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We present the principles of a particle-handling system for the International Space Station (ISS) with which experiments with astrophysical and planetological applications will be performed. The principle of dust deagglomera-tion ...
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We present the principles of a particle-handling system for the International Space Station (ISS) with which experiments with astrophysical and planetological applications will be performed. The principle of dust deagglomera-tion and dispersion was successfully tested in short-duration microgravity experiments. The flight of the systems on the ISS is planned for 2012.
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The numerical tools that are integrated in the M5 model of stirred media milling include the Discrete Element Method (DEM) for macroscale simulations, Finite Element Method (FEM) based Fluid-Structure Interaction (FSI) for mesosca...
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The numerical tools that are integrated in the M5 model of stirred media milling include the Discrete Element Method (DEM) for macroscale simulations, Finite Element Method (FEM) based Fluid-Structure Interaction (FSI) for mesoscale simulations and combined FEM and DEM for microscale simulation of grinding bead impacts. Statistical analyses of the impacts derived by DEM at a macro-level are used for optimization of the mill design and its operational parameters. The thermo-mechanical and hydrodynamical phenomena that occur at the meso-scopic FSI scale between the approaching grinding beads are analyzed by FEM for various impact scenarios with different combinations of impact velocity, direction and rotation as a function of macroscopic mill design. Therefore, the M5 concept takes into account global-local coupling so that the influences of macroscopic design can be derived at nano levels by downscale coupling of influential phenomena.
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Nanocrystalline yttria powders were synthesized from deagglomerated yttrium oxalate. The precipitation of this oxalate was carried in two different modes viz., addition of aqueous oxalic acid into yttrium nitrate solution (forward...
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Nanocrystalline yttria powders were synthesized from deagglomerated yttrium oxalate. The precipitation of this oxalate was carried in two different modes viz., addition of aqueous oxalic acid into yttrium nitrate solution (forward strike) and vice versa (reverse strike) followed by ultrasonication in acetone and water. Nanocrystalline yttria was obtained by calcining the oxalate in air at 1073 K. The bulk densities, specific surface area, X-ray crystallite size, size distribution of particles as well as the quantity of carbon residue in these powders were determined. The influence of the deagglomeration medium on the powder properties was analyzed. Scanning electron microscopy (SEM) showed that these powders comprised irregular agglomerates while the high resolution transmission electron microscopy (HRTEM) revealed that the constituent units of these agglomerates were randomly oriented cuboida1 nanocrystallites (20-40 nm). These powders were compacted at 120 MPa without any lubricant or binder and their sinterability was studied. Pellets with sintered density as high as 97.5% T.D. (theoretical density) could be obtained at a relatively low sintering temperature of 1873 K. Synthesis of nanocrystalline yttria powders by oxalate deagglomeration route as well as the systematic studies of their properties and sinterabilities are being reported for the first time. It was further demonstrated in this study that higher sintered densities could be obtained with less number of process steps and at a much lower compaction pressure. Samples prepared by reverse strike yielded a powder with characteristics most suitable for fabricating high density yttria bodies. 1673 K would be the optimum temperature for sintering the compacts made out of this powder. (C) 2014 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
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Industrial nanoparticles are not developed to be compatible with in vitro cell culture assays which are carried out in isotonic solutions at physiological pH and often in the presence of proteins. The tendency of nanoparticles to ...
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Industrial nanoparticles are not developed to be compatible with in vitro cell culture assays which are carried out in isotonic solutions at physiological pH and often in the presence of proteins. The tendency of nanoparticles to deagglomerate or agglomerate is strongly sensitive to these parameters. The state of agglomeration and the protein corona bear an important influence on the level of toxic effects via the change of transport mechanisms and surface coating. Here we rigorously characterized the interaction of nanoparticles with physiological media for in vitro nanotoxicology experiments. Beyond adsorption of proteins on metal oxide and polymeric nanoparticles, we quantified nanoparticle deagglomeration due to adsorbing proteins acting as protection colloids. We report on previously neglected, but indispensable testing of sterility and measures to ensure it. Our findings result in a checklist of pre-requirements for dispersion of nanoparticles in physiological media and for reliable attribution of potential toxic effects.
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Mixing experiments have been carried out to evaluate the mixing characteristics for anagitator- type Mixer using a binary, cohesive, fine powder system with different colors. The temporal variation in the state of mixing with time...
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Mixing experiments have been carried out to evaluate the mixing characteristics for anagitator- type Mixer using a binary, cohesive, fine powder system with different colors. The temporal variation in the state of mixing with time was measured by an optical method, and the power requirement was simultaneously monitored to estimate the changing flow-pattern with the charge ratio of powders in the vessel.
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We have achieved the covalent functionalisation of detonation nanodiamond by an esterification reaction of carboxylic acid chlorides on hydroxylated nanodiamond. The resulting "nanodiamond esters" with a surface loading of 0.3-0.4...
