Particles ultrafine

Kofman R ef al 1991 Melting of non-spherical ultrafine particles Z. Phys. D 20 267... 

The TEM is one of the most generally useful microscopes many thousands of them ate in daily use throughout the world. They ate appHcable to the study of ultrafine particles (eg, pigments abrasives and carbon blacks) as well as microtomed thin sections of plant and animal tissue, paper, polymers, composites of all kinds, foods, industrial materials, etc. Even metals can be thinned to sections thin enough for detailed examination. 

Fig. 11. Cross-sectional schematic of a Matsu2aka Elbow-Jet classifier where Fj = ultrafine particles, F2 = fine particles, M = medium particles, and...

As only a small proportion of the material is in contact with the roUs and friction on the rollers is low, hard materials can be processed with tittle wear. The high pressure action creates a slab of ultrafine particles which usually requires a low speed impact milting system to disagglomerate. Used in closed circuit with such a disagglomerator and an air classifier, such machines can reduce the energy requirement for fine grinding many minerals. 

Chemically Synthesized Powders. Chemical synthesis provides a means of produciag powders for manufacturiag advanced ceramics. Disadvantages of chemically synthesized raw materials are expense and difficulties ia scale-up and availabihty. Additionally, ultrafine particle-size powders produced by chemical synthesis pose some unresolved processiag problems ia the areas of handling and mixing. 

FIG. 20-6 Diagram of the Leeds and Northnip Ultrafine Particle Analyzer (UPA). 

For PM control from combustion sources, the tlue gas enters a coagulation area (e.g., ductwork, a chamber, or a cyclone) to reduce the number of ultrafine particles, and then a gas conditioner to cool the gas to a suitable temperature and saturation state. This is generally accomplished by means of a waste heat recovery heat exchanger to reduce the temperature of the flue gas or by spraying water directly into the hot flue gas stream. 

As discussed earlier, noncollagenous proteins, particularly albumin and to a lesser extent gelatin, in the form of microspheres and nanoparticles continue to be exploited as drug delivery systems. Oppen-heim (71) and Speiser (72) reviewed the technology developed to produce ultrafine particles, often referred to as nanoparticles. 

This method is one of the dry methods in which no chemical reaction is involved. Preparation of ultrafine particles by physical vapor deposition (PVD) dose not require washing and calcination, which are indispensable for chemical preparation such as in CP and DP methods. As waste water and waste gases are not by-produced, the arc plasma (AP) method is expected to grow in popularity as one of the industrial production methods for gold catalysts and as a clean preparation method. 

F. De Larrard. Ultrafine particles for the making of very high strength concretes. Cement Concrete Res, 19(2) 161-172, March 1989. 

Zhang X-G, Arikawa T, Murakami Y, Yahikozawa K, Takasu Y. 1995. Electrocatal3ftic oxidation of formic acid on ultrafine particles supported on glassy carbon. Electrochim... 

Particle sizes are conventionally described in different units depending on the size range involved. Coarse particles are measured in inches or centimeters fine ones, in terms of sieve size very fine ones in microns or millimicrons. The sizes of ultrafine particles are sometimes specified in terms of their surface per unit mass, this being commonly expressed in square meters per gram. 

Oberdorster, G., Oberdorster, E., and Oberdorster, J. (2005) Nanotoxicology an emerging discipline evolving from studies of ultrafine particles. Environmental Health Perspectives, 113 (7), 823-839. 

Khramov, M.I. and Parmon, V.N. (1993) Synthesis of ultrafine particles of transition-metal sulfides in the cavities of lipid vesicles and the light-stimulated transmembrane electron-transfer catalyzed by these particles. Journal of Photochemistry and Photobiology A-Chemistry, 71, 279-284. 

However, these results may need to be modified by the findings of Porstendorfer et al. (1987), Vanmarcke et al. (1987), and Knutson et al. (1985) that the "unattached" Po-218 containing molecules are actually part of an ultrafine mode (0.7 - 2.0 nm) in the activity size distribution. Thus, they are not free molecules and will move with a reduced diffusion coefficient based on the size of these ultrafine particles. 

Cohen, B.S., Deposition of Ultrafine Particles in the Human Tracheobronchial Tree A Determinant of the Dose from Radon Daughters, this volume (1987). 

Bricard, J., M. Cabone, G. Madeleine, and D. Vigla, Formation and Properties of Neutral Ultrafine Particles and Small Ions, in Aerosols and Atmospheric Chemistry (G.M. Hidy, ed.) pp. 27-43 Academic Press (1972). 

Scheibel, H.G. and J. Porstendorfer, Penetration Measurements for Tube and Screen Type Diffusion Battery in Ultrafine Particle Size Range, J. Aerosol Sci. 15 673-679 (1984). 

