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Author: Uhlemann, Margitta Ɨ DDC: 540 Ɨ

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Now showing 1 - 3 of 3
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    Calciothermic Synthesis of Very Fine, Hydrogenated Ti and Tiā€“Nb Powder for Biomedical Applications
    (Weinheim : Wiley-VCH Verl., 2020) Lindemann, Inge; Gebel, Bernhard; Pilz, Stefan; Uhlemann, Margitta; Gebert, Annett
    Due to their excellent biocompatibility, titanium and titaniumā€“niobium alloys are especially interesting for biomedical applications. With regard to favorable near-net shape production, Ti powder synthesis is the key hurdle. Extensive research has been in progress for alternative synthesis methods since decades. Herein, an efficient alternative method to the conventional powder production process to prepare spherical powders with very small sizes (<45ā€‰Ī¼m) for high-strength materials is shown. Very fine, hydrogenated Ti and Tiā€“Nb alloy powders are stable in air and are synthesized by calciothermic reduction in hydrogen. The herein presented reduction using CaH2 starts directly from the oxides instead of chlorides. Correlations of size and morphology of the as-synthesized TiH2 and (Ti,Nb)H2 powders with the precursors (TiO2, Nb2O5, and CaH2) are illustrated and are used to tailor the desired powders.
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    Pulse Reverse Plating of Copper Micro-Structures in Magnetic Gradient Fields
    (Basel : MDPI, 2022) Huang, Mengyuan; Uhlemann, Margitta; Eckert, Kerstin; Mutschke, Gerd
    Micro-structured copper layers are obtained from pulse-reverse electrodeposition on a planar gold electrode that is magnetically patterned by magnetized iron wires underneath. 3D numerical simulations of the electrodeposition based on an adapted reaction kinetics are able to nicely reproduce the micro-structure of the deposit layer, despite the height values still remain underestimated. It is shown that the structuring is enabled by the magnetic gradient force, which generates a local flow that supports deposition and hinders dissolution in the regions of high magnetic gradients. The Lorentz force originating from radial magnetic field components near the rim of the electrode causes a circumferential cell flow. The resulting secondary flow, however, is superseded by the local flow driven by the magnetic gradient force in the vicinity of the wires. Finally, the role of solutal buoyancy effects is discussed to better understand the limitations of structured growth in different modes of deposition and cell geometries.
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    Get more out of your data: A new approach to agglomeration and aggregation studies using nanoparticle impact experiments
    (Hoboken, NJ : Wiley, 2013) Ellison, Joanna; Tschulik, Kristina; Stuart, Emma J.E.; Jurkschat, Kerstin; OmanoviĀ“c, Dario; Uhlemann, Margitta; Crossley, Alison; Compton, Richard G.
    Anodic particle coloumetry is used to size silver nanoparticles impacting a carbon microelectrode in a potassium chloride/citrate solution. Besides their size, their agglomeration state in solution is also investigated solely by electrochemical means and subsequent data analysis. Validation of this new approach to nanoparticle agglomeration studies is performed by comparison with the results of a commercially available nanoparticle tracking analysis system, which shows excellent agreement. Moreover, it is demonstrated that the electrochemical technique has the advantage of directly yielding the number of atoms per impacting nanoparticle irrespective of its shape. This is not true for the optical nanoparticle tracking system, which requires a correction for the nonspherical shape of agglomerated nanoparticles to derive reasonable information on the agglomeration state.