Round-shaped Particles Research Articles

Effect of Pt Substitution by Cu on Structural and Morphological Changes in Fe-Pt Nanoparticles during Annealing as Studied by <I>In-situ</I> Transmission Electron Microscopy

Effects of substitution of Pt by Cu on the structural and morphological changes of Fe-Pt nanoparticles with chemical homogeneity and mono-dispersion, which were synthesized by the reverse micelle method, have been investigated by in-situ electron diffraction and HREM observation. In the Fe-Pt particles, initially with a chemically disordered face-centered cubic phase (Al), the phase transformation from Al to a chemically ordered face-centered tetragonal phase (L1 0 ) took place between 650 and 680°C. Polycrystalline Fe-Pt particles were reconstructed into Al single crystals between 550 and 650°C, followed by phase transformation from Al to L1 0 . The coalescence began almost concurrently with the phase transformation, i.e., between 650 and 680°C. Then, they turned to round-shaped single crystalline particles between 680 and 720°C. In the Fe(Pt,Cu) particles, the phase transformation from Al to L1 0 occurred between 550 and 600°C. Same processes, that is, the reconstruction to single crystals, the phase transformation from Al to L1 0 , the coalescence and the round-shaped particle formation were also observed in the Fe(Pt,Cu) nanoparticles. The temperatures, at which these processes took place, were substantially lower than those for the Fe-Pt nanoparticles.

Computation of Screening Phenonema in a Vertical Tumbling Cylinder

AbstractGranular materials are an integral part of our environment. Due to their wide variety of applications in industrial and technological processes, they have captured a great interest in the recent research, see [1] and [2]. The related studies are often based on numerical simulations and it is considered as challenging to investigate computational phenomena of dense granular systems. Particle screening is an essential technology in many industrial fields and important in granular studies. The particular problem of interest is the separation of round shape particles of different geometrical sizes using a rotating tumbling vertical cylinder. The concept of discrete element method (DEM) that considers the motion of each single particle individually is applied in this study. Particle‐to‐particle and particle‐to‐wall collisions will appear under the tumbling motion of the rotating structure. The normal and frictional forces between particles themselves and particles and surrounding walls of the structure are calculated according to the rules of a penalty method, which employs spring‐damper models for this purpose. As a result of collisions, the particles will dissipate kinetic energy due to the normal and frictional contact losses. Particle distribution and sifting rate of the separated particles have been studied taking into consideration different rotational speeds of the machine, various damping and frictional coefficients and different sizes of holes in the sifting plates at different levels of the structure. In an attempt to better understand the mechanism of the particle transport between the different layers of the sifting system, different computational studies have been performed. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Si–C–N–Fe nanostuctured ceramics from inorganic polymer precursors obtained by plasma polymerization

Multicomponent powders based on SiCN and SiCN containing iron systems are of great interest as starting materials for sintering advanced ceramics and composites with improved properties for high temperature applications.We report a versatile method by which are designed inorganic polymers with a defined composition as precursors for a ceramic with induced properties. The synthesis of Si–C–N and Si–C–N–iron polymer precursors are performed in improved configuration of plasma assisted chemical vapor deposition (CVD) coupled with chemical transport reaction (CTR) with inorganic monomers, hexamethyldisilazane and ferrocene/hexamethyldisilazane as precursors. Further, the resulted polymers are then pyrolysed at 1200 °C under nitrogen atmosphere into nanostructured ceramics (such as Si3N4, Fe3C).The conversion process of the polymer precursors into a nanostructured ceramic was followed mainly by FTIR, XRD, TEM and SEM investigation. Infrared spectroscopy of polymers revealed the presence of Si–C, Si–N, C–N and hydrogenated bonds. Transmission electron microscopy showed that the polymers are made of nanometric round-shape particles with the average particle size around 20–40 nm for SiCN and 40–80 nm for SiCN containing iron.

Fabrication of fine-grained Si3N4-Si2N2O composites by sintering amorphous nano-sized silicon nitride powders

Si3N4-Si2N2O composites were fabricated with amorphous nano-sized silicon nitride powders by the liquid phase sintering (LPS). The Si2N2O phase was generated by an in-situ reaction 2Si3N4(s)+1.5 O2(g)=3Si2N2O(s)+N2(g). The content of Si2N2O phase up to 60% in the volume was obtained at a sintering temperature of 1650°C and reduced when the sintering temperature increased or decreased, indicating the reaction is reversible. The mass loss, relative density and average grain size increased with increasing the sintering temperature. The average grain size was less than 500 nm when the sintering temperature was below 1700°C. The sintering procedure contains a complex crystallization and a phase transition: amorphous silicon nitride→equiaxial α-Si3N4→equiaxial β-Si3N4→rod-like Si2N2O→needle-like β-Si3N4. Small round-shaped β-Si3N4 particles were entrapped in the Si2N2O grains and a high density of staking faults was situated in the middle of Si2N2O grains at a sintering temperature of 1650°C. The toughness increased from 3.5 MPa·m1/2 at 1600°C to 7.2 MPa·m1/2 at 1800°C. The hardness was as high as 21.5 GPa (Vickers) at 1600°C.

