Average Particle Dimensions Research Articles

Magnetic properties and large coercivity of MnxGa nanostructures

To investigate structure–property correlations, high-coercivity MnxGa nanoparticles were synthesized by the method of sequential deposition of Ga and Mn fluxes using molecular beam epitaxy. Spontaneous nanostructuring was assisted by the use of an Au precursor and thermal annealing, and the growth properties, structure and magnetic properties were characterized. Atomic force microscopy revealed average particle dimensions of 100nm and X-ray diffraction revealed a dominant tetragonal D022 crystal structure. Magnetic characterization at room temperature identified the presence of two magnetic phases, dominated by a high-coercivity (2.3T) component in addition to a low-coercivity component.

Effective thermal conductivity of sintered porous media: Model and experimental validation

A model to estimate the effective thermal conductivity of sintered porous media for heat pipes is proposed in this paper. An elementary cell of a porous media is physically modeled as two metallic hemispheres in contact with a fluid film around them. The electrical circuit analogy is employed to determine the heat leaving the top and reaching the bottom of the cell. The thermal circuit consists of two parallel resistance paths, one for the solid spheres in contact and the other for the heat transfer in the fluid. A literature model is employed to calculate the thermal resistance within the hemispherical particles. Also, literature models are used for the determination of the geometry of the neck produced between particles during the sintering process. The neck dimensions are used to estimate the neck thermal resistance, which is in series with the hemisphere resistances. Effective thermal conductivity experimental data were obtained for porous materials produced with atomized copper powder, with particle diameters ranging from 20 to 50μm. The comparison between present model and data is good. Statistics of the particle size distribution is employed to determine average particle dimensions. The porosity and permeability of the material tested was characterized in the laboratory. The samples were tested in three conditions: vacuum and saturated with distilled water or methanol. Literature models for the effective thermal conductivity for bed packed (not sintered) porous media were also compared with the present model and data results.

Karakteristik Fisik Bubuk Kopi Arabika Hasil Penggilingan Mekanis dengan Penambahan Jagung dan Beras Ketan

Size reduction applied on Arabica Coffee bean may change its physical properties, where these properties are utilized for designing process including packaging and appliances for further processes. This research aims to investigate physical characteristics of Arabica coffee powder with addition of corn and rice milled through mechanical process. This experiment used two mechanical mills including hammer mill and disc mill. Before it is milled, coffee was mixed with other materials including corn and rice. Parameters observed were yield, moisture content, bulk density, and angle of respose, particle uniformity index, fineness modulus, and the average particle dimensions. Based on the results obtained, it was revealed that moisture content of each test still meet SNI standard with the maximum of 7%. Bulk density of coffee powder resulted using disc mill was higher compared with hammer mill. However, particle generated from milling process may be categorized as powder with medium cohesiveness based on its angle of repose. Dimensional average particle is proportional to the fineness modulus of coffee powder produced. Highest fineness modulus obtained from coffee powder without additives, and using a hammer mill is equal to 4.37 with the highest average dimensions of 2.05 mm, while the lowest fineness modulus that the coffee powder without any additional ingredients milled with a hammer mill is equal to 4.22, with the lowest average dimensions of 1.94 mm.

Characterization of synthetic hematite (α-Fe2O3) nanoparticles using a multi-technique approach

The aim of this work was to investigate the surface structure of aqueous hematite dispersions characterized by a large variability of morphology and particle size combining structural investigations obtained from Atomic Force Microscopy (AFM) and Transmission Electron Microscopy (TEM) techniques with in vitro particle size distributions and zeta potential measurements from Dynamic Light Scattering (DLS) technique, and we achieved a self-consistent and detailed characterization of hematite particles whose sizes and morphologies could be correlated to the synthesis conditions (type of added anion, Al substitution and pH). Surface AFM characterization provided an accurate analysis of particle microstructure and also indicated that the growth of microcrystals followed different surface roughness. DLS, AFM, and TEM techniques furnished complementary information on the average particle dimensions, whose variation could be attributed to the morphological difference of hematites, ranging from platy to regular or irregular hexagonal or ellipsoidal shape. Finally, a correlation between the average particle dimensions and the measured zeta potential was also been found in aqueous dilute suspensions characterized by neither pH nor-ionic-strength-control, for which a drop of zeta potential from positive to negative values was detected for hematite particle dimensions larger than a threshold size of ∼150nm.

