Dr.-Ing. Benjamin Bock-Seefeld (Verteidigung: 05/2026)
Novel approaches for manufacturing of carbon-bonded alumina filters with improved environmental sustainability
Zusammenfassung:
Ziel der Promotion war es, die Umweltverträglichkeit von kohlenstoffgebundenen Alumina-filtern für die Stahlschmelzefiltration hinsichtlich ihrer Zusammensetzung und Herstellung zu verbessern. Dafür wurde die schrittweise Substitution des herkömmlich eingesetzten Pechbinders durch ein umweltfreundlicheres Bindemittelsystem basierend auf Laktose und Tannin anhand von konventionellen Replikafiltern untersucht. In einem weiteren Schritt wurde ein neuartiges Filterherstellungsverfahren auf Grundlage von additiv-gefertigten, wasser-löslichen Filterschaumvorlagen und alginathaltigen Beschichtungsschlickern entwickelt, um die Filterschaumvorlage vor der thermischen Behandlung mittels Wasser zu entfernen und somit die Freisetzung von umweltschädlichen Gasen zu vermeiden. Die Analysen der Filterstrukturen nach der Verkokung und nach Kontakt mit einer Stahlschmelze bei 1650 °C zeigten, dass der ausschließliche Einsatz des umweltfreundlicheren Bindemittelsystems und das neuartige Filterherstellungsverfahren geeignet sind, um kohlenstoffhaltige Aluminafilter mit hinreichenden (thermo-)mechanischen Eigenschaften für die Stahlschmelzefiltration und erhöhter Umweltverträglichkeit herzustellen.
Dr.-Ing. Piotr Malczyk (Verteidigung: 10/2024)
Development and characterization of MgO and TiO2 reinforced Steel Ceramic Composites resistant to long-term contact with liquid aluminum alloys
Summary:
The PhD thesis provides detailed description of a successful development of MgO and TiO2 particle reinforced Steel Ceramic Composites (SCC) for molten aluminum alloy applications. For this purpose, the influence of MgO and TiO2 addition and subsequent pre-oxidation surface treatment on the structure of SCCs and their corrosion resistance against long-term contact with liquid aluminum alloys was investigated. The initiation and progression of corrosion processes were thoroughly analyzed by means of newly developed DSC-aided corrosion tests, high temperature electrochemical studies and adapted wettability measurements. The gained insights led to the recognition of most important factors contributing to the corrosion, including both the electrochemical and the chemical driving forces arising between the SCCs and aluminum alloy. The evaluation of long-term corrosion resistance was performed with the help of finger immersion tests, crucible corrosion tests and subsequent SEM/EDS/EBSD and XRD analyses aiming at the determination of elements most prone to the dissolution in the liquid aluminum alloy and formation of corrosion phases. The pre-oxidized MgO reinforced SCC revealed superior corrosion resistance, being capable of withstanding more than 168 h of contact with liquid aluminum alloy.
Dr.-Ing. Florian Kerber (Verteidigung: 03/2024)
Reciprocal influence between MgO-C refractory materials with different MgO grade and a steel melt and the resulting effect on non-metallic inclusions
Summary:
The thesis addressed the effect of a varying MgO grade in MgO-C refractories on both their behavior in contact with a steel melt and the resulting effect on the non-metallic inclusion (NMI) population in the solidified steel. For this purpose, immersion tests were conducted in a semi-industrial steel casting simulator. In addition, the effect of the steel melting process parameters on the NMI population was thoroughly investigated, providing a guideline for the result interpretation for future experiments in the steel casting simulator. Here, a fundamental concept of data evaluation for the NMI characterization in a steel matrix using automated feature analysis was developed. The main NMI types detected in the solidified steel samples were Al2O3 and MnSi-based inclusions. Their number density depended on the steel melt’s temperature and amount of dissolved oxygen. A lower MgO grade refractory specimen in contact with the steel melt resulted in a higher proportion of low melting phases on its surface compared to a higher MgO grade specimen. These low-melting phases promoted the formation of MnSi-based inclusions and triggered NMI agglomeration leading to the formation of large Al2O3 inclusions.