The Completion of the Platonic Atomic Polyhedra: The Dodecahedron

Binary AuPd nanoparticles in the 1–2 nm size range have been imaged by high-resolution electron microscopy (HREM). A dodecahedral atomic growth pattern is identified in the round-shaped particles (such a dodecahedron is shown as a ball model (left) and a simulated microscope image (right)), which make up 85 % of the total product. The results demonstrate the first experimental evidence of this Platonic form for metallic nanoparticles of this size. The stability of such structures has been validated through theoretical calculations.

Synthesis and Characterization of Nano‐Hetero‐Structured Dy Doped CeO2 Solid Electrolytes Using a Combination of Spark Plasma Sintering and Conventional Sintering

Doped ceria (CeO2) compounds are fluorite‐type oxides that show oxide ionic conductivity higher than yttria‐stabilized zirconia in oxidizing atmosphere. As a consequence of this, considerable interest has been shown in application of these materials for “low” (500°–650°C) temperature operation of solid oxide fuel cells (SOFCs). To improve the conductivity in dysprosium (Dy) doped CeO2, nano‐size round shape particles were prepared using a coprecipitation method. The dense sintered bodies with small grain sizes (<300 nm) were fabricated using a combined process of spark plasma sintering (SPS) and conventional sintering (CS). Dy‐doped CeO2 sintered body with large grains (1.1 μm) had large micro‐domains. The conductivity in the sintered body was low (−3.2 S/cm at 500°C). On the other hand, the conductivity in the specimens obtained by the combined process was considerably improved. The micro‐domain size in the grain was minimized using the present process. It is concluded that the enhancement of conductivity in dense specimens produced by the combined process (SPS+CS) is attributable to the microstructural changes within the grains.

Hexameric and Pentameric Slipped-Cofacial Dimers: Toward an Artificial Light-Harvesting Complex

[structure: see text] We prepared a zinc complex of bis(1-methylimidazolyl)-m-gable porphyrin. The automatically assembled coordinate species showed a complex mixture of wide molecular weight distributions accompanied with assemblies of specific assembly numbers. When this zinc complex was once dissociated by the addition of methanol and reorganized again by elimination of the methanol under high-dilution conditions in chloroform to facilitate intramolecular coordinate structure formation, two convergent assemblies were obtained through analysis by gel permeation chromatography. These assemblies gave round-shaped particles on solid substrates by probe microscopies (atomic force and scanning tunneling microscopies). These two components were separated by GPC and evidence from small-angle X-ray scattering measurements in solution with synchrotron radiation was consistent with hexameric and pentameric macrorings of the gable porphyrin. The porphyrin macrorings did not show any fluorescence quenching by assembly formation, and we anticipate that the macrorings of gable porphyrins represent a good model for an artificial light-harvesting complex.

Influence of particle morphology on nanostructural feature and conducting property in Sm-doped CeO 2 sintered body

Doped ceria (CeO 2) compounds are fluorite type oxides, which show oxide ionic conductivity higher than yttria stabilized zirconia (YSZ), in oxidizing atmospheres. As a consequence of this, considerable interest has been shown in application of these materials for ‘low (500–650 °C)’ or ‘intermediate (650–800 °C)’ temperature operation, solid oxide fuel cells (SOFCs). In this study, the authors prepared two kinds of nanosize Sm-doped CeO 2 particles with different morphologies: one type was round and the other was elongated. Processing these powders with different morphology produced dense materials with very different ionic conducting properties and different nanoscale microstructures. Since both particles are very fine and well dispersed, sintered bodies with high density (relative density >95% of theoretical) could be prepared using both types of powder particles. The electrical conductivity of sintered bodies prepared from these powders with different starting morphologies was very different. Materials prepared from particles having a round shape were much higher than those produced using powders with an elongated morphology. Measured activation energies of the corresponding sintered samples showed a similar trend; round particles (60 kJ/mol), elongated particles (74 kJ/mol). While X-ray diffraction (XRD) profiles of these sintered materials were identical, diffuse scatter was observed in the background of selected area electron diffraction pattern recorded from both sintered bodies. This indicated an underlying structure that appeared to have been influenced by the processing technology. Detailed observation using high-resolution transmission electron microscopy (HR-TEM) revealed that the size of microdomain with ordering of cations in the sintered body made from round shape particles was much smaller than that of the sintered body made from elongated particles. Accordingly, it is concluded that the morphology of doped CeO 2 powders strongly influenced the microdomain size and electrolytic properties in the doped CeO 2 sintered body.

