Zeitschriftenaufsätze ab 2018

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Balos, Sebastian; Labus Zlatanovic, Danka; Kulundzic, Nenad; Janjatovic, Petar; Dramicanin, Miroslav; Lanc, Zorana; Hadzistevic, Miodrag; Radisic, Slobodan; Rajnovic, Dragan; Pecanac, Milan
Influence of tool-base metal interference on the performance of an aluminium-magnesium alloy joined via bobbin tool friction stir welding. - In: Metals, ISSN 2075-4701, Bd. 13 (2023), 7, 1215, S. 1-16

Bobbin tool friction stir welding (BTFSW) is a variant of the FSW process which uses the special two-shoulder tool that forms the top and bottom of a weld surface. As such, a significant simplification of the welding setup is achieved. One of the dominant parameters of the BTFSW process is the interference between the tool shoulder pinch gap and the weld metal thickness. In this research, the influence of interference of the square pin tool with convex shoulders on process temperature, microstructure, tensile, impact, and bend performance were studied, and appropriate correlations were devised. The base metal was an aluminum-magnesium alloy in which the interference varied in the range of 0.1 to 0.5 mm. Wormhole defects and irregularities were found in all specimens except in the specimen welded with 0.4 mm interference. An optimal interference of 0.4 mm resulted in the best mechanical properties, which, in terms of tensile strength and reduction of area, were similar to the base metal. Furthermore, the impact strength was significantly higher, which was attributed to the grain refinement effect in the nugget zone.



https://doi.org/10.3390/met13071215
Tang, Xinyue; Lv, Xincha; Lou, Jiayi; Fan, Tieyan; Chen, Heng; Wang, Wenxin; Zhang, Shangcong; Zhao, Huaping; Zhang, Qingcheng; Wang, Shun; Lei, Yong
Rational design of a hierarchical candied-haws-like NiCo2O4Ni,Co-(HCO3)2 heterostructure for the electrochemical performance enhancement of supercapacitors. - In: ACS applied energy materials, ISSN 2574-0962, Bd. 6 (2023), 19, S. 9905-9914

Designing core-shell heterostructures with multicomponents, more electroactive sites, hierarchical structures, and stable geometrical configurations is an effective approach to enhance the electrochemical properties of supercapacitors. Herein, we report the fabrication of a hierarchical candied-haws-like NiCo2O4NiCo-hydrocarbonate heterostructure on Ni foam (NiCo2O4@NiCo-HCs), which consists of NiCo2O4 nanowires acting as “rebars” that are tightly strung with NiCo-HC nanoparticles. The strong interfacial reaction between the NiCo2O4 “core” and the NiCo-HC “shell” accelerates the charge transfer within the heterostructure, while the hierarchical structure containing quantities of paths and pores provides fast ion diffusion throughout the whole electrode, hence remarkably boosting the electrochemical performance of a NiCo2O4@NiCo-HC electrode. As expected, the NiCo2O4@NiCo-HC electrode shows a high specific capacitance of 3216.4 F g-1 at a current density of 1 A g-1 and 2259.9 F g-1 even at 20 A g-1 (1.6-fold that of the NiCo2O4 electrode and 5.5-fold that of NiCo-HCs). In addition, an assembled asymmetric supercapacitor NiCo2O4@NiCo-HCs//AC delivers a high energy density of 47.46 Wh kg-1 at a power density of 708.94 W kg-1, together with 96.2% capacitance retention after 6000 cycles, surpassing most of the reported analogues. These results suggest that our hierarchical candied-haws-like heterostructure design is potential for the performance enhancement of supercapacitors.



https://doi.org/10.1021/acsaem.3c01421
Shen, Fengxia; Shi, Xinbo; Shi, Jin
Novel bipolar membrane electrolyzer for CO2 reduction to CO in organic electrolyte with Cl2 and NaOH produced as byproducts. - In: Journal of CO2 utilization, ISSN 2212-9839, Bd. 77 (2023), 102595, S. 1-10

