Diameters Of Several Hundreds Research Articles

Electrodeposition of Gallium and Indium from Non-aqueous Electrolytes

In this work, we studied the electrodeposition of gallium and indium from 1,2-dimethoxyethane (DME)-based and dimethyl sulfoxide (DMSO)-based electrolytes, respectively.1,2 Cyclic voltammetry in combination with rotating (ring) disk electrode and electrochemical quartz-crystal microbalance were used to identify the redox chemistry and electrodeposition behavior of both metals. Scanning electron microscopy (SEM) was used to investigate the structural morphology of the deposited materials.Gallium electrodeposition was studied from a bath composed of gallium(III) chloride, an inert background salt and DME. The electroreduction process occurred in two steps: (1) from gallium(III) to gallium(I), and (2) from gallium(I) to gallium(0). Metallic gallium was deposited as spheres with diameters of several hundreds of nanometers that were stacked on top of each other. X-ray photoelectron spectroscopy revealed that each gallium sphere was covered by a thin gallium oxide shell. These shells prevent individual gallium spheres from agglomerating to larger entities. Electrochemical experiments indicated that these oxide layers were electrically conductive. It was demonstrated that electrodeposition proceeded via a droplet-on-droplet electrodeposition mechanism. A growth mechanism for an individual growing gallium sphere was also postulated.Indium electrodeposition was studied from a bath composed of indium(III) methanesulfonate, a background salt and DMSO. indium(III) methanesulfonate was synthesized from methanesulfonic acid and indium(III) oxide. The latter is an intermediate formed during the purification of indium from primary and secondary resources. Conversion of indium(III) oxide into metallic indium could therefore lower the energetic cost of its production. Analogously to gallium, Indium(III) is reduced to indium(I), and then to indium(0). It was demonstrated that indium(I) disproportionates to indium(III) and indium(0), leading to the formation of micron-sized metallic indium particles in the electrolyte. At 26 °C, indium deposited as smooth, flat films whereas at 160 °C, it deposited as liquid indium droplets. Electrodeposition of indium above its melting point enables the process to be performed in a continuous manner; indium droplets accumulate and grow, and will ultimately glide off the electrode, and drop to the bottom of the cell, forming a liquid pool from which the metal can be tapped off.In the attached figure, SEM images of (1) gallium deposited at 26 °C and (2) indium, deposited at 26 °C and 160 °C are shown. Figure 1

Flexible and strong Fe3O4/cellulose composite film as magnetic and UV sensor

Flexible and strong Fe3O4/cellulose composite films were prepared successfully by co-dispersing homemade Fe3O4 particles and cellulose in aqueous solvent followed by regeneration. The Fe3O4 particles were immobilized in the cellulose matrix via coordinate bonding with hydroxyl of cellulose, and formed clusters with diameter of several hundreds of nanometers which embedded in the cellulose matrix, endowing the composite films with excellent mechanical property and thermal stability. The composite films were thermally stable below approximately 290 °C, and can be folded and bended without fracture, which guarantees the wide application as sensors and devices. Due to the incorporation of Fe3O4, the composite film presented an excellent saturated magnetization, superparamagnetic property, as well as strong UV shielding property. It is noted that the composite films exhibited two extraordinary sensing capabilities against both UV exposure and magnetic field, with fast responsiveness and excellent reproducibility. The present work not only supplies a simple pathway to prepare sensors with excellent properties, but also utilizes the renewable resources, demonstrating both sustainability and great potentials.

Synthesis of Silicon Nitride Ceramic Fibers and the Effect of Nitrogen Atmosphere on their Morphology

