Ultrafine Particle Size Research Articles

Preparation of Ultra-Fine Powder Using Supercritical Fluids: A Review

The size of ultrafine particles ranges between 1~1000nm, including metal, non-metallic, organic, inorganic and biological powder materials. Because of its inherent surface effect, small size effect and quantum effect, it has special optical properties, thermal properties, magnetic properties and mechanical properties which had been widely used in various industrial fields. Supercritical fluid technology has been used to obtain ultra-fine powder of several kind of materials. This work is focused on the systematic production of ultra-fine powder using RESS and SAS process. A systematic summary is made and different measures adopted according to the related circumstances are presented. We also summarize the effect of the process parameters of RESS and SAS process. The ongoing and more extensive research on mechanism and control measures of size, morphology and size distribution of particle should provide a better understanding of particle formation mechanism and achieve the goal of integrated use of different measures to control particle preparation process in the near future.

The Preparation Technique of Nanometer Molybdenum Trioxide by Hydrothermal Synthesis

The technique of hydrothermal synthesis is used to prepare nanometer molybdenum trioxide through controlling the parameters such as the acidification condition, the reaction temperature, the reaction time and so on. The technique is under high temperature and high pressure by water as the solvent. Synthesized molybdenum trioxide powder is characterized by XRD, SEM, and HRTEM. The optimal reaction time is 40h, the optimum reaction temperature is 170°C, and the optimum pH value is 1.0. The results indicate that powder has an ultrafine particle size, high purity, and narrow size distribution, good fluidity, light agglomerate and is perfect in crystal.

Characterizing ultrafine particles and other air pollutants at five schools in South Texas

This study examined five schools with different ventilation systems in both urban and rural areas in South Texas. Total particle number concentration, ultrafine particle (UFP, diameter < 100 nm) size distribution, PM(2.5) , and CO(2) were measured simultaneously inside and outside of various school microenvironments. Human activities, ventilation settings, and occupancy were recorded. The study found a greater variation of indoor particle number concentration (0.6 × 10(3) -29.3 × 10(3) #/cm(3) ) than of outdoor (1.6 × 10(3) -16.0 × 10(3) #/cm(3) ). The most important factors affecting indoor UFP levels were related to various indoor sources. Gas fan heaters increased the indoor-to-outdoor ratio (I/O ratio) of total particle number concentrations to 30.0. Food-related activities, cleaning, and painting also contributed to the increased indoor particle number concentration with I/O ratios larger than 1.0. Without indoor sources, the I/O ratios for total particles varied from 0.12 to 0.66 for the five ventilation systems studied. The I/O ratio decreased when the outdoor total particle number concentration increased. Particles with diameters <60 nm were less likely to penetrate and stay airborne in indoor environments than larger particles and were measured with smaller I/O ratios. From an exposure assessment perspective, schools are important and little-studied microenvironments where students congregate and spend a large proportion of their active time. This study provides information for indoor and outdoor ultrafine particle concentrations at different types of school microenvironments. These data may allow future epidemiological studies to better estimate exposure and assess ultrafine particles health effects among students.

Research on ultrafine particle size measurement using small amounts of data

The paper puts forward a new method of ultrafine particle size measurement using small amounts of data of a dynamic light-scattering signal, and establishes an arithmetic model of the measurement by wavelet package transform. First, through the wavelet package transform, the ultrafine particle dynamic light-scattering signals were decomposed into multifrequency bands. Then, the noise of signals of different frequency bands were removed and the power spectrum of the wavelet packet coefficients of each frequency band was calculated. Finally, the ultrafine particle size distribution information could be deduced from inversing the power spectrum. The standard polystyrene particles of 100, 300, and 400 nm were measured using this method, and the inversion results indicated that this method can effectively remove noise and improve the accuracy of particle size measurement using small amounts of data.

