Showing papers on "Particle-size distribution published in 2005"

Characterization of indoor sources of fine and ultrafine particles: a study conducted in a full-scale chamber.

Abstract: Humans and their activities are known to generate considerable amounts of particulate matter indoors. Some of the activities are cooking, smoking and cleaning. In this study 13 different particle sources were for the first time examined in a 32 m3 full-scale chamber with an air change rate of 1.7 ± 0.1/h. Two different instruments, a condensation particle counter (CPC) and an optical particle counter (OPC) were used to quantitatively determine ultrafine and fine particle emissions, respectively. The CPC measures particles from 0.02 μm to larger than 1.0 μm. The OPC was adjusted to measure particle concentrations in eight fractions between 0.3 and 1.0 μm. The sources were cigarette side-stream smoke, pure wax candles, scented candles, a vacuum cleaner, an air-freshener spray, a flat iron (with and without steam) on a cotton sheet, electric radiators, an electric stove, a gas stove, and frying meat. The cigarette burning, frying meat, air freshener spray and gas stove showed a particle size distribution that changed over time towards larger particles. In most of the experiments the maximum concentration was reached within a few minutes. Typically, the increase of the particle concentration immediately after activation of the source was more rapid than the decay of the concentration observed after deactivation of the source. The highest observed concentration of ultrafine particles was approximately 241,000 particles/cm 3 and originated from the combustion of pure wax candles. The weakest generation of ultrafine particles (1.17 × 107 particles per second) was observed when ironing without steam on a cotton sheet, which resulted in a concentration of 550 particles/cm3 in the chamber air. The highest generation rate (1.47 × 1010 particles per second) was observed in the radiator test.

Sub-surface mechanical damage distributions during grinding of fused silica

Abstract: The distribution and characteristics of surface cracking (i.e. sub-surface damage or SSD) formed during standard grinding processes has been investigated on fused silica glass. The SSD distributions of the ground surfaces were determined by: (1) creating a shallow (18-108 {micro}m) wedge/taper on the surface by magneto-rheological finishing; (2) exposing the SSD by HF acid etching; and (3) performing image analysis of the observed cracks from optical micrographs taken along the surface taper. The observed surface cracks are characterized as near-surface lateral and deeper trailing indent type fractures (i.e., chatter marks). The SSD depth distributions are typically described by a single exponential distribution followed by an asymptotic cutoff in depth (c{sub max}). The length of the trailing indent is strongly correlated with a given process. Using established fracture indentation relationships, it is shown that only a small fraction of the abrasive particles are being mechanically loaded and causing fracture, and it is likely the larger particles in the abrasive particle size distribution that bear the higher loads. The SSD depth was observed to increase with load and with a small amount of larger contaminant particles. Using a simple brittle fracture model for grinding, the SSD depth distribution has been related tomore » the SSD length distribution to gain insight into ''effective'' size distribution of particles participating in the fracture. Both the average crack length and the surface roughness were found to scale linearly with the maximum SSD depth (c{sub max}). These relationships can serve as useful rules-of-thumb for nondestructively estimating SSD depth and to identify the process that caused the SSD. In certain applications such as high intensity lasers, SSD on the glass optics can serve as a reservoir for minute amounts of impurities that absorb the high intensity laser light and lead to subsequent laser-induced surface damage. Hence a more scientific understanding of SSD formation can provide a means to establish recipes to fabricate SSD-free, laser damage resistant optical surfaces.« less

Size and composition of airborne particles from pavement wear, tires, and traction sanding.

Abstract: Mineral matter is an important component of airborne particles in urban areas. In northern cities of the world, mineral matter dominates PM10 during spring because of enhanced road abrasion caused by the use of antiskid methods, including studded tires and traction sanding. In this study, factors that affect formation of abrasion components of springtime road dust were assessed. Effects of traction sanding and tires on concentrations, mass size distribution, and composition of the particles were studied in a test facility. Lowest particle concentrations were observed in tests without traction sanding. The concentrations increased when traction sand was introduced and continued to increase as a function of the amount of aggregate dispersed. Emissions were additionally affected by type of tire, properties of traction sand aggregate, and driving speed. Aggregates with high fragmentation resistance and coarse grain size distribution had the lowest emissions. Over 90% of PM10 was mineral particles. Mineralogy of the dust and source apportionment showed that they originated from both traction sand and pavement aggregates. The remaining portion was mostly carbonaceous and originated from tires and road bitumen. Mass size distributions were dominated by coarse particles. Contribution of fine and submicron size ranges were approximately 15 and 10% in PM10, respectively.

The role of pore size and structure on the thermal stability of gold nanoparticles within mesoporous silica.

