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search.filters.applied.f.access: openAccess × End date: 2024 × Start date: 2020 × Type: Article × Version: publishedVersion × Publisher: Amsterdam : Elsevier ×

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Now showing 1 - 10 of 67
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    Rare-earth-free MnAl-C-Ni permanent magnets produced by extrusion of powder milled from bulk
    (Amsterdam : Elsevier, 2020) Feng, Le; Freudenberger, Jens; Mix, Torsten; Nielsch, Kornelius; Woodcock, Thomas George
    Rare-earth-free MnAl-C-Ni permanent magnets have been produced for the first time by extruding powders milled from bulk. The resulting materials, fabricated using different conditions, contained a large volume fraction (> 0.92) of the desired τ-phase. In terms of the maximum energy product, the best performance obtained for a whole, transverse section of the extruded material was (BH)max = 46 kJm−3, and was (BH)max = 49 kJm−3 for a sample taken from near the edge of this section. Analysis showed that this material was comparable to the long-established benchmark, comprising MnAl-C-based magnets extruded in industry from bulk or from gas-atomised powder. Such materials are no longer available. The microstructure of the materials produced here consisted of fine, recrystallised grains, which exhibited an <001> fibre texture with intermediate texture quality and of larger, non-recrystallised regions, which contained hierarchical twinning and a high density of defects. The volume fraction and size of the non-recrystallised regions was greatly reduced by decreasing the size of the initial powder particles. This led to a large increase in the squareness factor of the demagnetisation curve and consequently to the high (BH)max values observed.
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    Revealing all states of dewetting of a thin gold layer on a silicon surface by nanosecond laser conditioning
    (Amsterdam : Elsevier, 2021) Ernst, Owen C.; Uebel, David; Kayser, Stefan; Lange, Felix; Teubner, Thomas; Boeck, Torsten
    Dewetting is a ubiquitous phenomenon which can be applied to the laser synthesis of nanoparticles. A classical spinodal dewetting process takes place in four successive states, which differ from each other in their morphology. In this study all states are revealed by interaction of pulsed nanosecond UV laser light with thin gold layers with thicknesses between 1 nm and 10 nm on (100) silicon wafers. The specific morphologies of the dewetting states are discussed with particular emphasis on the state boundaries. The main parameter determining which state is formed is not the duration for which the gold remains liquid, but rather the input energy provided by the laser. This shows that each state transition has a separate measurable activation energy. The temperature during the nanosecond pulses and the duration during which the gold remains liquid was determined by simulation using the COMSOL Multiphysics® software package. Using these calculations, an accurate local temperature profile and its development over time was simulated. An analytical study of the morphologies and formed structures was performed using Minkowski measures. With aid of this tool, the laser induced structures were compared with thermally annealed samples, with perfectly ordered structures and with perfectly random structures. The results show that both, structures of the laser induced and the annealed samples, strongly resemble the perfectly ordered structures. This reveals a close relationship between these structures and suggests that the phenomenon under investigation is indeed a spinodal dewetting generated by an internal material wave function. The purposeful generation of these structures and the elucidation of the underlying mechanism of dewetting by short pulse lasers may assist the realisation of various technical elements such as nanowires in science and industry. © 2020
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    Encapsulation of bacteria in bilayer Pluronic thin film hydrogels: A safe format for engineered living materials
    (Amsterdam : Elsevier, 2023) Bhusari, Shardul; Kim, Juhyun; Polizzi, Karen; Sankaran, Shrikrishnan; del Campo, Aránzazu
    In engineered living materials (ELMs) non-living matrices encapsulate microorganisms to acquire capabilities like sensing or biosynthesis. The confinement of the organisms to the matrix and the prevention of overgrowth and escape during the lifetime of the material is necessary for the application of ELMs into real devices. In this study, a bilayer thin film hydrogel of Pluronic F127 and Pluronic F127 acrylate polymers supported on a solid substrate is introduced. The inner hydrogel layer contains genetically engineered bacteria and supports their growth, while the outer layer acts as an envelope and does not allow leakage of the living organisms outside of the film for at least 15 days. Due to the flat and transparent nature of the construct, the thin layer is suited for microscopy and spectroscopy-based analyses. The composition and properties of the inner and outer layer are adjusted independently to fulfil viability and confinement requirements. We demonstrate that bacterial growth and light-induced protein production are possible in the inner layer and their extent is influenced by the crosslinking degree of the used hydrogel. Bacteria inside the hydrogel are viable long term, they can act as lactate-sensors and remain active after storage in phosphate buffer at room temperature for at least 3 weeks. The versatility of bilayer bacteria thin-films is attractive for fundamental studies and for the development of application-oriented ELMs.
