A PM1.0/2.5/10 Trichotomous sampler has been developed to determine if the particles in the saddle point between the coarse and fine particle modes (specifically the 1.0 μm to 2.5 μm size range) are primarily coarse or fine mode particles. The sampler consists of a standard high volume sampler with two high volume virtual impactors (one with a cut size of 2.5 μm and the other with a cut size of 1.0 μm) inserted between the PM10 inlet and the 8 × 10 inch after filter. Filters in this sampler were analyzed with ion chromatography (IC) to determine SO4−2 concentrations, representing a specie primarily found in the fine mode aerosol and proton-induced X-ray emission (PIXE) for determining concentrations of Si, S, Ca and Fe, representing species normally found in coarse mode aerosols. Application of this sampler to Phoenix, AZ, representing an arid region, showed that particles in the saddle point consisted of about 75% of particles from the coarse mode and about 25% from the fine mode.
Particles within the nanometer size regime (1–100 nm) exhibit properties across quantum and classical mechanics. An example of the quantum mechanical nature of some particles includes their ability to bend light and change color appearance in suspension. An example of the classical mechanical nature of some particles includes their tendency to agglomerate in suspension. Both of these phenomenons are extensively studied in the literature and are the subject of many research projects that examine the utility of nanoparticles in biomedical and environmental applications. However, these unique properties have also been shown to induce unintentional toxicological effects in various biological and ecological systems. In this paper, the applications and implications of engineered nanoparticles in aqueous suspensions will be reviewed and discussed relevant to the particle’s structure on the nanometer size scale and its subsequent biological activity at the cellular level.
The particle size of conventional commercial phosphor powders used in lighting and displays is in the range from several micrometers to tens of micrometers and it is known that submicrometer-sized phosphors can facilitate a decrease in their consumption and improved resolution of phosphor screens. When the particle size becomes comparable to wavelengths of light, the optical properties of phosphor powders undergo remarkable qualitative changes so that the luminescence performance of nanophosphor screens, along with a very pronounced influence of the particle size, becomes dependent on several additional parameters such as packing density of nanoparticles, refractive index and chemical composition of the medium between them. This brings about both advantages and disadvantages which are discussed in this review of recent literature on the synthesis, deposition, and applications of nanophosphors.
Particulate fires and explosions cause substantial loss of life and property. With the goal of understanding, preventing, or at least mitigating particulate fire and explosion hazards, we review basics. We distinguish between ‘hazard’ and ‘risk’ and discuss the fire and explosion hazards of particulates, the many factors determining such hazards, hazard indexes, and ways to reduce fire and explosion hazards. While our primary goal is to improve safety, we briefly discuss how fundamental knowledge can be extracted from weapon technology based on particulate combustion. We review the prevention of and protection against particulate explosions and discuss ongoing and future research.
Generally, in order to learn about a certain quality of a population, a small portion (sample) is extracted and analyzed for the desired property. In order to obtain accurate information, the sample has to represent the stream it is taken from (plant feed, intermediate product, and/or final product). In materials processing sampling of materials (powders or slurries) is very important to the quality control and quality assurance purposes. This sample can be too large and has to be further subdivided, or too small and a two-stage sampler has to be introduced. In most cases, the desired property is determined by analyzing a sample as small as a few milligrams. In this regard, obtaining a representative sample is not as straightforward as it sounds. For homogeneous materials, it is easy to use statistical probabilities to estimate numbers and sizes of samples that accurately represent the whole population. However, this is not so easy in the actual practice especially dealing with inhomogeneous materials. Therefore, sampling representativeness, perhaps the most important aspect of sampling practice is emphasized in this paper. Sampling strategies and equipment for dry materials and slurries are discussed with links to related literature and sampling equipment manufacturers.
Metal oxide nano-microstructures are applied in photocatalytic surfaces, sensors or biomedical engineering, proving the versatile utilization of nanotechnology. However, more complex or interconnected nano-microstructures are still seldomly met in practical applications, although they are of higher interest, due to enhanced structural, electronic and piezoelectric properties, as well as several complex biomedical effects, like antiviral characteristics. Here we attempt to present an overview of the novel, facile and cost-efficient flame transport synthesis (FTS) which allows controlled growth of different nano-microstructures and their interconnected networks in a scalable process. Various morphologies of nano-microstructures synthesized by FTS and its variants are demonstrated. These nano-microstructures have shown potential applications in different fields and the most relevant are reviewed here. Fabrication, growth mechanisms and properties of such large and highly porous three-dimensional (3D) interconnected networks of metal oxides (ZnO, SnO2, Fe2O3) nano-microstructures including carbon based aerographite material using FTS approaches are discussed along with their potential applications.
