Determination of transport parameters in [EMIm]Cl-based ionic liquids - diffusion and electrical conductivity. - In: Electrochimica acta, ISSN 1873-3859, Bd. 366 (2021), 137370
The density, electrical conductivity and diffusion coefficients of anions and cations in the ionic liquid AlCl3/1-ethyl-3-methylimidazolium chloride, [EMIm]Cl, were determined to study physical correlations of these important parameters. The density was measured for different molar ratios of AlCl3:[EMIm]Cl from 0.5:1 to 2.0:1 at ambient temperature. The diffusion coefficient of the electrochemically active heptachloroaluminate complex, Al2Cl7-, was measured for a molar ratio of 2:1 in the range of 25˚C to 100˚C. The corresponding current density and potential transients were discussed regarding the decomposition of the [EMIm]+ cation and deviation from the theoretical Cottrell behavior. The electrical conductivity was measured for molar ratios of 1.5:1 and 2:1 in the range of 25˚C to 100˚C. Both the diffusion coefficient and electrical conductivity can be described well by an Arrhenius law. The diffusion coefficients of AlCl4-, Al2Cl7- and [EMIm]+ were estimated from the Nernst-Einstein and Stokes-Einstein relation. The results indicate a strong impact of ion pairing in these electrolytes.
https://doi.org/10.1016/j.electacta.2020.137370
Development of the phase composition and the properties of Ti2AlC and Ti3AlC2 MAX-phase thin films - A multilayer approach towards high phase purity. - In: Applied surface science, Bd. 537 (2021), 147864
MAX phase thin films have been synthesized by thermal treatment of a Ti-Al-C multilayer system. The preparation of the multilayer system was carried out via magnetron sputtering. Based on the thickness ratio among the individual nanoscale monolayers (Ti, Al, C), the resulting MAX phase stoichiometry can be controlled. This paper describes the synthesis of both Ti2AlC and Ti3AlC2 MAX phases from the same precursor multilayer system which is composed of a sequence of Ti/Al/C pure elemental single layers with thicknesses of 14, 6, and 3.5 nm, respectively. This sequence is repeated 22 times with a total thickness of around 500 nm. Rapid thermal treatment tests were performed to study the phase development. The Ti2AlC MAX phase forms in a temperature range below 850 ˚C, whereas the Ti3AlC2 MAX phase starts to form at temperatures above 850 ˚C and reaches its highest phase purity at 950 ˚C. The thin film structures were studied by X-ray diffraction and Raman spectroscopy. Furthermore, the electrical and mechanical properties were investigated to gain more insights regarding the phase transformation and their influence on the thin film properties.
https://doi.org/10.1016/j.apsusc.2020.147864
Nanoparticle gas phase electrodeposition: fundamentals, fluid dynamics, and deposition kinetics. - In: Journal of aerosol science, ISSN 1879-1964, Bd. 151 (2021), 105652, S. 1-15
This communication uncovers missing fundamental elements and an expanded model of gas phase electrodeposition; a relatively new and in large parts unexplored process, which combines particle generation, transport zone and deposition zone in an interacting setup. The process enables selected area deposition of charged nanoparticles that are dispersed and transported by a carrier gas at atmospheric pressure conditions. Two key parameters have been identified: carrier gas flow rate and spark discharge power. Both parameters affect electrical current carried by charged species, nanoparticle mass, particle size and film morphology. In combination, these values enable to provide an estimate of the gas flow dependent Debye length. Together with Langmuir probe measurements of electric potential and field distribution, the transport can be described and understood. First, the transport of the charged species is dominated by the carrier gas flow. In close proximity, the transport is electric field driven. The transition region is not fixed and correlates with the electric potential profile, which is strongly dependent on the deposition rate. Considering the film morphology, the power of the discharge turns out to be the most relevant parameter. Low spark power combined with low gas flow leads to dendritic film growth. In contrast, higher spark power combined with higher gas flow produces compact layers.
