Mean Edge Length Research Articles

Optimization of reaction parameters in hydrothermal synthesis: a strategy towards the formation of CuS hexagonal plates

BackgroundFor decades, copper sulphide has been renowned as the superior optical and semiconductor materials. Its potential applications can be ranged from solar cells, lithium-ion batteries, sensors, and catalyst systems. The synthesis methodologies of copper sulphide with different controlled morphology have been widely explored in the literature. Nevertheless, the understanding on the formation chemistry of CuS is still limited. The ultimate approach undertaking in this article is to investigate the formation of CuS hexagonal plates via the optimization of reaction parameters in hydrothermal reaction between copper (II) nitrate and sodium thiosulphate without appending any assistant agent.ResultsCovellite (CuS) hexagonal plates were formed at copper ion: thiosulphate ion () mole ratio of 1:2 under hydrothermal treatment of 155°C for 12 hours. For synthesis conducted at reaction temperature lower than 155°C, copper sulphate (CuSO4), krohnite (NaCu2(SO4)(H2O)2] and cyclooctasulphur (S8) were present as main impurities with covellite (CuS). When mole ratio was varied to 1: 1 and 1: 1.5, phase pure plate-like natrochalcite [NaCu2(SO4)(H2O)] and digenite (Cu9S5) were produced respectively. Meanwhile, mixed phases of covellite (CuS) and cyclooctasulphur (S8) were both identified when mole ratio was varied to 1: 2.5, 1: 3 and 1: 5 as well as when reaction time was shortened to 1 hour.ConclusionsCuS hexagonal plates with a mean edge length of 1 μm, thickness of 100 nm and average crystallite size of approximately (45 ± 2) nm (Scherrer estimation) were successfully synthesized via assisting agent- free hydrothermal method. Under a suitable mole ratio, we evidenced that the formation of covellite (CuS) is feasible regardless of the reaction temperature applied. However, a series of impurities were attested with CuS if reaction temperature was not elevated high enough for the additional crystallite phase decomposition. It was also identified that mole ratio plays a vital role in controlling the amount of cyclooctasulphur (S8) in the final powder obtained. Finally, reaction time was recognized as an important parameter in impurity decomposition as well as increasing the crystallite size and crystallinity of the CuS hexagonal plates formed.

Synthesis of Zinc Hydroxystannate Single-Crystalline Nanocubes and its Flame Retardancy for Rigid PVC

Zinc hydroxystannate (ZnSn(oh)6 , ZHS) nanocubes have been obtained for the first time through a simple method by hydrolyzation of Tin (Ⅳ) chloride (SnCl4.5H2O ) reacting with zinc chloride (ZnCl2) in aqueous alkali at the presence of solid sodium hydroxide (NaOH ). The X-ray diffraction data show that the phase obtained has a cubic-type structure. The Environmental Scanning Electron Microscope (ESEM) images testify that the product grows into cubic poly-crystals having a mean edge length of 380nm, with a standard deviation 20 nm.. Fire retardant (FR) properties of rigid polyvinyl-chloride (PVC) using the prepared ZHS and traditional antimony trioxide (Sb2O3) as fire retardant and smoke suppressant are evaluated by Cone Calorimeter.

Crystal Shape Engineering of Silicon Nanoparticles in a Thermal Aerosol Reactor

In this work, the capability of gas phase synthesis for crystal shape engineering of silicon nanoparticles (SiNPs) in a hot wall reactor is demonstrated. Therefore, the necessary boundary conditions for the formation of monodisperse spherical SiNPs as well as octahedral-shaped particles from silane pyrolysis are systematically deduced. The different shapes of the SiNPs are ascribed to different growth regimes (reaction limitation, diffusion limitation) depending on the global process parameters. Single crystalline, defect-free, spherical particles with a mean diameter of 30 nm (geometric standard deviation below 1.1) and octahedra with a mean edge length of about 100 nm could be obtained solely by process parameter adjustment. Particle size and shape as well as crystallinity were characterized by scanning electron microscopy and X-ray diffraction. The inner structure and faceting of the particles were analyzed in detail by high resolution transmission electron microscopy. A model that elucidates the orien...

