Browsing by Author "Angelini, Alberto"

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GRK2802: Effect of Surface-active Elements on the Wetting Behavior and Surface Tension of Steels: Assessing Sessile Drop and Maximum Bubble Pressure Techniques
(Technische Universität Bergakademie Freiberg, 2026-04-29) Bellé, Matheus Roberto; Neubert, Lukas; Baraka, Abdelrahman A.; Angelini, Alberto; Song, Jinwen; Volkova, Olena
This study investigates the influence of surface-active elements (Si, S, and B) on the surface tension (σ) and wetting behavior of molten steels and provides a direct comparison between the Maximum Bubble Pressure (MBP) and Sessile Drop (SD) measurement techniques. High-silicon electrical steels (ES) (3 - 6 wt% Si) and Mn-B steels (WS) with controlled B and S contents were examined at 1500 - 1650 °C. The results show that the increasing Si content decreases both σ and contact angle, enhancing the wettability on MgO. ES steels exhibit a characteristic parabolic temperature (T) dependence of σ, attributed to Si-O interactions and surface oxidation effects. In WS steels, S reduces σ, and the T coefficient becomes increasingly positive with rising S content. B displays an ambiguous effect: MBP measurements show a slight σ reduction with increasing B, whereas SD measurements indicate the opposite trend. Steel infiltration into porous MgO affects the contact line, causing reduced wetting angles and deviations in SD σ values. Across all compositions and temperatures, SD consistently yields higher σ values than MBP. This discrepancy is primarily linked to surface depletion of volatile species (Mn and S) during SD experiments, while the continuous surface renewal in MBP minimizes compositional changes. The findings demonstrate that both alloy chemistry and measurement technique significantly influence the determined interfacial properties. Overall, this work provides a comprehensive assessment of how surface-active elements govern wetting and σ in steel-MgO systems and highlights methodological considerations essential for interpreting high-temperature interfacial measurements in steelmaking research.
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GRK2802: Enhanced strength and high reactivity of Al2O3-MgAl2O4-C ceramic filters with in-situ β-SiC whiskers: Role of nano-Al2O3
(Technische Universität Bergakademie Freiberg, 2026-04-27) Song, Jinwen; Yan, Wen; Volkova, Olena; Cheng, Zhenyu; Neubert, Lukas; Angelini, Alberto; Bellé, Matheus Roberto; Li, Yuanbing
The role of nano-Al2O3 content on the phase composition, microstructure, mechanical properties, and purification performance for molten steel of Al2O3-MgAl2O4-C ceramic filters was investigated through XRD, SEM, EDS, as well as immersion test with molten steel. Results indicate that nano-Al2O3 firstly improves slurry retention performance, increases filter strut thickness, and ensures uniform distribution without cracks. Furthermore, during the sintering process, nano-Al2O3 accelerates the mass transfer (Mg2+ and Al3+) between microporous Al2O3-MgAl2O4 particle and nano-Al2O3 due to its high sintering reactivity, which promotes the development and growth of neck connections among the microporous Al2O3-MgAl2O4 particles, resulting in a substantial improvement in the mechanical properties. Regarding molten steel purification, on the one hand, its high reactivity significantly promoted the carbothermal reduction reaction, generating reductive gases that interact with and adsorb [Al], [O], and Al2O3 inclusions in the molten steel, quickly forming a continuous and uniform Al2O3-MgAl2O4 reaction layer at the interface. On the other hand, high mechanical strength also improves filter’s resistance to molten steel erosion and avoids contamination of the molten steel. Together, these two effects synergistically contribute to the purification of molten steel. The filter N5, with 5 wt% nano-Al2O3, not only exhibits excellent mechanical properties with a cold compressive strength of 1.41 MPa and 1.21 MPa after three thermal shock tests, but also demonstrates high purification efficiency, reducing inclusions by 44% and lowering the total oxygen content from 56.3 ppm to 26.1 ppm. Finally, the role of nano-Al2O3 in sintering behavior and purification function, as well as the comprehensive molten steel purification mechanism were proposed.