Dissertations from 2018

Anzahl der Treffer: 695
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Sauni Camposano, Yesenia Haydee; Jaekel, Konrad; Riegler, Sascha S.; Matthes, Sebastian; Glaser, Marcus; Peter, Nicolas J.; Vardo, Emina; Bartsch, Heike; Schwaiger, Ruth; Bergmann, Jean Pierre; Gallino, Isabella; Schaaf, Peter
Controlling propagation velocity in Al/Ni reactive multilayer systems by periodic 2D surface structuring. - In: Advanced engineering materials, ISSN 1527-2648, Bd. n/a (2024), n/a, 2302272, S. 1-11

The chemical energy released as heat during the exothermic reaction of reactive multilayer systems has shown potential applications in various technological areas, e.g., in joining applications. However, controlling the heat release rate and the propagation velocity of the reaction is required to enhance their performance in most of these applications. Herein, a method to control the propagation velocity and heat release rate of the system is presented. The sputtering of Al/Ni multilayers on substrates with periodic 2D surface structures promotes the formation of growth defects into the system. This modification in the morphology locally influences the reaction characteristics. Tailoring the number of 2D structures in the substrate enables the control of the velocity and maximum temperature of the propagation front. The morphology of the produced reactive multilayers is investigated before and after reaction using scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. In addition, the enthalpy of the system is obtained through calorimetric analysis. The self-sustained and self-propagating reaction of the systems is monitored by a high-speed camera and a high-speed pyrometer, thus revealing the propagation velocity and the temperatures with time resolution in the microsecond regime.

Wang, Honglei; Cheng, Pengfei; Wu, Bing; Yan, Yong; Schaaf, Peter; Sofer, Zdeněk; Wang, Dong
2D metal phosphorous trichalcogenides (MPCh3) for sustainable energy storage and conversion: nanoarchitectonics and advanced applications. - In: Advanced functional materials, ISSN 1616-3028, Bd. n/a (2024), n/a, 2407432, S. 1-22

2D metal phosphorous trichalcogenides (MPCh3) have attracted considerable attention in sustainable energy storage and conversion due to their distinct physical and chemical characteristics, such as adjustable energy bandgap, significant specific surface area, and abundant active sites. However, research on 2D MPCh3 primarily focuses on electrocatalysis, and understanding its energy conversion and storage mechanisms remains incomplete. This review comprehensively summarizes recent advancements in energy storage and conversion using 2D MPCh3-based materials of various structures. It begins with a discussion of the distinctive properties and preparation techniques of 2D MPCh3, followed by a focus on the rational design and development of these materials for diverse energy-related applications, including rechargeable batteries, supercapacitors, electrocatalysis, photocatalysis, and desalination. Finally, it outlines the key challenges and prospects for future research on 2D MPCh3 materials.

Vardo, Emina; Sauni Camposano, Yesenia Haydee; Matthes, Sebastian; Glaser, Marcus; Bartsch, Heike; Hildebrand, Jörg; Bergmann, Jean Pierre; Schaaf, Peter
Impact of substrate thickness and surface roughness on Al/Ni multilayer reaction kinetics. - In: Advanced engineering materials, ISSN 1527-2648, Bd. n/a (2024), n/a, 2302269, S. 1-10

Reactive multilayers comprising alternating nanoscale layers of Al and Ni exhibit potential across various applications, including localized heating for welding and joining. Control over reaction properties is pivotal for emerging applications, such as chemical time delays or neutralization of biological or chemical weapons. In this research, insights are offered into the intricate interplay between substrate thickness, surface roughness, and the behavior of Al/Ni reactive multilayers, opening avenues for tailored applications in various domains. To observe this interplay, silica with various thicknesses from 0.4 to 1.6 μm is deposited on polished single-crystalline Si and rough poly-Si base substrates. Additionally, to analyze the impact of varying silica thickness along the sample length on reaction behavior, silica in steplike shape is fabricated. Subsequently, Al/Ni multilayers with 5 μm total thickness and 20 or 50 nm bilayer periodicities are deposited. Reaction velocity and temperature are monitored with a high-speed camera and pyrometer. In the results, it is indicated that silica thickness significantly affects self-propagation in multilayers. The reaction is not self-sustained for silica layers ≤ 0.4 μm, depending on bilayer periodicity and substrate roughness. The velocity increases or decreases based on the direction of reaction propagation, whether it moves upward or downward, in relation to the thickness of silica.

