Cube-shaped Particles Research Articles

A Study on the Magnetic and Photoluminescence Properties of Eu<SUP><I>n</I>+</SUP> and Sm<SUP>3+</SUP> Doped Fe<SUB>3</SUB>O<SUB>4</SUB> Nanoparticles

In this paper, Eu(n+), Sm3+ doped Fe3O4 nanoparticles were prepared via solvothermal method, in which Ferric chloride is used as the iron source, and anhydrous EuCl3, SmCl3 as doping source. Eu, Sm valence in doped Fe3O4 nanoparticles, and effects of Eu, Sm doping amount on their structure, morphology, magnetic properties and PL properties were discussed. The results show, the Eu ions had doped Fe3O4 nanoparticles in the mixed-valence state, when the Eu and Sm doping amount were increased, the doped Fe3O4 nanoparticles changed from hollow nanospheres into spherical particles, and finally changed into uniform cube-shaped particles with 13 nm in diameter. Moreover, the doping sites for doping ions in doped Fe3O4 nanoparticles were discussed from Rietveld analysis of XRD pattern of the doped Fe3O4 nanoparticles. And the changes of the magnetic and PL properties with the doping amount were further discussed. It was found that higher Sm(3+)-doping amount led to stronger magnetic dipole transitions, while the Eu(n+)-doping amount had little effect on the magnetic dipole transitions, thus resulting in different changes in their saturation magnetization with doping amount.

Study of polyol synthesis reaction parameters controlling high yield of silver nanocubes

The influence of the parameters and conditions of sodium sulfide-induced reaction of polyol synthesis of silver nanoparticles on the yield of cube-shaped particles and the optical properties of colloids is studied. The protocol proposed by Skrabalak et al. for the synthesis of nanocubes in small volumes (Nature Protocols, 2007, vol. 2, p. 2182) is taken as an initial variant for optimization. The effects of the reagent concentrations, degree of ethylene glycol oxygenation, the presence of impurities, reaction time, and temperature are studied. Suspensions containing nanoparticles with different shapes and sizes, including polydisperse particles of irregular shapes, silver nanocubes with a yield of 0 to 97%, nanoprisms, and nanorods, can be produced by varying the synthesis parameters. The key parameters controlling the yield of nanocubes are the degree of ethylene glycol oxygenation and the presence of trace amounts of ions of other metals (not silver). It is established that variations in the reaction time make it possible to vary the sizes of nanocubes in the range of 30–60 nm. Suspensions with high contents of cube-shaped particles are shown to exhibit three maxima in the plasmon extinction resonance spectrum at wavelengths of 350, 390, and, depending on the particle size, 435–470 nm.

Precursor Effect on Hydrothermal Synthesis of Sodium Potassium Niobate Fine Particles and Their Piezoelectric Properties

Controlled synthesis of sodium potassium niobate (NaxK1-xNbO3: NKN) fine particles with different K/Na ratios was successfully achieved by the two-step hydrothermal reaction at 100 °C for 24 h and 200–250 °C for 3 h using niobium pentachloride as a soluble precursor. As a result of the effect of the K/Na ratio in the starting solution, NKN particles with an orthorhombic sodium niobate were formed in the NaOH/KOH ratios from 10/8 to 7/11. When the NaOH/KOH ratio was adjusted to 10/8, cubic-shaped particles were obtained, and the mean particle size with the size distribution was 3.0±1.2 µm. In contrast, by aging at 250 °C, NKN particles with orthorhombic potassium niobate crystal structure were obtained in the NaOH/KOH ratios from 5/13 to 1/17. Furthermore, monodispersed and octahedral-shaped NKN fine particles with a tetragonal crystal structure were formed as a single phase at 200 °C with the NaOH/KOH ratio of 6/12. The octahedral-shaped particles had a hierarchical built-up structure of cubic-shaped nanoparticles. The sodium and potassium ratio in the NKN crystal structures was further characterized by Rietveld analysis. All the NKN ceramics, prepared starting from the present hydrothermal method, had a highly porous structure. However, these ceramics exhibited high d33 values of ca. 100 pC/N. This result means that the octahedral-shaped NKN particles have high potential as lead-free piezoelectric materials.