Electrochemical reduction of CO2 to valuable products, powered by renewable energy, provides a promising strategy for reducing our dependence on fossil fuels. But up to now, no technology has been implemented for large-scale industrial applications. Without massive utilization of CO2, many vital practical problems, such as reducing CO2 emissions, storing renewable energy, and alleviating environmental pollution, cannot be resolved through this route. Herein, we propose a novel electrolyzer for CO2 electro-reduction, which is separated into three chambers by a bipolar membrane and a cation exchange membrane. In the cathodic chamber, CO2 is reduced to CO in organic electrolytes. In the anodic chamber, Cl- is oxidized to Cl2 in NaCl aqueous solution. In the central chamber, NaOH is obtained. The generated CO and Cl2 can be used as feedstock to produce phosgene (CO+Cl2 =COCl2). Through this route, phosgene can be produced from CO2 and NaCl, with NaOH generated as a byproduct. By substantially increasing the product value, we can promote CO2 electro-reduction technology to industrial applications.



https://doi.org/10.1016/j.jcou.2023.102595
Heidenreich, Manuel; Schur, Johannes; Müller, Jens; Capraro, Beate; Gitzel, Wanja Mario; Jacob, Arne; Töpfer, Jörg
Fabrication of self-biased circulators with integrated hexagonal microwave ferrites using LTCC technology. - In: Ceramic forum international, ISSN 0173-9913, Bd. 100 (2023), 2, S. E38-E46

Next-generation magnetic microwave devices for satellite communication technologies require passive components including circulators that manipulate electromagnetic signals at high frequency. For this, circulators have to be integrated into LTCC microwave communication modules. Substituted M-type hexagonal ferrites represent a class of microwave magnetic materials with self-biasing ability and ferromagnetic resonance frequencies in the range of 25–50 GHz. The authors report on different options for integration of self-biased ferrites into LTCC multilayer devices, including drop-in sintered ferrites, and cofiring of screen-printed ferrite layers or ferrite tapes. Sintered substituted hexagonal microwave ferrites with preferential orientation were fabricated by compaction of powders in a magnetic field and sintering, whereas ferrite thick films were prepared by screen-printing, drying in an external magnetic field, and sintering at 900 ˚C. The magnetic texture of the ferrites is characterised using XRD, EBSD, and magnetic measurements. The substituted ferrites exhibit a ferromagnetic resonance frequency at about 30 GHz with nonreciprocal properties, and were integrated in a LTCC Y-junction circulator. Test results indicate that hexagonal ferrites are promising materials for self-biased circulators fabricated in LTCC technology for microwave components at Ka-band frequencies around 30 GHz.



Francis, Roslin; Butt, Safwat Irteza; Singh, Jasmeet; Guelzow, Peter; Eimertenbrink, Ralf; Hein, Matthias
Suitability of dual-band, dual-polarized patch antennas with a superstrate for the miniaturization of Ku-band antenna arrays for automotive applications. - In: Applied Sciences, ISSN 2076-3417, Bd. 13 (2023), 19, 10867, S. 1-13

The extension of low-earth orbit (LEO) services to non-terrestrial mobile communications has huge potential for eliminating network white spots and providing high-speed, low-latency links with worldwide geographic coverage. State-of-the-art user terminals for mobile platforms are too large for integration into a passenger vehicle. Antenna elements loaded with a dielectric superstrate could potentially lead to a considerable miniaturization of the user terminal. As per link budget calculations, an array with a gain of 27 dBi is necessary to ensure a throughput of 25 Mbps in the downlink at the Ku-band. A conventional array with a gain of 6 dBi per element, assuming a 12 × 12 arrangement with half-wavelength spacing, would require a footprint of 36 λ2 at 10 GHz to achieve this target and appears unsuitable for automotive integration. This paper proposes a low-profile, dual-band, dual-polarized, vertically stacked patch antenna with superstrate loading and shows that the inclusion of the superstrate improves the antenna’s gain by at least 3 dB. Therefore, compared to a conventional array, a superstrate-loaded array would need only half of the number of elements to meet the target gain, thus occupying only half of the surface area, and offers better integration for automotive applications. Requiring half of the number of elements also implies considerably reduced design complexity and cost.