Riegler, Sascha S.; Sauni Camposano, Yesenia Haydee; Jaekel, Konrad; Frey, Maximilian; Neemann, Christian; Matthes, Sebastian; Vardo, Emina; Chegeni, Maryam R.; Bartsch, Heike; Busch, Ralf; Müller, Jens; Schaaf, Peter; Gallino, Isabella
Nanocalorimetry of nanoscaled Ni/Al multilayer films: on the methodology to determine reaction kinetics for highly reactive films. - In: Advanced engineering materials, ISSN 1527-2648, Bd. 0 (2024), 0, 2302279, S. 1-10

Free-standing Ni/Al multilayer films with a planar morphology, a bilayer thickness of 20 nm, and an average composition of Ni50Al50 (at%) deposited by direct current magnetron sputtering are investigated by nanocalorimetry and conventional calorimetry. Both the novel fast differential scanning calorimeter (FDSC) Flash DSC 2+ from Mettler-Toledo (MT) and conventional calorimeter MT DSC 3 are used to cover a range of heating rates from 0.1 to 10^4 K s^−1. A quantitative kinetic study of the interdiffusion and phase reaction sequence is performed via a Kissinger analysis covering five orders of magnitude of heating rates. Using the calorimetric data, the derived apparent activation energies suggest monotonic reaction kinetics over the entire range of heating rates applied. To correct the thermal lag at the highest heating rates with the FDSC for nonadhered free-standing films, a new methodology for its correction is used. Overall, this work extends the application of commercial FDSC to nonadhered films.

Smyrnova, Kateryna; Sahul, Martin; Haršáni, Marián; Beresnev, Vyacheslav; Truchlý, Martin; Čaplovič, L’ubomír; Čaplovičová, Mária; Kusý, Martin; Kozak, Andrii; Flock, Dominik; Kassymbaev, Alexey; Pogrebnjak, Aleksandr Dmitrievič
Composite materials with nanoscale multilayer architecture based on cathodic-arc evaporated WN/NbN coatings. - In: ACS omega, ISSN 2470-1343, Bd. 9 (2024), 15, S. 17247-17265

Hard nitride coatings are commonly employed to protect components subjected to friction, whereby such coatings should possess excellent tribomechanical properties in order to endure high stresses and temperatures. In this study, WN/NbN coatings are synthesized by using the cathodic-arc evaporation (CA-PVD) technique at various negative bias voltages in the 50-200 V range. The phase composition, microstructural features, and tribomechanical properties of the multilayers are comprehensively studied. Fabricated coatings have a complex structure of three nanocrystalline phases: β-W2N, δ-NbN, and ε-NbN. They demonstrate a tendency for (111)-oriented grains to overgrow (200)-oriented grains with increasing coating thickness. All of the data show that a decrease in the fraction of ε-NbN phase and formation of the (111)-textured grains positively impact mechanical properties and wear behavior. Investigation of the room-temperature tribological properties reveals that with an increase in bias voltage from −50 to −200 V, the wear mechanisms change as follows: oxidative &flech; fatigue and oxidative &flech; adhesive and oxidative. Furthermore, WN/NbN coatings demonstrate a high hardness of 33.6-36.6 GPa and a low specific wear rate of (1.9-4.1) × 10-6 mm3/Nm. These results indicate that synthesized multilayers hold promise for tribological applications as wear-resistant coatings.

Zhao, Yuguo; Björk, Emma M.; Yan, Yong; Schaaf, Peter; Wang, Dong
Recent progress in transition metal based catalysts and mechanism analysis for alcohol electrooxidation reactions. - In: Green chemistry, ISSN 1463-9270, Bd. 26 (2024), 9, S. 4987-5003

In order to address energy and environmental challenges effectively, there is a need to promote renewable energy-driven electrochemical conversion technologies, particularly electrosynthesis. Electrosynthesis has the potential to convert abundant molecules into valuable chemicals and fuels. However, the widespread adoption of electrosynthesis is often hindered by the slow oxygen evolution reaction (OER). To overcome this limitation, we can employ the more efficient alcohol electrooxidation reaction (AOR), utilizing renewable biomass-derived alcohols as an alternative to OER for producing high-value chemicals. Consequently, the development of efficient AOR catalysts, in conjunction with cathodic reduction reactions (hydrogen evolution, oxygen, and nitrogen electroreduction, etc.), is crucial for sustainable and environmentally-friendly advancements. A thorough understanding of AOR mechanisms is essential for catalyst design and can be achieved through the utilization of in situ characterization techniques and density functional theory (DFT) calculations. This review summarizes recent progress in AOR catalysts, with a particular focus on the electrooxidation of monohydric alcohols, polyols, and associated studies on reaction mechanisms. Additionally, the review identifies key factors impeding AOR development and provides insights into future prospects.

Jaekel, Konrad; Riegler, Sascha Sebastian; Sauni Camposano, Yesenia Haydee; Matthes, Sebastian; Glaser, Marcus; Bergmann, Jean Pierre; Schaaf, Peter; Gallino, Isabella; Müller, Jens; Bartsch, Heike
Influence of increasing density of microstructures on the self-propagating reaction of Al/Ni reactive nanoscale multilayers. - In: Advanced engineering materials, ISSN 1527-2648, Bd. 0 (2024), 0, insges. 21 S.

