Submicrometric particle

Submicrometric particle Airborne particle with a diameter less than one... 

The key to the successful preparation of this new composite is the identification of a surfactant, PE-b-PEG, that is capable of stabilizing the emulsion and promoting the dissolution of the PE. Then submicrometre particles of low-density PE silica and high-density PE silica are synthesized by carrying out a silica sol-gel polycondensation process within emulsion droplets of TEOS-dissolved PE, at elevated temperatures (78 and 130°C for low- and high-density PE, respectively). 

Hitchins J, Morawska L, Wolff R, Gilbert D (2000) Concentrations of submicrometre particles from vehicle emissions near a major road. Atmos Environ 34 51-59... 

In the free atmosphere, the rate of production of small ions is in balance with the rate of neutralisation by recombination and the rate of attachment to condensation nuclei. Condensation nuclei, otherwise called Aitken nuclei, are submicrometric particles mainly produced by combustion processes. If slight differences in the rates of attachment of positive and negative ions are ignored,... 

Referring to the stack filter, the report of the Court of Inquiry (Penney, 1957) stated Iodine vapour had come through the filter but the major part of the particulate material had been caught by the filter . This was published before analyses of the filter material were available, and was incorrect. Most of the activity on the filter was associated with a yellow powder (Crouch Swainbank, 1958). The powder comprised chain aggregates of submicrometre particles of lead and bismuth oxides, which originated as a fume in the reactor. The distribution of fission products on the powder, as between volatile and refractory elements, was similar to that found in the environment. 

Field-loss rates have also been measured after dry deposition of particulate activity. Witherspoon Taylor (1970, 1971) and Peters Witherspoon (1972) used silicaceous particles, labelled with 134Cs, in three size ranges, 1-44 fim, 44-88 nm and 88-175 fim. Millard et al. (1983) used submicrometre particles labelled with 141Ce or 134Cs. All reported field loss as showing an initial rapid phase lasting a few days, followed by one or more slow phases. In the period from a few days to about five weeks after application of the activity, the values of XG were in the range 0.02-0.06 d-1, with no obvious correlation with particle size, or with the incidence of rainfall. 

Fig. 6.14. Rate of resuspension from grass after exposure to wind for 10 h of x, 5- m particles , 2-/

Figure 6.15 shows the effect of ageing on the resuspension of the submicrometre particles. The wind tunnel was operated continuously for 100 h with a wind speed of 12 m s-1, and periodic measurements of A were made. Thereafter, the strip of ground treated with particles was... 

Fig. 6.15. Resuspension of submicrometre particles of tungstic oxide up to 100 h - wind tunnel operated at 12 m s-1 after 100 h - periods of natural weathering (hatched) in intervals between further operation of wind tunnel.

In the pulmonary region, air velocities are too low to impact particles small enough to reach that region, and the mechanisms of deposition are sedimentation and Brownian diffusion. The efficiency of both processes depends on the length of the respiratory cycle, which determines the stay time in the lung. If the cycle is 15 breaths/min, the stay time is of the order of a second. Table 7.1 shows the distance fallen in one second and the root mean square distance travelled by Brownian diffusion in one second by unit density particles (Fuchs, 1964). Sedimentation velocity is proportional to particle density, but Brownian motion is independent of density. Table 7.1 shows that sedimentation of unit density particles is more effective in causing deposition than Brownian diffusion when dp exceeds 1 pm, whereas the reverse is true if dp is less than 0.5 pm. For this reason, it is appropriate to use the aerodynamic diameter dA equal to pj dp when this exceeds 1 pm, but the actual diameter for submicrometre particles. 