https://doi.org/10.3390/app131910867
Schuler, Ramona; Marquardt, Christoph; Kalev, Georgi; Langer, Andreas; Konschake, Marko; Schiedeck, Thomas; Bandura, Julia; Goos, Matthias
Technical aspects of a new approach to intraoperative pelvic neuromonitoring during robotic rectal surgery. - In: Scientific reports, ISSN 2045-2322, Bd. 13 (2023), 17156, S. 1-13

It has been found that rectal surgery still leads to high rates of postoperative urinary, fecal, or sexual dysfunction, which is why nerve-sparing surgery has gained increasing importance. To improve functional outcomes, techniques to preserve pelvic autonomic nerves by identifying anatomic landmarks and implementing intraoperative neuromonitoring methods have been investigated. The objective of this study was to transfer a new approach to intraoperative pelvic neuromonitoring based on bioimpedance measurement to a clinical setting. Thirty patients (16 male, 14 female) involved in a prospective clinical investigation (German Clinical Trials Register DRKS00017437, date of first registration 31/03/2020) underwent nerve-sparing rectal surgery using a new approach to intraoperative pelvic neuromonitoring based on direct nerve stimulation and impedance measurement on target organs. Clinical feasibility of the method was outlined in 93.3% of the cases. Smooth muscle contraction of the urinary bladder and/ or the rectum in response to direct stimulation of innervating functional nerves correlated with a change in tissue impedance compared with the pre-contraction state. The mean amplitude (Amax) of positive signal responses was Amax = 3.8%, negative signal responses from a control tissue portion with no stimulation-induced impedance change had an amplitude variation of 0.4% on average. The amplitudes of positive and negative signal responses differed significantly (statistical analysis using two-sided t-test), allowing the nerves to be identified and preserved. The results indicate a reliable identification of pelvic autonomic nerves during rectal surgery.



https://doi.org/10.1038/s41598-023-41859-y
Mohammadkarimi, Shiva; Neitzel, Benedikt; Lang, Maximilian; Puch, Florian
Investigation of the fiber length and the mechanical properties of waste recycled from continuous glass fiber-reinforced polypropylene. - In: Recycling, ISSN 2313-4321, Bd. 8 (2023), 6, 82, S. 1-20

This paper explores the mechanical recycling of continuous fiber-reinforced thermoplastics (CFRTPs) waste into injection molded products, focusing on the influence of recycling parameters on fiber length and mechanical properties. CFRTPs are gaining attention for their promising attributes, including weight-specific mechanical properties, short cycle times, storability, and recyclability, making them suitable for diverse applications. However, as CFRTP production rates rise, recycling strategies become crucial for sustainability. This study investigates the processability of CFRTP waste, defines size reduction conditions, and evaluates the impact of various compounding parameters such as temperature, screw speed, and fiber volume content during extrusion. The research findings indicate that higher screw speeds lead to fiber length reduction, whereas elevated temperatures result in longer fibers. Increased fiber volume intensifies interactions, resulting in shorter lengths. Additionally, the study examines the influence of injection molding parameters such as back pressure, screw speed, and initial fiber length on the resulting fiber length and mechanical properties of injection molded specimens, emphasizing the need for precise parameter control to optimize performance in recycled CFRTPs. Key findings are that increasing the initial fiber length from 260 μm to 455 μm results in an average fiber length after injection molding of 225 μm and 341 μm, respectively. This implies that longer initial fibers are more prone to breakage. Regarding the mechanical properties, increasing back pressure from 20 bar to 60 bar results in a reduction in Young’s modulus of approximately 40 MPa. Higher screw speed also reduces modulus by approximately 70 MPa due to intensified fiber-screw interactions. However, back pressure and screw speed have neutral effects on the tensile strength and the elongation at break.



