Monographs from 2018

Results: 685
Created on: Wed, 27 Mar 2024 23:02:58 +0100 in 0.0898 sec


Diemar, Andreas; Gerth, Uwe; Lahmer, Tom; Teichert, Gerd; Könke, Carsten
Numerische Ermittlung von Zielgrößen und Prozessparametern des Einsatzhärtens unter Berücksichtigung des lokalen Beanspruchungszustandes versagensrelevanter Konstruktionsdetails :
Numerical determination of target values and process parameters of case hardening, taking into account the local stress state of failure-relevant construction details. - In: HTM - journal of heat treatment and materials, ISSN 2194-1831, Bd. 78 (2023), 6, S. 352-368

Through the thermochemical process of case hardening, the local material strength of steel components can be increased. In addition to the increase in stress due to the notch effect, the shape of construction details also has an effect on key component properties after case hardening, such as edge hardness and case hardening depth. The component-related specification of target values for case hardening is currently based on empirical values or expert knowledge. In addition, the effect of design details during case hardening is not taken into account when specifying process parameters in the control and regulation software of case hardening systems. This article presents a concept for the numerical determination of target values and process parameters for case hardening based on the stress state of the component. Compared to the empirically based determination of target values and process parameters for case hardening, the application of the concept makes it possible to adapt the case hardening of components to their stress in the failure range and thus significantly increase the energy and resource efficiency of case hardening.



https://doi.org/10.1515/htm-2023-0023
Bohm, Sebastian; Grunert, Malte; Schwarz, Felix; Runge, Erich; Wang, Dong; Schaaf, Peter; Chimeh, Abbas; Lienau, Christoph
Gold nanosponges: fascinating optical properties of a unique disorder-dominated system. - In: Journal of the Optical Society of America, ISSN 1520-8540, Bd. 40 (2023), 6, S. 1491-1509

Nanoporous gold is a three-dimensional bulk material that is percolated with a random network of nanometer-sized ligaments and made by selective corrosion of bimetallic alloys. It has intriguing geometric, catalytic, and optical properties that have fascinated scientists for many decades. When such a material is made into the form of small, 100-nm-sized particles, so-called nanosponges emerge that offer much flexibility in controlling their geometric, electronic, and optical properties. Importantly, these particles act as an antenna for light that can efficiently localize optical fields on a deep subwavelength scale in certain hotspots at the particle surface. This makes such nanosponges an interesting platform for plasmonic sensing, photocatalysis, and surface-enhanced Raman spectroscopy. Since the optical properties of these nanosponges can be controlled to a large degree by tuning their geometry and/or composition, they have attracted increasing attention in recent years. Here, we provide a concise overview of the current state of the art in this field, covering their fabrication, computational modeling, and specifically the linear and nonlinear optical properties of individual and hybrid nanosponges, for example, plasmon localization in randomly disordered hotspots with a size <10 nm and a long lifetime with an exceptionally high Purcell factor. The resulting nonlinear optical and photoemission properties are discussed for individual and hybrid nanosponges. The results presented have strong implications for further applications of such nanosponges in photonics and photocatalysis.



https://doi.org/10.1364/JOSAB.479739
Glaser, Marcus; Matthes, Sebastian; Riegler, Sascha Sebastian; Hildebrand, Jörg; Bergmann, Jean Pierre; Schaaf, Peter; Gallino, Isabella
Characterization of plastic-metal hybrid composites joined by means of reactive Al/Ni multilayers - evaluation of occurring thermal regime. - In: Engineering for a changing world, (2023), 4.3.056, S. 1-16