As previously mentioned, past studies used non-filtered air with unknown concentrations of trace gases at unknown relative humidities. Also, many of the studies used plastic aging chambers that may have introduced volatile monomers into the air. These unknown factors are important to determine in order to fully understand the nature of the ultrafine particle mode. According to the classical thermodynamic theory of ion cluster formation (Coghlan and Scott, 1983), the relative humidity and trace gases will affect the existence of condensation nuclei. Megaw and Wiffen (1961) observed an increase in nuclei formation with the presence of sulfur dioxide. 

In order to examine the process of ultrafine particle formation, a joint series of experiments were conducted at the Denver Research Center of the U.S. Bureau of Mines. In the Denver radon chamber, the activity size distribution of the ultrafine mode was measured using the mobility analyzer designed by Chu and Hopke (1985), the separate single screen method (Holub and Knutson, 1987), and the stacked single screen method (Holub and Knutson, 1987) for various relative humidities and for various concentrations of SO. The results... 

It has been found that the "unattached" fraction is an ultrafine particle aerosol with a size range of 0.5 to 3 nm. In order to initiate studies on the formation mechanism for these ultrafine particles, a series of experiments were made in the U.S. Bureau of Mines radon chamber. By introducing SO into the chamber, particles were produced with an ultrafine size distribution. It has been found that the particle formation mechanism is supressed by the presence of radical scavengers. These experiments suggest that radiolysis following the decay of Rn-222 gives rise to the observed aerosol and the properties of the resulting aerosol are dependent on the nature and the amount of reactive gas present. 

It has been reported for many years that condensation nuclei can be produced by ionizing radiation. Recent studies have improved the measurement of the activity size distribution of these ultrafine particles produced by radon and its daughters (Reineking, et al., 1985 Knutson, et al., 1985). It seems that the Po-218 ion is formed by the radon decay, is neutralized within a few tens of milliseconds, and then attached to an ultrafine particle formed by the radiolysis generated by the polonium ion recoil. Although there will be radiolysis along the alpha track, those reactions will be very far away (several centimeters) from the polonium nucleus when it reaches thermal velocity. The recoil path radiolysis therefore seems to be the more likely source of the ultrafine particles near enough to the polonium atom to rapidly incorporate it. 

These ultrafine particles have high mobility and can coagulate... 

Thus, there is a size threshold that must be reached before a cluster of atoms becomes big enough to be detected and turns into a "condensation nuclei". Recent work by Madelaine and coworkers (Perrin, et al, 1978 Madelaine, et al., 1980) have extended the size of measurable ultrafine particles to the order of 0.003 ym. They find rapid coagulation of this ultrafine aerosol to a larger average diameter one that is easily observable. 

The Po-218 activity was also attached to particles in the accumulation mode peak in the 0.1 to 1.0 pm range. The Po-214 (RaC ) activity was only observed in the accumulation mode and not associated with the ultrafine particles. Thus, the initial motion and deposition of much of the polonium-218 may be related to the transport by these ultrafine clusters. 

In order to examine the process of ultrafine particle formation, a joint series of experiments were conducted at the Denver Research... 

The hydroxyl radicals produced by water molecule radiolysis react promptly with oxidizable species such as SOg in air and form a condensed phase. These molecules further coagulate and become ultrafine particles. The radon concentration in the... 

Figure 2 and Figure 3 show the size distribution of these ultrafine particles measured by separate single screens (EML), stacked single screen (USBM), and the mobility analyzer (UI). 

Figure 4 shows the size distribution of these ultrafine particles at low humidities being shifted up in size by increasing SOp concentration. There is an overlap of spectra at 11 ppb and 110 ppb of SOp concentrations. Figure 5 reveals the same results at higher humidities, but the overlapped spectra were separated with a smaller size distribution at 110 ppb in the the presence of additional water vapor. We also obtained two different size distributions at 1.1 ppm in two sets of experiments. Thus, there are still some uncertainties in understanding the size distribution of ultrafine particles. 

It has been found that the activity which is conventionally referred to as the "unattached" fraction is actually an ultrafine particle aerosol with a size range of 0.5 to 3 nm. The hydroxyl radical from water molecule radiolysis is a key element to the particle formation mechanism. By injecting different concentrations of S02 into the test chamber, a possible particle formation mechanism has been suggested as follows Oxidizable species such as S02 reacts promptly with hydroxyl radicals and form a condensed phase. These molecules coagulate and become ultrafine particles. 

The size distribution of these ultrafine particles can be shifted upwards with the increase of S02 concentrations. 

The deposition of ultrafine particles has been measured in replicate hollow casts of the human tracheobronchial tree. The deposition pattern and efficiency are critical determinants of the radiation dose from the short lived decay products of Rn-222. The experimental deposition efficiency for the six airway generations just beyond the trachea was about twice the value calculated if uniform deposition from laminar flow is assumed. The measured deposition was greater at bifurcations than along the airway lengths for 0.2 and 0.15 ym diameter particles ... 

Few data are available on the deposition of ultrafine particles (dradon decay products in a rubber latex cast of a human windpipe which extended from the epiglottis to a few cm below the Carina. Martin and Jacobi (1972)... 

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