https://doi.org/10.3390/recycling8060082
Brätz, Oliver; Arnim, Mareike; Eichler, Stefan; Gericke, Andreas; Hildebrand, Jörg; Bergmann, Jean Pierre; Kuhlmann, Ulrike; Henkel, Knuth-Michael
Mechanical properties of MAG butt welded dissimilar structural steel joints with varying strength from grade S355 up to S960. - In: Welding in the world, ISSN 1878-6669, Bd. 67 (2023), 12, S. 2791-2802

Mixed connections made of normal-strength and high-strength structural steels allow for optimized material usage and production effort in applications where, as a result of different mechanical effects on materials of the same type, it would otherwise be necessary to adjust the plate thickness. Reduced material consumption and smaller weld geometries can thus generate ecological and economic advantages. When welding high-strength structural steels, however, significant softening can occur in the heat-affected zone, which can influence the load-carrying behavior of the overall joint. Since there are currently no appropriate standards for butt welds made of steels with different strengths up to S960, a separate design concept is required. In this paper, the weldability and load-carrying capacity of multilayer MAG welded butt joints designed as mixed connections of a normal-strength structural steel S355 and a high-strength structural steel in the range S690 to S960 are investigated. Extensive experimental investigations are carried out, in which other influencing variables such as the filler metal used, the heat input, the plate thickness, and the weld geometry are varied in order to identify their effects on the load-carrying capacity of the welded joints. Among other things, the results form the basis for an empirically based design model for mixed connections.



https://doi.org/10.1007/s40194-023-01600-9
Wieboldt, Rieke; Lindt, Kevin; Pohlmeier, Andreas; Mattea, Carlos; Stapf, Siegfried; Haber-Pohlmeier, Sabina
Effects of salt precipitation in the topmost soil layer investigated by NMR. - In: Applied magnetic resonance, ISSN 1613-7507, Bd. 54 (2023), 11/12, S. 1607-1631

The drying of highly concentrated aqueous salt solutions in sand and soil has been investigated by one-dimensional spatially resolved low-field relaxation measurements of 1H nuclei in water as well as high-field MRI of 1H and 23Na nuclei of water and sodium ions. Water evaporates until the solutions in the solid matrix reach saturation conditions, when salt begins to crystallize. Depending on salt type and conditions, such as actual soil water content and air humidity, this crystallization can occur above (efflorescent) or below (subflorescent) the soil surface. Both effects occur in nature and affect the evaporation behavior of water. The formation of salt precipitate domains is demonstrated by MRI, where the precipitate domains remain penetrable to water. Complete drying is achieved in the top 2 mm of soil with the exception of strongly hygroscopic perchlorates which maintain a constant amount of liquid water under ambient laboratory conditions and dry air. This situation is considered similar to the co-existence of perchlorates and water in strongly eutectic mixtures on Mars.



https://doi.org/10.1007/s00723-023-01568-1
Gabash, Aouss;
Review of battery storage and power electronic systems in flexible A-R-OPF frameworks. - In: Electronics, ISSN 2079-9292, Bd. 12 (2023), 14, 3127, S. 1-15

This paper provides an overview of power electronics and its applications in various fields, emphasizing power conditioning and minimizing losses for high energy efficiency. It discusses the distinction between unidirectional and bidirectional converters and their applications in power systems. The significance of unidirectional and bidirectional power flow in different scenarios is explored. The importance of battery storage systems (BSSs) for grid stabilization, frequency regulation, and renewable energy integration is highlighted. The paper focuses on flexible active-reactive optimal power flow (A-R-OPF) frameworks in battery storage and power electronic systems, reviewing existing research, identifying gaps, and offering new perspectives. It addresses the challenges and potential of grid-scale energy storage for reliable and cost-effective power systems with high renewable energy penetration. The need for energy curtailment, demand response, and smart grid implementation is discussed. The paper emphasizes comprehensive coordination, new power lines, European collaboration, and smart grid implementation to meet the dynamic needs of Europe’s power grids.



https://doi.org/10.3390/electronics12143127