Promotionen von Kollegiat:innen des Graduiertenkollegs GRK 2802

Kohorte I

Reliable Determination and Interpretation of Thermal Transport Properties in MgO-C Refractories

Summary:

MgO-C refractories are widely used in steelmaking vessels, where they are exposed to high temperatures, molten steel, slag attack, mechanical loading, and repeated thermal cycling. Their thermal diffusivity and thermal conductivity are important for evaluating heat transfer, temperature gradients, thermal stresses, and thermal shock resistance. However, their reliable interpretation of these properties is challenging due to the heterogeneous and direction-dependent microstructure. In this study, the temperature-dependent thermal transport behaviour of MgO-C refractories was investigated using laser flash analysis and the transient plane source method. The results show that the measured thermal diffusivity and thermal conductivity should be regarded as effective values rather than purely intrinsic material property. By distinguishing the effects of sample preparation, thermal history, measurement methods, and microstructural differences associated with the compaction pressure, this study provides a basis for the reliable interpretation of the thermal conductivity properties of MgO-C refractory materials.

Corrosion and Electrolysis Performance of a Recyclate-based MgO–316L Cermet as a Carbon-Free Anode Candidate for Primary Aluminum Production

Abstract:

A recyclate-based MgO–316L cermet was investigated as a carbon-free anode candidate for primary aluminum production. Current-free degradation resulted primarily from MgO fluorina-tion and molten salt infiltration. Oxidation formed oxide and spinel phases that could mitigate corrosion of the Mg-containing fraction. Under anodic polarization during electrolysis, the relative contribution of steel-phase degradation increased. Compared with the as-sintered anode, pre-oxidation at 900 °C reduced material degradation under both chemical and electrochemical conditions, but impaired metallic connectivity and increased cell voltage. Although both anodes enabled aluminum formation, continued degradation prevented stable operation under the investigated conventional aluminum production conditions in Na-cryolite. Alternative Mg-containing phases, molten salt compositions and lower temperatures reduced Mg loss and highlighted promising directions for future research.

Thermophysical properties of Low-S Al-Killed Mn-B Steel and Its High-Temperature Interaction with MgO-C Refractories Containing Recycled Materials and Environmentally Friendly Binders

Zusammenfassung:

Im GRK 2802 wurden kohlenstoffgebundene Magnesia-Feuerfestmaterialien mit Rezyklaten und umweltfreundlichen Bindemitteln entwickelt, um CO2-Fußabdruck und Toxizität zu reduzieren. Deren physikalische und chemische Wechselwirkung mit flüssigem Stahl ist entscheidend für den Reinheitsgrad hinsichtlich Verunreinigungen und nichtmetallischer Einschlüsse. Zur Prüfung der Kompatibilität mit dem in der Automobilindustrie bedeutenden Al-killed Mn-B-Stahl wurden Hochtemperaturversuche durchgeführt. Die thermophysikalischen Eigenschaften des Stahls (Dichte, Oberflächenspannung, dynamische Viskosität) wurden in Abhängigkeit von B- und S-Gehalten und Temperatur mittels Maximum-Bubble-Pressure- und Schwingtiegel-Methode bestimmt. Eintauchversuche unter verschiedenen Bedingungen untersuchten die Wechselwirkung von Feuerfestmaterialien mit Stahl und flüssiger Schlacke. Die Charakterisierung erfolgte mittels chemischer Analyse sowie mikroskopischer und spektroskopischer Verfahren.

 

Mesostructure-Resolved Modeling and Evaluation of Thermal Shock in MgO-C Refractories Using a Virtual Laboratory Framework

Summary:

Thermal shock resistance is a key property controlling the performance and service life of refractory materials subjected to rapid temperature variations in high-temperature applications. In MgO-C refractories, this behavior is governed not only by bulk material properties but also by mesostructural characteristics such as aggregate size distribution, graphite morphology and orientation, and interfacial interactions between constituent phases. Since conventional experimental and analytical methods provide only limited access to these coupled mesostructural effects, this thesis develops a mesostructure-resolved computational framework for the thermo-mechanical evaluation of thermal shock resistance in MgO-C refractories. The framework combines synthetic mesostructure generation, phase-resolved thermoelastic material modeling, coupled thermo-mechanical cohesive interface debonding, and fracture-based thermal shock characterization within a virtual laboratory concept. A preprocessing tool is developed to generate idealized two-dimensional mesostructures, while a user-defined cohesive zone formulation implemented in Abaqus represents interfacial debonding and associated heat transfer. In addition, a modified Hasselman-type thermal shock resistance (TSR) parameter is proposed for direct numerical evaluation from finite element simulations. The results demonstrate that mesostructural parameters such as graphite volume fraction, aggregate particle size distribution, and graphite orientation systematically influence the evaluated thermal shock response, and that the proposed mesostructure-sensitive TSR parameter enables comparison across different configurations. The work establishes a computational basis for systematic mesostructure-informed investigation of thermal shock behavior in refractory materials.

Thermophysical Properties of Molten High-Silicon Electrical Steels and Related Interactions with Carbon-Bonded MgO Refractories Based on Recyclates and Environmentally Friendly Binders

Zusammenfassung:

Im Rahmen des GRK 2802 wurden neuartige MgO-C Feuerfestmaterialien auf Basis von Rezyklaten und umweltfreundlichen Bindern entwickelt. Deren chemisch-physikalische Kompatibilität mit flüssigen Stählen stellt eine essenzielle Voraussetzung dar, um eine gleichbleibend hohe Stahlqualität sicherzustellen. Zur Bewertung dessen wurden Finger-Eintauch-Prüfungen durchgeführt, bei denen MgO-C mit Elektrostählen in Kontakt gebracht wurde. Die Stähle variieren insbesondere hinsichtlich ihres Siliziumgehalts und besitzen eine hohe technologische Relevanz im Kontext der Energiewende und Elektromobilität. Für eine fundierte Analyse der Wechselwirkungen ist zudem die Erforschung der thermophysikalischen Eigenschaften der flüssigen Stähle von Bedeutung. Es wurden für beruhigte und unberuhigte Elektrostähle die Viskosität (Vibrationsfinger- und Schwingtiegelviskosimetrie), Dichte und Oberflächenspannung (Maximum-Bubble-Pressure-Methode) erforscht.

Cermet composites based on MgO-recyclates and 316L stainless steel as carbon-free anodes for the Hall-Héroult-Process

Summary:

This work investigates MgO-316L composites as candidate inert anodes for aluminium electrolysis in cryolite melts, focusing on the influence of processing and pre-oxidation on microstructure and functional properties. The composites exhibit a two-phase structure, with conductivity governed by the metallic network. Pre-oxidation alters phase composition and porosity, promoting oxide formation and increasing brittleness. Electrolysis at 1000 °C shows that MgO undergoes fluorination and dissolution; however, corrosion progresses gradually, maintaining electrical contact through continuous exposure of the metallic phase. Intermediate pre-oxidation reduces corrosion, while excessive oxidation impairs conductivity. The results demonstrate that stable operation is achieved through controlled degradation governed by thermodynamics and microstructure.