Intracellular protein delivery by hollow mesoporous silica capsules with a large surface hole

We prepared cell membrane-permeable hollow mesoporous silica capsules (HMSCs) by a simple new method. CTAB micellar assembly in cholesterol emulsion gave rise to a novel capsular morphology of the HMSC particles. The HMSCs consisted of mesostructured silica walls with a large surface hole (25–50 nm) and the average particle dimension was 100–300 nm. They exhibited high surface areas of up to 719.3 m2 g−1 and a mesoporous range of pores of 2.4–2.7 nm. The surface-functionalized HMSCs could also be prepared by a similar co-condensation method using tetraethoxysilane with various organoalkoxysilane precursors in the presence of cholesterol. These organically modified HMSCs could be further modified on demand. For example, a carboxy-functionalized HMSC could be surface-functionalized by a green fluorescent 5-aminofluorescein (AFL) through an amidation reaction to afford a fluorescent AFL–HMSC. The hollow capsular morphology of the HMSCs with a large surface hole enabled us to develop very efficient intracellular delivery systems for membrane-impermeable ions, molecules, and various functional proteins. Non-covalent sequestration and delivery of proteins as well as covalent linkage of fluorescent molecules on the silica surface are effective for this system. The highly negatively charged green fluorescent probe mag-fluo-4 could be intracellularly delivered into HeLa cells by HMSC without any difficulty. The HMSCs could also effectively transport large functional proteins such as antibodies into HeLa cells. The efficiency of protein delivery by HMSC seems to be 3–22-fold higher than that of mesoporous silica nanospheres (MSNs) based on confocal laser scanning microscopy (CLSM) analysis.

Structural characterization of amylose-long chain fatty acid complexes produced via the acidification method

Amylose molecular inclusion complexes, or V-amylose, have been studied as a possible nano-sized delivery system for unsaturated fatty acids. This study aimed to study three different structural levels of V-amylose produced via an acidification method. Molecular attributes were studied using XRD, DSC and 13C CP/MAS NMR, nanostructures using SAXS and AFM, and the microscopic level by SEM and AFM. 13C labeled fatty acids revealed head groups were entrapped in both COO- and COOH forms. SAXS data, showed that conjugated linoleic acid yield particles with the highest values for parameters like average crystalline lamellar thickness ( φ = 0.46) and characteristic particle dimension ( R g = 1011). AFM revealed surface roughness increases from 7.72 ± 4.34 nm to 11.54 ± 6.05 nm during the formation of V-amylose. The insights described contribute to the understanding of V-amylose structure and help establish a model for V-amylose structure which may prospectively be used in the fabrication of a novel delivery system.

Studying different dimensions of amylose–long chain fatty acid complexes: Molecular, nano and micro level characteristics

Recently amylose inclusion complexes, or V-amylose, have drawn much attention as a possible vehicle for the nanoencapsulation of unsaturated fatty acids. This study aimed to study three different structural strata of V-amylose, the molecular attributes using XRD, DSC and 13C CP/MAS NMR and the nanostructures using SAXS. Using these methods it was noted that decreased degree of fatty acid unsaturation induces the formation of more organized and well defined structures. Specifically, calculations based on SAXS data show that regardless of the crystallization temperature saturated SA yields the highest values for parameters like average crystalline lamellar thickness ( φ = 0.26) and characteristic particle dimension ( R g = 9.6). SEM shows this trend extends even into the microscopic level. Overall, this study shows that in the case of long chain fatty acids, increased fatty acid unsaturation impairs the structure of amylose inclusion complexes.

