Particle fabrication from aerosols

Solid submicron particles may form from condensable molecules generated in a gas by chemical or physical processes. Thi.s method is used routinely for the commercial production of line particles and materials fabricated from them, as well as for pilot and laboratory scale production. Similar processes occur in fine particle formation in many other ca.ses ranging from coal combustion to meteor burn-up on entering Earth s atmosphere. The smallest individual particles composing such aerosols prittiary particles) range from less than 10 nm to about I jum, depending on the application. 

FIGURE 22.12 Electrospray source with chamber facility. (Reprinted from J. Aerosol Sci., 39, Yao, J., Lim, L.K., Xie, I, Hua, J., and Wang, C.-H., Characterization of electrospraying process for polymeric particle fabrication, 987-1002, Copyright 2008, with permission from Elsevier.)... 

Plutonium is so toxic that processing and fabrication are always done in sealed cells or glove boxes, but accidental dispersions of aerosol occur from time to time. Following combustion of Pu metal chips in a production area at Rocky Flats, Colorado, in 1964, airborne contamination was widespread. Alpha tracks from individual particles caught on membrane filters were detected on nuclear film, and the Pu content, and hence the particle size, was deduced (Fig. 5.2, curve E). The activity median diameter was 0.3 /urn (Mann Kirchner, 1967). The same method, used during normal operations in a production area at Los Alamos, gave activity median diameters in the range 0.15 to 0.65 /urn (Moss et al., 1961). However, when a spill occurred, followed by clean-up operations, the Pu particles were found to be associated with inert dust particles of mass median diameter 7 /urn. 

Filters have been extensively used in households and industry for removing particles from air or liquid. In the case of enviromental protection filters are used to remove pollutants from air or water. In military, filters are used in uniform garments and isolating bags to decontaminate aerosol dusts, bacteria, while maintaining permeability to moisture vapor for comfort. A respirator is another example requiring an efficient filtration function. The same properties are also needed for some fabrics used in the medical field. ... 

Filtration, in the most general sense, may be defined as the removal of particles from the aerosol. This occurs either by their attachment to nonaerosol media (walls, vegetation, "fabric filters", etc.) or to larger particles which are subsequently removed. Since particle transport in the gas is intimately involved, a characterization of the gas flow field and the detailed mechanisms of particle kinetic theory near a surface must be invoked. Classically, filtration was treated as the simple adhesion of a single particle to a surface. However, it is now known that after the first particles adhere, subsequent ones tend to be captured by the initial ones to form chains. Impaction of a large particle upon such a chain or other break-off processes can cause resuspension. Thus, filtration is dependent upon properties of the aerosol and gas as a whole [1.9,10]. 

Plutonium is so toxic that processing and fabrication are always done in sealed cells or glove boxes, but accidental dispersion of aerosol occurs from time to time. Cheng et al. (2004) used a Lovelace Multi-jet cascade impactor for collecting aerosols during the release of an undetermined amount of Pu02 from a glovebox system, in a room within a Plutonium Facility (PF-4) at Los Alamos National Laboratory (LANL), Los Alamos, NM. They examined the plutonium particle activity size distribution. A plot of the aerodynamic size distribution and... 

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