Surface modification of titanium by pulsed laser radiation of femtosecond duration

The effect of an infrared pulse laser with femtosecond radiation (λ = 744 nm, τ ≈ 120 fs, E ≤ 8 mJ) on the surface of Ti of commercially purity in the submicrocrystalline state is investigated using scanning electron microscopy (SEM). Laser irradiation leads to the formation of a surface nanorelief consisting of alternating projections (bars) and hollows (grooves). After surface treatment under a water layer, cube-shaped particles are formed on Ti surface; they are composed of many tightly contiguous rectangular plates.

Fabrication and application of MFe2O4 (M = Zn, Cu) nanoparticles as anodes for Li ion batteries

In this work, MFe2O4 (M = Zn, Cu) nanoparticles were successfully prepared by a hydrothermal method. The structure, morphology, microstructure, specific surface area and electrochemical properties of the resultant particles were characterised by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, nitrogen physical adsorption, charge–discharge test and cyclic voltammetry (CV) method, respectively. The resulting ZnFe2O4 and CuFe2O4 products were sphere-like and cubic-shaped particles and their average size was about 30–40 nm and 60–70 nm, respectively. The initial discharge capacities of ZnFe2O4 and CuFe2O4 electrodes reached 1287.5 mAh g−1 and 1412.3 mAh g−1, respectively, at a current density of 0.2 mA cm−2 in a potential range of 0.0–3.0 V. This indicated that Cu is a better counter ion than Zn. The resulting MFe2O4 nanoparticles are expected to be a promising candidate of anode materials for Li ion batteries. The reaction mechanism of MFe2O4 nanoparticles in Li ion batteries was also discussed based on the CV of Li/MFe2O4 cell.

Novel standing Ni–Pt alloy nanocubes

The synthesis of novel cubic shaped-standing Ni–Pt alloy nanoparticles is reported. Incorporation of a few percent of Pt atoms in the presence of chloride ions and oleylamine, which helps to control the growth and prevents agglomeration, facilitates the formation of highly monodispersed cubic shaped particles. Furthermore, these cubic-shaped particles stand on their corners, which is believed to be due to the magnetic interaction between particles whose easy axis is in the [111] direction. The formation of these unique shaped particles with different sizes has been realized by using platinum particles as seeds. It should be noted that these particles are highly reproducible and holds great potential for catalytic applications.

Combined Analytical Transmission Electron Microscopy Approach to Reliable Composition Evaluation of KTaO3

We have made an effort to obtain a reliable quantitative composition of KTaO3, which belongs to the group of incipient ferroelectrics. A combination of two analytical spectroscopic methods of transmission electron microscopy was employed for the nanoscale analysis: energy-dispersive X-ray and electron energy-loss spectroscopy. Because of the volatile nature of alkali-based compounds, special attention was paid to optimization of acquisition parameters. The latter were tested on KTaO3 single-crystal specimen by applying various electron doses and monitoring the K/Ta ratio. The case study was based on the analysis of calcined KTaO3 powder prepared from a stoichiometric mixture of K2CO3 and Ta2O5, and KTaO3 ceramic prepared from the latter powder by hot pressing. At nanoscale, the particles of microscopically homogeneous powder appeared to have a slight excess of K relative to the nominal composition. Additionally, 5–20 nm sized nanoparticles, possessing both K- and Ta-rich compositions, were found to be attached to the cubic-shaped powder particles. Hot-pressed KTaO3 ceramic revealed exaggerated grain growth with compositional deviations of up to 5% within large grains as well as in matrix grains composition. The majority of analyzed matrix grains, however, showed a slight excess of Ta relative to the nominal composition.

Colloidal Synthesis of Air-Stable Crystalline Germanium Nanoparticles with Tunable Sizes and Shapes

Nanoparticles of elemental germanium have interesting optical and electronic properties and relatively low toxicity, making them attractive materials for biological and optoelectronic applications. The most common routes to colloidal Ge nanoparticles include metathesis reactions involving Zintl salts, hydride reduction of Ge halides, and thermal decomposition of organogermane precursors. Here we describe an alternative “heat-up” method for the synthesis of size- and shape-tunable Ge nanoparticles that are both crystalline and air stable. The readily available reagents GeI4, oleylamine, oleic acid, and hexamethyldisilazane are combined in one pot and heated to 260 °C, where a rapid nucleation event occurs and multifaceted nanoparticles of crystalline Ge form. By varying the concentration of GeI4, the nanoparticle size can be tuned from 6 to 22 nm with narrow size distributions. Adding trioctylphosphine yields cube-shaped particles, and switching the solvent to octadecene yields one-dimensional nanostructures. The Ge nanoparticles, which are fully air stable for more than 6 months, were characterized by XRD, TEM, HRTEM, EDS, XPS, DRIFT, and UV−visible spectroscopy.