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    Recent advances for flame retardant rubber composites: Mini-review
    (Amsterdam : Elsevier, 2023) Lai, Liangqing; Liu, Jia; Lv, Zhen; Gao, Tianming; Luo, Yongyue
    Flame retardant rubber composites have attracted a great attention during the past decades owing to their irreplaceable roles in complex industrial systems. Large amounts of efforts have been made to improve the flame retardant ability, developing high efficiency flame retardant systems which can reduce the release of heat, smoke and toxic gases while not deteriorate overall properties is becoming more and more important. This review briefly outlines the recent developments of flame retardant natural rubbers, silicon rubbers, some kinds of artificial rubbers and polyurethane elastomer composites, focuses on the design, development, mechanism and applications of advanced high-performance flame-retardant methods. Finally, outlooks the future tendency including more environmental-friendly strategies, higher flame-retardant efficiency and development of multifunctional flame-retardant rubber composites are proposed.
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    In situ detection of cracks during laser powder bed fusion using acoustic emission monitoring
    (Amsterdam : Elsevier, 2022) Seleznev, Mikhail; Gustmann, Tobias; Friebel, Judith Miriam; Peuker, Urs Alexander; Kühn, Uta; Hufenbach, Julia Kristin; Biermann, Horst; Weidner, Anja
    Despite rapid development of laser powder bed fusion (L-PBF) and its monitoring techniques, there is still a lack of in situ crack detection methods, among which acoustic emission (AE) is one of the most sensitive. To elaborate on this topic, in situ AE monitoring was applied to L-PBF manufacturing of a high-strength Al92Mn6Ce2 (at. %) alloy and combined with subsequent X-ray computed tomography. By using a structure borne high-frequency sensor, even a simple threshold-based monitoring was able to detect AE activity associated with cracking, which occurred not only during L-PBF itself, but also after the build job was completed, i.e. in the cooling phase. AE data analysis revealed that crack-related signals can easily be separated from the background noise (e.g. inert gas circulation pump) through their specific shape of a waveform, as well as their energy, skewness and kurtosis. Thus, AE was verified to be a promising method for L-PBF monitoring, enabling to detect formation of cracks regardless of their spatial and temporal occurrence.
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    Development and characterization of a metastable Al-Mn-Ce alloy produced by laser powder bed fusion
    (Amsterdam : Elsevier, 2021) Gabrysiak, Katharina; Gustmann, Tobias; Freudenberger, Jens; Neufeld, Kai; Giebeler, Lars; Leyens, Christoph; Kühn, Uta
    Laser powder bed fusion (LPBF) can help to overcome two challenges occurring by casting of metastable Al alloys: (1) the high amount of casting defects and (2) the limited part size while maintaining rapid solidification of the whole cross-section. In this study, an Al92Mn6Ce2 alloy was processed crack-free without baseplate heating by LPBF. The high cooling rate during fabrication has a significant impact on the microstructure, which was characterized by SEM, TEM and XRD. The processing through LPBF causes a high amount and a strong refinement of the intermetallic Al20Mn2Ce precipitates. This leads, compared to suction-cast specimens, to a higher hardness (180 HV 5) and a higher tolerable compressive stress (>1200 MPa) associated with a pronounced plasticity without failure up to a strain of 40%. The extraordinary mechanical properties of additively manufactured Al92Mn6Ce2 can extend the possibilities of producing novel LPBF lightweight structures for potential applications under harsh conditions.