Single-drop agglomeration of fine mineral admixtures for concrete and water requirement of pastes

This paper deals with water requirement determination of fine mineral admixtures for concrete by a simple and rapid test based on “single-drop” agglomeration. Eighteen fine and very fine mineral admixtures for concrete, different in origin and characteristics are tested. The influence of cement and high-range water-reducing admixtures are also studied. The “single-drop” test results are compared with standard tests proposed in concrete technology. The water–fine mineral admixture ratio of the formed agglomerate is proportional to the water requirement of the mineral admixture determined by the standard tests for concrete mixtures. However, the frictional forces between particles are not taken into account by the “single-drop” test and consequently the dispersing effect of high-range water-reducing admixtures. Round- and angular-shaped particles present a linear function between the water–fine mineral ratio and fineness, which is determined by the BET specific surface area or the average particle size of the minerals. Irregular-shaped particles present two to three times higher water–fine mineral ratio than that of round-shaped particles with equivalent fineness. In this case, the very low granular packing of mixtures exclude any use in concrete. When there is low cement content, the water–fine mineral-plus-cement ratio and consequently the porosity of binary blended mixtures increase significantly because of interaction phenomena between cement particles and water.

Morphology/Behavior Relationship in Reversible Electrochemical Lithium Insertion into Graphitic Materials

Different types of graphite particles, including synthetic flakes, natural graphite flakes, graphite fibers, round-shaped graphite particles (mesocarbon microbeads), and combinations of graphite flakes and disordered carbon particles were studied as electrode materials in lithium insertion/deinsertion processes. We suggest that the morphology of the graphite particles plays an important role in their stability. One of the key factors is the structure of the facets, perpendicular to the basal planes, through which Li insertion takes place. The smoother these facets are, and which contain fewer crevices, the more stable are the graphite particles in Li insertion reactions. This is attributed to the fact that the surface reactions of the cathodically polarized graphite electrodes in the nonaqueous Li salt solutions involve gas formation, which may have a detrimental effect on the integrity of the graphite particles. Another important factor is the existence of some degree of disorder and distortion in the graphite structure. More distortion in the ordered graphite structure may lead to higher stability. A clue to the understanding of the factors that determine stability or destruction of lithiated graphite electrodes is the pronounced detrimental effect of the presence of propylene carbonate in ethylene carbonate-based solutions, as discussed herein. Another important factor dealt with in this paper is the correlation between the morphology of the graphite particles and their orientation in practical electrodes. The major tools for this study included chronopotentiometry, electron microscopy, and X-ray diffraction. © 2002 The Electrochemical Society. All rights reserved.

Bruchzähigkeit von Verbundwerkstoffen

Fracture Toughness Testing of Composites. Metal matrix composites of improved mechanical properties, compared with properties of unreinforced metal matrix, may be produced by combination of matrix material with different ceramic reinforcement components using various production technologies. However, using metal matrix composites in structural applications is limited by relative low ductility and toughness values. The fracture toughness testing because of its theoretical background may be a reliable method to interpret the fracture behavior of metallic material. The basic objective of the present work was to investigate the fracture behavior of magnesium-matrix composites. The heat treatable, creep resisting QE22 alloy was investigated as matrix material and SiC particles of different geometries and dimensions were used as reinforcement. The powder metallurgical technique was applied to produce the composites. The Short-Rod method was utilized to measure the fracture toughness. It turned out that the addition of SiC particles reduces the fracture toughness. This affects the composites of all particle volume per cents and geometries. However, the composites with blocky type particle posses higher fracture toughness compared with those of sharp shape and round shape particles. In the fact, the fracture behavior of magnesium is predominately affected by its hcp-crystal system. Therefore, improvement of fracture toughness of magnesium composites is more by using the proper shape of reinforcement and controlled procedure but less by matrix properties such as chemical composition and microstructure possible.

