Composition Of Small Particles Research Articles

Methods of determining the amount of harmful particles released into the environment as a result of car tire wear

This article describes determining methods of metal emissions in the composition of small particles coming by brake mechanisms details and tire wear as a result of vehicle movement, and dust to be formed by comparative analysis on asphalt-concrete roads of different compositions. A significant contributor to particulate matter in cities is traffic-related sources. Traffic-related particles can be divided into exhaust particles released by the incomplete combustion of fuel and the volatilization of lubricants during combustion and formed by brake mechanism parts, tire wear and road surface wear, and accumulated due to turbulence caused by road traffic. The method of determining the metal concentration in the formed particles gives information on the physico-chemical properties of the particles.

Scanning electron microscopy as a useful tool for the analysis of non-conductive materials

Scanning electron microscopy (SEM) in the analysis of non-conductive samples became one of the most important methods for the investigation of material properties. In this work, we used SEM microstructure analysis for the investigation of the origin of cracks in granite composites and also, we tested the porosity inside the regenerated carbon biowaste, potentially used as a clean source of carbon for the future applications in materials production. Additionally, the morphology and the chemical composition of small particles used for the moulding processes of plastics were also tested. The importance of the microstructure investigation was supported by Energy-Dispersive X-ray Spectroscopy (EDS) often used for the chemical composition evaluation of these non-conductive materials.

Effective Protocol for Daily High-quality Direct Posterior Composite Restorations: Layering and Finishing.

Currently, there is a trend towards simplification of materials and clinical procedures. Simplification and quality can go together if the dentist works with materials and techniques that are well proven in vitro and in vivo. The placement of a high-quality class-1/2 direct posterior composite restoration can be time efficient following a standardized layering protocol and using composite materials that adapt well to the tooth surface and are able to mimic the natural tooth. When these materials are applied in a controlled way, finishing and polishing can also be shortened. In this article, an effective layering and finishing/polishing protocol for medium-sized class-1/2 direct posterior composite restorations is presented. Following the histo-anatomic buildup of natural teeth, dentin must be concave, as opposed to convex enamel. An isochromatic, medium-opaque, highly filled flowable composite is used to replace dentin. Enamel is replaced with a medium-translucent small-particle hybrid composite. Enamel is modelled in an anatomical way, following a successive cusp-by-cusp buildup approach. Clinical experience shows that the combination of both materials used according to this so-called bi-laminar histo-anatomical layering approach results in restorations that blend in very well within the surrounding tooth structure. Following a simplified finishing and polishing protocol, the composite restorations will have a correct contour, seamless margins, and a smooth, glossy surface.

Quantification of APT physical limitations on chemical composition of precipitates in Fe–Cr alloys

Among the different nano-features at the origin of embrittlement of Fe–Cr alloys and steels, α′ precipitates play a major role in alloys with Cr content higher than about 10at.%. If Atom Probe Tomography (APT) is recognized as an efficient technique for characterizing α′ precipitates, discussions remain on its ability to measure the actual composition of small particles. Two APT limitations are at the origin of these discussions: its lateral resolution (and on a smaller scale the depth resolution) and local magnification effects due to the difference in field evaporations between the matrix and the particles. In this study, the impacts of these two limitations are quantified for the first time using numerical approaches and an analytical model. This will provide an overview of the interpretation for the α’ particles chemical composition experimentally measured by APT.The results show that: (i) the major effect of local magnification is ion focussing with no mixing in the core of the particles for particle radius larger than 1 nm, (ii) lateral resolution is the main contributor to the composition bias. Depending on the lateral resolution, the core of the small particles may be diluted by matrix atoms but the dilution does not exceed 5.2 at.%. The extent of the decrease in measured Cr concentration of the particles depends on the Cr concentration difference between particles and the surrounding matrix.

Absolute effective elastic constants of composite materials

The objective is to determine the mechanical properties of the composites formed in two types, theoretically. The first composite includes micro-particles in a matrix while the second involves long, thin fibers. A fictitious, homogeneous, linear-elastic and isotropic single material named as effective material is considered during calculation which is based on the equality of the strain energies of the composite and effective material under the same loading conditions. The procedure is carried out with volume integrals considering a unique strain energy in a body. Particularly, the effective elastic shear modulus has been calculated exactly for small-particle composites by the same procedure in order to determine of bulk modulus thereof. Additionally, the transverse shear modulus of fiber reinforced composites has been obtained through a simple approach leading to the practical equation. The results have been compared not only with the outcomes in the literature obtained by different method but also with those of finite element analysis performed in this study.