Abstract: Highly dispersed gold particles (<2 nm) were synthesized within the pores of mesoporous silica with pore sizes ranging from 2.2 to 6.5 nm and different pore structures (2D-hexagonal, 3D-hexagonal, and cubic). The catalysts were reduced in flowing H2 at 200 degrees C and then used for CO oxidation at temperatures ranging from 25 to 400 degrees C. The objective of this study was to investigate the role of pore size and structure in controlling the thermal sintering of Au nanoparticles. Our study shows that sintering of Au particles is dependent on pore size, pore wall thickness (strength of pores), and pore connectivity. A combination of high-resolution TEM/STEM and SEM was used to measure the particle size distribution and to determine whether the Au particles were located within the pores or had migrated to the external silica surface.

Particle Size Distribution in Highway Runoff

Abstract: Particles in highway runoff contain various sorbed pollutants, and many best management practices (BMPs) are selected for particle removal efficiency, which makes particle size distribution a crucial BMP design parameter. Particles between 2 and 1,000 μm in diameter were quantified for three rainfall events during the 2002–2003 rainy season at three highway sites in west Los Angeles. Rainfall, runoff flow rate, and a large suite of water quality parameters were also measured. An experimental protocol was developed for bottle cleaning, sample storage, and mixing that provided repeatable results. Particle aggregation occurred which required samples to be analyzed in less than 6 h ; the concentration of small particles decreased with a corresponding increase in the concentration of larger particles in stored samples. The particle concentration decreased as the storm progressed and the number of large particles decreased more rapidly than the total number of particles. Particles demonstrated a strong first fl...

Measurements of cloud droplet activation of aerosol particles at a clean subarctic background site

Abstract: [1] Two years of continuous aerosol particle size distribution measurements provided the basis for this cloud droplet activation study. The cloud droplet activation of aerosol particles was studied in Pallas, a clean background site in northern Finland. A slightly different approach compared with traditional methods is presented by measuring simultaneously the cloud interstitial particle size spectrum and a nearby out-of-cloud particle size spectrum. The main advantage of this approach is that one can determine the activated fraction of different-size particles over the whole submicron-size range and that a large number of cloud activation events can be analyzed. The number of cloud droplet activation days peaked in late autumn and was lowest in summer. The annual variation of “cloud droplet activation” events followed the annual pattern of low clouds (those below 1000 m). A relation was found between the total particle number concentration outside the cloud and the number of activated particles. A larger particle concentration led to a higher number of activated particles, a lower activation percent, and a larger activation diameter (D50). D50 was on average 80 nm and varied from 50 to 128 nm. The average fraction of activated particles during the cloud events was 47% and varied from 9 to 86%. The cleaner and colder air masses from the northern Atlantic or the Arctic Ocean had, on average, 15 nm lower D50 than the more polluted air masses from south and east containing more particles. The annual variation of the number of the activated particles and other variables were also closely related to the annual variation of particle concentration (high in summer and low in winter). On average 87 and 30% of accumulation and Aitken mode particles, respectively, were activated. Aitken mode particles were observed to cover up to 55% of the total number of activated particles (i.e., number of formed droplets), which demonstrates that they have a significant effect on cloud droplet activation and must be taken into account when estimating the aerosol indirect climate effects.

A statistical approach to estimate the 3D size distribution of spheres from 2D size distributions

Abstract: Size distribution of rigidly embedded spheres in a groundmass is usually determined from measurements of the radii of the two-dimensional (2D) circular cross sections of the spheres in random flat planes of a sample, such as in thin sections or polished slabs. Several methods have been devised to find a simple factor to convert the mean of such 2D size distributions to the actual 3D mean size of the spheres without a consensus. We derive an entirely theoretical solution based on well-established probability laws and not constrained by limitations of absolute size, which indicates that the ratio of the means of measured 2D and estimated 3D grain size distribution should be π/4 (≈.785). Actual 2D size distribution of the radii of submicron sized, pure Fe 0 globules in lunar agglutinitic glass, determined from backscattered electron images, is tested to fit the gamma size distribution model better than the log-normal model. Numerical analysis of 2D size distributions of Fe 0 globules in 9 lunar soils shows that the average mean of 2D/3D ratio is 0.84, which is very close to the theoretical value. These results converge with the ratio 0.8 that Hughes (1978) determined for millimeter-sized chondrules from empirical measurements. We recommend that a factor of 1.273 (reciprocal of 0.785) be used to convert the determined 2D mean size (radius or diameter) of a population of spheres to estimate their actual 3D size.