Transient Three-Dimensional Mathematical Model and Experimental Investigation of a Wet Devolatilizing Wood in a Hot Fluidized Bed

Devolatilization of a single wet wood particle in a hot atmospheric fluidized bed is studied through a mathematical model and experiments. A typical tropical woody biomass, “Casuarina Equisetifolia”, is used in the study. A three-dimensional (3D) transient model with detailed consideration of (i) fuel anisotropy, (ii) fuel moisture, (iii) shrinkage during drying and devolatilization, (iv) heat generation, and (v) variable properties with a suitable reaction scheme is developed to determine the devolatilization time (τd) and char yield (Yc) of cubic/cuboidal wood particles at various initial fuel moisture contents and bed temperatures. Experiments are conducted for 10, 15, 20, and 25 mm cube-shaped wood particles at bed temperatures of 1023, 1123, and 1223 K. The model predictions agree well with the measured data (present experiments and those reported in the literature) within ±10% for the devolatilization time and ±11% for the char yield, supporting the validity of the overall structure of the model. A ...

The structure of the cytoplasm of lens fibers as determined by conical tomography

Studies using conventional electron microscopy describe the cytoplasm of lens fiber cells as having essentially an amorphous structure. We hypothesized that significant structural detail might have been lost as a result of projecting the entire thickness of the section (50–100nm) onto a single plane (the “projection artifact”). To test this hypothesis, we studied the 3D-structure of rat lens cortical fibers before and after extracting the “soluble” crystallins with low ionic strength buffers to make “ghosts.” Tomographic series in conical geometry were collected at 55° tilts and by 5° rotations until completing a 360° turn by low dose methods. They were aligned using fiduciary points, reconstructed with the weighted back projection algorithm and refined by projection matching. Analysis of the 3D-maps included semiautomatic density segmentation using a computer program based on the watershed algorithm. We found that the cytoplasm of cortical fibers, though appearing amorphous in regions of the highest density, was in fact comprised of an ordered structure resembling a “clustered matrix.” The matrix was comprised of thin (∼6nm diameter) filaments bent sharply at 110–120° angles and studded with cube-shaped particles (the “beaded” filaments). In cortical fibers, the particles measured a=14±2, b=13±2 and c=10±2.4nm (n=30, mean±SD) and were spaced at distances measuring 27.5±2.4nm apart (n=8, mean±SD), center-to-center. The matrix was formed as “beaded” filaments, bound to clusters of “soluble” proteins, crossed each other at nearly perpendicular angles. The matrix also made contact with the plasma membrane at a large number of distinct regions. We thus concluded that the cytoplasm of cortical lens fibers is comprised of a cytoskeletal matrix of “beaded” filaments that organize the “soluble” crystallins in separate regions. The association of this matrix with the plasma membrane allows the lens to maintain its structural integrity, while its association with crystallins yields its long-term transparency. Loss of either function likely would play a significant role in cataract formation.

Distinct element modelling of cubic particle packing and flow

Processing of granular and powder materials is important in many engineering applications. The unpredictable behaviour of bulk solids often causes problems such as unsteady flows during handling and processing. Mixing and packing of powders are also of great importance, but experimental observation of such processes is not always convenient. Simulation is a powerful tool here. In this paper, a model for cube-shaped particles is developed using the Distinct Element Method. It introduces a model based on multi-contact principles. The cube shape was considered as an archetypal regular polyhedral shape with fundamentally different characteristics to spheres in packing and flow. Specific industrial applications are also noted. The study closely compares laboratory experiments and simulations in terms of static packing, flow pattern and flow rates for cubes and spheres. The results show that the multiple-contact model is a better solution for surface–surface contact than the single-contact version and should be used for polyhedral shapes. The simulation and experimental results are generally in close agreement demonstrating that the DEM cube model is a feasible tool. The cubes show “better” packing characteristics but “worse” flow properties as expected, however, it is noted that the system is fairly small in terms of number of particles and wall effects are quite significant here.