Characteristics of airborne ultrafine and coarse particles during the Australian dust storm of 23 September 2009

Particle number concentrations and size distributions, visibility and particulate mass concentrations and weather parameters were monitored in Brisbane, Australia, on 23 September 2009, during the passage of a dust storm that originated 1400 km away in the dry continental interior. The dust concentration peaked at about mid-day when the hourly average PM2.5 and PM10 values reached 814 and 6460 μg m−3, respectively, with a sharp drop in atmospheric visibility. A linear regression analysis showed a good correlation between the coefficient of light scattering by particles (Bsp) and both PM10 and PM2.5. The particle number in the size range 0.5–20 μm exhibited a lognormal size distribution with modal and geometrical mean diameters of 1.6 and 1.9 μm, respectively. The modal mass was around 10 μm with less than 10% of the mass carried by particles smaller than 2.5 μm. The PM10 fraction accounted for about 68% of the total mass. By mid-day, as the dust began to increase sharply, the ultrafine particle number concentration fell from about 6 × 103 cm−3 to 3 × 103 cm−3 and then continued to decrease to less than 1 × 103 cm−3 by 14 h, showing a power-law decrease with Bsp with an R2 value of 0.77 (p < 0.01). Ultrafine particle size distributions also showed a significant decrease in number during the dust storm. This is the first scientific study of particle size distributions in an Australian dust storm.

Relationships of Outdoor and Indoor Ultrafine Particles at Residences Downwind of a Major International Border Crossing in Buffalo, NY

PP-31-006 Background/Aims: This aim was to assess the penetration of ultrafine particle (UFP) into homes and the resulting change in particle size distributions as particles move indoors near a major diesel traffic source. Because people spend most of their time in their homes, exposure estimates for epidemiological studies are generally determined using ambient concentrations. The findings of this study will contribute to improved size-resolved UFP exposure estimates for near roadway exposure assessments and epidemiological studies. Methods: During winter 2006, indoor and outdoor UFP size distribution measurements for particles with diameters from 5.6 to 165 nm were made at 5 homes in a neighborhood directly adjacent to the Peace Bridge Complex, a major international border crossing connecting Buffalo, New York to Fort Erie, Ontario. Monitoring with 1-second time resolution was conducted for several hours at each home. Participants were instructed to keep all external windows and doors closed and to refrain from cooking, smoking, or other activity that may result in elevating the indoor UFP number concentration. Results: Overall, particle concentrations indoors were lower and less variable than particle concentrations outdoors, with average indoor-outdoor ratios ranging from 0.1 to 0.5 (mean 0.34) for particles between 5.6 and 165 nm in diameter. Conclusion: With no indoor sources, the average indoor/outdoor ratios were lowest (0.2) for 20 nm particles, higher (0.3) for particles less than 10 nm, and highest (0.5) for particles 70–165 nm.

Spatial Measurements of Ultrafine Particles Using an Engine Exhaust Particle SizerTMwithin a Local Community Downwind of a Major International Trade Bridge in Buffalo, New York

Ultrafine particles (UFP) can be defined as having at least one dimension that is less than 100 nanometers. Because of their dimensions, they exhibit unique properties that affect atmospheric transport, exposures, and possibly health endpoints. Freshly generated Diesel particulate matter (DPM) is predominantly in the ultrafine particle size range size range, which in practice is defined by the detection characteristics of the sampling instrument. During two seasons, an Engine Exhaust Particle SizerTM (TSI, St. Paul, MN) detects particles over a range of 5.6–560 nm was used to continuously measure real-time particle size distributions along several streets that extend from the Peace Bridge (PB), a major international trade bridge, into a the nearby adjacent neighborhood that has reported a high prevalence rate of asthma (Lwebuga-Mukasa 2000). The Peace Bridge connects Buffalo, NY, USA to Fort Erie, ON, Canada. During summer 2004, one minute average particle number concentrations were continuously monitored along neighborhood streets near the Peace Bridge Complex (PBC) plaza out to about 2 km. Ultrafine particle counts as a function of bridge traffic showed downwind UFP levels at 300 m ranging from 60,000–70,000 p/cm3. Upwind background UFP levels at the shore line of Lake Erie were typically 8,000–10,000 p/cm3 under similar traffic and meteorological conditions. During winter 2006, additional measurements were conducted in front of several homes that were part of a separate indoor-outdoor exposure study (CitationMcAuley et al. 2010). Sampling at the homes was done during the weekdays when heavy diesel truck traffic was highest. Results showed that most of the UFP number concentrations fell between 10–20 nm in front of homes with UFP levels ranging from 59,000 p/cm3 at couple hundred m downwind to 81,000 p/cm3 several hundred m directly downwind of the Peace Bridge under similar diesel trucks traffic and meteorological conditions.