Graphene (GR) is a flat monolayer of sp2-bonded single carbon atoms densely packed into a honeycomb crystal lattice. Due to its unique characteristics, GR is expected to contribute to enhanced nanoelectronic, bio-electronic devices, etc. in the near future. However, the single-layered GR sheets have a tendency to form irreversible aggregates or even to restack easily due to strong attraction between sheets. Preventing of aggregation and restacking of GR is achieved by the dimensional transition from flat sheets to fractal-dimensional, nearly spherical crumpled balls using aerosol spray pyrolysis. This review first introduces the fabrication of crumpled GR and GR-composite by aerosol spray pyrolysis, and then discusses the material properties of GR: strain-hardening, compression and aggregation-resistant behavior. Finally, we introduce effective applications of hollow crumpled GR balls for oil absorbent and crumpled GR-composites for glucose biosensor, respectively.
It is thought that inhaled dusts such as asbestos and man-made mineral fibers in the lung repeatedly induce persistent inflammation and finally lead to pulmonary fibrosis and respiratory cancer. There have been many studies about whether a variety of factors, such as oxidative stress including free radicals, chemokines, inflammatory cytokines, and fibrosis-related cytokines are related to pulmonary fibrosis, lung cancer and malignant mesothelioma. In this paper, we introduce the relationship between these factors and these diseases. It is important to determine what physicochemical properties of fibrous materials such as asbestos are related to asbestos-related diseases. We show the relationship between the physicochemical properties of not only asbestos but also other fibrous materials and inflammation, fibrosis and biopersistence in the lung.
The paper describes the physics of particle adsorption and the spontaneous dispersion of powders that occurs when they come in contact with a fluid-liquid interface. The dispersion can occur so quickly that it appears explosive, especially for small particles on the surface of mobile liquids like water. Our PIV measurements show that the adsorption of a spherical particle at the interface causes an axisymmetric streaming flow about the vertical line passing through the particle center. The fluid directly below the particle rises upward, and near the surface, it moves away from the particle. The flow, which develops within a fraction of second after the adsorption of the particle, persists for several seconds. The flow strength, and the volume over which it extends, decrease with decreasing particle size. The streaming flow induced by the adsorption of two or more particles is a combination of the flows which they induce individually. The flow not only causes particles sprinkled together onto a liquid surface to disperse, but also causes a hydrodynamic stress which is extensional in the direction tangential to the interface and compressive in the normal direction. These stresses can cause the breakup of particle agglomerates when they are adsorbed on a liquid surface.
Two types of powder processing techniques, Mechano-Chemical-Bonding (MCB) and MCB plus ball-milling (BM) with reduced time, have been employed to process the nickel-based oxide-dispersion-strengthened (ODS) alloy powders with composition of Ni-20Cr-5A1-3W-1.5Y2O3 to explore the alternate routes for fabricating, homogenizing and mechanical alloying (MA) the ODS alloy powders, which are usually processed by a prolonged ball-milling or rod-milling technique. In order to examine and evaluate the microstructure, morphology, blending homogeneity and MA effect of alloying powders, the commercial ball-milled ODS MA 956 alloy powders and experimental alloy powders processed by MCB only and MCB plus BM were subjected to microscopic and spectroscopic characterization and analysis using X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). A FIB (focus ion beam) lift-out technique was employed to prepare the TEM cross-section samples of processed powders. The results showed that the MCB plus BM with reduced time could produce the ODS alloying powders with homogeneous lamellate structure similar to MA 956 powders processed by conventional BM technique with a prolonged period of time. The ODS alloy powders processed by MCB plus BM are to be utilized to fabricate the bulk ODS alloy product in the further research phase.
