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- ItemMitigating the Effect of High Overpotential during Al Deposition on Aluminium-Graphite Battery Performance(Weinheim : Wiley-VCH, 2025) Mukundan, Charan; Drillet, Jean-FrancoisThis study investigates the impact of current density on electrode potential during aluminium (Al) dissolution/deposition step from/on an Al foil as well as the charge-discharge behaviour of aluminium-graphite batteries (AGB) in various AlCl3-based electrolytes. Preliminary experiments in a cell with graphite blocking electrodes evidenced higher chemical stability of 1 : 1.5 Urea : AlCl3 electrolyte, followed by 1 : 1.5 TEA : AlCl3 and 1 : 1.5 EMIMCl : AlCl3. In Al−Al symmetric cells, current densities above 1 mA cm−2 led to a notable rise in overpotential up to 100 mV during Al deposition in both TEA : AlCl3 and Urea : AlCl3 electrolytes mostly due to low surface area of native Al foil. Similar trend was observed in AGB full cells, where higher overpotentials during Al deposition caused ‘incomplete’ AlCl₄− intercalation in natural graphite (NG), resulting in capacity fade at current densities in the range between 0.5 and 5 A g−1. By adjusting the upper cut-off voltage (UCV) during charging step as a function of applied current value according to respective electrolyte stability, a significant improvement in specific capacity and energy density was achieved during charging and discharging steps. For instance at 1 A g−1, the specific energy density of AGB increased by 10 % in EMIMCl : AlCl3, 48 % in TEA : AlCl3, and an impressive 250 % in Urea : AlCl3.During long-term cycling post-UCV adjustment, the capacities of AGB increased by 10 %, 13 %, and 27 % for AGBs with EMIMCl : AlCl3, TEA : AlCl3 and Urea : AlCl3, respectively with a negligible capacity fade of less than 1 % for EMIMCl : AlCl3 and TEA : AlCl3, and a 9 % capacity fade for Urea : AlCl3.
- ItemSynthesis of Highly Active and Stable Carbon by a Soft-Template Hydrothermal Route as Pt Substrate for Oxygen Reduction Reaction(Weinheim : Wiley-VCH, 2023) Antony, Jithin; Sakthivel, Mariappan; Drillet, Jean-FrancoisN-doped mesoporous carbon spheres were synthesized by a microwave-assisted ammonia-catalyzed hydrothermal route (CFAHM) by using Pluronic® F127 as a soft-template and m-Aminophenol as both carbon and nitrogen source. Their physical and electrochemical properties were compared with those of carbon samples obtained by a conventional hydrothermal method (CFAH). The best results in terms of particle size, surface area, pore size distribution, conductivity and N-content of the as-prepared CFAHM samples were obtained in 17 M NH4OH at 120 °C for 5 min. After 1100 °C pyrolysis step, conductivity of CFAHM increased to 5.64 S cm−1 compared to 8.64 S cm−1 for CFAH sample. Remarkably, GDE experiments with xylene-swelled CFAHM-supported platinum exhibited an excellent activity for ORR (181 mA cm−2 @ 0.7 V) and ECSA retention (80 % after 10,000 ADT) under half-cell conditions in 1 M H2SO4 at room temperature compared to only 57 mA cm−2 and 13 % for GDE with Pt/CVulcan reference material.
- ItemImpact of Aluminium Electrode Potential during Charging on Aluminium-Ion Battery Performance with TEA-AlCl3 Electrolyte(Weinheim : Wiley-VCH, 2023) Mukundan, Charan; Eckert, Martin; Drillet, Jean-FrancoisIn aluminium (Al) symmetric cell, potentials during Al deposition on an Al foil at 1 mA cm−2 were 60–70 mV higher in TEA-AlCl3 electrolyte compared to those measured with EMIMCl-AlCl3 reference. Because of higher electrochemical stability of TEA-AlCl3 solution, cut-off voltage of charging step in AIB full-cell was set to 2.45 V compared to 2.40 V for the reference cell. During long-term cycling at 1 A g−1, the specific capacity of the AIB cell employing TEA-AlCl3 increased from 60 to 94 mAh g−1 (57 %) after 1000 cycles while that of cell with EMIMCl-AlCl3 was quite constant at about 60 mAh g−1. This behaviour was explained by continuous decreasing in Al electrode potential at End-of-Charge state (EOC) during deposition reaction (charging step) in TEA-AlCl3 allowing an increase in graphite electrode potential and consequently in AIB cell capacity over the whole experiment. This increase in capacity was accompanied by a raise of defect sites in graphite material.
