Microplastic fragments in the aquatic environment constitute a major threat for the health and fitness of organisms. However, our quantitative understanding in the microplastic load in typical ...natural river systems is severely limited due to the large uncertainties associated with the sources and the pathways of the microplastic contamination. To address this knowledge gap, we performed direct numerical simulations of the dynamics and distribution of microplastic particles in turbulent open channel flow at moderate Reynolds numbers. The particle dynamics is characterised by four nondimensional parameters, namely: Reynolds number of the open channel flow (Reb $R{e}_{b}$), nondimensional particle diameter (dp+ ${d}_{p}^{+}$) and Galileo (Ga $Ga$) and Stokes (St $St$) numbers of the particles of which the latter two include the particle‐fluid density ratio (β $\beta $). To limit our scope to the most relevant configuration, we focused on the distribution of weakly buoyant microplastic particles at β=0.95 $\beta =0.95$, whereas the remaining parameters were adjusted to cover the orders of magnitude that can be found in a typical laboratory facility, as well as a natural river. Our simulation results show that the steady‐state microplastic distribution in the turbulent flow is influenced by the Stokes and the Galileo numbers significantly, which ranges from the complete accumulation on the free surface to the homogeneous distribution, and somewhere in between. Moreover, the Galileo number, alongside the flow Reynolds number, were also shown to influence the temporal scaling of the transient behaviour of the gradual accumulation of the microplastics towards the free surface. Both of our findings highlight the complex nature of the particle–turbulence interactions, and motivate further investigations in this approach.
An instantaneous view of simulated turbulent open chanel flow (main direction into the page). Colour and vectors: primary and cross‐stream velocity components. Microplastic particles that are slightly lighter than water do not necessarily lead to complete accumulation on free surface, as they can be pulled down by turbulence.
The use of pulsed dc‐sputtering sources for reactive magnetron sputtering with oxygen offers a possibility to suppress the negative effects of target poisoning (such as arcing). This results in a ...wide process range for the selection of a desired operating point. The control of target poisoning plays a major role in maintaining constant coating properties and affects the stoichiometry of the reactive coating, as well as the coating rate and the economic impact of the coating process. In a hysteresis, the target poisoning during the reactive sputtering of titanium under oxygen addition proceeds nonlinearly. Without the use of a suitable target poisoning control technique, the sputtering process can abruptly change to an unstable state. As a result, variations of stoichiometry can occur during the deposition process. A proven method for maintaining a stable reactive sputtering process is the control of oxygen flow with the input variable target voltage. By determining the typical oxygen hysteresis at constant target power and constant argon flow, an operating point for the control loop is derived. The desired target voltage then serves as the input variable for the control loop of the target poisoning. The controlling technique for target poisoning is a basic requirement for the production of the photolytic active anatase phase of titanium dioxide (TiO2) using reactive magnetron sputtering. The photocatalytic equipment of surfaces with a titanium dioxide coating in the anatase phase can be realized with the reactive pulsed dc magnetron sputter ion plating process (DC‐MSIP). The pulsed DC‐MSIP process facilitates coating a variety of surfaces at temperatures below 200°C in an environmentally friendly manner.
This work addresses the formation of photocatalytically active TiO2 using reactive pulsed dc magnetron sputtering method. A technique for the control of target poisoning in reactive sputtering with oxygen is presented.