Ultrafine particles have been defined as those, which are smaller than 0.1 pm. Another classification is into submicrometre particles, which are smaller than 1 pm, and supermicrometre particles, which are larger than 1 pm. The terminology that has been used in the wording of the ambient air quality standards, and also for characterisation of indoor and outdoor particle mass concentrations, includes PM2.5 and PM fractions and the total suspended particulate (TSP). PM2.5 (fine particles) and PM, are the mass concentrations of particles with aerodynamic diameters smaller than 2.5 and 10 pm, respectively (more precisely the definitions specify the inlet cutoffs for which 50% efficiency is obtained for these sizes). TSP is the mass concentration of all particles suspended in the air. There have been references made in the literature to PMj or PMq 1 fractions, which imply mass concentrations of particles smaller than 1 and 0.1 pm, respectively. These terms should be used with caution, as particles below 1 pm, and even more those below 0.1 pm, are more commonly measured in terms of their number rather than their mass concentrations, and therefore these terms could be misleading. 

The long-term goal of the chemistry of atmospheric aerosols is to establish analytical methods for determining the chemical composition of particular submicrometric particles. At the present time, this requirement is partially satisfied by two methods— electron and ion microprobes, which are based on the analysis of a point-concentrated electron or ion beam. By use of the ion microprobe it is possible to determine essentially all the elements, whereas the electron microprobe is suitable only for elemeiits with a greater atomic mass than sodium. 

Health risks (excluded the use of common chemicals for chromatography) Not significative Grinding produces submicrometric particles, dangerous if inhaled. Some monomers (acrylamide, styrene) are toxic... 

Gonzalez et al. first reported CoSn2 on metal foam obtained by electrodeposition of amorphous Co-Sn alloy and subsequent annealing [77]. It was observed that low current densities and short electrodeposition times favor the formation of discrete submicrometric particles (Volmer-Weber model] and the electrochemical behavior in lithium cell was very good, while the capacity in sodium cell was lower. 

Fig. 6.3 The structural and electrochemical characteristics of nano- and sub-micrometric size LiMni,3Nii,3Coi,302 particles synthesized by SCR and further calcined in air at 700 °C/1 h and 900 °C/22 h, respectively, (a) The XRD patterns of nano- and submicronic LiMnioNiioCoiBOj particles, (b) HRTEM image of nanoparticle annealed at 700 °C/1 h, (c) slow-scan-rate CVs, and (d) rate capabUities inset shows the voltage profiles) measured from electrodes comprising LiMniBNiiaCoi 302 nano- and submicrometric particles in EC-DMC (1 2)/1.5 M LiPF solution. Reproduced with permission from [35], copyright (2009) The Electrochemical Society...

Y. Mori, B. Scarlett, H.G. Merkus, Effects of ionic strength of eluent on size analysis of submicrometre particles by sedimentation field-flow fractionation. J. Chromatogr. A 515, 21-35 (1990). doi 10.1016/S0021-9673(01)89298-0... 

P.J. Wyatt, Submicrometre particle sizing by multiangle light scattering following fractionation. J. Colloid Interface Sci. 197(1), 9-20 (1998). doi 10.1006/jcis. 1997.5215... 

Colloids and colloidal particles refers nowadays to dispersed systems with submicrometre particles (x 1 pm) characterised by high particle difiusion coefii-cients, slow sedimentation, or even sedimentation-diffusion equilibria, weak light scattering, significance of non-viscous particle interactions, suspension stmcturing, etc. 

When a radioactive nuclide decays, electrons are stripped from the parent atom by its recoil and decay products are formed as positive ions. These ions can attract liquid and even solid material, thus forming clusters of atoms or particles in the submicron region ranging from 0.001 to 0.01 pm. Air is permanently ionised by radiation from the natural radioactivity of air and by cosmic radiation which consists mostly of positively charged particles, 85% protons, 10% alpha particles with a smaller percentage of positively charged stripped nuclei of heavier elements, such as Fe, Co and Ni, etc. Production of an ion pair requires 35.6 eV if ionisation is by alpha particles and 32.5 eV if by fast electrons. In the free atmosphere, the rate of production of small ions is in balance with the rate of neutralisation by recombination and the rate of attachment to condensation nuclei. Condensation nuclei are mostly the Aitken nuclei, which are submicrometre particles in the range 0.005 to 0.01 pm. 

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