Sub-μm particle size distributions in a suburban Mediterranean area. Aerosol populations and their possible relationship with HONO mixing ratios

This study presents, for the first time, long-term data of sub-μm particle number size distributions in the particle size range of 14–670 nm in the Mediterranean area of Rome. Data are analysed in terms of possible aerosol populations. A particular “event” including also measurements of nitrous acid mixing ratios in the atmosphere is further analysed. High statistical correlations are established: At daytime, between the unknown HONO formation rate and the product of NO 2, J NO 2 , relative humidity, and sub-μm particle surface area concentration. At nighttime, between the volume concentration of the small Aitken mode particles and the HONO mixing ratios. The study would provide information on fine and ultrafine aerosol particle size distribution down to 14 nm in the Mediterranean suburban area of Rome. Besides, it would support previous works which have already provided several evidences for the existence of relations between the sub-μm aerosol populations and HONO. Our conclusions include speculations on possible daytime HONO formation mechanisms on particle surfaces in the accumulation mode size range, and nighttime mass formation mechanisms in common for the small Aitken mode particles and HONO.

Particle formation and growth at five rural and urban sites

Abstract. Ultrafine particle (UFP) number and size distributions were simultaneously measured at five urban and rural sites during the summer of 2007 in Ontario, Canada as part of the Border Air Quality and Meteorology Study (BAQS-Met 2007). Particle formation and growth events at these five sites were classified based on their strength and persistence as well as the variation in geometric mean diameter. Regional nucleation and growth events and local short-lived strong nucleation events were frequently observed at the near-border rural sites, upwind of industrial sources. Surprisingly, the particle number concentrations at one of these sites were higher than the concentrations at a downtown site in a major city, despite its high traffic density. Regional nucleation and growth events were favored during intense solar irradiance and in less polluted cooler drier air. The most distinctive regional particle nucleation and growth event during the campaign was observed simultaneously at all five sites, which were up to 350 km apart. Although the ultrafine particle concentrations and size distributions generally were spatially heterogeneous across the region, a more uniform spatial distribution of UFP across the five areas was observed during this regional nucleation event. Thus, nucleation events can cover large regions, contributing to the burden of UFP in cities and potentially to the associated health impacts on urban populations. Local short-lived nucleation events at the three near-border sites during this summer three-week campaign were associated with high SO2, which likely originated from US and Canadian industrial sources. Hence, particle formation in southwestern Ontario appears to often be related to anthropogenic gaseous emissions but biogenic emissions at times also contribute. Longer-term studies are needed to help resolve the relative contributions of anthropogenic and biogenic emissions to nucleation and growth in this region.

ChemInform Abstract: Preparation of Ultrafine Particles of Copper by Reduction in a W/O Emulsion System.

Ultrafine particles (UFP) of Cu were prepared by reduction in a w/o emulsion system, in which Cu(II) ions dissolved in aqueous droplets were reduced by a reducing agent. This method gave a very narrow particle size distribution. Moreover, the average size of UFP could be controlled by choosing the concentration of Cu ions.

A flat premixed flame reactor to study nano-ash formation during high temperature pulverized coal combustion and oxygen firing

This paper deals with the development of a laboratory reactor to study ultrafine ( D < 100 nm) and nano ( D < 30 nm) ash formation during pulverized coal combustion and oxy-firing. The reactor consists of an atmospheric pressure flat laminar premixed flame homogeneously doped with pulverized coal particles, monodisperse in size. It is accessible to diagnostics and sampling systems and it allows investigating the early stage of particle formation in a wide range of pulverized coal combustion operative conditions, in terms of gas composition and temperature. Coal combustion in an oxygen enriched gas mixture was investigated by performing on-line high resolution differential mobility analyses (DMA) and thermophoretic samplings for atomic force microscopy (AFM) image analyses. Ultrafine particle size distribution functions in a size range extending down to 1 nm have been measured. Three types of high volatile bituminous coals have been tested. Ultrafine particles, commonly neglected at the exhaust of pulverized coal combustors, form with huge number concentration and they represent a not negligible fraction of total ashes also in volume/mass. Nano-ashes are the most abundant in number and they also significantly contribute to ultrafine particle mass concentration. This not negligible contribution slight increases with the coal chlorine content while the shape of the nano-ash size distribution function is quite unaffected by the used coal type.