Present challenges in material science and joining technology are ever more subject to the desire for lightweight construction and engineering. Plastic-metal composites are suitable material combinations but also require the development and investigation of appropriate joining technologies. A particularly promising approach is the application of reactive multilayer foils. As an innovative method, these foils provide the possibility of flexible and low-distortion joining of dissimilar materials. The underlying reaction mechanism offers fast exothermic reaction propagation with well-known exothermic power output while the energy source is introduced directly into the joining zone. In this work, hybrid lap joints between semi-crystalline polyamide 6 and structured austenitic stainless steel X5CrNi18-10 were joined using reactive Al/Ni multilayer foils. The self-propagating reaction provides immediate temperatures that are well above the melting point of used plastic but decays rapidly after only a few milliseconds. To support ongoing investigations regarding composite formation, analysis of occurring thermal regime is in the focus of this work. Conducted experiments are supported by accompanying thermal simulation in ANSYS Workbench. Besides the estimation regarding sensitivity of thermal material parameters the evaluation of formed melting zone and resulting thermally influenced area is a central topic.



https://doi.org/10.22032/dbt.58913
Tan, Xi-Nu; Li, Feitao; Liu, Yu-Shun; Qiu, Ri-Sheng; Liu, Qing
Microstructure and properties of as-cast Zr-2.5Nb-1X (X = Ru, Mo, Ta and Si) alloys for biomedical application. - In: Rare metals, ISSN 1867-7185, Bd. 42 (2023), 10, S. 3497-3509

https://doi.org/10.1007/s12598-023-02291-3
Große-Knetter, Jörn; Schaaf, Peter
Das physikalische Praktikum : Handbuch 2023/2024 für Studentinnen und Studenten der Physik. - Göttingen : Universitätsverlag Göttingen, 2023. - (Universitätsdrucke)
Mathew, Sobin; Reiprich, Johannes; Narasimha, Shilpashree; Abedin, Saadman; Kurtash, Vladislav; Thiele, Sebastian; Scheler, Theresa; Hähnlein, Bernd; Schaaf, Peter; Jacobs, Heiko O.; Pezoldt, Jörg
Gate-tunable hysteresis response of field effect transistor based on sulfurized Mo. - In: AIP Advances, ISSN 2158-3226, Bd. 13 (2023), 9, 095224, S. 095224-1-095224-7

Hysteresis effects and their tuning with electric fields and light were studied in thin film molybdenum disulfide transistors fabricated from sulfurized molybdenum films. The influence of the back-gate voltage bias, voltage sweep range, illumination, and AlOx encapsulation on the hysteresis effect of the back-gated field effect transistors was studied and quantified. This study revealed the distinctive contribution of MoS2 surface, MoS2/SiO2 interface defects and their associated traps as primary sources of of hysteresis.



https://doi.org/10.1063/5.0165868
Cheng, Pengfei;
Broadband solar energy harvesting enabled by micro and nanostructured materials. - Ilmenau : Universitätsbibliothek, 2023. - 1 Online-Ressource (IV, 145 Seiten)
Technische Universität Ilmenau, Dissertation 2023

In der kommenden Ära des "Carbon Peak und der Kohlenstoffneutralität" ist es besonders wichtig, neue Energietechnologien zu entwickeln, die kostengünstig, umweltfreundlich und im industriellem Maßstab herstellbar sind, um die herkömmlichen fossilen Brennstoffe zu ersetzen, die weithin als Verursacher des Treibhauseffekts und häufiger extremer Wetterlagen gelten. Solarenergie ist sozusagen eine unerschöpfliche Energieform, die jedem Land der Erde kostenlos zur Verfügung steht. Daher ist sie im Vergleich zu Kernenergie, Windenergie und blauer Energie die vielversprechendste Alternative zu fossiler Energie. In dieser Arbeit werden breitbandige Materialien zur Gewinnung von Solarenergie als Lichtabsorber für Anwendungen zur Umwandlung von Solarenergie, wie Stromerzeugung, Wasserdampferzeugung und Wasserstofferzeugung, vorgestellt. Zunächst wird schwarzes Silizium (b-Si) mit einer Vielzahl von Mikro-Nanostrukturen durch reaktives Ionenätzen (RIE) hergestellt. Die so hergestellten b-Si-Proben mit ultra-breitbandiger Lichtabsorption können für die photo-thermoelektrische (P-TE) Stromerzeugung, die photothermische (PT) Wasserverdampfung und die photoelektrochemische (PEC) Wasserreduktion verwendet werden, was die Leistung der Solarenergieumwandlung aufgrund ihrer hervorragenden Lichtabsorption im gesamten Sonnenspektrum verbessert. Darüber hinaus wurde eine metastabile Atomlagenabscheidung (MS-ALD) mit Selbstorganisation zur Herstellung großflächiger plasmonischer 3D-AgSiO2 Hybrid-Nanostrukturen entwickelt. Diese zeigen auch eine ultrabreitbandige sehr hohe Absorption im gesamten Sonnenspektrum. Wenn sie für die P-TE- und PT-Wasserverdampfung verwendet werden, verbessert sich die Leistung der Solarenergieumwandlung im Vergleich zu b-Si-Proben.