Characterization and reactivity of silicatic consolidants

In this study some results on the reactivity of silicatic consolidants employed for the conservation of valuable artistic and cultural porous materials are discussed. In particular, a colloidal suspension of silica made by particles with an average diameter of 10–15 nm, a sodium silicate and an ethyl silicate consolidant are studied. The chemical–physical characterization of xerogels achieved from the examined products were carried out determining the superficial area (BET method) and the average dimension of particles (SAXS) while the chemical structure of xerogels were investigated through NMR MAS spectroscopy of the 29Si nucleus. The investigation on reactivity between silica and stone support was executed by mixing consolidants with calcite and quartz powder to simplify as much as possible the system otherwise very complex. On silica produced by the three examined consolidants structural differences are revealed and these diversities can be responsible for the dissimilar reactivity of the silicatic systems towards the stone, in particular with regard to the carbonatic component.

Friction and wear behaviour of CrN coating at temperatures up to 500 °C

CrN coatings prepared by low arc deposition technology on hardened steel substrates were studied in this paper. Wear testing was done using a high temperature tribometer (pin-on-disc); the maximum testing temperature was 500 °C in order to prevent significant softening of substrate. Evaluation of friction coefficient with the number of cycles was measured at different temperatures and the wear rates of coatings and balls were determined. Three different materials were used as counter-parts: 100Cr6 bearing steel, Si 3N 4 and Al 2O 3 balls with a diameter of 6 mm. The coating microstructure was studied by X-ray diffraction (XRD) measured in situ up to 600 °C; the chemical composition was obtained by energy dispersive X-ray analysis (EDX). Mechanical properties of these coatings were studied by scratch and microhardness testing. Morphology of coating surface, ball scars, wear tracks and wear debris were examined by scanning electron microscopy (SEM). The experiments have shown strong dependency of tribological parameters on temperature. Wear of CrN coating sliding against the 100Cr6 ball was not measurable. Generally, the wear rate of coating increases with temperature when sliding with ceramic balls. The wear debris analysis has shown that the tribochemical wear is dominant at high temperature (Si 3N 4 balls), while the sliding process with the Al 2O 3 balls can be described as a three-body wear with the wear particles consisting mainly of chromium oxides conglomerated into relatively homogenous layer protecting coating from rapid wear. The average dimension of wear particles decreases with temperature, while the protecting layer thickness increases.

Evolution of microstructure of nickel base superalloy at high temperatures

The evolution of primary and secondary γ′ precipitates in the high γ′ volume fraction Rene 80 Ni based superalloy has been examined during aging at elevated temperatures for periods up to 1750 h. While the increase in average dimension of particles followed the cube rate Lifshitz, Slypzof and Wagner (LSW) law, r3t – r30=Kt, there were significant discrepancies between the experimental and theoretical particle size distributions (PSDs) and inconsistency with the kinetic constants associated with the two populations of particles. These differences are attributed to the influence of elastic coherency strains which have not been considered in conventional capillarity driven coarsening models. During thermal exposure at 871°C, coalescence of primary cuboidal γ′ was predominant in early stages of aging, while the microstructure was relatively stable at longer aging times. The stability of the microstructure at longer aging times is attributed to the formation of the network of closely spaced dislocations at the γ/γ′ interface which would cause the loss of internal misfit stresses associated with the growth. Secondary spheroidal γ′ particles were initially coarsened and their volume fraction gradually decreased until they completely dissolved after 500 h at 871°C or 1 h at 982°C.

Influence of ultrasound on nanostructural iron formed by electrochemical reduction

A method for control of particle dimensions of nanostructural amorphous iron powder obtained by electrochemical reduction under the effect of ultrasonic oscillations in reaction medium is described in this paper. Depending on the character of ultrasonic oscillations nanostructural powders were obtained differing both in average dimension and distribution of particle dimensions. In the case of simultaneous sonocation using ultrasonic vibrations with frequencies differing from each other by a factor of ten (20 and 200 kHz), the effect is complex, but includes narrowing of the average particle dimension.

