Ultrafme particles

Oberdorster G, Sharp Z, Atudorei V, Elder A, Gelein R, Kreyling W, Cox C (2004). Translocation of inhaled ultrafme particles to the brain. Inhal. Toxicol. 16 437 145. 

Oberdorster G, Oberdorster E, Oberdorster J (2005) Nanotoxicology an emerging discipline evolving from studies of ultrafme particles. Environ Health Perspect 113 823-839. 

In Figure 3, the simulated ultrafme aerosol concentrations (in the size ranges defined in the legend) are compared to observations. It is remarkable that, even though sulfuric acid concentrations remained quite low most of the day (never exceeding lxl07/cm3), the ultrafme particle count rose dramatically late in the morning (after -10 00). Model calculations that include the IMN mechanism reproduce this behavior, whereas classical BHN theory would have forecast no particle formation under the circumstances. The calculated ultrafme particle abundances also appear to respond to... 

Phase 2. Intermediate precursor supersaturation causes selective ion activation and growth in an environment of charged and neutral molecular clusters generates ultrafme particle concentrations of 1000 s-10,000 s/cm3 [33],... 

Microtrac Ultrafme Particle Analyzer operates using photon correlation spectroscopy in the controlled reference mode, extends Microtrac s lower size to 0.003 with an upper limit of 6.5 pm. 

Leeds and Northrup Microtrac Ultrafme Particle Analyzer (VPA) uses the controlled reference method, using a sapphire tipped waveguide that collects back-scattered light within 100 pm of probe tip, to cover the size range 0.003 to 6.5 pm. 

Leeds and Northrup Microtrac Series 9200 Ultrafme Particle Analyzer Model 9230 operates in the 0.003 pm to 6 pm size range (Figure 10.19) and gives reproducible results in the concentration range 2 to 2000 ppm... 

The synergy effect which is observed on composition as 4% Si02 with 5% CaCOs can be explained as an expansion of the decohesion zone around CaC03 particles due to the presence of a high density of well dispersed ultrafme particles. 

In addition to the three modes described above, recent measurements have shown that there is often a distinct particle mode under 10-nm diameter (Fig. 2). There is no current agreement for the name of particles in this mode, which are interchangeably called ultrafme particles, nanoparticles, or nucleation mode particles. There are also alternative definitions for these terms, which can be a source of confusion. For example, the term ultrafme particles is sometimes employed to refer solely to particles with Dp = 3 -10 nm (e.g., in nucleation studies) or to all particles with Dp < 100 nm (e.g., in health and emission studies). Similarly, the term nanoparticles is sometimes employed as a description for all particles of Dp < 50 nm (regardless of mode), sometimes for particles of 10-nm diameter or less, and occasionally for any particle with Dp < 1 pm. In this review we use the common current definitions of ultrafme particles as those with Dp < 100 nm and nanoparticles as those with Dp < 50 nm. 

As shown in Figure 1, within an atmospheric aerosol the smallest particles usually dominate the total number of particles, while the accumulation and coarse modes often determine the total surface area and volume (i.e., mass), respectively. For example. Figure 3 shows results from a study in Atlanta where nanoparticles (Dp = 3-10 nm) and nano- and ultrafme particles (Dp = 10-100 nm) contributed approximately 30 and 60%, respectively, to the total particle number concentration (Dp < 2 pm). However, in terms of particle mass, the accumulation mode particles were dominant, and nanoparticles with Dp < 10 nm contributed insignificantly. 

As discussed previously, growth and chemical reactions of nanoparticles lead to changes in their compositions. Thus the inferences in composition described above should hold only for fresh nanoparticles correlations should weaken with atmospheric aging of the particles. It would be desirable to compare these expectations against actual field measurements of particle compositions. However, quantitative measurements of the chemical composition of ambient ultrafme particles are available only for the larger members of this class (Dp 50-100 nm). Available data, from urban areas in Southern California, indicate that organic compounds represent approximately half of the ultrafme particle mass. The remaining mass is contributed by trace metal oxides, elemental carbon, sulfate, nitrate, ammonium, sodium, and chloride (Cass et al. 2000). 

