Particle size ultrafine particles

Long-range transport (LRT) of particles from wildfires greatly inerease in small fine particles (PM 1 to 0.2 particles) or ultrafine particles. LRT is the second of four criteria of hazardous (organic) particles. Other properties of partiele hazard are persistence (previously discussed), bioaccumulation (particles suffieiently small to avoid phagocytosis), and adverse biological (biomedical) effects. PM 1 to 0.2 particles are the smallest portion of fine particles, which we call the aceumulation mode (1,2). They are the closest to ultrafine (nano) particles in size (structure) and funetion. 

The precursor glass powders may be produced by various methods, the simplest being the milling of quenched glass to an average particle size of 3—15 p.m. Sol gel processes, in which highly uniform, ultrafine amorphous particles are grown in a chemical solution, may be preferable for certain apphcations. 

Property Technical grade Controlled particle size (CPS) " CPS-ultrafine (UF) usp"... 

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. 

Solids separation based on density loses its effectiveness as the particle size decreases. For particles below 100 microns, separation methods make use of differences in the magnetic susceptibility (magnetic separation), elec trical conductivity (electrostatic separation), and in the surface wettability (flotation and selec tive flocculation). Treatment of ultrafine solids, say smaller than 10 microns can also be achieved by utilizing differences in dielectric and electrophoretic properties of the particles. 

The smaller the particle size, the lower the wavelength at which maximum scattering occurs. Thus, ultrafine (20-50nm) T1O2 is used as a UV filter in skin care and cosmetic products. (Sec V. P. S. Jl din, Chem. Br. 29, 503-5 (1993).)... 

Ultrafine Ammonium Perchbrate (UFAP). For high burning rate propints a fine particle size AP is required and is produced by 3 processes ... 

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. 

Due to particle sizes in the micrometer range, parenteral suspensions are generally limited to either subcutaneous or intramuscular routes of administration. However, ultrafine suspensions can be approached by high-pressure homogenization [200]. The particle size obtained from this technique is in the 100 500 nm range, thus intravenous administration is possible [201]. General information on parenteral formulations is given in Chapter 12. 

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. 

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). 

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. 

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. 

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. 

Catalytic activity and electrochemical performance generally increase as the NiO and YSZ particle sizes are reduced. However, ultrafine powders are prone to agglomeration during the milling and mixing process the distributions of the phases (and hence the percolation threshold and many other important properties) are determined by the agglomeration size, not by the primary particle size. 

The pulmonary lymphatic system contributes to the clearance of fluid and protein from the lung tissue interstitium and helps to prevent fluid accumulation in the lungs [108], The lymphatic endothelium allows micron-sized particles (e.g. lipoproteins, plasma proteins, bacteria and immune cells) to pass freely into the lymph fluid [103], After administration of aerosolised ultrafine particles into rats, particles were found in the alveolar walls and in pulmonary lymph nodes [135], which suggests that drainage into the lymph may contribute to the air-to-blood transport of the inhaled particles. 

PM causes its health effects, especially its effect on cardiovascular health, are unclear there is some evidence that chemical composition of PM is not as important as particle size, with the greatest risks associated with what is designated as PM 2.5 (particle size less than 2.5 pm). Some experimental evidence suggests (but does not establish) that so-called fine (0.25 to 1.0 pm) and ultrafine (<0.25 pm) are the most potent toxicants, but regulation is now focused on PM 2.5. Regulation of PM and the primary air pollutants is highly contentious, because the costs of controlling them are enormous. 

One hint of possible trouble to come is provided by the information we described in Chapter 4, related to airborne particulate matter (PM). The available evidence ascribes significant increases in the risks of asthma and other respiratory diseases, certain cardiovascular conditions, and lung cancer to PM exposure, particularly those that average less than 2.5 pm (2500 nm) in size. As we noted, the chemical composition of these particles varies widely, depending upon source, but may not be as important as particle size as a risk determinant. Moreover, there is some experimental evidence pointing to the so-called ultra-fines, PM with dimensions below 100 nm, as significant contributors to PM risk. In addition some experimental studies have demonstrated that ultrafines not only distribute themselves throughout the airways, but seem to be able to translocate to other parts of the body - liver, heart, perhaps the CNS. 

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