Atomic force microscopy (AFM), transmission electron microscopy (TEM) and scanning electron microscopy (SEM) of nanoscale plate-shaped second phase particles

The feasibility of accurately measuring the size and the volume fraction of nanoscale plate-shaped precipitates by atomic force microscopy (AFM) has been explored. For quantitative evaluations their unhandy geometry is conveniently described by superellipsoids. The experimental alloy Ni69Co9Al18Ti4 served as a model system: plate-shaped disordered γ-precipitates form in the L12 long-range ordered γ′-matrix. The results obtained by AFM are compared with those derived from transmission (TEM) and from high-resolution scanning electron microscopy (SEM). The agreement between the AFM and the TEM results is good. In spite of the low number of SEM images taken, the same holds for the SEM results. In addition, magnetic force microscopy was applied; its results are acceptable. The main advantages of AFM are (i) the numerical output for all three dimensions, (ii) the simplicity of its operation and (iii) the lower cost of the microscope itself. The first point allows the numerical AFM output data to be directly subjected to automated computer-based evaluations. All present experimental and evaluation procedures are also applicable to cube-shaped particles with rounded edges and corners as found, for example, in γ′-strengthened nickel-based superalloys.

Synthesis of TiO 2 nanocubes induced by cellulose nanocrystal (CNC) at low temperature

Abtract A novel and facile approach to prepare TiO2 nanocubes at 90 °C in 4.5 h is presented, and it employs only TiCl4 and cellulose nanocrystal (CNC) as the starting materials. Introduction of CNC which acts as morphology-inducing and coordinate agent results in accelerating the crystal growth of TiO2 particles and promoting the formation of nanocubes. Transmission electron microscopy (TEM) reveals regular cube-shaped particles with uniform particle size. High-resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) indicates that particles with high crystallinity grow along the [001] and [110] directions. X-ray power diffraction (XRD) shows the peaks of dominant anatase crystal phase and cellulose. Thermal gravity analysis (TGA) suggests that CNC particles are probably embedded in the TiO2 nanoparticles.

Influence of coating properties on paper-to-paper friction of coated paper

Coated paper-to-coated paper friction properties were examined in relation to printing runnability difficulties like erroneous double feeding of paper sheets. Higher ratios of precipitated calcium carbonate (PCC) to clay in mixed pigment coatings resulted in higher static and kinetic coefficients of friction (COFs). Microroughness in the order of pigment particle size is considered to relate to COF, because cube-shaped particles of PCC resist sliding. Calendering decreased COF at larger amounts of PCC, but did not change COF of the sole clay formulation at all. Addition of ground calcium carbonate (GCC) decreased COF. The rate of decrease in kinetic COF with increasing number of sliding for the GCC-rich formulation was higher than that for the PCC-rich formulation, presumably because protruding parts, characteristic of the GCC-rich formulation, on the surface were selectively flattened. Addition of styrene-butadiene (SB)-latex up to 14pph decreased COF, but static COF had the highest value at 18pph. The antislip property (as a rubber) of SB-latex developed only in the static mode. Among lubricants formulated, the wax type decreased COF the most remarkably with more effect on kinetic COF than on static COF.

Hydrothermal Synthesis of Zn2SnO4 as Anode Materials for Li-Ion Battery

Spinel Zn2SnO4 particles with the cubic shape are prepared via a hydrothermal reaction under mild conditions. The hydrothermal conditions, such as alkaline concentration, reaction temperature, and duration time, have an important influence on the product structure and the performance of the electrode prepared with the product. The optimized product is cube-shaped Zn2SnO4 crystalline, which is prepared with 0.4 M of NaOH solution at 200 degrees C for 24 h. These cube-shaped Zn2SnO4 particles with the spinel structure exhibit a large electrochemical capacity of 988 mA h/g and a relatively good capacity retention as anode materials for Li-ion battery. The structures of the as-prepared product and specimens taken from the electrodes after charging-discharging cycles are analyzed by X-ray diffraction, scanning electron microscopy, and transition electron microscopy techniques. In particular, it is found for the first time that the spinel Zn2SnO4 structure exists to a great extent after the first cycle and contributes to the extremely high reversible capacity during the following cycles.