https://doi.org/10.22032/dbt.57584
Li, Feitao;
Nanometallurgical mechanisms during formation of Au-SiOx and Au-CuO nanostructures. - Ilmenau : Universitätsbibliothek, 2023. - 1 Online-Ressource (XXII, 98 Seiten)
Technische Universität Ilmenau, Dissertation 2023

Die Verbesserung der Metallurgie hält mit der Entwicklung der menschlichen Zivilisation Schritt. Aufstrebende Nanotechnologie-Industrien fördern kontinuierlich traditionelle metallurgische Untersuchungen bis hinunter in den Nanobereich. Daher wird ein neuer Begriff, Nanometallurgie, vorgeschlagen, um sich besser an die aufkommenden interdisziplinären Domänen anzupassen. Um die Mechanismen hinter verschiedenen nanometallurgischen Prozessen zu verstehen, sind zahlreiche Studien erforderlich, die für die maßgeschneiderte Herstellung von Nanostrukturen für unterschiedliche Anforderungen erforderlich sind. Die aktuelle Dissertation konzentriert sich auf das Wachstum zweier unterschiedlicher eindimensionaler Nanostrukturen: SiOx-Nanodrähte, katalysiert durch metallische Dünnfilme und CuO-Whisker, induziert durch thermische Oxidation. Die Bildung von SiOx-Nanodrähten basiert auf der Änderung des physikalischen Zustands der Si-Quelle ist gut etabliert. Es wurde jedoch nur wenig an der Existenz und Konkurenz mehrerer Si-Quellen geforscht. Nach dem schnellen hermischen Prozessieren von SiO2/Si-Systemen, die mit metallischen Einzel- oder Doppelschichten in einer reduzierenden Atmosphäre abgeschieden wurden, werden drei Si-Quellen, erstens Si-Diffusion aus dem Substrat, zweitens SiO-Gas aus der SiO2-Zersetzung und drittens aus der Si-Aktivoxidation identifiziert. Ihre relative Beteiligung und Einfluß hängt von dem Dicken der SiO2-Schichten ab. Zunehmende Dicke der SiO2-Schicht behindert die Si-Diffusion und die Zersetzung der SiO2-Schicht, was die Konzentrationen der zersetzten Bereiche verringert und wiederum die aktive Si-Oxidation schwächt. Außerdem werden die Einflüße verschiedener Si-Quellen durch die Glühzeit, Temperatur und Atmosphäre gesteuert. Daher wird eine kontrollierbare Bildung verschiedener Au-SiOx-Nanostrukturen erreicht, indem unterschiedliche Dicken der SiO2-Schicht und Temperparameter entworfen werden. Zwei nanometallurgische Prozesse, der Kirkendall-Effekt im Nanomaßstab und das Wachstum von Oxid-Nanodrähten während der Oxidation von Metallen, haben große Aufmerksamkeit erhalten. Ihre Entwicklung hängt stark von der Oxidationsgeschwindigkeit ab. In Anbetracht der Tatsache, dass die Oxidation normalerweise ein diffusionskontrollierter Prozess ist und das Legieren ein üblicher Weg ist, um die Diffusion verschiedener Metalle zu kontrollieren, werden gemischte und facettierte Au-Cu-Nanopartikel durch die Festkörperentnetzung der Au/Cu-Doppelschicht gebildet. Die Existenz von Kirkendall-Hohlräumen und CuO-Whiskern kann durch Oxidation bei unterschiedlichen Temperaturen beobachtet werden, was zur Bildung von Au-CuO-Nanostrukturen führt. Darüber hinaus wird das Oxidationsverhalten von Cu auf verschiedenen Facetten von Au-Cu-Nanopartikeln überprüft und mit den Oxidationsraten von Kristallebenen in Beziehung gesetzt.