The effect of nitrogen gas flow rate on the morphology of silicon nitride fibers obtained via carbothermal nitridation heat treatment method was investigated. A precursor containing silicon, oxygen and carbon was obtained by a sol-gel method from a mixture of tetraethyl orthosilicate, polyvinyl alcohol, H2O and ethanol. A white wool-like product was obtained by heat treating the precursor placed in an alumina crucible under a 0.5 MPa nitrogen gas pressure at 1500oC with different nitrogen gas flow rates. The mass-based production rates of the samples obtained from the precursor powder were 20-30% for the different nitrogen gas flow rates. X-ray diffraction analysis revealed that the samples contained α-Si3N4 as the major phase along with β-Si3N4, Si2N2O and a small amount of amorphous product as minor phases. Unique twisted fibers with diameters of several hundreds of nanometers were found among the straight fibers by SEM observation. Elemental analysis using energy dispersive X-ray spectroscopy indicated that silicon and nitrogen were contained in the twisted fibers along with approximately 68 at.% of oxygen and several at.% of aluminum, which might have come from the crucible material. The SiAlON-like structures might have been formed by the partial dissolution of Al and O in the Si3N4 fibers. It was considered that the twisted morphology of some fibers might be formed by co-existing of β-SiAlON and/or amorphous phase regions in the Si3N4 fiber and resultant distortion of the fibers.

Polarimetric Study of Near-Earth Asteroid (1566) Icarus

Abstract We conducted a polarimetric observation of the fast-rotating near-Earth asteroid (1566) Icarus at large phase (Sun–asteroid–observer’s) angles α = 57°–141° around the 2015 summer solstice. We found that the maximum values of the linear polarization degree are P max = 7.32 ± 0.25% at phase angles of α max = 124° ± 8° in the V-band and P max = 7.04 ± 0.21% at α max = 124° ± 6° in the R C-band. Applying the polarimetric slope–albedo empirical law, we derived a geometric albedo of p V = 0.25 ± 0.02, which is in agreement with that of Q-type taxonomic asteroids. α max is unambiguously larger than that of Mercury, the Moon, and another near-Earth S-type asteroid (4179) Toutatis but consistent with laboratory samples with hundreds of microns in size. The combination of the maximum polarization degree and the geometric albedo is in accordance with terrestrial rocks with a diameter of several hundreds of micrometers. The photometric function indicates a large macroscopic roughness. We hypothesize that the unique environment (i.e., the small perihelion distance q = 0.187 au and a short rotational period of T rot = 2.27 hr) may be attributed to the paucity of small grains on the surface, as indicated on (3200) Phaethon.

A simple approach to manufacture ceramic coils based on liquid rope coiling effect

AbstractA micrometer scale method based on the principle of liquid rope coiling with the assistance of nonsolvent‐induced phase inversion is introduced to fabricate YSZ coils. The YSZ coils with the filament diameter of several hundreds of micrometer exhibit stable spring properties and excellent elongation at failure. With the spring rate in the range from ~2 N/mm to ~21 N/mm and the elongation up to 4.36%, both the two properties can be effectively controlled and tailored since they both strongly depend on the geometric dimensions varied with the process parameters. Besides, the simple method provides an alternative method for the large‐scale production and customization of ceramic coils with diverse applications.

Core–shell-structured carbon nanofiber-titanate nanotubes with enhanced photocatalytic activity

Core–shell materials have been developed extensively because of their advanced properties and multifunctionality. Many approaches involving different synthesis techniques have been used for the preparation of various core–shell nanostructures. In this study, we synthesized core–shell-structured carbon nanofiber (CNF)-titanate nanotubes (TiNT) by electrospinning, carbonization, and subsequent alkaline hydrothermal treatment. The CNF core could act as a support, and the TiO2-decorated TiNT shell could act as a photocatalyst. TiNT shells with diameters of several hundreds of nanometers and composed of 10-nm-diameter nanotubes are formed on the CNF surface. The formation of TiNTs on the CNF surface was observed using SEM, HR-TEM, XRD, and XPS analyses. Core–shell-structured CNF-TiNTs exhibited efficient photocatalytic activities for CH3CHO oxidation, which was attributed to the existence of photocatalytically active TiO2-TiNT composites on the CNF surface, which could easily absorb UV light. Additionally, the surface area increase as a result of the alkaline hydrothermal treatment may also be responsible for the efficient photocatalytic activity of core–shell-structured CNF-TiNTs.

