Particles, deposition ultrafine

Soot (CVD, reactive deposition) Ultrafine particles formed by gas phase decomposition (CVD) and nucleation (e.g. carbon soot). See also Ultrafine particles. 

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. 

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

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. 

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)... 

This paper will present some results of a set of experiments carried out in the hollow airway cast system with ultrafine particles which are or particular interest for the calculation of the dose to the bronchial epithelium from the short lived radon daughters. Detailed deposition efficiencies and intrabronchial distributions are presented elsewhere (Cohen, et al., 1986). 

Cohen, B. S., R. G. Sussman and M. Lippmann, Deposition of Ultrafine Particles in Hollow Airway Casts of the Human Tracheobronchial Tree. In Preparation. 

Another concept relating to the decay products is that of the "unattached" fraction. Although it is now known that the decay product atoms are really attached rapidly to ultrafine particles (0.5 to 3 nm in diameter), there is a long history of an operationally defined quantity called the "unattached" fraction. These decay products have much higher mobilities in the air and can more effectively deposit in the respiratory system. Thus, for a long time the "unattached" fraction has been given extra importance in estimating the health effects of radon decay products. Typically most of the "unattached" activity is Po-218 and the value of unattached frac-... 

Fig. 9.4.6 Apparatus for the matrix isolation method. Organic liquids are sublimed into a Dewar vessel through a solvent feeder to form a cryogenic matrix on the Pyrex glass wall cooled with liquid nitrogen. Inert gas is introduced via gas inlet. A target material in a crucible is heated in a gas to form ultrafine particles, which are deposited on a cryogenic matrix. The processes are repeated several times until enough particles are accumulated on a cryogenic matrix. (From Ref. 10.)...

In this equation, the diffusion coefficient D is related to air viscosity r A and particle diameter dp, with k being the Boltzmann constant and T the absolute temperature. It is clear from this description that diffusion is a rather slow deposition mechanism compared with impaction and sedimentation processes because it depends on the thermal velocity of the particles and not on airflow. It is the primary transport mechanism for small particles and is important when the transport distance becomes small, as in the deep lung. Efficiency of this deposition mechanism can be increased significantly by breath-holding because a portion of the ultrafine particles that are not deposited will be exhaled by the patient. 

Several epidemiological studies show that fine and ultrafine (<0.1 pm) particulate matter and air pollution can pose adverse health effects including respiratory, cardiovascular, allergic, and carcinogenic diseases (Kiinzli et al., 2000 Donaldson et al., 2003 Bernstein et al., 2004). It appears also that ultrafine particles, after deposition in the lung and gain access to the pulmonary interstitium, can penetrate the systemic circulation and exert more toxicity than coarse and fine particles (Oberdorster, 2001 Bernstein et al., 2004). 

Jaques PA, Kim CS (2000) Measurement of total lung deposition of inhaled ultrafine particles in healthy men and women. Inhal Toxicol 12 (Suppl l) 715-731... 

Sun JD, Wolff RK, Kanapilly GM. 1982. Deposition, retention, and biological fate of inhaled benzo[a]pyrene adsorbed onto ultrafine particles as a pure aerosol. Toxicol Appl Pharmacol 65 231-244. 

IKelectroNtiitic forces fail for uncharged ultrafine particles, there are at least two Ollier possible removal mechanisms. Ultrafine parlieics can diffuse to tlic collecting plates or cun coagulate with charged courser panicles that then deposit. Coagulation is discussed in Chapter 7. The other mechanism, difftisional transport, appears with electrostatic precipitation in the combined (lux expression (3.91), which, for u,/ > c, reduces to l7 = u,/iioc. 

Particle transport and deposition from lurbuieni flows by inertial forces are not well understood and has been the subject of considerable experimental and theoretical study, Correlaiions for rates of particle deposition from lurbuieni pipe flow are discussed in this chapter. The concentrations are a.s.sumed to be sufficiently small to neglect the effects of the particles on the turbulence. Inertial effects can also be used to focus beams of aerosol particles. This effect can be pniduced for suhmicron and even ultrafine particles as described at the end olThe chapter. 

Studies on deposition and translocation of Ti02 particles in a subchronic 3-month in vivo assay showed significant differences between inhaled ultrafine (around 20 nm) and fine (around 200 nm) nanoparticle fractions. Ultrafine particles were cleared significantly less, and translocation to the lymph nodes and other organs was increased in comparison to fine particles [73]. 

As mentioned several times before, the natural adhesion forces (see Section 5.1.1), caused, for example, by molecular (e.g. van-der-Waals) or electrical forces (e.g. due to asymmetric molecular structures), may become much larger than the separation forces which are mass and shape related. Therefore, if collisions or, generally speaking, contact between ultrafine particles occur, a rather strong bond will develop. This phenomenon is also responsible for the fact that most nano-sized particles do not exist as individuals but as assemblies of many particles (Fig. 10.41) this might be a problem in those applications where ultrafine particles must be deposited individually or in monolayers (see Chapter 12). For the effective separation of such particles from gases, however, agglomeration is desired and must be promoted. 

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