Calcium carbonate particles with various shapes and morphologies were prepared via precipitation in an octylamine/water self-assembly bilayer systems. Crystal structure and shape of the CaCO3 particles were determined by the water to octylamine molar ratio R of the bilayer. At R = 16.0, phase pure calcite particles with a “hopper crystal” morphology were formed, the average particle size of the hopper crystal is 10 μm with well-defined edges on the hopper faces. Decrease the R ratio to 7.2 eventually leads to the formation of 3 μm tabular CaCO3 particles which are predominated by vaterite structure. For an intermediate R of 10.8, spherical vaterite aggregates and rhombohedral calcite particles were produced. Thermal decomposition of the CaCO3 particles was observed at around 710°C. The mechanism of particle evolution in the self-assembly bilayer, particularly the formation of “hopper crystal” calcite was discussed.
An ideal mass flow meter should have the following properties: it should be non-invasive so as not to disrupt the flow profile; it should be easily installed on the conveying line to provide on-line and continuous measurements; it should be able to provide an accurate indication of the mass flow rate regardless of the orientation of the measurement section, inhomogeneities in the solids’ distribution, irregularities in the velocity profile, or variations in particle size, moisture content and material properties.A mass flow meter as described in this paper has been developed which uses a thermal method, a direct, noninvasive approach to measuring the mass flow rate. The thermal method uses the principle of heat transfer to solid particles in a flowing fluid to determine the mass flow rate of particles. The mass flow meter is designed such that temperature sensors are located at two ends of a heated pipe section. In the experiments carried out, measurements of gas and solids’ temperature were taken and used to calculate the heat transferred to the solids. The mass flow rate obtained using the thermal mass flow meter was compared to that using load cells. The results obtained are analysed and presented in this paper.
Pulsed plasma processes open up the possibility of using very high plasma densities and modulated deposition in the synthesis of thin films and nanoparticles. The high plasma densities lead to a high degree of ionization of the source material, which creates new possibilities for surface engineering. Ions can, in contrast to atoms, be easily controlled with regard to their energy and direction, which is beneficial for thin film growth. Furthermore, ions can also increase the trapping probability of material on nanoparticles growing in the gas phase. The pulsed sputter ejection of source material also has other consequences: the material in the plasma and the material arrival on the growth surface will fluctuate strongly resulting in high level of supersaturation during pulse-on time. In this paper, an overview of the generation and properties of highly ionized pulsed plasmas is given. In addition, the use and importance of these types of discharges in the fields of thin-film and nanoparticle growth are also summarized.
In general a force will act on a particle illuminated by light or other radiation and absorbing part of the flux, and as a consequence a motion will result. It is caused by the interaction of gas molecules with the particle’s surface, which is hotter than the surroundings. This surface must be inhomogeneous with respect to accommodation and/or temperature. Gas molecules, impacting and reflected from the particle’s surface with accommodation, transfer some momentum from the particle and thus cause the force. For a temperature variation on the particle’s surface, the force points from the hot to the cold part, thus in the direction of the incident radiation, and under very special conditions it can be the opposite. A particle’s surface having a variation in accommodation coefficient will cause a force from the locations of higher to lower accommodation. Usually this will cause both a linear force and a torque. The latter in combination with Brownian rotation will result in a zero net force. But it is possible that an external torque acting on the particles causes an orientation. The torque can be caused by magnetic or electric fields on magnetic or electric dipoles in the particles or by gravity orienting inhomogeneous particles. For micrometer- and nanometer-sized particles, the photophoretic force can exceed gravity. Photophoresis is important for levitation in the stratosphere and for planet formation, it can also be used for on-line particle separation, or in clean-room technology or in geo-engineering.
Agglomerate size distribution is a pretreatment step in low grade heap leach operations. The present work focuses on modeling the evolution of size distribution in batch agglomeration drum. Up to now there has been no successful work on modeling of crushed ore agglomeration although the framework for population balance modeling of pelletization and granulation is readily available. Different batch agglomeration drums were used to study the agglomeration kinetics of copper, gold and nickel ores. The agglomerate size distribution is inherently subject to random fluctuation due to the very nature of the process. Yet, with careful experimentation and size analysis the evolution of size distribution can be followed. The population balance model employing the random coalescence model with a constant rate kernel is shown to work well in a lab scale agglomerator experiments. It was observed that in a small drum agglomerates begin to break in a short time whereas the growth is uniform in the larger drum. The experimental agglomerate size distributions exhibit self-preserving size spectra which confirms the applicability of coalescence rate based model. The present work lays out the fundamentals for applying the population balance concept to batch agglomeration, specifically crushed ore agglomeration. The experimental difficulties and how to overcome them are described.