Application of Supercritical Carbon Dioxide in Energetic Materials Processes: A Review

Abstract: The preparation of micro- and nanostructured energetic materials has recently drawn considerable attention as a potential method that can be used to obtain energy release more rapidly than conventional materials. Formation of solid particles with well-defined properties (e.g., particle size, particle size distribution, particle shape) and free of solvent inclusions for production of energetic materials using compressed gases were studied. It is possible to process moderately solids, like energetic materials that are difficult to comminute due to their sensitivity to mechanical or thermal stress. The characteristics of compressed gases allow the variation of morphology of solid particles in a wide range. It is possible to produce crystalline particles with a small size and narrow size distribution without defects (i.e., free of solvent inclusions). In this paper, the different processes to form very fine particles of explosives and propellant with supercritical fluids are reviewed. The first method is the ...

Drop size distribution in highly concentrated liquid–liquid dispersions using a light back scattering method

Abstract: New data are presented on drop size distribution at high dispersed phase fractions of organic-in-water mixtures, obtained with a light back scattering technique (3 Dimensional Optical Reflectance Measurement technique, 3D ORM). The 3D ORM technique, which provides fast, in-situ and on-line drop distribution measurements even at high concentrations of the dispersed phase, is validated using an endoscope attached to a high-speed video recorder. The two techniques compared favourably when used in a dispersion of oil (density (p) = 828 kg m(-3), viscosity (mu) = 5.5 mPa s, interfacial tension (sigma(i)) = 44.7 mNm(-1)) in water for a range of 5-10% dispersed phase fractions. Data obtained with the ORM instrument for dispersed phase fractions up to 60% and impeller speeds 3 50 - 5 50 rpm showed a decrease in the maximum and the Sauter mean drop diameters with increasing impeller speed. Phase fractions did not seem to significantly affect drop size. Both techniques showed that drop size distributions could be fitted by the log-normal distribution. (c) 2005 Society of Chemical Industry

Deposition of polycrystalline thin films with controlled grain size

Abstract: Difficulties in controlling the grain size and size distribution in polycrystalline thin films are a major obstacle in achieving efficient performance of thin film devices. In this paper we describe a sputtering technology that allows the control of the grain size and size distribution in sputtered films without the use of seed layers, substrate heating or additives. This is demonstrated for three different materials (Cr, NiFe and FeMn) via transmission electron microscopy imaging and grain size analysis performed using the cumulative percentage method. The mean grain size was controlled only via the sputtering rate. We show that higher sputtering rates promote the growth of larger grains. Similar trends were obtained in the standard deviation, which showed a clear reduction with the sputtering rate.

Influence of Mie scattering on nanoparticles with different particle sizes and shapes: Photometry and analytical ultracentrifugation with absorption optics

Abstract: Nanoparticles are used in large quantities for very different applications. A precise determination of the diameter and the particle size distribution which is responsible for the application properties is therefore essential. Reliable methods for measuring the above mentioned quantities are photometric measurements and analytical ultracentrifugation with an UV optics detector. Both methods are ruled by the Mie effect, that is scattering and absorption of the particles as function of the diameter, the wavelength, and the shape of the particles. The extinction coefficients e=τ/c for spheres, rods, and core shell particles have been calculated and plotted over a wide range of the size parameter πd/λ. Two examples for multimodal latex particles and core shell particles have been given and demonstrate the applicability of the method.

Monte-Carlo simulation of soot particle coagulation and aggregation: the effect of a realistic size distribution

Abstract: The evolution of the morphology of primary soot particles was investigated in a laminar premixed flame with the emphasis on the effect of a realistic particle size distribution. A time-dependent Monte-Carlo method was used to calculate flame trajectories of single particles. In the nucleation zone of the flame, particles were grown by coagulation and simultaneous surface growth. The particles for coagulation were selected according to a pre-calculated size distribution obtained by solving the dynamics of the entire soot particle ensemble. In the post-nucleation zone, defined by the point of transition from coalescent to aggregate growth, only surface growth was applied to the particles. The simulation results provide further support to the notion that particle nucleation and the presence of small particles influence the morphology of primary particles and the location of transition. It is demonstrated that the mean size of subparticles comprising the primary particles is substantially smaller when using a realistic size distribution in the nucleation zone of the investigated flame. This, in turn, reduces the degree of aggregation of the primary particles at the time of transition to an extent that surface growth is able to recover their spherical shape in the post-nucleation zone.

Toner and production method of the same, and image forming method

Abstract: The object of the present invention is to provide a toner having a uniform composition of toner materials among toner particles, excelling in charge stability, enabling high-quality images without substantially causing fog and toner scattering, and having a small diameter and a narrow particle size distribution. The present invention also provides an effective production method of the toner, and an image forming method and the like using the toner. For this end, the present invention provides a method for producing a toner in which a dissolved and dispersed solution of toner materials is dispersed as dispersion particles in an aqueous medium containing no organic resin fine particles to prepare an oil droplet-in-water dispersion, and organic resin fine particles are added to the oil droplet-in-water dispersion to thereby granulate a toner in the presence of the organic resin fine particles.