- ItemAbschlussbericht zum DFG-Transferprojekt "Simulationsgestützte Werkzeug- und Prozessauslegung beim Microfinishen mit metallisch gebundenen Honwerkzeugen"(Hannover : Technische Informationsbibliothek, 2025) Biermann, Dirk; Wiederkehr, Petra; Heining, Ines; Tilger, MeikInnerhalb des Ergebnistransferprojektes sollten aufbauend auf den bisherigen Ergebnissen Untersuchungen zur Herstellung konvexer Konturen mittels Microfinishen durchgeführt und Simulationsmodelle zur prototypischen Prozess- und Werkzeugauslegung entwickelt werden. Die aus den vorhergehenden Grundlagenprojekten gewonnenen Erkenntnisse sollten im Rahmen des Transferprojektes prototypisch auf eine industrielle Anwendung und ein neues Werkzeugkonzept übertragen werden. Hierzu haben das Institut für Spanende Fertigung (ISF) und der Lehrstuhl Virtual Machining (VM) gemeinsam mit den Firmen NAGEL Maschi- nen- und Werkzeugfabrik GmbH, ELGAN-Diamantwerkzeuge GmbH & Co. KG und der Alicona Imaging GmbH die im Rahmen des Transfervorhabens notwendigen Forschungs- und Entwicklungsarbeiten durchgeführt. Es erfolgten experimentelle Untersuchungen zur Konditionierung von metallisch gebundenen Honwerkzeugen, um eine geeignete Prozess- kette für das Profilieren, Schärfen sowie das Einlaufen der Werkzeuge zu definieren. Parallel zu den technologischen Untersuchungen erfolgte die Entwicklung einer geometrisch- physikalischen Honsimulation. Das Ziel der Simulationsentwicklung war es, unterschiedliche Werkzeugkonfigurationen, bspw. durch eine Variation der Korngröße oder der Werkzeugges- talt, und Prozesskenngrößen im Hinblick auf die resultierende Kontur der bearbeiteten Wel- lenabsätze analysieren und mittels Microfinishbearbeitung gezielt einstellen zu können. Zur detaillierten Abbildung der komplexen Prozessführung wurden neben der Modellierung der Kraftregelung auf Einzelkornbasis neue Modelle entwickelt, welche zum einen bei der Be- rechnung der Einzelkornkraft die Orientierung der Korntopographie in Relation zur Schnitt- richtung berücksichtigten und zum anderen die explizite Beschreibung der Bindung und die Berücksichtigung der Bindungsverschleißmechanismen im Werkzeugmodell ermöglichten. Zur Validierung des entwickelten Simulationssystems wurden verschiedene Parameterkonfi- gurationen zunächst simulativ systematisch untersucht und anschließend experimentelle Untersuchungen für ausgewählte Werkzeug- und Prozesskonfigurationen durchgeführt. Die Ergebnisse der experimentellen Werkzeug- und Prozessanalyse konnten hierbei dazu ein- gesetzt werden, die Simulationsparametrierung zu optimieren und den Einfluss unterschied- licher Werkzeugkonfigurationen auf die resultierende Werkstückgestalt zu analysieren. Durch die gewonnenen Erkenntnisse konnten die Projektpartner zum einen reproduzierbare Ergeb- nisse für die Werkzeugkonditionierung durch die neu entwickelten Methoden erzielen. Zum anderen tragen die Ergebnisse der experimentellen und simulationsgestützten Untersuchun- gen zu einem verbesserten Prozessverständnis bei. Zusätzlich konnte das Potenzial aufge- zeigt werden, durch eine simulationsgestützte Werkzeugauslegung den ökonomische Auf- wand bei der Werkzeugentwicklung für die Projektpartner perspektivisch zu reduzieren.
- ItemCavitation Control using Mesoscale Surface Structuring in Marine Engineering and Hydraulic Systems(Hannover : Technische Informationsbibliothek, 2025-06-02) el Moctar, Bettar Ould; Kadivar, EbrahimWe propose a passive cavitation control method to mitigate undesirable effects, such as structural vibration in the context of marine engineering and hydraulic systems. For this aim, we used different mesoscale surface structures, such as scalloped and sawtooth riblet structures, finned and roughness structures to control the cavitating flow around circular cylinders, and hydrofoils. We performed extensive experiments to investigate the effects of wall roughness and riblet structures on the dynamics of cavitation, cavitation instability and turbulence structures in the cross flow around and in the wake of a circular cylinder, and a hydrofoil at different cavitating regimes and various Reynolds numbers. We used high-speed cameras to visualize the cavitation structure and a Particle Image Velocimetry (PIV) method to measure the velocity fields. In addition, we measured the forces acting on the smooth cylinder and on the cylinders with different mesoscale surface structures, and we also performed an acoustic measurement, using a hydrophone located downstream of the cylinders. Finally, we numerically studied the dynamics of the cavitation flow around a benchmark hydrofoil with and without passive control methods and compared our numerical results with our experimental data. Our results showed that the mesoscale surface structures were very efficient in suppressing or mitigating cavitation. The cavitation-induced vibration exciting forces acting on the cylinders and hydrofoils with riblet structures were significantly reduced compared to the cases without cavitation control. Furthermore, a substantial reduction in the cavitation volume and the sound pressure level in the low- and middle-frequency ranges were observed for the hydrofoils with riblet structures. The large-scale cloud cavity on the hydrofoil with scalloped and sawtooth riblets was changed to a small-scale cavity, which modified the cavitation dynamics on the hydrofoil surface and controlled unsteady cloud cavitation.