https://doi.org/10.22032/dbt.58531
Mejia Chueca, Maria del Carmen; Graske, Marcus; Winter, Andreas; Baumer, Christoph; Stich, Michael; Mattea, Carlos; Ispas, Adriana; Isaac, Nishchay Angel; Schaaf, Peter; Stapf, Siegfried; Jacobs, Heiko O.; Bund, Andreas
Electrodeposition of reactive aluminum-nickel coatings in an AlCl3:[EMIm]Cl ionic liquid containing nickel nanoparticles. - In: Journal of the Electrochemical Society, ISSN 1945-7111, Bd. 170 (2023), 7, 072504

The electrodeposition of aluminum-nickel coatings was performed by pulsed direct current in the ionic liquid (IL) 1.5:1 AlCl3:EMIm]Cl containing nickel nanoparticles (Ni NPs), for reactive dispersion coating application. Several electrochemical and characterization techniques were used to shed more light on the mechanism of Ni particle incorporation into the Al matrix. Thus, particle incorporation at the early stage of the deposition would mainly take place via particle adsorption at the substrate. However, as the thickness of the coating increases, it seems that the main mechanism for particle incorporation is via the reduction of ions adsorbed at the particles surface. Although a considerable high incorporation of Ni NPs has been achieved from the IL containing the highest concentration of Ni NPs (i.e. ∼33 wt% from a 20 g/L of Ni NPs bath), a high concentration of NPs in the IL resulted having a negative effect in terms of quality of the coatings, due to solidification of the electrolyte in a poorly conductive compound. Moreover, almost equivalent amounts of Ni and Al (Ni ∼45 wt.%and Al ∼44 wt.%) have been detected in some areas of the coatings. Such a layer composition would be desired for the targeted application.



https://doi.org/10.1149/1945-7111/ace382
Jaekel, Konrad; Sauni Camposano, Yesenia Haydee; Matthes, Sebastian; Glaser, Marcus; Schaaf, Peter; Bergmann, Jean Pierre; Müller, Jens; Bartsch, Heike
Ni/Al multilayer reactions on nanostructured silicon substrates. - In: Journal of materials science, ISSN 1573-4803, Bd. 58 (2023), 31, S. 12811-12826

Fast energy release, which is a fundamental property of reactive multilayer systems, can be used in a wide field of applications. For most applications, a self-propagating reaction and adhesion between the multilayers and substrate are necessary. In this work, a distinct approach for achieving self-propagating reactions and adhesion between deposited Ni/Al reactive multilayers and silicon substrate is demonstrated. The silicon surface consists of random structures, referred to as silicon grass, which were created by deep reactive ion etching. Using the etching process, structure units of heights between 8 and 13 µm and density between 0.5 and 3.5 structures per µm^2 were formed. Ni and Al layers were alternatingly deposited in the stoichiometric ratio of 1:1 using sputtering, to achieve a total thickness of 5 µm. The analysis of the reaction and phase transformation was done with high-speed camera, high-speed pyrometer, and X-ray diffractometer. Cross-sectional analysis showed that the multilayers grew only on top of the silicon grass in the form of inversed cones, which enabled adhesion between the silicon grass and the reacted multilayers. A self-propagating reaction on silicon grass was achieved, due to the thermally isolating air pockets present around these multilayer cones. The velocity and temperature of the reaction varied according to the structure morphology. The reaction parameters decreased with increasing height and decreasing density of the structures. To analyze the exact influence of the morphology, further investigations are needed.



https://doi.org/10.1007/s10853-023-08794-9