Synthesis and photoluminescence properties of perovskite KMgF3:Eu nanocubes

Abstract

High-yield, size-controlled synthesis of silver nanoplates and their applications as methanol-tolerant electrocatalysts in oxygen reduction reaction

A novel method for the synthesis of as-prepared Ag nanoplates in high yield and the control of their dimensions has been developed. In this method, hexadecyltrimethyl ammonium ions (CTA +) are used as a trace additive in a seed solution for blocking the seed surface to govern the growth direction on nanoplate in the growth pathway, leading to a high-yield production of the Ag nanoplates with mixed morphologies, mainly triangular nanoplates and nanodisks. The spectra of the obtained nanoplate solution showed a high-intensity peak attributed to the in-plane dipole resonance and a low-intensity peak at 400 nm. By decreasing the amount of CTA +, the mean edge length of triangular nanoplates could be changed from ∼78.7 nm–∼124.8 nm. The in-plane dipole resonance peak corresponding to change in the mean edge length shifted from 630 nm to 785 nm, respectively. The mean edge length of triangular nanoplates could also be controlled from 70 nm to 148 nm by decreasing the CTA +-adsorbed seed amount. To investigate the practical feasibility of application of the proposed method, the prepared nanoplates were used as a methanol-tolerant electrocatalyst in an oxygen reduction reaction (ORR). An analysis conducted using a rotating ring-disk electrode showed that these nanoplates have high activity towards the ORR and that the electron transfer numbers ( n) were 3.85, 3.83, 3.81, and 2.94 for 70 nm, 124 nm, 148 nm nanoplates, and macroscopic Ag electrode, respectively. If the present of methanol, the corresponding n values of 3.82, 3.81, 3.78, and 2.30 were detected. Despite working in the methanol-tolerant solution, the prepared Ag nanoplates still exhibited high electroactivity and their ORR proceeded via an approaching 4-electron pathway.

Hydrothermal synthesis and magnetic properties of CoS 2 nano-octahedrons

Uniform single-crystalline CoS 2 nano-octahedrons have been prepared in high yield by a simple hydrothermal process. The octahedral structures exhibit a high geometric symmetry with smooth surfaces and the mean edge length is ~ 120 nm. X-ray diffraction, scanning electron microscopy, transmission electron microscopy were used to characterize the samples. Contrast experiments indicate that the capping agent poly(vinyl pyrrolidone) (PVP) and the complexing agent sodium citrate play important roles for the formation of octahedral CoS 2 nanostructures. A possible formation mechanism was proposed based on the evolution of this morphology as a function of hydrothermal time. Additionally, the magnetic properties of the CoS 2 nano-octahedrons were discussed in detail.

Statistical comparison of clouds and star clusters

The extent to which the projected distribution of stars in a cluster is due to a large-scale radial gradient, and the extent to which it is due to fractal sub-structure, can be quantified -- statistically -- using the measure ${\cal Q} = \bar{m}/\bar{s}$. Here $\bar{m}$ is the normalized mean edge length of its minimum spanning tree (i.e. the shortest network of edges connecting all stars in the cluster) and $\bar{s}$ is the correlation length (i.e. the normalized mean separation between all pairs of stars). We show how ${\cal Q}$ can be indirectly applied to grey-scale images by decomposing the image into a distribution of points from which $\bar{m}$ and $\bar{s}$ can be calculated. This provides a powerful technique for comparing the distribution of dense gas in a molecular cloud with the distribution of the stars that condense out of it. We illustrate the application of this technique by comparing ${\cal Q}$ values from simulated clouds and star clusters.

Measuring clustering in 2dv space

The statistical descriptor is a robust and useful tool for distinguishing and quantifying the degree of radial or multiscale clustering in objects such as open clusters. is calculated as m/s, where is the mean edge length of the minimum spanning tree and is the mean distance between cluster members, or correlation length. is obtained using only two-dimensional position data. Here, we investigate the performance of in three dimensions, both when true three-dimensional data are available and when the radial velocity of cluster components is used as a proxy for position: this is known as 2dv space. True three-dimensional data offer an improvement in the resolution of and as diagnostic indicators of clustering, a scatter plot of versus proving to be a particularly clear method of interpreting the information. Results are not satisfactory when 2dv information is used, as the data from cluster types which are clearly distinguishable using 2d information alone become overlapping and confused when 2dv information is used. We therefore recommend that the 2d method is used, unless true 3d positions of cluster members are available. The use of the versus plot is particularly recommended, as adding extra discrimination between cluster types, compared with that achieved using alone.