Surface structuring methods are crucial in semiconductor manufacturing, as they enable the creation of intricate structures on the semiconductor surface, influencing the material’s electrical, mechanical, and chemical properties. This study employs one such structuring method known as reactive ion etching to create black Si structures on silicon substrates. After thermal oxidation, their influence on the reaction of Al/Ni nanoscale multilayers is. For this purpose, various densities of thermally oxidized black Si structures are investigated. It reveals distinct reactive behaviors without corresponding differences in energy release during differential scanning calorimetry measurements. Higher oxidized black Si structure densities result in elevated temperatures and faster reaction propagation, showing fewer defects and reduced layer connections in cross-sectional analyses. The properties of the reactive multilayers on high structure density show the same performance as a reaction on flat thermal SiO2, causing delamination when exceeding 23 structures per µm2. Conversely, lower structure density ensures attachment of reactive multilayers to the substrate due to an increased number of defects, acting as predetermined breaking points for the AlNi alloy. By establishing the adhesion between the reacted multilayer and the substrate, surface structuring could lead to a potential increase in bond strength when using reactive multilayers for bonding.

Matthes, Sebastian; Glaser, Marcus; Vardo, Emina; Sauni Camposano, Yesenia Haydee; Jaekel, Konrad; Bergmann, Jean Pierre; Schaaf, Peter
Tailoring the reaction path: external crack initiation in reactive Al/Ni multilayers. - In: Advanced engineering materials, ISSN 1527-2648, Bd. 0 (2024), 0, 2302271, S. 1-6

The influence of intentionally externally induced cracks in reactive Al/Ni multilayer systems is investigated. These cracks affect the reaction dynamics and enable tailoring of the reaction path and the overall velocity of the reaction front. The influence of layer variations onto mechanical crack formation and resulting reaction behavior are investigated. High-speed camera imaging shows the meandering propagation of the reaction front along the crack paths. Therefore, the mechanical cracking process significantly changes the total velocity of the reaction front and thus offers a possibility to control the self-propagating high-temperature synthesis process. It is shown that the phase formation remains unaffected despite the applied strains and cracks. This favorable stability in phase formation ensures predictability and provides insight into the adaptation of RMS for precision applications in joints. The results expand the understanding of mechanical cracking as a tool to influence high-temperature synthesis in reactive multilayer coatings and provide an opportunity to expand the range of applications.

Glaser, Marcus; Ehlich, Kai; Matthes, Sebastian; Hildebrand, Jörg; Schaaf, Peter; Bergmann, Jean Pierre
Influence of metal surface structures on composite formation during polymer-metal-joining based on reactive Al/Ni multilayer foil. - In: Advanced engineering materials, ISSN 1527-2648, Bd. 0 (2024), 0, insges. 34 S.

Progressive developments in the field of lightweight construction and engineering demand continuous substitution of metals with suitable polymers. However, the combination of dissimilar materials results in a multitude of challenges based on different chemical and physical material properties. Reactive multilayer systems offer a promising joining method for flexible and low-distortion joining of dissimilar joining partners with an energy source introduced directly into the joining zone. Within this publication, hybrid lap joints between semi-crystalline polyamide 6 and surface-structured austenitic steel X5CrNi18-10 (EN 1.4301) were joined using reactive Al/Ni multilayer foils of the type Indium-NanoFoil®. Main objective is to examine possibilities of influencing crack initiation in the foil plane by variation of joining pressure and different metal surface structures with regard to geometry, density and orientation. Thus, the position of foil cracks is superimposed onto the metal structure and associated filling with molten plastic is improved. Consequently, characterisation of occurring crack positions as function of joining pressure and metal structure, analysis of the composite in terms of structural filling and joint strength as well as possible causes of crack initiation are evaluated.

Mejia Chueca, Maria del Carmen; Winter, Andreas; Abdi, Azadeh; Baumer, Christoph; Ispas, Adriana; Stich, Michael; Riegler, Sascha; Ecke, Gernot; Isaac, Nishchay Angel; Graske, Marcus; Gallino, Isabella; Schaaf, Peter; Jacobs, Heiko O.; Bund, Andreas
A novel method for preparation of Al-Ni reactive coatings by incorporation of Ni nanoparticles into an Al matrix fabricated by electrodeposition in AlCl3:1-eethyl-3-methylimidazolium chloride (1.5:1) ionic liquid containing Ni nanoparticles. - In: Advanced engineering materials, ISSN 1527-2648, Bd. 0 (2024), 0, 2302217, S. 1-17

Al/Ni reactive coatings are fabricated via electrochemical deposition (ECD) at different applied voltages for reactive bonding application. AlCl3:1-ethyl-3-methylimidazolium chloride ([EMIm]Cl) (1.5:1) ionic liquid electrolyte is used as source of Al, whereas Ni is in the bath and incorporated into final coatings as nanoparticles (NPs). Scanning electron microscopy and Auger electron spectroscopy reveal a homogeneous Ni particle dispersion, as well as a high amount of particle incorporation into the Al matrix. A maximum of 37 wt% (22 at%) of Ni is detected via atomic absorption spectroscopy in the Al/Ni coating deposited at −0.1 V from an electrolyte containing 20 g L−1 of Ni NPs. Previous literature show that for bonding application an ideal concentration is around 50 at% of Ni and 50 at% Al. However, this is achieved using high vacuum, time-consuming processes, and costly techniques like evaporation and magnetron sputtering. The ECD used in this work represents a more cost-efficient approach which is not reported up to date for the aforementioned application. The reactivity of the coatings is confirmed by Differential scanning calorimetry. Herein, an exothermic reaction is detected upon the mixing of Al and Ni occurring at high temperatures.