FTIR, XRD, SEM and solid state NMR investigations of carbonate-containing hydroxyapatite nano-particles synthesized by hydroxide-gel technique

Nano-crystalline hydroxyapatite (HA), Ca 10(PO 4) 6(OH) 2 has been synthesized by a precipitate conversion technique using hydroxide gel at lower temperatures, e.g. 80 °C. HA crystallizes in hexagonal structure (space group: P6 3/ m) having lattice parameters: a=9.347 A ̊ and c=6.862 A ̊ and around 17 nm in crystallite-size for the 80 °C-heated sample. SEM micrographs show hexagonal crystallites of average particle dimensions approximately 50×20 nm for 80 °C heated sample. The structure analysis by XRD, FTIR, 1H and 31P MAS NMR show the existence of structural disorder at the particle surface that either does not form hydrogen bonding due to lack of adequate bonding parameters or forms a very weak dipolar bonding. The structural disorder has been explained as a result of chemical interactions between the phosphate groups either with the surface adsorbed water or the hydroxyl groups at the surface of the nano-particles.

An Investigation of Submicrostructural Evolution of Freshly Precipitated ZrO2 in Digestion for Ultrafine Sulfated ZrO2 Catalysts by SAXS Technique

Coupled with XRD, BET, and TEM, the small-angle X-ray scattering (SAXS) technique has been effectively used to probe and characterize the submicrostructure of freshly precipitated hydrous zirconia and its evolution during digestion. It has been found that fresh hydrous zirconia particles possess an average diameter of about 5 nm and rather rough surfaces describable in terms of fractal concepts. The digestion of zirconia precipitates at 100°C with their mother liquors may remarkably smooth the particles' rough surface and provoke fractal aggregation of the particles but make little change in average particle dimensions. A local dissolution–reprecipitation mechanism is regarded as a basic process to accompany particle surface smoothing, particle aggregation, and coarsening at the neck areas between joint particles, which may greatly strengthen the particle networks and enhance their resistance to crumbling while calcinated at high temperatures. On the basis of the submicrostructural features unraveled by SAXS, a coherent and significant physical picture has been raised out to demonstrate and interpret the relationship underlying the submicrostructure, the surface area variation, and the heating behavior of hydrous zirconia precipitates.

Ammonium ion adsorption with sepiolite: use of transient uptake method

Extent of environmental pollution is increased by technological development. Especially in industrialized areas, ecological equilibrium is affected by wastewater formed with industrial wastes. The more important pollutants for water are nitrogen compounds, which are threatening the human health. Ammonium removal from solution was investigated using Turkish sepiolite, having average particle dimension of 2.05 mm. Ammonium uptake experiments for two different adsorbent quantities were performed for the solutions having initial solution concentrations in the range of 8.333–222.23 mmol NH 4 +/l, and equilibrium isotherms were performed at 25°C. Around 60% ammonium removal, of which 90% was achieved within 500 s, was observed. Maximum adsorbed amount was 3.50 mmol NH 4 +/g. The exponential decrease model for the variation of the solution concentration with time, gave reasonably good agreement with the experimental data. The effective diffusion coefficients were estimated around 1.4×10 −10 m 2/s.

Production of protein nanoparticles by electrospray drying

The feasibility of producing relatively monodisperse and biologically active insulin particles by electrospray drying is demonstrated. The process entails dissolving dry insulin in an acidic ethanol–water solution. The solution is then electrosprayed and, after solvent evaporation, dry residues can be collected on suitable deposition substrates. Particles were sized visually, using a scanning electron microscope (SEM), and aerodynamically, using an inertial impactor. When electrosprays of nearly saturated solutions were operated in the stable cone-jet mode, impactor data showed that the particle average aerodynamic diameter ranged from about 88 to 110 nm in diameter and the distributions were quasi-monodisperse with relative standard deviation estimated at approximately 10%. SEM obsevations for the same conditions showed average particle dimensions ranging from 98 to 117 nm, with predominantly doughnut shapes. Smaller particles can be generated by decreasing the insulin concentration and/or by spraying smaller liquid flow rates. Although the maximum production rate for monodisperse insulin nanoparticles from a single cone-jet is low, at about 0.23 mg h -1 overall production can be increased by multiplexing the device with microfabrication techniques. Increasing production rate from a single cone-jet by at least one order of magnitude can be achieved also by increasing the liquid flow rate. The resulting particles have larger sizes, on the order of 600 nm, but particle monodispersity is compromised and particle morphology is drastically modified, probably as a consequence of a different electrospray operating mode. The biological activity of the electrospray-processed insulin samples was confirmed by comparing binding properties on insulin receptors against a control sample.