Nanopowders or nanoparticles can be used as building blocks for the preparationof new materials with a prescribed structure. Monte Carlo simulations have shownthat the morphological properties (bulk porosity and surface roughness) of agranular deposit can be tailored by properly adjusting the velocity of theparticles approaching the deposit. Based on these theoretical predictions,experiments have been conducted to prepare nanostructured materials from carbonnanoparticles. By electrohydrodynamic atomization of a liquid suspension (carbonnanoparticles dispersed in ethanol), an electrospray of small droplets isgenerated. The charged droplets are driven by the electric field with theethanol evaporating along the droplet path, leaving dry nanoparticles thatdeposit on the collecting surface. The surface roughness of the resultingmaterial has been characterized as a function of the voltage drop. Moreover,catalytic suspensions of platinum supported on carbon nanoparticles (Pt/C) inNafion®-alcohol solutions have been electrosprayed overcarbon paper to prepare electrodes for proton exchange membrane fuel cells(PEMFC). The fuel cell power density was measured as a function of the platinumloading and the range of parameters leading to optimal platinum utilization wasobtained.
Core-shell nanoparticles and other nanostructured particles have high potential in applications such as heterogeneous catalysis and energy conversion and storage. However, a hurdle in their utilization is that typically, large amounts of such nanostructured materials are required. Gas-phase coating using atomic layer deposition (ALD, a variant of chemical vapour deposition) can be used to provide the surface of a particle with either an ultrathin continuous coating or a decoration of nanoclusters. When carried out in a fluidized bed, ALD is an attractive way of producing nanostructured particles with excellent scale-up potential.We demonstrate the fabrication of catalysts by deposition of the active phase (Pt) on fluidized nanoparticles (TiO2 P25) at atmospheric pressure. We show that ALD is a technique that 1) guarantees efficient use of the precursor; 2) allows precise control of the size and loading; 3) can be used for low and medium loading of catalysts by adjusting the number of repeated cycles; 4) leads to high-quality (low impurities level) end-products.
Large quantities of concrete waste are being produced continuously throughout the world, of which only a fraction are downcycled as construction backfill or as road-base. Seeking total concrete recyclability, this work concerns the development of microwave-based solutions for the separation of individual constituents of concrete. By focusing on the interaction between microwaves and concrete at the microscopic level, the paper makes important connections between local changes in the microwave-heated concrete texture and macroscopic changes in mechanical properties. Through analysis of the concrete texture using SEM imaging, it is found that the microwave heating of concrete causes fracture porosity. The size and shape of fracture porosity can be correlated with recycling performance indicators; namely aggregate liberation, concrete strength and product fineness. In particular, the work finds that only a short exposure to microwaves promotes the formation of a primary fracture network responsible for selective liberation of aggregates. Longer exposure to microwave heating creates a secondary network of smaller fractures that spreads throughout the cement phase, which is directly associated with the changes in mechanical strength of concrete and product fineness.The work introduces the concept of textural versus physical liberation, and shows that while microwave heating creates a high selective textural liberation of aggregate particles, the comminution of microwave-heated concrete may not necessarily yield high physical liberation. The work concludes that the key to designing a microwave-based process for concrete recycling resides in finding comminution and separation technologies that can best harvest the benefits of the textural and mechanical changes produced by microwave heating.
The Discrete Element Method (DEM) is increasingly used to simulate the motion of granular material in engineering devices. The most widely used shape to model granular particles is the sphere due to its simplicity which facilitates computations. However, with increasing advancement and popularity of the DEM approach, a more accurate representation of real granular shapes is becoming intensely important. This paper is an attempt to predict the bulk density of granular particles of cylindrical shape by DEM. The method used to model tube-like particles is the composite method where the tube-like particle is composed of a number of spherical sub-shapes. The results show that the DEM prediction of the bulk density of tube-like particles were accurate provided that a sufficient number of spherical sub-shapes was used to construct the particle. In addition, the bulk density of granular particles in the shape of 32-face polyhedrons was also investigated. It was shown that 32-face polyhedrons can be approximated as spheres provided that the rolling resistance of the shape is taken into consideration.
KONA Powder and Particle Journal No.31(2014), in the Editorial Board (p. EdBrd31_1) two editors’ affiliations were reversed. The right ones are as follows: L. Gradon (Univ. of Warsaw, POLAND), J. M. Valverde (Univ. of Seville, SPAIN).