The TiO2 thin film, Ag NP and three Ag‐NP/TiO2 composite thin films (COMP‐Agn; n = 20, 50, and 75 Ag mol%) were successfully fabricated on quartz glass. The optical properties of the composite ...electrodes were investigated, and the results indicate a surface plasmonic resonance peak at 410 nm while the electrical resistivity of the composite thin films improved up to 6.9 × 10−5 Ω cm. The photo‐response threshold of the Ag‐NP/TiO2 composite thin films was enhanced and shifted into the visible and near‐infrared when the chlorophyll dye was adsorbed onto them. The hall effect was performed on the fabricated thin films and the charge carrier concentrate value confirmed that the Ag/TiO2 with Ag concentrate >45% are found to be p‐type. The n‐types were observed till the Ag content in TiO2 was increased up to 45 mol%. COMP‐Ag75 has a charge carrier concentration of 1.3 × 10−19 cm−3 as a p‐type electrode was then employed to construct a p‐DSSC. Such enhancement on photovoltaic activity can be attributed to the generated Z‐scheme system in the anatase/rutile phase‐junction Ag/TiO2 photocathode enhances the separation, diffusion, and transformation of electron/hole pairs inside the structure. This p‐DSSC exhibits a photon‐electrical conversion efficiency (PCE) of 0.37%. The PCE recorded is equal to or greater than those of traditional high‐efficiency n‐DSSCs. This allows the creation of a new generation of photocathodic p‐DSSCs with previously unheard‐of unprecedentedly high concentrations of Ag (up to 80 mol%) evenly scattered in a TiO2 matrix, and this efficacy is the highest ever reported for a p‐type working Ag/TiO2/chlorophyll/iodine electrode. This may enable the use of this electrode as a component of photosensitizer tandem devices.
A p‐type architecture for dye sensitized solar cells where the active region is sandwiched between 75% Ag/25%TiO2 highly conductive photocathode thin film on quartz glass and activated carbon‐FTO film.
Highlights
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The 75 mol% Ag/TiO2 composited higher conductive p‐type electrode was fabricated.
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The Electrode found to have a visible plasmon peak at 410 nm and electrical conductivity of 6.7 × 10−5 cm.
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This p‐type electrode was then employed as a working electrode to construct a p‐DSSC.
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This p‐DSSC exhibits a photon‐electrical conversion efficiency (PCE) of 0.37%.
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Although the PCE is lower, this electrode can be a component of photosensitizer tandem devices.
Microplastic (MP) particles with sizes between 1 and 1000 µm are widely distributed worldwide. Origin, transport pathways, and fate are poorly known, as sampling, sample preparation, and detection ...methods are major challenges. In addition, reference materials that mimic environmental particles are lacking. The most challenging is the yield of MP particle production and the need for resource‐intensive grinding with liquid nitrogen. In this paper, a machine is designed to produce aged microplastic particles as reference material candidates with high yield. The machine is based on ultraviolet aging of a thin foil and mechanical fragmentation using clean air. An example of aging and fragmentation of high‐density polyethylene with additional physical and chemical characterization of shape, size, aging state by carbonyl index, and density is presented.
New method for producing aged microplastics in high yield that can be used to produce reference materials for validation. An example of aging and fragmentation of high‐density polyethylene is also presented with additional physical and chemical characterization of shape, size, aging state by carbonyl index, and density.
Polycrystalline silicon has a wide range of applications in the semiconductor industry. Instead of components whose dimensions are of the same order of magnitude in all three spatial directions, thin ...slices are primarily used there. Deviating mechanical properties have been noticed among such thin configurations. In this work, we systematically investigate the size‐dependent effective elastic properties of polycrystalline silicon. This is realized by gradually reducing the thickness of such components, starting from a structure usually referred to as representative volume element. Based on the framework of continuum mechanics, we specify unit cell problems for aggregates whose microstructures are build artificially based on first‐order properties through tessellations. The effective responses of virtual material tests are determined by the aid of the finite element method. Based on a larger number of computational simulations with different but equivalent microstructures, the effective elastic properties of silicon polycrystals are evaluated statistically. The findings are examined with regard to geometrically‐induced symmetries by several methods. For the unconstrained configurations examined here, results show an increase in the scattering of the results where the average stiffness decreases with decreasing structural thickness. These outcomes are also compared to analytical estimates for silicon bulk configurations. This comparison indicates that the average stiffness varies in between a reasonable mean and the isotropic first‐order lower bound of the silicon bulk. Compared to experimental findings, admissible bounds of the stiffnesses are clearly outlined.
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Silicon crystal aggregates were studied with respect to their mechanical properties.
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Artificially generated aggregate samples are subjected to virtual material tests based on computational mechanics.
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Sample thickness is decreased systematically up to application‐relevant slices.
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Effective properties obtained decrease in the range bounded by the geometric and harmonic mean of analytical estimates.