Generation of Monodisperse Protein Nanoparticles by Electrospray Drying

AbstractThe feasibility of producing relatively monodisperse and biologically active protein particles by electrospray drying is demonstrated. The process entails dissolving dry powder in an electrosprayable solution. The solution is then dispersed and, after solvent evaporation, dry residues can be collected on suitable deposition substrates. The process was demonstrated in the case of insulin. Particles were sized visually, using a scanning electron microscope (SEM), and aerodynamically, using an inertial impactor. When electrosprays of nearly saturated solutions were operated in the stable cone-jet mode, impactor data showed that the particle average aerodynamic diameter ranged from about 88 to 110 nm in diameter and the distributions were quasi-monodisperse with relative standard deviation estimated at approximately 10%. SEM observations for the same conditions showed average particle dimensions ranging from 98 to 117 nm, with predominantly doughnut shapes. Smaller particles can be generated by decreasing the insulin concentration and/or by spraying smaller liquid flow rates. The biological activity of the electrospray-processed insulin samples was confirmed by comparing binding properties on insulin receptors against a control sample. Although the maximum production rate for monodisperse insulin nanoparticles from a single cone-jet is low, at about 0.23 mg/hour, overall production can be increased by multiplexing the device with microfabrication techniques.

Precision equipment for reproducing particle sizes and numerical concentrations in aerosols, suspensions, and powders

Precision equipment is described for reproducing the unit of numerical concentration and size for particles in aerosols, suspensions, and powders in the concentration range from 4·107 to 4·1013 m−3 with average particle dimensions of 1–100 μm. The apparatus is based on small-angle laser-beam scattering and Beer's law. The optical system is described. The residual systematic error in reproducing the numerical concentration and unit does not exceed 12% in the above concentration and size ranges.

An analysis of Martian photometry and polarimetry

The physical parameters that influence the photometric and polarimetric properties of a solid are enumerated and used to guide a comparison of laboratory measurements with observations of Mars. Both the bright and dark areas of Mars are found to be covered by a fine powder. Furthermore, they appear to have a very similar chemical composition. It is argued that goethite is a major constituent of both regions. The particles on the bright areas are characterized by an average particle radius of 25 μ, while those on the dark areas have a mean size of 100 μ outside of the period of seasonal darkening and about 200 μ near the peak of the darkening. The seasonal darkening of the dark areas is the result of a change in the average particle dimension without an accompanying chemical change.The Martian atmosphere has much less of an influence on the photometric and polarimetric observations than was previously supposed. The observed lack of contrast in the blue appears to be largely the result of an intrinsic loss of surface contrast, and not an effect of a hypothetical atmospheric blue haze.

Spin-Reversing Scattering and Nuclear Magnetic Resonance in Superconducting Tin

The residual nmr shift in superconducting tin was measured in samples of average particle dimension between 150 and 600 \AA{} and in samples containing up to 1 at.% Pb or In impurity. The results suggest that the dominant contribution is attributable to the Pauli paramagnetism, which is modified by spin-reversing scattering in the superconductor. In this interpretation, the results are consistent with the BCS theory of superconductivity.

Studies on the Size and Shape of Clay Particles in Aqueous Suspension

AbstractThe size and shape of clay particles in aqueous suspension have been determined by means of five experimental techniques—electro-optical birefringence, ultracentrifugation, viscometry, optical transmission and electron microscopy. Five clay minerals—montmorillonite, illite, hectorite, nontronite and attapulgite—each subdivided into five size fractions, were studied. The average particle dimensions in each fraction are tabulated.An evaluation of the experimental techniques is presented. It is concluded that for a preliminary survey of the particle size and shape of clay minerals the technique of electron microscopy is best. However, once a model for the particles is obtained, a combination of the techniques of electro-optical birefringence and viscometry becomes more useful in characterizing the size and shape of the particles in suspension.