Mädler, Lutz
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Mädler, Lutz
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Mädler, Lutz
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Mädler, L.
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Item-typ:Veröffentlichung, Influence of the Nonlocal Effect on the Optical Properties of Nonspherical Plasmonic Semiconductor NanoparticlesNoble metals are commonly used as plasmon materials because of their high density of free electrons, but semiconductor materials are also becoming of interesting in this field because its electron density can be varied by doping. Metal nitrides can be an alternative to noble metals because of their low absorption loss and high electron density. Among others, TiN and ZrN seem to be most suitable as alternative plasmonic materials because their optical properties are dominated by conduction electrons near the plasmon frequency. There is the flame spray pyrolysis process, which is currently developed to produce such kind of nanoparticles. In this paper, based on an extension of the discrete sources method, the effect of the hydrodynamic Drude model of the quantum nonlocal effect on the optical characteristics of semiconductor nanoparticles is analyzed. The influence of accounting for the nonlocal effect (NLE) on the optical properties under spherical particles deformation has been investigated. It has been shown that accounting for the NLE leads to a plasmon resonance blue shift and a damping similar to noble metals. It was found that smaller particles demonstrate larger NLE influence than larger ones. Besides, the influence of polarization on the local and nonlocal responses of 3D nonspherical semiconductor particles has been investigated as well. Using simulation accounting for the nonlocal effect, it is shown that the extinction of a nonspherical ZrN particles exceeds that of a gold particle.Wissenschaftlicher ArtikelBand:3131 15 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Redox Activity and Nano–Bio Interactions Determine the Skin Injury Potential of Co3O4-Based Metal Oxide Nanoparticles toward Zebrafish(American chemical society, 2020-03-19); ; ; ; Redox-active metal oxide nanoparticles show varying oxidizing capacities and injury potentials toward biological systems. Here, two metal oxide libraries including transition-metal-doped Co3O4 and PdO-Co3O4 with strong chemical contacts were design-synthesized and used to investigate their biological injury potential and mechanisms using zebrafish as a model organism. Among different dopants, Cu significantly increased the oxidizing capacity of Co3O4. An increased amount of PdO resulted in higher density of heterojunctions, which also led to higher oxidizing capacity. The oxidizing capacity of these nanoparticles was positively correlated with higher mortality of dechorionated embryos and severe larval skin injury upon exposure. Using transgenic zebrafish Tg(LysC:eGFP), we show in real time that the redox-active nanoparticles induced skin injury and activated the infiltration of immune cells. Such inflammatory response was confirmed by the increased mRNA expression level of Nrf2a, HO-1, IL-1β, and IL-6 genes. Although the exposure to the nanoparticles alone was not lethal, the skin injury did lower the tolerance level against other environmental contaminants. More importantly, after withdrawing from the nanoparticle exposure, larvae with skin injury could recover within 24 h in uncontaminated medium, indicating such injury was transient and recoverable.Wissenschaftlicher ArtikelBand:14Heft:433 37 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Rare-Earth-Doped Y4Al2O9 Nanoparticles for Stable Light-Converting Phosphors(American Chemical Society, 2019-12-24); ; ; ; The ternary mixed metal oxides with high specific surface area are industrially important for sensors, catalysis, energy storage, and optoelectronics. However, synthesis of such metal oxides is always challenging, especially when multicomponent mixtures occur due to very narrow formation temperature windows. Flame spray pyrolysis is one of the best known techniques which enable formation of pure phases optimizing the temperature profile via control over the fuel/oxidizer ratio. Here, Y4Al2O9 (monoclinic phase of yttrium aluminum oxide, also known as YAM) and Y4–xEuxAl2O9 (x = 0.05–1.0) were strategically synthesized with specific precursor–solvent chemistry. While the hydrated yttrium nitrate with 28.2% water was unsuitable for the formation of crystalline Y4Al2O9 particles, the use of organic precursor–solvent combinations (Y/Al 2:1) resulted in 16 nm phase pure, highly crystalline Y4Al2O9 particles. All the materials were characterized by using X-ray diffraction with Rietveld refinement, Raman spectroscopy, and transmission electron microscopy. To develop a stable light-converting phosphor, the Y4Al2O9 host was doped with Eu to investigate the photoluminescence properties of Y4–xEuxAl2O9 (x = 0.05–1.0). The results indicated increased photoluminescence intensity with increasing Eu3+ concentration up to x = 