Characterization of Shock-Recovered BaSi2 Powder

Shock recovery experiments at pressures of up to 22 GPa on BaSi2 powder are performed using a propellant gun. The shocked samples are characterized using X-ray diffraction analysis, Raman spectroscopy, and scanning electron microscopy (SEM). Only the orthorhombic BaSi2 phase is detected and no evidence of amorphization or phase transition is obtained. The SEM images reveal that the BaSi2 powder is consolidated at pressures below 10 GPa, whereas many cavities in addition to whiskers with diameters of several hundreds of nanometers are formed on the surface of the sample shocked at 10 GPa. These whiskers are due to the eruption of BaSi2 vapor from the cavities and the subsequent mixing of this vapor with air. The shock-induced heat may be the cause of this vaporization.

Treatment of emerging contaminants in wastewater treatment plants (WWTP) effluents by solar photocatalysis using low TiO2 concentrations

The optimal photocatalyst concentration for industrial wastewater treatment in current photoreactor designs is several hundreds of milligrams per liter. However, the elimination of emerging contaminants (ECs), which are present at extremely low concentrations in waste water treatment plants (WWTP) effluents might be accomplished at much lower catalyst (TiO2) concentrations. One of the main drawbacks of reducing catalyst loading below the optimum is the loss of useful photons which instead are transmitted through the TiO2 suspension without being absorbed by the catalyst. Accordingly, in this work, laboratory and solar pilot-scale experiments were performed with real WWTP effluents to evaluate the kinetics of photocatalytic degradation of 52 emerging contaminants under realistic (ppb) concentrations. The analysis of the samples was accomplished by solid phase extraction (SPE) followed by liquid chromatography–mass spectrometry (LC–MS). In view of the results, low concentrations of TiO2 of the order of tens of milligrams per liter were found to be insufficient for the degradation of the ECs in photoreactors with a short light-path length (29cm). However, it was established that solar reactors of diameters of several hundreds of millimetres could be used for the efficient removal of ECs from WWTP effluents. The results presented show a general methodology for selecting the most efficient reactor diameter on the basis of the desired catalyst concentration.

Fluidized Bed Chemical Vapor Deposition of Silicon on Carbon Nanotubes for Li-Ion Batteries

Silicon was deposited on balls of entangled multi-walled carbon nanotubes (CNT) with a mean diameter of several hundreds of microns, by Fluidized Bed Chemical Vapor Deposition from silane (SiH4). The weight total percentage of deposited silicon was between 30 and 70%, to test their efficacy in Li-ion battery anodes. TEM and SEM imaging revealed that silicon deposits were of the form of nanoparticles uniformly dispersed on the whole CNT surface. The diameter of these nanoparticles increases with the deposited silicon percentage from 18 to 36 nm whereas their density remains constant at 5 10(22) nanoparticles/g of CNT. This indicates a low affinity of chemical species born from silane pyrolysis with the CNT surface for nucleation. The increase of the silicon nanoparticles diameter leads to the decrease of the specific surface area and the porous volume of the balls, probably due to the filling of the pores of the CNT network by silicon. A slight increase of the mean diameter of the balls was observed for the two highest silicon percentages, certainly due to the ability of the CNT network to be deformed under the mechanical stress induced by the silicon nanoparticles growth.

Preparation of monodisperse mesoporous carbon microspheres from poly(furfuryl alcohol)–silica composite microspheres produced in a microfluidic device

Uniform-sized carbon microspheres with diameters of several hundreds of microns and adjustable mesopore structure were obtained from poly(furfuryl alcohol)–silica (PFA–SiO2) microspheres. The PFA–SiO2 composite microspheres were synthesized via the phase transfer of FA and the subsequent polymerization in aqueous silica sol droplets formed in a simple microfluidic device, followed by carbonization and HF etching to remove the silica template. It was found that the resultant carbon microspheres were mesoporous, and their mesoporosity depended on the flow rate of the oil phase and the residence time of the microdroplet in the device during the preparation of PFA–SiO2 microspheres. The carbon microspheres exhibited heterogeneous structure with submicron-sized ball-like carbon particles embedded in the smooth carbon matrix. The highest mesoporous volume and mesoporosity of carbon microspheres reached 1.10 cm3 g−1 and 85%, respectively, and the mesopores were in the range of 2–20 nm. Mesoporous silica microspheres embedded with submicron-sized cavities could also be prepared by burning-off the carbon in the carbon–SiO2 microspheres.