https://doi.org/10.1016/j.jaerosci.2020.105652
Active scanning probes in nanostructure fabrication. - In: Design strategies for synthesis and fabrication, (2020), S. 18-1-18-12
Richtiger Name des Verfassers: Mathias Holz
https://dx.doi.org/10.1201/9780367341558-18
Anwendungen der Schwingquarzmethode in der Galvanotechnik. - In: ZVO-Report, (2020), 2, S. 42
Abscheidung von dekorativen Chromschichten mittels niederfrequenter Pulsabscheidung zur Anpassung des optischen Erscheinungsbilds. - In: WOMag, ISSN 2195-5905, Bd. 9 (2020), 6, S. 1-8
Das optische Erscheinungsbild von galvanisch abgeschiedenen Chromschichten ist eines der wichtigsten Kriterien für deren dekorative Anwendung. Für die dekorative Verchromung werden zunehmend Elektrolyte auf Basis von dreiwertigem Chrom als Ersatz für die bisher verwendeten Elektrolyte auf Basis von sechswertigem Chrom eingesetzt. Chrom aus Elektrolyten mit dreiwertigen Chromverbindungen neigt jedoch dazu, bei Dicken über 100 nm einen gelblichen Farbton zu haben, was für die meisten Anwendungen unerwünscht ist. Die Farbverschiebung hängt mit einer Änderung der Oberflächenmorphologie aufgrund des Wachstums der Chromkeime zusammen. Durch die Verwendung von gepulstem Strom mit Einschaltzeiten im Bereich von Sekunden wird das unerwünschte Kornwachstum unterdrückt und die Bildung frischer Kerne begünstigt. Dadurch bilden sich kompakte Chromschichten mit feinerem Gefüge und verbesserten Farbwerten. Ein bläuliches Aussehen und ein hoher Glanz werden bis zu einer Dicke von mehr als 200 nm beibehalten. Basierend auf den Ergebnissen wird eine Kombination aus konstantem und gepulstem Strom vorgeschlagen, die ein ähnliches visuelles Erscheinungsbild ergibt wie nur bei gepulstem Strom, jedoch die angestrebte Schichtdicke in deutlich kürzerer Zeit erreicht.
https://dx.doi.org/10.7395/2020/Leimbach1
Synthesis and characterization of size controlled bimetallic nanosponges. - In: Multifunctional materials, (2020), S. 1-34
Metallic and bimetallic nanosponges with well-defined size and form have attracted increasing attention due to their unique structural properties and their potential for many applications. In this chapter, the recently developed methods for the synthesis and preparation of metallic and bimetallic nanosponges are presented. These methods can be mainly cataloged in two groups: dealloying-based methods and reduction reaction-based methods. Different topographical reconstruction methods for the investigation of their structural properties are then reviewed briefly. The optical properties of the metallic nanosponges are clearly different from those of the solid counterparts due to the tailored disordered structure. The recent advances in the exploration of the distinct linear and non-linear optical properties of the nanosponges are summarized.
https://doi.org/10.1515/9783110345001-001
Sintered porous glasses hosting luminescent species of different nature: Eu3+ ions and Tb3+-doped Ba2TiSi2O8 glass-ceramic powder. - In: Journal of non-crystalline solids, ISSN 0022-3093, Bd. 531 (2020), 119846
Im Titel sind "3+" hochgestellt, "2" und "8" tiefgestellt
We report on the employment of a nano-porous Vycor-type glass as host for two luminescent substances of very different physical and chemical nature, which share the same porous space. Firstly, BTS:Tb^3+ glass-ceramic nano-powders were infiltrated in the porous structure and secondly Eu^3+ ions from a nitrate aqueous solution were included afterwards. Upon sintering, the porous silica matrix collapses, embedding both luminescent species. We focused on the micro and nano-structure of the sintered glasses. Upon sintering a europium silicate phase crystallizes as monocrystalline hexagonal nano-rods, which coexist with amorphous round particles below 100 nm enriched in Eu and Si. Both kinds of particles are embedded in a cristobalite matrix. The interesting microstructure is reported for the first time. The sintering heating rate influences the microstructure after the sintering. The microstructure was investigated by a last generation TEM microscope with aberration correction, EDXS and an exhaustive electron diffraction analysis. The inclusion of BTS:Tb^3+ is only limited, and thus, the its role in the optical properties of the final material is negligible. Luminescence upon UV excitation shows the characteristic emission peaks of Eu^3+. This work highlights the possibility of combining several luminescent materials inside a silica matrix.
https://doi.org/10.1016/j.jnoncrysol.2019.119846
Crystallization of BaF2 from droplets of phase separated glass - evidence of a core-shell structure by ASAXS. - In: CrystEngComm, ISSN 1466-8033, Bd. 22 (2020), 30, S. 5031-5039
Im Titel ist "2" tiefgestellt
https://doi.org/10.1039/C9CE02003A
Multiferroic bismuth ferrite: perturbed angular correlation studies on its ferroic α-β phase transition. - In: Physical review, ISSN 2469-9969, Bd. 102 (2020), 22, S. 224110-1-224110-11
https://doi.org/10.1103/PhysRevB.102.224110