0.5, i.e., Y3.5Eu0.5Al2O9, and a subsequent drop or decrease in intensity for x ≥ 0.7. Hence, Y3.5Eu0.5Al2O9 is proposed for a potential light-converting phosphor.Wissenschaftlicher ArtikelBand:3Heft:116 11 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Additive manufacturing of high modulus steels: New possibilities for lightweight designThis work demonstrates the feasibility of fabricating bulk nanostructured high modulus steels in-situ by additive manufacturing. This ideal match of novel processes and alloy concepts opens up new pathways for lightweight design by producing light, stiff, strong and ductile components with minimal geometric restraints. On the example of an Fe – Ti – B alloy, a conventional processing sequence of melting and casting pre-alloys, gas-atomisation and laser powder bed fusion (selective laser melting) led to finely dispersed metastable particle and matrix phases. A simple annealing step transformed them into the desired equilibrium constituents of ductile ferrite (matrix) and light and stiff TiB2 (particles), with only minimal changes in particle size (about 20–150 nm in diameter) and distribution (mainly on the matrix grain boundaries). This nano-scaled composite structure promises an extremely attractive property profile, i.e. an increased stiffness/ratio at elevated strength and without deteriorated ductility. However, the not yet optimized parameters of the laser fusion process led to the formation of few pores and cracks, which prevented the complete assessment of the property profile of the manufactured samples. Material and processing strategies for the further development of this promising lightweight design approach – including the suitability of other powder metallurgy processing routes – are outlined and discussed.Wissenschaftlicher ArtikelBand:3218 34 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Effect of hot gas atomization on spray forming of steel tubes using a close-coupled atomizer (CCA)Hot gas atomization in spray forming has been used for the first time to improve the quality of spray-formed tubular deposits. This technique reduces gas consumption and produces smaller droplets than cold gas atomization. The flight velocity and cooling rate of the atomized droplets increase with increasing gas temperature. These features can further influence the quality of the spray-formed deposits. Until now, spray-formed tubes have not been used on industrial scale due to insufficient deposit quality in terms of porosity and bonding to the substrate. Using a close-coupled atomizer (CCA), qualitative improvements of the as-sprayed deposits have been previously studied. In the present study, a comparative investigation is done to find the influence of hot gas atomization on the spray forming of the bearing steel AISI 52100 (100Cr6) using a close-coupled atomizer. The spray-formed deposit with hot gas atomization (gas temperature about 300 °C) shows lower deposit surface temperature and smaller grain size in comparison to the deposit produced under cold gas atomization condition due to smaller droplet diameter and higher cooling rate of the droplets. Moreover, the as-sprayed deposits under hot gas atomization show a higher relative density at a lower deposit surface temperature, which extends the process window for the flexible production of spray-formed tubes.Wissenschaftlicher ArtikelBand:28228 23 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, The impact of metal doping on fumed silica structure and amino acid thermal condensation catalytic properties(Springer, 2021-08-18); ; ; ; Fumed silica nanoparticles (FSN) are one of the most common synthetic forms of silica, but prolonged exposure leads to cell toxicity and apoptosis due to reactive oxygen species (ROS) generation and cell membrane perturbation resulting from hydrogen bonding and electrostatic interactions. Increasing attention is being put on synthesizing FSN material that is safer both for workers involved in large-scale industrial production, and consumers coming in contact with FSN additives. In the present work, we explore the molecular structural differences and efficacy of Al- and Ti-metal-doped FSN which has previously been shown to reduce toxicity effects of FSN. We use a combination of 29Si and 27Al solid-state magic angle spinning (MAS) NMR, Raman spectroscopy, and thermogravimetric analysis (TGA) to probe the surface and bulk structure and quantify the adsorption capacity and reactivity of the metal-doped FSN with respect to amino acid thermal condensation. Alanine was selected as the amino acid of choice for its simplicity and ubiquity in biochemical reactions. The results indicate that metal doping has a modest impact on the fumed silica molecular structure with a small decrease in amino acid adsorption capacity and thermal condensation reactivity as a function of increased metal doping.Wissenschaftlicher ArtikelBand:5644 73 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Porosity and microstructure of steel tubes spray-formed by close-coupled atomizer(Elsevier, 2020-02); ; ; ; Close-coupled atomizers (CCA) can be used to reduce the porosity of spray-formed deposits compared to free fall atomizers (FFA), possibly due to smaller size and higher velocity of the atomized droplets. Previous studies on spray-formed AISI 52100 (100Cr6) tubular deposits show that CCA leads to less porosity in the inner and outer surface regions of the tubular deposits. However, there are very few investigations on the thermal profiles of the spray-formed deposits and on the influences of process conditions during spray forming via CCA. To provide insight into the thermal profile of the deposits, in this study in-situ measurement of the deposit surface temperature is performed by a two color pyrometer and the substrate temperature is measured by means of thermocouples. The porosity and microstructure of the spray-formed deposits under various process conditions are investigated by means of optical microscopy and image analysis. This investigation shows that the deposit thickness has a higher influence on the deposit surface temperature than the gas to melt flow rate ratio (GMR). Higher deposit temperature results in lower porosity and larger grain size. Moreover, the deposition positions on the deposit length has an influence on the porosity. The porosity in the vicinity of the substrate is higher at the deposit end position than the deposit start position. Finally, the present study suggests an optimal deposit surface temperature range for spray forming of highly dense tubular deposit by CCA.Wissenschaftlicher ArtikelBand:27618 13 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Influence of sintering necks on the spectral behaviour of ITO clusters using the Discrete Dipole Approximation(Elsevier, 2015-03-04); ; ; ; In this paper we study the spectral behaviour of indium tin oxide (ITO) nanoparticle clusters using different sinter neck models for the connections between the primary particles. The investigations include light scattering calculations based on the Discrete Dipole Approximation (DDA). The corresponding clusters are generated using the Cluster–Cluster algorithm proposed by Filippov et al. Different sintering neck models led to significantly different spectral features. A spectral neck factor that reveals the thickness of the necks connecting the primary particles with a simple measurement method is introduced.Wissenschaftlicher ArtikelBand:15972 104 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Implementation of parcel method for surface reactions in DSMC(Elsevier, 2019-05-06); ; ; ; The parcel concept in Direct Simulation Monte Carlo method has been added to the reaction algorithm to the DSMC solver in OpenFOAM to reduce computational demand. Parcel per cell is checked for different cell sizes and different parcel sizes to obtain the right cell size for a given system. At this cell size, diffusion of CO in O2 is simulated in a porous structure to ascertain the feasibility of this concept. After adding adsorption and reaction models, concentration profiles are obtained for different temperatures and different time steps. These profiles are compared with the single molecule algorithm written by Pesch et al. [14]. The local surface coverages and reaction rates are evaluated at a parcel size ranging from 10 to 100 to further validate the new approach. Computational time demand reduces by half at maximum parcel size to reach similar steady state results as that of the single molecule approach.Wissenschaftlicher ArtikelBand:187135 104 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Processing soft ferromagnetic metallic glasses: on novel cooling strategies in gas atomization, hydrogen enhancement, and consolidationProcessing soft ferromagnetic glass-forming alloys through gas atomization and consolidation is the most effective technique to produce bulk samples. The commercial viability of these materials depends on commercial purity feedstock. However, crystallization in commercial purity feedstock is several orders of magnitude faster than in high purity materials. The production of amorphous powders with commercial purity requires high cooling rates, which can only be achieved by extending the common process window in conventional gas atomization. The development of novel cooling strategies during molten metal gas atomization on two model alloys ({(Fe0.6Co0.4)0.75B0.2Si0.05}96Nb4 and Fe76B10Si9P5) is reported. Hydrogen inducement during liquid quenching significantly improved the glass-forming ability and soft magnetic properties of {(Fe0.6Co0.4)0.75B0.2Si0.05}96Nb4 powders. Spark plasma sintering experiments verified that amorphous rings could be produced regardless of the cooling strategies used. While the saturation magnetization was almost unaffected by consolidation, the coercivity increased slightly and permeability decreased significantly. The magnetic properties of the final bulk samples were independent of feedstock quality. The developed cooling strategies provide a great opportunity for the commercialization of soft ferromagnetic glass-forming alloys with commercial purity.Wissenschaftlicher ArtikelBand:5926 25