Measurements of ultrafine particle size distribution near Rome

This paper presents the results of an experimental investigation into the particle number concentration and size distribution of ultrafine particles (UFPs) near the city of Rome. Measurements were made using Scanning Mobility particle Sizer System (SMPS), at Montelibretti station in October and November, 2007. The major focus of this study was the evaluation of aerosol size distribution from 4 to 70 nm using scanning mobility particle size with a high resolution Nano Differential Mobility Analyzer (DMA). Cluster analysis and factor analysis were used to analyze the correlation of different diameter particle fractions with related gaseous pollutants and meteorological parameters. The results obtained showed that over the measurements period the daily average particle total number concentration was 19,000 cm− 3. There was a weekly cycle which makes it evident that the values on workdays were higher than the values on the weekends by a factor of around 1.3. The cluster analysis and factor analysis conducted with an hourly data set suggest that the N30–50 (number concentration of particles with diameter between 30 and 50 nm) and the N50–70 closely correlated to NOx and relative humidity, while the N4–10, N10–30 and N4–70 consort with solar radiation, temperature and wind speed.

Mechanochemical synthesis of nanostructured SiO 2–SiC composite through high-energy milling

Under ambient conditions, silica (SiO 2) and graphite (C) were milled in a ring mill at up to 18 000 s, followed by heat treatment at 1000 °C. A SiO 2–SiC nanocomposite with a ratio of 86.3:13.7 was obtained. The formation of an amorphous phase in the powder, the low degree of long-range order in the remaining crystalline particles, the large grain boundaries associated with the ultrafine crystallites, the high internal strain in the remaining crystalline SiO 2, the ultrafine particle size, and the intimate mixing of reactants increased the reaction kinetics and reaction driving force for the SiC phase in the nanocomposite.

In-situ synthesis of WC–Co composite powder and densification by sinter-HIP

Abstract In the present study, a complete route which integrates in-situ synthesis of WC–Co composite powder and sinter-HIP is proposed to prepare the ultrafine tungsten carbides. Owing to the in-situ reduction and carbonization reactions of WO2.9, Co3O4 and carbon black powders at 1000 °C, the composite powder with pure phase constitution and ultrafine particle size is synthesized with a rapid procedure. The WC–Co bulk material prepared by the sinter-HIP densification of the composite powder exhibits homogeneous and ultrafine microstructure, as well as the excellent mechanical properties. The proposed method shows potential to be developed as a promising industrial route owing to its advantages of low-cost raw materials and short-term in-situ reactions.

Relationships of outdoor and indoor ultrafine particles at residences downwind of a major international border crossing in Buffalo, NY

During winter 2006, indoor and outdoor ultrafine particle (UFP) size distribution measurements for particles with diameters from 5.6 to 165 nm were taken at five homes in a neighborhood directly adjacent to the Peace Bridge Complex (PBC), a major international border crossing connecting Buffalo, New York to Fort Erie, Ontario. Monitoring with 1-s time resolution was conducted for several hours at each home. Participants were instructed to keep all external windows and doors closed and to refrain from cooking, smoking, or other activity that may result in elevating the indoor UFP number concentration. Although the construction and age for the homes were similar, indoor-to-outdoor comparisons indicate that particle infiltration rates varied substantially. Overall, particle concentrations indoors were lower and less variable than particle concentrations outdoors, with average indoor-outdoor ratios ranging from 0.1 to 0.5 (mean 0.34) for particles between 5.6 and 165 nm in diameter. With no indoor sources, the average indoor-outdoor ratios were lowest (0.2) for 20-nm particles, higher (0.3) for particles <10 nm, and highest (0.5) for particles 70-165 nm. This study provides insight into the penetration of UFP into homes and the resulting change in particle size distributions as particles move indoors near a major diesel traffic source. Although people spend most of their time in their homes, exposure estimates for epidemiological studies are generally determined using ambient concentrations. The findings of this study will contribute to improved size-resolved UFP exposure estimates for near roadway exposure assessments and epidemiological studies.