Single-Crystal-like Materials by the Self-Assembly of Cube-Shaped Lead Zirconate Titanate (PZT) Microcrystals

We demonstrated the formation of single-crystal-like materials that contain preferentially oriented arrays of lead zirconate titanate (PZT) cube-shaped particles by self-assembly. Hydrothermally synthesized PZT particles with a bulk composition of Zr/Ti = 70/30 were used in making microcrystal arrays. Spreading a suspension containing PZT cube-shaped particles, 2-propanol, and mineral oil at the air-water interface produced a one-dimensional planar array of PZT particles on the water surface. The array so formed was subsequently transferred onto a flat or curved substrate. X-ray diffraction and electron backscattered diffraction analyses revealed that most of the cube-shaped particles in the array were oriented with their pseudocubic (001) direction aligned parallel to the normal direction of the substrate surface. Filling the arrays with matrixes produced monolayer or multilayer textured composites. The piezoelectric properties of oriented cube-shaped micron-sized particles in the self-assembled arrays were measured using a modified atomic force microscope to reveal the ferroelectric nature of the PZT arrays.

Quasi-static effective permittivity of periodic composites containing complex shaped dielectric particles

A methodology is described for computing the quasi-static effective permittivity of a two-dimensional (2-D) or three-dimensional (3-D) lattice of dielectric particles. The particles in this composite material may have complicated shapes. This methodology uses a moment method based technique to determine the electric dipole moments of the particles immersed in a uniform electric field. The effective permittivity is then obtained using an appropriate macroscopic model. With this methodology, the mutual interaction between particles can be accounted for accurately. The computed effective permittivity for round cylinders and spheres suspended in a host are compared with our previous T-matrix method results as well as the Maxwell Garnett (MG) formula predictions. Three additional examples involving square (2-D), rounded square (2-D), and spherical (3-D) dielectric inclusions are also given, illustrating the shape effects on the computation of the quasi-static effective permittivity. While the square- and cubic-shaped particles can possess great mutual interaction, surprisingly their effective permittivity is well predicted for all volume fractions by the simple MG formula in both 2-D and 3-D problems.

Light Propagation through Weakly Absorbing Layers of Dielectric Cube-Shaped Particles

Light propagation through ensembles of dielectric particles with various packing density is studied by the method of physical modeling in the SHF range. Monolayers and multilayers of weakly absorbing cube-shaped particles with the refractive index n = 1.5 are investigated. Particle dimensions are comparable to the incident radiation wavelength. Dependences of the transmittance T and the scattering efficiency factor Q on the diffraction parameter ρ are obtained for ensembles of particles with various overlap factors η. For monolayers of particles, the effect of an enhanced transmittance with increasing packing density of particles is observed. Conditions are specified at which the monolayer transmittance is equal to zero. It is shown that the Mie formulas, derived for spherical particles, can be used to calculate the optical characteristics of an ensemble of particles with chaotic orientation of particle sides, if the diameter of an equivalent sphere is set equal to the cube edge length multiplied by a correction factor of 1.15. Transition to an ordered orientation of cube-shaped particle sides leads to increase in the scattering efficiency factor for ρ > 2.

1502 PNN-PT 系セラミックスの合成と電気機械的特性

Relaxor-type ferroelectric perovskites, (1-x)Pb(Ni_<1/3>Nb_<2/3>)O_3・xPbTiO_3 with x between 0.32 and 0.4,were prepared through process of heat treatment and then acid treatment of oxide mixtures containing PbO in amount greater than in the perovskite composition. The perovskite phases were crystallized without the formation of pyrochlore phase from the mixtures 5PbO+(1-x)NiO+(1-x)Nb_2O_5+3xTiO_2 at 950℃. By leaching with a 1N acetic acid solution to remove the excess PbO, the perovskite phases were obtained in discrete and cube-shaped particles of 1-5μm size. The ceramic sintering was made at 1180℃ for 3h. Relatively good dielectric and electromechanical properties were observed in the ceramics with x=0.34 to 0.39. The most remarkable was that the ceramic with x=0.36 showed a large longitudinal strain of 0.28% at 1600V/mm near room temperatures.

Systematic Analysis of Micromagnetic Switching Processes

Guided by the properties of the Stoner-Wohlfarth model, the switching behavior of general inhomogeneous micromagnetic configurations is investigated. In most cases the extrapolation of a suitably defined local susceptibility to infinity is demonstrated to lead to the switching point. Only conventional tools of numerical micromagnetics are needed in this calculation. For certain, symmetric classes of switching events we have to resort to indirect methods to determine the switching fields. Examples for the successful application of the proposed methods to various switching phenomena in cube-shaped particles with uniaxial anisotropy are given to validate the procedures.