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We have achieved the covalent functionalisation of detonation nanodiamond by an esterification reaction of carboxylic acid chlorides on hydroxylated nanodiamond. The resulting "nanodiamond esters" with a surface loading of 0.3-0.4 mmol g~(-1) of alkyl groups have been characterized by FTIR spectroscopy, thermogravimetry and elemental analysis. They exhibit a significantly improved dispersibility in organic solvents such as tetrahydrofuranc and dichloromethane.
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The crucial parameter in the analysis of impact events is the impact velocity v_i. In case of inertial impactors v_i was assumed to be 85% of the average gas jet velocity, following the work of Marple. Numerical analysis of the im...
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The crucial parameter in the analysis of impact events is the impact velocity v_i. In case of inertial impactors v_i was assumed to be 85% of the average gas jet velocity, following the work of Marple. Numerical analysis of the impact process in low pressure impactors shows that this assumption is inappropriate and leads to overestimation of v_i,- near the inset of particle deposition, while, v_i is underestimated in the regime of high impact velocities. In this paper the whole process of nanoparticle acceleration and impact in low pressure impactors is investigated numerically. In order to assure correct numerical procedures, the employed methods are thoroughly validated by comparison with experimental results. Finally, a new analytical model for the calculation of v_i- on the basis of similarity theory is proposed that is independent of the impactor geometry and particle properties and holds well for the whole incompressible region. The model allows to perform defined collision experiments in low pressure impactors regarding impact velocity, without need of demanding numerical effort that is often beyond the scope of experimental studies. The model replaces the old rule of thumb and allows a quantitative re-evaluation of existing experimental data, e.g. on nanoparticle agglomerate fragmentation.
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Wetting is the first step in the dispersion process of any powder. Understanding how the powder surface and the liquid properties affect the speed and intensity of the wetting process provides a set of tools to determine the dispe...
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Wetting is the first step in the dispersion process of any powder. Understanding how the powder surface and the liquid properties affect the speed and intensity of the wetting process provides a set of tools to determine the dispersion efficiency as a whole, and an effective dispersion allows the reduced use of the powder to achieve the specified final properties. This article reports experimental results on the wetting behavior of five different TiO_2 samples by liquids with different values of surface tension [deionized (DI) water and DI water containing surfactants] and its effect on the dispersion process. The selection of the TiO_2 samples was based on different particles sizes with similar surface properties, and similar sizes with different surface properties. The samples were characterized in terms of their specific surface area and particle size distribution. The wetting behavior was evaluated by a capillary rise technique (Washburn) to measure liquid penetration height and rate, and the time evolution of the particle size distribution. The results show that larger particles presented faster wettability and that liquids with lower surface tension facilitate the wetting of the powder. The energy required to deagglomerate the powder is inversely proportional to the wetting speed: the faster the wetting the easier it will be to disperse the particles, with less energy required.
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Stability of airborne nanoparticle agglomerates is important for occupational exposure and risk assessment in determining particle size distribution of nanomaterials. In this study, we developed an integrated method to test the st...
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Stability of airborne nanoparticle agglomerates is important for occupational exposure and risk assessment in determining particle size distribution of nanomaterials. In this study, we developed an integrated method to test the stability of aerosols created using different types of nanomaterials. An aerosolization method, that resembles an industrial fluidized bed process, was used to aerosolize dry nanopowders. We produced aerosols with stable particle number concentrations and size distributions, which was important for the characterization of the aerosols' properties. Next, in order to test their potential for deagglomeration, a critical orifice was used to apply a range of shear forces to them. The mean particle size of tested aerosols became smaller, whereas the total number of particles generated grew. The fraction of particles in the lower size range increased, and the fraction in the upper size range decreased. The reproducibility and repeatability of the results were good. Transmission electron microscopy imaging showed that most of the nanoparticles were still agglomerated after passing through the orifice. However, primary particle geometry was very different. These results are encouraging for the use of our system for routine tests of the deagglomeration potential of nanomaterials. Furthermore, the particle concentrations and small quantities of raw materials used suggested that our system might also be able to serve as an alternative method to test dustiness in existing processes. (C) 2015 The Authors. Published by Elsevier Ltd.
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Barium titanate powders were synthesized by the modified solid-state method with ultrasonic (5 min) and mechanochemical (12 h) deagglomeration methods. The structure of the samples was verified using Fourier transform infrared spe...
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Barium titanate powders were synthesized by the modified solid-state method with ultrasonic (5 min) and mechanochemical (12 h) deagglomeration methods. The structure of the samples was verified using Fourier transform infrared spectroscopy (FT-IR) and X-ray diffractometer (XRD). Scanning electron microscopy (SEM) analysis of the powders showed that using ultrasonic deagglomeration significantly decreased the particle size with perfect homogeneity in the shortest time. The particle size of the powders was calculated as 44.7 nm and 80.4 nm for ultrasonic and mechanochemical deagglomeration, respectively. The sintered pellet by ultrasonic method had no abnormal grain growth, and the grain sizes were between 10 and 30 pm. The pellet by mechanochemical method had an abnormal grain growth, and the grain sizes were between 10 and 100 pm. The results showed that ultrasonication remarkably improved the structure of the samples in the shortest time.
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