A hybrid flotation–gravity circuit for improved metal recovery

The performance of a novel hybrid flotation–gravity concentration circuit was evaluated in which a Knelson Continuous Variable Discharge (CVD) separator was used as a scavenger for flotation tailings. Flotation tailings from the Eskay Creek Gold Mine were used for the study. Batch and pilot scale laboratory tests and plant trials were performed. Results of the batch and pilot tests showed that a product with a small yield (<5%), a high upgrade ratio and significant Au (sulphide mineral) recovery could be achieved. Plant trials confirmed the laboratory test results and hybrid flotation–gravity circuit in which CVD scavenging was followed by a regrinding-flotation process, could increase overall plant gold recoveries. In view of the results, there is also potential for improvements in metal recoveries for other sulphide mineral flotation systems. The paper describes how the results influence the selection of the target grind size and thereby impact grinding energy requirements, plant processing rate and could lead to further improvements in metal recovery by reducing flotation losses at the ultrafine particle size range.

TiO2 Nanoflakes Modified with Gold Nanoparticles as Photocatalysts with High Activity and Durability under near UV Irradiation

Titania nanoflakes modified with gold nanoparticles (NPs) were successfully prepared by depositing of Au NPs onto TiO2 nanoflakes using a direct “green” process in the absence of organic capping agents. The photocatalyst has been characterized by transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and UV−vis diffuse reflectance spectroscopy. Results of these analyses revealed that the Au NPs (∼1 nm) are homogeneously dispersed on the surface of highly crystalline TiO2 (anatase) nanoflakes with a narrow size distribution. Further, XPS studies indicate a strong electronic interaction between Au (in metallic state) and TiO2. Inspiringly, the photocatalyst showed high-efficiency and ultrastability for the degradation of the nonbiodegradable azo dye brilliant red X-3B under near UV irradiation with activity 4.3 times higher than that exhibited by the commercial Degussa P25. Durability tests established that the catalyst remains intact even after 15 consecutive experiments. The ultrafine metal particle size and strong metal−support interaction were considered as the key factors for the overall photocatalytic activity of the metal-semiconductor composite system.

Synthesis of Ultrafine Carbon Black by Pyrolysis of Polymers Using a Direct Current Thermal Plasma Process

A direct current thermal plasma system was developed and applied to synthesize ultrafine carbon black by using PS (polystyrene) and HDPE (high density polyethylene) as carbon sources. The precursors were pyrolyzed at different temperatures and the pyrolysis products were employed to investigate the actual synthesis of carbon black through the plasma jet. Spherical carbon nanoparticles with a high degree of turbostratic structure were obtained, showing a fingerprint graphite structure with a large surface area and ultrafine particle size. The carbon black was characterized by transmission and scanning electron microscopy, powder X-ray diffraction, Raman spectroscopy, and nitrogen physisorption. Particle size distribution and dispersion stability in solvents were also investigated.

Grain size, chemistry, and structure of fine and ultrafine particles in stainless steel welding fumes

A combined SEM–TEM study was performed on samples of metal inert gas (MIG) stainless steel (SS) arc welding fumes to characterize fine and ultrafine particle fractions in terms of size distributions, crystal structures, and chemistry. Overall observations indicate that welding fumes consist of a complex mixture of magnetite-like nanocrystals and non-spinel particles in different phases, with distinguishing grain size distributions and chemical features. Results confirm the great health hazard posed by MIG-SS ultrafine particles and illustrate the complex array of morphological and chemical features characterizing airborne dusts in working environments. The possible implications of these features in interaction and toxicity mechanisms are discussed.

Ultrafine Particles Deposition Inside Passenger Vehicles

Although commuting time typically accounts for only 6% of the day for Americans, it has become a significant source of exposure to ultrafine particles (d p < 0.1 μ m) from vehicular emissions. Particle deposition onto surfaces, as an important particle loss mechanism, has been studied extensively in the indoor environments. However since air velocities, surface area to volume ratios and other contributing factors differ greatly between indoor and in-cabin environments, conclusions from indoor studies may not be directly applied to in-cabin microenvironments. In this study, ultrafine particle deposition rates were characterized under a range of air velocities and surface areas conditions inside different types of passenger vehicles. A diesel generator was used as a particle source and a Scanning Mobility Particle Sizer (SMPS) was used to measure ultrafine particle size distribution inside the test vehicles. As in-cabin air velocities increased from natural convection (< 0.02 m s–1 ) to 0.65 m s–1 , ultrafi...