Room-temperature Preparation of BaMoO4 Nano-octahedra by Microemulsion Method

Abstract Uniform barium molybdate nano-octahedra with a mean edge length of 50 nm have been prepared in Triton X-100 water-in-oil (w/o) microemulsions at room temperature. BaMoO4 nano-octahedra present tetragonal single crystals. The size of these nano-octahedra can be tuned conveniently by changing the reagent concentrations and the molar ratio of water and Triton X-100.

Estimation of spanning tree mean-edge using node sampling

Suppose a finite graph containing several vertices, each connected with single or multiple edges. This constitutes a graph population of vertices and edges for example, the population like a tree having a sub-graph in the form of spanning tree. The paper contains mixture of the graph structure and sampling procedure together by virtue of mean-edge estimation of spanning tree using the remaining edges of graph as an auxiliary source of information. A new sampling procedure (node sampling) is derived for this purpose and estimation strategy is proposed to obtain this goal. An optimal sub-class of estimators is obtained. Mathematical conditions for minimum bias and optimum mean squared error are derived and theoretical results are numerically supported with the help of an example of graph population. Almost all the sample estimates of mean-edge length of spanning tree are found within the confidence limits.

Synthesis and Real-Time Magnetic Manipulation of a Biaxial Superparamagnetic Colloid

Superparamagnetic colloidal plates were synthesized from tetrabutylammonium stabilized Ca(2)Nb(3)O(10) nanosheets and oleic acid-stabilized Fe(3)O(4) nanoparticles. Modification with 3-aminopropyltrimethoxysilane produces amine-terminated Ca(2)Nb(3)O(10) with an amine concentration of 0.43 +/- 0.06 groups per Ca(2)Nb(3)O(10) unit as follows from spectroscopic quantification with trinitrobenzenesulfonic acid as a dye. Treatment of the modified sheets in THF/ethanol with 5.3 nm oleic acid-stabilized magnetite nanoparticles yields pseudo-2D assemblies that consist of 2 nm thick nanosheets decorated on both sides with a dense collection (9.3 +/- 0.5 x 10(3) particles per square micrometer per side) of magnetite particles. In noncoordinating or weakly coordinating solvents, these composite particles further aggregate into stacked aggregates with a mean edge length of 1.6 +/- 0.7 microm and a thickness of 79 +/- 30 nm. The colloidal plates were characterized by elemental analysis, X-ray powder diffraction, and infrared and UV/vis spectroscopy. SQUID measurements show that films of the aligned particles are superparamagnetic at room temperature. The magnetic hysteresis that is observed at 5 K reveals that the plates have a magnetic anisotropy with the easy axis in the plane of the plates and the hard axis perpendicular to it. Calculations show that the magnetic anisotropy is a direct consequence of the two-dimensional distribution of the magnetic nanoparticles on the sheets. Optical microscopy reveals that when suspended in ethanol or THF, the colloidal plates can be rotated in real time with a variable external magnetic field (200 Oe). Magnetic alignment of the particles in suspensions also produces asymmetric light scattering patterns and magnetic birefringence. These effects and the observed magneto-orientational properties make the biaxial colloids interesting as components in displays and as magnetic actuators.

Hydrothermal synthesis of CaSnO3 cubes

A hydrothermal process was employed to rationally synthesize CaSnO3 micro/nano-cubes with perovskite structure. The mean edge length of the cubes varies from 500 nm to 1.1 μm as a function of PVP surfactant concentration.