Identification of long-lived clusters and their link to slow dynamics in a model glass former

We study the relationship between local structural ordering and dynamical heterogeneities in a model glass-forming liquid, the Wahnström mixture. A novel cluster-based approach is used to detect local energy minimum polyhedral clusters and local crystalline environments. A structure-specific time correlation function is then devised to determine their temporal stability. For our system, the lifetime correlation function for icosahedral clusters decays far slower than for those of similarly sized but topologically distinct clusters. Upon cooling, the icosahedra form domains of increasing size and their lifetime increases with the size of the domains. Furthermore, these long-lived domains lower the mobility of neighboring particles. These structured domains show correlations with the slow regions of the dynamical heterogeneities that form on cooling towards the glass transition. Although icosahedral clusters with a particular composition and arrangement of large and small particles are structural elements of the crystal, we find that most icosahedral clusters lack such order in composition and arrangement and thus local crystalline ordering makes only a limited contribution to this process. Finally, we characterize the spatial correlation of the domains of icosahedra by two structural correlation lengths and compare them with the four-point dynamic correlation length. All the length scales increase upon cooling, but in different ways.

The Study on the Precipitation Behavior of the Second Phase Particles for Fine Grain and High Strength IF Steel

The new type SFG HSS (super fine grain, high strength steel sheet) has been developed by adding solid-solution strengthening elements to conventional IF steel such as Si, Mn. The precipitation behavior of the second phase particles was observed and studied by a carbon extraction replica technique used transmission electron microscopy (TEM). The shape of the small second particles is similar to spherical and ellipse, the sizes of which are 10~30nm. It is seen that the particles are dispersed on the matrix. The precipitate composition of small particles is Nb (CN) and the precipitate composition of large particles is NbC examined by energy dispersive X-ray (EDX). It is noted that the yield strength is low as well as the tensile strength is high by the PFZ which is free of precipitate called precipitated free zone on the one side of the grain boundary. The results of microstructure shows that the second phase particles pinned on grain boundary not only can inhibit the grain growth, but also the grain can be fined.

Tuning ofL10atomic order in Co-Pt nanoparticles:Ab initioinsights

Monte Carlo simulation of the atomic configurational behavior of Co-Pt nanoparticles is performed in wide temperature-composition-size ranges. The simulation is based on bulk and local (inhomogeneous) cluster expansions calculated from first principles. A sharp drop of equilibrium $L{1}_{0}$ order is predicted for small equiatomic particles at low temperatures. This drop is explained by the interplay of two effects. First, the strong Pt and Co segregation to the first and second surface layers, respectively (core/Co/Pt or ``onion2shell'' profile) cause a depletion of Pt atoms within the core of small Co-Pt particles. Second, $L{1}_{0}$ is an adaptive structure on the fcc-restricted ground-state phase diagram of Co-Pt. Nevertheless, we show that a remarkable degree of $L{1}_{0}$ order can be restored by tuning the total composition of small Co-Pt particles.

Development of an improved method to perform single particle analysis by TIMS for nuclear safeguards

A method is described that allows measuring the isotopic composition of small uranium oxide particles (less than 1 μm in diameter) for nuclear safeguards purposes. In support to the development of reliable tools for the identification of uranium and plutonium signatures in trace amounts of nuclear materials, improvements in scanning electron microscopy (SEM) and thermal ionization mass spectrometry (TIMS) in combination with filament carburization and multiple ion counting (MIC) detection were investigated. The method that has been set up enables the analysis of single particles by a combination of analytical tools, thus yielding morphological, elemental and isotopic information. Hereby individual particles of certified reference materials (CRMs) containing uranium at femtogram levels were analysed. The results showed that the combination of techniques proposed in this work is suitable for the accurate determination of uranium isotope ratios in single particles with improved capabilities for the minor abundant isotopes.

Characterizing Mineral Dusts and Other Aerosols from the Middle East—Part 2: Grab Samples and Re-Suspensions

The purpose of the Enhanced Particulate Matter Surveillance Program was to provide scientifically founded information on the chemical and physical properties of dust collected during a period of approximately 1 year in Djibouti, Afghanistan (Bagram, Khowst), Qatar, United Arab Emirates, Iraq (Balad, Baghdad, Tallil, Tikrit, Taji, Al Asad), and Kuwait (northern, central, coastal, and southern regions). To fully understand mineral dusts, their chemical and physical properties, as well as mineralogical inter-relationships, were accurately established. In addition to the ambient samples, bulk soil samples were collected at each of the 15 sites. In each case, approximately 1kg of soil from the top 10 mm at a previously undisturbed area near the aerosol sampling site was collected. The samples were air-dried and sample splits taken for soil analysis. Further sample splits were sieved to separate the < 38 μ m particle fractions for mineralogical analysis. Examples of major-element and trace-element chemistry, mineralogy, and other physical properties of the 15 grab samples are presented. The purpose of the trace-element analysis was to measure levels of potentially harmful metals while the major-element and ion-chemistry analyses provided an estimate of mineral components. X-ray diffractometry provided a measure of the mineral content of the dust. Scanning electron microscopy with energy dispersive spectroscopy was used to analyze chemical composition of small individual particles. From similarities in the chemistry and mineralogy of re-suspended and ambient sample sets, it is evident that portions of the ambient dust are from local soils.