Effect of surface treatment of substrates on epitaxial α-Fe 2O 3 films by coating-pyrolysis process

Using a coating-pyrolysis process, an α-Fe 2O 3 film, which consists of densely packed epitaxial α-Fe 2O 3 particles with a rectangular shape, was obtained when an iron 2-ethylhexanoate solution was spin-coated onto an α-Al 2O 3 (012) substrate rinsed with methanol, and subsequently annealed in air. When the α-Al 2O 3 substrate was rinsed with other conventional solvents, such as toluene, etc., round-shaped particles were formed on the substrate. Since densely packed rectangular crystals of α-Fe 2O 3 were formed only on the substrate rinsed with methanol, methanol molecules adsorbed on the α-Al 2O 3 substrate are considered to promote α-Fe 2O 3 to form a densely packed layer of rectangular crystals. The ordered adsorption of iron 2-ethylhexanoate molecules through methanol molecules is discussed.

Microstructural Observation of Silicon Nitride Ceramics Sintered with Addition of Titania.

Si3N4 sintered body was obtained by pressureless sintering and then post-HIPing with addition of small amount of TiO2 (3mass%). Sintering additives were 5mass% Y2O3, 3mass% Al2O3 and 3mass% AlN. It was found that round-shaped particles with diameter 0.2-0.5μm were distributed within the grain-boundary phase. The particles contained high density crystalline imperfections. They contained Ti and N, and were identified as TiN by energy-dispersive-type X-ray microanalysis and X-ray diffractometry. The grain-boundary phase was mainly an amorphous phase containing Si, Y, Al and O, but it did not contain Ti. Formation of TiN from TiO2 by reduction and nitridation was suggested based on thermodynamic calculations and crystal chemical considerations. High density crystalline imperfections may be introduced during reduction of TiO2 particles. It is believed that the grain-boundary distribution of round-shaped TiN particles contributes to the improvement of wear resistance of Si3N4 ceramics.

Electrochemical STM observation of LiMn2O4 thin films prepared by pulsed laser deposition

Abstract Spinel LiMn2O4 thin films were prepared by pulsed laser deposition. The surface morphology change of the film with potential cycling between 3.5 and 4.25 V was observed in 1 M LiClO4/PC by electrochemical scanning tunneling microscopy. After cycling, small round-shaped particles of 120–250 nm in diameter appeared on the surface. The number of the newly formed particles increased with repeated cycling while the size decreased. The observed morphology change suggested that the small particle were formed from the solution through a kind of dissolution/precipitation reactions.

Lipid-induced organization of a primary amphipathic peptide: a coupled AFM-monolayer study.

To better understand the nature of the mechanism involved in the membrane uptake of a vector peptide, the interactions between dioleoylphosphatidylcholine and a primary amphipathic peptide containing a signal peptide associated with a nuclear localization sequence have been studied by isotherms analysis of mixed monolayers spread at the air-water interface. The peptide and the lipid interact through strong hydrophobic interactions with expansion of the mean molecular area that resulted from a lipid-induced modification of the organization of the peptide at the interface. In addition, a phase separation occurs for peptide molar fraction ranging from about 0.08 to 0.4 Atomic force microscopy observations made on transferred monolayers confirm the existence of phase separation and further reveal that mixed lipid-peptide particles are formed, the size and shape of which depend on the peptide molar fraction. At low peptide contents, round-shaped particles are observed and an increase of the peptide amount, simultaneously to the lipidic phase separation, induces morphological changes from bowls to filamentous particles. Fourier transform infrared spectra (FTIR) obtained on transferred monolayers indicate that the peptide adopts a beta-like structure for high peptide molar fractions. Such an approach involving complementary methods allows us to conclude that the lipid and the peptide have a nonideal miscibility and form mixed particles which phase separate.

Estructura y textura de la fase Al<sub>3</sub>CaZn en una chapa laminada de la aleación superplástica Al-5 % Ca-5 % Zn

The structure of the intermetallic phase Al3CaZn present in the superplastic sheet alloy Al-5 % Ca-5 % Zn has been determined by means of x-ray diffraction (XRD) and electron diffraction (TEM). Also, the texture of this phase has been studied by means of pole figures and the orientation distribution function (ODF). The Al-5 % Ca-5 % Zn alloy is formed by a fine grained aluminum matrix (d ≈ 2-3 μm) and 20 % vol. of Al3CaZn in the form of round-shaped particles with 0.2-0.5 μm diameter. This alloy undergoes superplastic behavior in a wide range of strain rates and temperatures. It has been found in this work that the structure of the second phase is body-centered tetragonal, with lattice parameters a = b = 0.422 nm and c = 1.131 nm. The texture of the alloy is formed by the fiber , i.e., the crystallites are oriented preferentially with the c-axis perpendicular to the rolling plane. The texture sharpens after severe annealings.

