, Reiche Zeche, Fuchsmühlenweg 9

Die vorliegende Dissertationsschrift widmet sich der CFD-gestützten Untersuchung von Hochtemperaturversuchen, die für das Verständnis der Wärme- und Stoffübertragung im Labormaßstab von entscheidender Bedeutung sind. Mithilfe der CFD-Modellierung werden komplexe Temperatur- und Stoffverteilungen in Versuchsanlagen detailliert analysiert. Dies umfasst ein Modell zur Abbildung des Wärme- und Stoffübergangs im HITECOM-Reaktor und damit zur Identifizierung kritischer Betriebsbedingungen, ein Modell zur Analyse der Partikelbewegung im KIVAN-Reaktor unter inhomogenen Temperatur- und Strömungsbedingungen sowie die modellgestützte Analyse der Stofftransportlimitierungen in einer DMT-Thermowaage. Die Kombination von CFD-Modellierung und experimentellen Daten unterstützt die Entwicklung präziser kinetischer Modelle und verbessert die Vorhersage des Stoffumsatzes. Diese Ergebnisse tragen wesentlich zur Weiterentwicklung und Optimierung von Hochtemperaturprozessen in verschiedenen Industriezweigen bei.

• Herr Dipl.-Chem. Konrad Burkmann
• Freitag, 20. Dezember 2024, 13:30 Uhr
• Hörsaal UBH-0205, Universitätsbibliothek/Hörsaalzentrum, Winklerstraße 3, EG

Im Rahmen der Dissertation wurden die Borhydride von Ca, Sr, Ba, Y, La, Zr und Hf hergestellt und deren thermodynamische Daten durch kalorimetrische Messungen ermittelt. Weiterhin wurden DFT-Berechnungen zur Ergänzung der experimentellen Datenbasis eingesetzt. Es folgte ein Vergleich aller ermittelten Daten mit abgeschätzten Werten. Auf Basis der bestimmten thermodynamischen Daten erfolgten umfangreiche Berechnungen zum Zersetzungsverhalten der Boranate, welche mit den experimentellen Befunden verglichen wurden. Weiterhin wurden Gleichgewichtsberechnungen zur Rehydrierbarkeit der reinen Boranate genutzt, um Aussagen zu deren Eignung als Wasserstoffspeichermaterialien abzuleiten. Abschließend wurden Berechnungen zum Design von reaktiven Hydridmischungen anhand des thermodynamischen Tunens ausgeführt, wobei aussichtsreiche Kandidaten in der Gruppe der untersuchten Erdalaklimetallboranate für experimentelle Untersuchungen identifiziert werden konnten.