Characterizing Mineral Dusts and Other Aerosols from the Middle East—Part 1: Ambient Sampling

The purpose of the Enhanced Particulate Matter Surveillance Program was to provide scientifically founded information on the chemical and physical properties of dust collected over a period of approximately 1 year in Djibouti, Afghanistan (Bagram, Khowst), Qatar, United Arab Emirates, Iraq (Balad, Baghdad, Tallil, Tikrit, Taji, Al Asad), and Kuwait (northern, central, coastal, and southern regions). Three collocated low-volume particulate samplers, one each for the total suspended particulate matter, < 10 μ m in aerodynamic diameter (PM10) particulate matter, and < 2.5 μ m in aerodynamic diameter (PM2.5) particulate matter, were deployed at each of the 15 sites, operating on a ‘1 in 6’ day sampling schedule. Trace-element analysis was performed to measure levels of potentially harmful metals, while major-element and ion-chemistry analyses provided an estimate of mineral components. Scanning electron microscopy with energy dispersive spectroscopy was used to analyze the chemical composition of small individual particles. Secondary electron images provided information on particle size and shape. This study shows the three main air pollutant types to be geological dust, smoke from burn pits, and heavy metal condensates (possibly from metals smelting and battery manufacturing facilities). Non-dust storm events resulted in elevated trace metal concentrations in Baghdad, Balad, and Taji in Iraq. Scanning-electron-microscopy secondary electron images of individual particles revealed no evidence of freshly fractured quartz grains. In all instances, quartz grains had rounded edges and mineral grains were generally coated by clay minerals and iron oxides.

Correlation between chemical composition and size of very small oxide particles in the MA957 ODS ferritic alloy

ODS (oxide dispersion strengthened) alloys have superior creep properties. As it is well known, these excellent creep properties result from very fine oxide particles dispersed with the matrix. However, there is no common understanding about the nature of the very small oxide particles. Two hypotheses arise from the literature, 1: non-stoichiometric Y-, Ti-, O-enriched clusters and 2: stoichiometric Y 2Ti 2O 7. In this work, both chemically extracted residue method and extraction replica method were applied to the commercial ODS ferritic alloy, MA957. These samples were then observed using XRD (X-ray diffractometry) and FEG–STEM (field emission gun–scanning transmission electron microscopy) with EDS (energy dispersive X-ray spectrometer). From the results, it was concluded that the composition of small particles is related to the particle size. They exhibit at least two types of phase, 1: non-stoichiometric Y-, Ti-, O-enriched clusters from ∼2 to ∼15 nm (Y/Ti < 1) and 2: stoichiometric Y 2Ti 2O 7 from ∼15 to ∼35 nm. Based on the result, it is suggested that the appropriate increase of titanium content compared to yttrium content in oxide particles by modifying the chemical compositions of ODS alloys could be an effective way to obtain a finer dispersion of oxide particles.

On phase changes in nanosystems

The phase diagram of nanoparticles is known to be a function of their size and shape. Moreover, the fact that the matter reservoir is limited in nanosystems is shown here to lead to new effects. The effect of matter depletion leads to constraints on the nucleation and growth of new phases. The state diagram temperature–composition of small particles is treated within a regular solution model. In binary nanoalloys, the solubility and equilibrium compositions after the separation don't coincide.

Effect of weak nonsphericity on linear and nonlinear optical properties of small particle composites

A small particle composite in which the inclusions are slightly nonspherical and distributed in shape is considered. Within the framework of the mean-field approximation, the functions of linear and nonlinear optical responses are calculated in terms of a nonsphericity parameter specifying the width of the distribution function in shape. To estimate the effect of weak nonsphericity on the functions, their second derivatives with respect to the nonsphericity parameter are computed. The derivatives are shown to be complexly structured surfaces in the coordinates (Re(εi/εm), Im(εi/εm)), where εi and εm are the inclusion and matrix permittivity, respectively. Based on the results obtained, applicability area of the classical Maxwell Garnett theory is discussed. The main conclusion is that weak nonsphericity is significant only in the close vicinity of a dipole resonance of a single ball made of inclusion material. At the same time, the role of nonsphericity increases with decreasing the imaginary part of inclusion permittivity.