Photoluminescence of confined excitons in nanoscale C 60 clusters

Formation of C 60 aggregates has been found in toluene, benzene and carbon disulfide (CS 2) solutions by means of photoluminescence spectroscopy. From the detailed investigation of the temperature dependence of luminescence, it has been confirmed that the C 60 aggregates are formed at freezing temperature of these solvents in the cooling process. The 0 0 transition energy of their luminescence spectrum has been found to be blue-shifted in comparison with that of C 60 crystal. It has been also found that the irradiation of ultraviolet light upon the C 60 aggregates in benzene at 265 K transforms them to stable substances under atmosphere, which look like round-shaped nanoscale particles in the high-resolution TEM images.

Leupeptin causes an accumulation of lipofuscin-like substances and other signs of aging in kidneys of young rats: further evidence for the protease inhibitor model of aging.

The "protease inhibitor model of aging" has been proposed on the basis of observations that young rat brains, livers, and retinas exposed to a protease inhibitor, leupeptin, accumulate lipofuscin-like substances (LLS) that are similar to age pigment, and also display a variety of other manifestations of aging. In order to validate this hypothesis in more general terms, the present study reports attempts to induce age-like changes in kidney cells of young rats. Male F-344 rats (4-5 weeks of age) were continuously infused intraperitoneally (i.p.) with various doses of leupeptin (1-50 mg/100 g/day) for 2 weeks. Control animals received saline solution and normal aged rats (27-30 months-old) received no treatment. Animals were sacrificed and subjected to histological examination. In kidneys of leupeptin-, but not saline-treated rats, generally round-shaped PAS-positive particles were clearly observed, which were predominantly distributed in proximal convoluted tubules, and which resembled particles in normal aged kidneys. With increasing drug doses, particles tended to become bigger and more numerous. The dominant accumulation of LLS in cells of the proximal convoluted tubules had a fine morphologic configuration that resembled age pigments in old rats. Also, there was a concomitant thickening of the basement membrane that was present in leupeptin-treated and aged kidneys, but not in controls. The results, therefore, support the protease inhibitor model of aging and provide an experimental tool for probing the cellular mechanisms of aging.

Novel methods of microparticulate production: application to drug delivery.

The purpose of this paper is to present two novel techniques, electrostatic spraying and oscillating capillary nebulization, for the production of microspheres of uniform reproducible particle size distribution. Cholesterol was chosen as a model compound to show the utility of both procedures. The processes for each method are described, illustrating their simplicity and absence of an external detrimental phase. Scanning electron microscopy was used to assess morphology while laser diffraction analysis was used to determine particle size. Electrostatic spraying of cholesterol yielded particles of round shape, smooth surface, and uniform distribution of particle size ranging between 10-30 microns and 100-300 microns. Oscillating capillary nebulization of cholesterol molten at 170 degrees C produced microspheres with an average diameter ranging from 22 microns to 30 microns when gas back pressures controlling the vibration of the capillary ranged from 60 to 90 psi. Electrostatic spraying and oscillating capillary nebulization are one-step procedures that result in high production yields. Both techniques are easy to set up and afford both production speed and reproducibility. The absence of a detrimental external phase makes them particularly appealing for the microencapsulation of proteins and polynucleotides in polymers with low melting temperatures. The feasibility of production of cholesterol microspheres can be extrapolated to the production of excipient-free microspheres of steroids.

Evaluation of Homogeneity for Sintered Hydroxyapatite by CT-Values

Hydroxyapatite was prepared from calcium nitrate and disodium hydrogenphosphate solutions. Heating this at 1000°C for 1h yielded round-shaped hydroxyapatite particles with diameters of about 0.5μm. A green compact of the hydroxyapatite (green compact-I) was fromed by an uniaxial compression process (300kg/cm2), and then a green compact II was made by an isotropic compression (1000kg/cm2) of the green compact-I. A hydroxyapatite sintered body (porous structure) was obtained by heating the green compact-II at 1150°C for 2h. Internal homogeneities of these green compacts and sintered bodies were evaluated from CT-values measured with a CT-scanner. Depending on the method proposed in this study to indicate homogeneity using the ratio of the standard deviation of linear absorption coefficient to linear absorption coefficient, the green compact-I was most homogeneous, followed by the green compact-II. The sintered body was comparatively inhomogeneous.