Health effects. More epidemiological and clinical studies are needed to further examine the hypothesis that nano- and ultrafme particles are responsible for adverse human health effects. It will be especially valuable to perform experiments that allow elucidation of the particle properties that are responsible for toxicity, such as number concentration, surface area concentration, or specific chemical species. 

Brock CA, Schroder F, Ka rcher B, Petzold A, Busen R, Fiebig M (2000) Ultrafme particle size distributions measured in aircraft exhaust plumes. J Geophys Res 105 26555-26567 Brunekreef B (2000) SESSION 2 What properties of particulate matter are responsible for health effects Inhal Toxicol 12 (Suppl 1) 15-18... 

Ultrafme Particle Size 27, 28, 97, 98 - hydrous aluminrun silicate. 27 and 28 are spray dried... 

Precise control of nanometer-scale structures has become one of the most important subjects in both physics and chemistry. Of many nano-scale materials, ultraflne particles are of intense interest as they are expected to show unique properties which fine particles have never possessed. Usually ultrafme particles are prepared by grinding an already fine particle. We discuss here the synthesis of such molecular-based ultraflne particles through supramolecular self-assembly of 10 simple molecular components. Further, their stability and inclusion and catalytic properties will be described. 

The various compositions of catalyst were synthesized using citrate precursor technique to get ultrafme particles. For example to get ZnFe204 the precursor Zn3Fe6(C6Hs07)8 I2H2O was calcined at 550° C for 5h to get final product. 

If ultrafme particles can be agglomerated, the mass of the new entity is equal to the sum of aU particles in the structure and mass related forces as well as inertia increase proportionately. After agglomeration, ultrafine particles, in their new form, can be removed in standard dust collection devices such as cyclones and packed bed filters. 

Similar applications of tumble/growth agglomeration are conceivable if powders or suspensions of metallic solids (obtained by precipitation or other ultrafme particle formation methods, for example in nanotechnology (Chapter 11)) must be converted into a dry, freely flowing granular material for further processing. 

Ultrafme particles (UFP), defined as being in a size range from a few micrometers down to nanometers, feature natural adhesion tendencies, which strongly increase with decreasing linear dimensions or increasing specific surface area. On the one hand, this may be a disadvantage, because nanosized particles always exist as agglomerates (Fig. 11.1, Chapter 11) and, if individual nanoscale particles are required, special... 

While for quite some time particles with sizes down to a few hundred micrometers have been successfully removed by conventional dust collection (mostly using gravitational and centrifugal or other field forces) and dry and wet filtration, air borne (Fig. 8.1) and suspended solid pollutants continued to be a great problem. Because of the small mass of fine and ultrafme particles they do not settle, even if high-field forces are produced, and they follow the flow lines in filter media so that impacts, which are necessary for collection (Fig. 8.2), do not take place. 

Ultrafme particles that are suspended in a fluid exhibit Brownian motion, a random movement resulting from the impact with molecules of the fluid surrounding the particles. In spite of the randomness of the motion, it is very unlikely that particle-to-particle impacts will occur because the amplitudes of the movement and the par-... 

In addition, existing and new innovative technologies use the phenomena and fundamentals of agglomeration for purposes other than size enlargement. Specifically, they produce changes or improvements of the properties of particulate solids or achieve modifications of the surfaces of solids. Others manipulate individual particles or deposit ultrafme particles onto substrates in a controlled manner and subsequently bond them with the base material and/or with each other. 

We report here the synthesis of tailor-made hollow silica nano spheres containing ultrafme particles of Rh, Ir or Rh/Ir bimetals in their cavities by using a crystal template method in a reversed micelle system. The preparation of ultra fine particles in a reversed micelle system has received considerable... 

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