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    Multiproxy approach to the reconstruction of soil denudation events and the disappearance of Luvisols in the loess landscape of south-western Poland
    (Amsterdam : Elsevier, 2022) Loba, Aleksandra; Zhang, Junjie; Tsukamoto, Sumiko; Kasprzak, Marek; Beata Kowalska, Joanna; Frechen, Manfred; Waroszewski, Jarosław
    Loess landscapes are highly susceptible to soil redeposition processes and thus may provide detailed insights into the record of denudation processes. Using optically stimulated luminescence dating and the soil micromorphology of 12 soil profiles, we reconstructed a complete record of denudation processes in south-western Poland. The first episode of soil redeposition took place around 9.1 ka. The denudation events that followed were attributed to the Neolithic (6.4 ± 0.3 ka), early Bronze Age (3.8 ± 0.2 ka), early and late Middle Ages (1.5 ± 0.1 ka and 0.7 ± 0.03 ka, respectively) and early Modern (0.4 ± 0.02 ka). As a consequence of the denudation processes, the soil cover in the studied area had been strongly reshaped. The predominant Luvisols had experienced progressive erosion processes that led first to a significant shallowing of the eluvial and argic horizons (truncated Luvisol) and, after some time, to their complete removal. Further thinning of the loess mantles had exposed geological substrates with very weak pedogenic alternations, thus pushing their transformation towards Regosol types. Similarly, Regosols occurred in toeslopes where freshly eroded material had been deposited, and where diagnostic horizons had not yet developed. Modern soil erosion rates in the studied loess area have considerably increased, and it is estimated that the Luvisol status may be completely transformed within approximately 80–300 years, if not sooner, due to progressive climate change.
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    Perspectives from CO+RE: How COVID-19 changed our food systems and food security paradigms
    (Amsterdam : Elsevier, 2020) Bakalis, Serafim; Valdramidis, Vasilis P.; Argyropoulos, Dimitrios; Ahrne, Lilia; Chen, Jianshe; Cullen, P.J.; Cummins, Enda; Datta, Ashim K.; Emmanouilidis, Christos; Foster, Tim; Fryer, Peter J.; Gouseti, Ourania; Hospido, Almudena; Knoerzer, Kai; LeBail, Alain; Marangoni, Alejandro G.; Rao, Pingfan; Schlüter, Oliver K.; Taoukis, Petros; Xanthakis, Epameinondas; Van Impe, Jan F.M.
    [no abstract available]
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    Investigation on the potential of applying bio-based edible coatings for horticultural products exemplified with cucumbers
    (Amsterdam : Elsevier, 2022) Rux, G.; Labude, C.; Herppich, W.B.; Geyer, M.
    Plastic packaging for fresh horticultural produce has many advantages but generates plastic waste and ecological alternatives are required. Edible coatings can retard many processes related to loss of quality. Hydrophobic lipid-based coatings are preferably applied for fresh fruits and vegetables. The approval of such coatings for products with edible peels in EU is increasingly under discussion. However, investigations on the efficiency of various edible coatings on soft-skinned fruit and vegetables are rare and it is currently unclear whether the consumer will accept them. Therefore, this study investigates (1) important characteristics of a lipid-based coating and (2) its ability to maintain the post-harvest quality of fresh cucumbers. This was evaluated by a comparative storage test under common suboptimal retail conditions (20 °C; 65% RH). The study also evaluates (3) the general perception of consumers about and their acceptance of the application of edible coatings on fresh fruit and vegetables with edible peels. The investigated coating was able to drastically reduce water loss (54–68%) and fruit respiration (approx. 33%) of fresh cucumber. The reduction of tissue stiffness was delayed by 2 days, thus, prolonged shelf life. Majority of consumer (77%) endorse the application of edible coatings as an alternative to plastic packaging, but emphasized important requirements for them.
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    In situ grown palladium nanoparticles on polyester fabric as easy-separable and recyclable catalyst for Suzuki-Miyaura reaction
    (Amsterdam : Elsevier, 2021) Xu, Tiefeng; Lu, Panting; Wohlrab, Sebastian; Chen, Wenxing; Springer, Armin; Wu, Xiao-Feng; Lu, Wangyang
    Palladium nanoparticles supported on low-melting polyester (Pd/LMPET) fabric were prepared through a microwave irradiation assisted method. In this way, in situ growth of Pd nanoparticles onto an easy to handle material was initiated and proceeded. The results of the characterization revealed that the palladium nanoparticles were well-dispersed on the surfaces of the polyester fibers. The Pd/LMPET fabrics were then employed in the Suzuki-Miyaura coupling. They exhibited excellent catalytic activity in ethanol/water under air atmosphere at 50 °C. Importantly, the Pd/LMPET fabrics could be separated from reaction mixture conveniently and they can still maintain good activity after 8 cycles without Pd leaching. © 2021 The Authors