Interference technique in grazing-emission electron probe microanalysis of submicrometer particles

The distribution of X-ray radiation from a small particle, situated on a flat support and excited by an electron beam, is analyzed theoretically. The interference pattern, appearing within the region of grazing take-off angles, is shown to contain valuable information about the particle structure and composition. It also provides the resources for extracting this information that are valid even in conditions of extremely low signals (e.g. for very small samples), when the effect of background suppression for angles of the total reflection region is insufficient. Characteristic elements of the interference pattern are found that are relatively independent on the noise caused by the support radiation. Algorithms for this noise correction and elimination are proposed. An approximate formalism for the particle structure retrieval, based on the Fourier-transformation properties, is described. Potential applications of the proposed technique are illustrated with numerical models of spherical and hemispherical particles, both homogeneous and of ‘core-and-shell’ structures, with total sizes between 30 and 200 nm. The additional possibilities of studying the shape, structure and elemental composition of small particles have been demonstrated. The general conditions of the experimental realization of proposed methods are discussed.

PREDICTIVE AND BOUNDARY MODULUS MODELS FOR COMPOSITES WITH GREATER THAN ONE Ef/Em RATIOS

The authors have proposed a simple model that predicts dental composites' (small glass particle composites) elastic moduli very well. The fit of this model to other small particle composite materials is demonstrated in this paper to be the best of the current models. With volume filler fractions varying from 0 to 1, and Ef/Em ratios from 670, 000 to approximately 1.7, this paper compares results from the literature to the various models. The models analysed are, iso-strain, iso-stress, Hashin-Shtrikman's upper and lower, Ravichandran's upper and lower, Kerner's, Einstein's, Chantler's and the law of mixtures for particulate composites equations. The results show that the models that best predict the experimental data are Chantler's models. These models provide a guide to the expected modules for a two-phase reinforced particulate composite. At the extremes lie the Hashin-Shtrikman upper and lower boundaries which will include nearly all generated data but provide poor predictability.

Particle size effect on the complex permeability for permalloy composite materials

Complex permeability /spl mu/*(=/spl nu/'-i/spl mu/) of permalloy (Fe/sub 0.55/Ni/sub 0.45/) composite materials has been studied in the frequency range from 10 kHz to 2 GHz for two different particle sizes of permalloys (particle diameter d<45 /spl mu/m and d<6 /spl mu/m). Low frequency permeabilities of small particle composites have larger values than those of large particle ones and natural resonance frequency of small particle composites is lower than that of large particle ones. The ac electrical resistivity in low frequency range shows a drastic increase at about 40 vol% permalloy content with decreasing permalloy content indicating the disconnection of embedded permalloy particles. These properties can be realized considering the eddy current in composite materials.

Reduction of composite contraction stress through non-bonded microfiller particles

Objectives. To determine the reduction in composite polymerization stress through the addition of non-bonded microfiller particles. Methods. Microfillers that were unsilanated, silanated, and treated with a nonfunctional silane were added to dental resin and to a small-particle composite. The contraction stress generated by these materials was measured by polymerizing them between glass plates mounted in a mechanical testing machine. The maximum force was recorded 15 min after photo-initiation. Results were analysed by ANOVA (analysis of variance)/Tukey's test ( p≤0.05). Results. The addition of non-functional silanated microfillers to dental resin resulted in a significant 50% decrease in polymerization stress. The addition of unsilanated microfillers did not reduce the contraction stress. When added to small-particle composite, the unsilanated microfillers produced a significant 30% reduction in contraction stress compared to the composite containing silanated microfillers. The non-functional silanated microfillers did not reduce the contraction stress in the small-particle composite. Significance. The polymerization shrinkage of dental composite can impose high levels of stress on the tooth surfaces to which it is bonding. This contraction stress can lead to failure of bond formation with the surrounding tooth structure. Microfiller particles that are not bound to the resin matrix might provide sites for relief of internal stresses, significantly reducing contraction stress in dental composite.

Nonlinear optics of fractal nanomaterials: Small-particle composites and self-affine thin films

Fractal nanostructured materials, such as nanocomposites and self-affine thin films, are shown to possess giant optical nonlinearities. The enhancement results from the sub-wavelength localization of dipolar modes and strong local field fluctuations.

Investigations of precipitates in heat treated AgPd30/CuSn6 layers

The subject of the investigations are precipitation zones, which grew as a result of chemical diffusion in AgPd30/CuSn6 bimetals. These precipitation zones have been characterized by metallography, electron probe microanalysis and x-ray diffraction. The growth of precipitation zones in the plating layer and in the substrate layer in dependence on time have been determined. The use of x-ray diffraction alone for the identification of the precipitates could not supply satisfying results in every case. This problem was solved by the application of electron probe microanalysis using a correction method, which allows the estimation of the chemical composition of small particles.