The statistical analysis of star clusters

We review a range of statistical methods for analysing the structures of star clusters, and derive a new measure , which both quantifies and distinguishes between a (relatively smooth) large-scale radial density gradient and multiscale (fractal) subclustering. The distribution of separations p(s) is considered, and the normalized correlation length (i.e. the mean separation between stars, divided by the overall radius of the cluster) is shown to be a robust indicator of the extent to which a smooth cluster is centrally concentrated. For spherical clusters having volume-density n?r? (with between 0 and 2) decreases monotonically with , from ?0.8 to ?0.6. Since reflects all star positions, it implicitly incorporates edge effects. However, for fractal star clusters (with fractal dimension D between 1.5 and 3) decreases monotonically with D (from ?0.8 to ?0.6). Hence , on its own, can quantify, but cannot distinguish between, a smooth large-scale radial density gradient and multiscale (fractal) subclustering. The minimal spanning tree (MST) is then considered, and it is shown that the normalized mean edge length [i.e. the mean length of the branches of the tree, divided by , where A is the area of the cluster and is the number of stars] can also quantify, but again cannot on its own distinguish between, a smooth large-scale radial density gradient and multiscale (fractal) subclustering. However, the combination does both quantify and distinguish between a smooth large-scale radial density gradient and multiscale (fractal) subclustering. IC348 has and ? Ophiuchus has , implying that both are centrally concentrated clusters with, respectively, ? 2.2

Large-scale synthesis of single-crystalline perovskite nanostructures.

Single-crystalline perovskite nanostructures with reproducible shape have been prepared using a simple, readily scaleable solid-state reaction in the presence of NaCl and a nonionic surfactant. Pristine BaTiO3 nanowires have diameters ranging from 50 to 80 nm with an aspect ratio larger than 25. Single-crystalline SrTiO3 nanocubes with a mean edge length of 80 nm have been produced using a similar procedure.

A Scheme for Generating Unstructured Grids on Spheres with Application to Parallel Computation

Numerical solution of differential equations on the surface of the sphere requires grid generation. Examples include numerical simulations of mantle convection, weather, and climate. Because of their ability to offer local resolution at modest computational cost, unstructured grids are attractive in this context. However, unstructured grids suffer from drawbacks such as high computational overhead and inefficient generation schemes. Here we present a scheme for generating unstructured grids on the surface of the sphere that overcomes these limitations. We also show how the scheme can be easily used to allow efficient domain decomposition for parallel computations. The surface of the sphere is covered with a spherical spiral, which is used to provide an underlying structure for the grid. The spiral is populated by nodes, which are then connected using an advancing front technique to generate near-equilateral spherical triangular elements. Methods for producing local grid refinement by adjusting the pitch of the spherical spiral are discussed, as is the extension of the method to the case of coupled pressure–velocity solvers. The same general idea of a spherical spiral also serves as the starting point for an algorithm to subdivide the grid into subdomains for parallel computation. The resulting unstructured grids are generally of very high quality: in uniform grids, 99.4% of the elements have areas between 90 and 107% of the mean element area, and 99.8% of the edges have lengths between 84 and 132% of the mean edge length. The quality of the grids increases with mesh density. Partitioning of the nodes and elements produces well-balanced and compact subdomains, with a maximum load imbalance that is small and rises gradually with number of subdomains. The proposed scheme produces grids that combine the benefits of an unstructured mesh with the structure conferred by the underlying spherical spiral. For example, this underlying structure greatly facilitates tasks such as element searching. This scheme is an attractive alternative for generating unstructured triangular grids on the sphere.

Preparation of monodisperse peanut-type α-Fe 2O 3 particles from condensed ferric hydroxide gel

Recently, it has been found that monodisperse pseudocubic hematite particles 1.65 μm in mean edge length can be obtained in large quantities of the order of the molality with a yield close to 100%, by adding 100 ml of 5.4 N NaOH to 100 ml of well-stirred 2.0 M FeCl 3 and aging the resulting condensed gel of Fe(OH) 3 for 8 days at 100°C. The method was provisionally referred to as the gel—sol method. As an application of this technique, when 90 ml of 6.0 N NaOH and 10 ml of sulfate or phosphate solution were added instead of 100 ml of 5.4 N NaOH, the pseudocubic particles turned into peanut-type particles via an ellipsoidal shape with increasing concentration of the additives.

Minimal spanning tree approach to percolation and conductivity threshold

The minimal spanning tree (MST) method to analyse order and disorder in distributions of objects is used to investigate the percolation transition on a triangular lattice. It is shown numerically that the value of the threshold probability is retrieved, simultaneously with a new geometrical parameter: the mean edge length. This is expected to be useful in the conductivity studies of percolation networks such as dielectric breakdown, conductivity and other propagation phenomena. The potentialities of the method in dealing with an extensive study of percolation on continuous as well as lattice systems are also exhibited.