Internal structure and colloidal behaviour of covalent whey protein microgels obtained by heat treatment

Covalently cross-linked whey protein microgels (WPM) were produced without the use of a chemical cross-linking agent. The hierarchical structure of WPM is formed by a complex interplay of heat denaturation, aggregation, electrostatic repulsion, and formation of disulfide bonds. Therefore, well-defined spherical particles with a diameter of several hundreds of nanometers and with relatively low polydispersity are formed in a narrow pH regime (5.8–6.2) only. WPM production was carried out on large scale by heating a protein solution in a plate-plate heat exchanger. Thereafter, the microgels were concentrated by microfiltration and spray dried into a powder. The spherical structure of the WPM was conserved in the powder. After re-dispersion, the microgel dispersions fully recovered their initial structure and size distribution. Due to the formation of disulfide bonds the particles were internally covalently cross-linked and were remarkably stable in a large pH range. Because of the pH dependent charge of the constituents the particles underwent significant size changes upon shifting the pH. Small angle X-ray scattering experiments were used to reveal their internal structure, and we report on the pH-induced structural changes occurring on different length scale. Our experiments showed that close analogies could be drawn to internally cross-linked and pH-responsive microgels based on weak polyelectrolytes. WPM also exhibited a pronounced swelling at pH values below the isoelectric point (IEP), and a collapse at the IEP. However, in contrast to classical microgels, WPM are not build up by simple polymer chains but possess a complex hierarchical structure consisting of strands formed by clusters of aggregated denatured proteins that act as primary building blocks. They were flexible enough to respond to changes of the environment, and were stable enough to tolerate pH values where the proteins were highly charged and the strands were stretched.

Effect of addition of dendritic C 60 amphiphiles on the structure of cationic surfactant solutions

The aggregation behavior of two water-soluble carboxylic C 60 derivatives, dendritic methano[60] fullerene octadeca acid ( 1) and ennea acid ( 2), in aqueous solutions was investigated. Both 1 and 2 were highly soluble in pure water and buffer solutions with pH ⩾7.0. Their spectral properties, especially those in the visible region, were found to be influenced greatly by solution parameters and additives. In pure water, dynamic laser light scattering (DLS) measurements revealed that both 1 and 2 could form aggregates. When 1 or 2 was added to micelle solution of a cationic surfactant, tetradecyltrimethylammonium hydroxide (TTAOH), unilamellar vesicles with diameters of several hundreds of nanometers were detected by freeze–fracture transmission electron microscope and DLS both below and above the critical micellar concentration of TTAOH. Vesicle formation was greatly suppressed when 1 or 2 was added to tetradecyltrimethylammonium bromide micelle solution and no vesicles were detected for 1 or 2 mixed with the aqueous solutions of tetrabutylammonium hydroxide or tetramethylammonium hydroxide, indicating that counterions and the hydrophobic chain length of the cationic surfactants played important roles in vesicle formation. At the same time, for mixtures of 1 and 2 with anionic surfactant sodium dodecyl sulfate, no vesicles were detected. In highly concentrated NaCl solutions, it was found that 1 and 2 could also form vesicles, which could be due to the shielding of the electrostatic interactions among hydrophilic parts of 1 and 2.

Growth of SiC nanowires within stacked SiC fiber fabrics by a noncatalytic chemical vapor infiltration technique

An atmospheric pressure chemical vapor infiltration (CVI) process without metallic catalysts was applied for the growth of SiC nanowires within stacked SiC fiber fabrics. We investigated the effect of the concentration of a reactant gas (CH 3SiCl 3, MTS) on the growth behavior and microstructure of the SiC nanowires. At high concentration of MTS in a H 2+MTS mixture gas, one-dimensional (1D) SiC deposits with diameters of several hundreds of nanometers were formed. Microstructures of the 1D SiC deposits exhibited a strong positional dependency throughout the thickness direction of the stacked fabric due to a depletion of the MTS gas. On the other hand, single-crystalline SiC nanowires with average diameters of 50–60 nm could be obtained at a low concentration of MTS. The SiC nanowires also exhibited a homogeneous growth both in the plane of each fabric layer and throughout the thickness of the sample.

