Eldorado - Repositorium der TU Dortmund

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Aktuellste Veröffentlichungen

Ring‐size control and guest‐induced circularly polarized luminescence in heteroleptic Pd3A3B3 and Pd4A4B4 assemblies
(Wiley, 2024-07-29) Ebbert, Kristina E.; Benchimol, Elie; Platzek, André; Drechsler, Christoph; Openy, Joseph; Hasegawa, Shota; Holstein, Julian J.; Clever, Guido H.
Two new structural motifs within the class of heteroleptic PdnAnBn assemblies, namely syn-cis-Pd3A3B3 bowls and bowl- (syn) or saddle- (anti) shaped cis-Pd4A4B4 rings are introduced. All of the ten examples share a common longer fluorenone-based bis-monodentate ligand, equipped with meta-pyridine donor groups. The ring size (3- vs. 4-membered) and conformational preference (bowl vs. saddle) are controlled by the choice of the shorter ligand. These carry para-pyridine donors, different aromatic backbones (benzene, thiophene or selenophene) and either no or small or bulky endohedral substituents, serving to control the nuclearity of the heteroleptic rings through different effects (ligand angle, charge distribution or backbone bulk). Moreover, the luminescence of the fluorenone ligand is conserved in the formed architectures. Emission intensity as well as host–guest properties vary depending on the inward-pointing functions. All Pd3A3B3 assemblies are shown to bind chiral guest BINOL bis-sulfonate which imparts its chirality to the entire host–guest complex. This results in a guest-induced circular dichroism (CD) and circularly polarized luminescence (CPL) with dissymmetry factor glum up to 10−3.
Oxidation behavior of vanadium in annealed AlCrVY(O)N thin films characterized by X‐ray absorption spectroscopy
(Wiley, 2024-12-22) Schneider, Eric; Ontrup, Finn; Scholz, Gordon; Savelkouls, Jaqueline; Lopes Dias, Nelson Filipe; Sternemann, Christian; Lützenkirchen‐Hecht, Dirk; Tillmann, Wolfgang; Paulus, Michael
Great efforts are being made to optimize tool coatings for use at elevated process temperatures. The reason for this is to enable machining with minimized lubrication quantities. During operation, temperatures between 300 and 1000 °C can occur depending on the material and tool design. Thus to enable the machining of high-strength materials, the tool coatings must be optimized with regard to their temperature resistance, which is also significantly affected by their oxidation properties. AlCrVY(O)N thin films are potential candidates for such coating applications as the addition of V to AlCrN favors the formation of so-called Magnéli phases at high temperatures, that is, V oxides with varying stoichiometry, to reduce friction. X-ray absorption spectroscopy is applied to characterize the oxidation behavior of V in the thin films prepared in a combined dcMS/HiPIMS process for as-deposited AlCrVY(O)N thin films and after thermal treatment in the ambient atmosphere. The V average oxidation state is determined by analyzing the pre-edge feature at the V K-edge. Systematic changes in preoxidation, a high oxidation resistance below 800 °C, and promoted V oxidation for higher preoxidized coatings above 800 °C are found.
A monolithic finite element approach for interface capturing in multiphase flow problems
(2026) Afaq, Muhammad Aaqib; Turek, Stefan; Sokolov, Andriy
Multiphase flows are fundamental to diverse industrial applications, from inkjet technology and droplet formation to bubble dynamics in chemical reactors. Despite their prevalence, the numerical simulation of interfacial dynamics remains a significant challenge due to the stiff non-linearities introduced by surface tension and the geometric complexities of moving boundaries. Traditional numerical frameworks often struggle with restrictive capillary time step constraints, the need for frequent interface reinitialization, and the inaccuracies associated with explicit curvature estimation. This thesis presents a robust, monolithic finite element solver designed for the simultaneous calculation of velocity, pressure, and interface position in incompressible multiphase flows. Building upon curvature free level set and indicator-based material function formulations, the proposed method eliminates the need for explicit calculation of interface normals and curvature. This approach bypasses the traditional capillary time step restriction and removes the necessity for separate redistancing or reinitialization procedures, which are integrated directly into the non-linear formulation. The governing equations are discretized using the high-order stable FEM pair Q_2⁄(P_1^disc ) for velocity and pressure, while a Q_2approximation is employed for the interface scalar fields. The resulting non-linear system is resolved using a discrete Newton solver with a divided difference evaluation of the Jacobian matrices. To handle the resulting saddle-point problems, a suitable linear solver is implemented within the FeatFlow software framework. The accuracy, stability, and mass conservation properties of the solver are rigorously validated against established test cases and benchmark, including the static bubble, the oscillating bubble, and the rising bubble cases. The results demonstrate that the monolithic coupling provides an efficient and robust framework capable of handling high surface tension coefficients without compromising interface integrity, offering a significant advancement over decoupled or explicit interfacial solvers.
Microscale modeling of damage mechanisms in dual‐phase steel DP800
(Wiley, 2024-08-29) Niehüser, Alexander; Mosler, Jörn
Dual-phase steels are very popular in the automotive industry due to their high strength while maintaining good formability. The macroscopic formability of this polycrystalline material is governed by deformations and damage mechanisms at the microscale. To describe the mechanical properties associated with these mechanisms, a crystal plasticity theory is coupled with interface models and integrated into representative volume elements (RVEs) of DP800 in a thermodynamically consistent manner. The interface models capture decohesion at the grain boundaries via a cohesive interface model as well as the initiation and propagation of micro-cracks (damage) within the quasi-brittle martensite phase via a phase-field approach. In this contribution, the focus lies on the conceptual framework combining above models in a finite element setting. Furthermore, the interaction and activation of the different (damage) mechanisms will be shown in order to highlight the predictive capabilities of the presented framework.
Insights into the mechanochemical glass formation of zeolitic imidazolate frameworks
(Deutsches Elektronen-Synchrotron, DESY, Hamburg, 2024-06-14) Xue, Wen-Long; Das, Chinmoy; Weiß, Jan-Benedikt; Henke, Sebastian
Metal–organic framework (MOF) glasses, known for their potential in gas separation, optics, and solid-state electrolytes, benefit from the processability of their (supercooled) liquid state. Traditionally, MOF glasses are produced by heating MOF crystals to their melting point and then cooling the liquid MOF to room temperature under an inert atmosphere. While effective, this melt-quenching technique requires high energy due to the high temperatures involved. It also limits the scope of new material development by restricting the compositional range to only those combinations of metal ions and linkers that are highly thermally stable. An alternative, mechanical milling at room temperature, has demonstrated its capability to transform MOF crystals into amorphous phases. However, the specific conditions under which these amorphous phases exhibit glass-like behavior remain uncharted. In this study, we explore the mechanochemical amorphization and vitrification of a variety of zeolitic imidazolate frameworks (ZIFs) with diverse linkers and different metal ions (Zn2+, Co2+ and Cu2+) at room temperature. Our findings demonstrate that ZIFs capable of melting can be successfully converted into glasses through ball-milling. Remarkably, some non-meltable ZIFs can also be vitrified using the ball-milling technique, as highlighted by the preparation of the first Cu2+-based ZIF glass.