Fabrication of a Highly Transparent Conductive Thin Film from Polypyrrole/Poly(methyl methacrylate) Core/Shell Nanospheres

Polypyrrole (PPy)/poly(methyl methacrylate) (PMMA) core/shell nanospheres with diameters of several tens of nanometers have been synthesized by two-step microemulsion polymerization, and highly transparent conductive thin films have been fabricated using the nanospheres as a filler in a PMMA matrix. The PPy/PMMA core/shell nanoparticles and their composite films have been extensively characterized using transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), Fourier-transform infrared (FT-IR) and UV-vis spectroscopies, and electrical-conductivity measurements. The fabricated polymer films containing the PPy/PMMA core/shell nanofillers show a much better transparent conductive performance than that of uncoated PPy nanoparticles with similar dimensions or bulk PPy particles with diameters of several hundreds of nanometers. The PMMA shell promotes compatibility of the conductive fillers with the PMMA matrix and enhances dispersion of the PPy/PMMA core/shell nanofillers. In addition, the nanometer-thick PMMA shell has a lower glass-transition temperature (Tg), and can be effectively annealed to form a conductive-filler network with a high electrical conductivity at a relatively low filler content.

Multiple voltage electron probe microanalysis of fission gas bubbles in irradiated nuclear fuel

The accurate analysis of locally retained fission gas in nuclear fuel is inherently difficult since the physical form under which it is stored varies from an atomic dispersion to bubbles with a diameter of several hundreds of nanometers. One of the techniques that has been applied since more than 20 yr is electron probe microanalysis (EPMA). This technique, however, is difficult to apply in a quantitative manner if the studied materials are inhomogeneous at the scale of the electron–solid interaction volume. In this paper, a method is developed to analyse a system of gas bubbles distributed in a solid matrix. It is based on the geometric modelling of a gas bubble dispersion and the assessment of its influence on the emitted X-ray intensity. The calculation exploits experimental results acquired at different accelerating voltages. The resulting more accurate analysis of gas retained in nuclear fuel may lead to a better insight in the gas release mechanisms.

Structure of Cuprammonium Regenerated Cellulose Hollow Fiber (BMM Hollow Fiber) for Virus Removal

An attempt to analyze the pore structure of the cuprammonium regenerated cellulose hollow fiber (BMM hollow fiber) in order to clear up its filtration mechanism was made. The electron microscopy was employed to get the concrete images of the structure. The cellulose particles of rod-like shape with circular cross section having mean diameter of about 50 nm were its constructing units. The pores were classified into two types, i.e., the pore with the average diameter of about 50 nm and another with the diameter of several hundreds to several thousands nm. The former was estimated to be the capillary formed among neighboring cellulose particles and the latter to be the void formed as a vacant space which was originated by the phase separation as polymer lean phase. The frequency distribution curve of the void size showed several peaks indicating the occurrence of the boundary breakage between voids originated by the elongation of the fiber in the spinning process. The performances of BMM depends mainly on the existence of capillaries, then BMM with higher ability may be obtained by means of the spinning method which can decrease the occurrence of structure breakage due to the elongation during spinning.

The Wolf-Rayet Stars in 30 Doradus

Giant HII regions as sites of massive star formation.Giant HII regions are the brightest extragalactic emission line objects that can be studied in detail. With diameters of several hundreds of parsecs, these nebulae can be easily resolved out to distances of a few Mpc. Typically 100 or more 0 stars are required to account for the observed ionization of the nebular gas and this implies that the cores of giant HII regions contain populous young star clusters. The stars in these clusters have essentially the same age and chemical composition. Thus, giant HII region cores provide excellent sites where theories of the formation and evolution of massive stars and, in particular, of Wolf-Rayet (WR) stars can be tested.