Particle evolution

Figure 5. Successive UV-vis spectra of silver particle evolution and fluorescein (F) reduction in aqueous CTAB solutions containing [AgNOj] = 10 M, [CTAB] = 0.01 M, [NaBHJ = 5xl0 M and [F] = 5xl0 M. (Reprinted from Ref [28], 1999, with permission from American Chemical Society.)...

The problem of dust particle evolution in turbulent stratified flows near the sources of accidental heat release is of great practical importance for description of dust explosions and large fires. 

Non-metallic Clusters, Quasi-metallic Clusters, and Nanosized Metallic Particles -Evolution from Bonds to Bands in Aqueous Solution... 

Danilin, M.Y., J.M. Rodriguez, M.K.W. Ko, D.K. Weisenstein, R.C. Brown, R.C. Miake-Lye, and M.R. Anderson, 1997 Aerosol particle evolution in an aircraft wake Implications for the high-speed civil transport fleet impact on ozone, J. Geophys. Res., 102,21,453-21,463. 

Let us first consider the catalyst/polyolefin particle in the early stage of its evolution. The particle consists of the solid catalyst carrier with catalyst sites immobilized on its surface, polymer phase, and pores. The first-principle-based meso-scopic model of particle evolution has to be capable of describing the formation of polymer at catalyst sites, transport of monomer(s) and other re-actants/diluents through the polymer and pore space, and deformation of the polymer and catalyst carrier (including its fragmentation). Similar discrete element modeling techniques have been applied previously to different problems (Heyes et al., 2004 Mikami et al., 1998 Tsuji et al., 1993). 

The mathematical model of catalyst/polymer particle evolution consists of the set of differential-algebraic equations (61)-(64). The constitutive equations describing the force interactions, transport of monomer, phase equilibria at the interface between polymer and pore phase as well as the rules for connectivity of micro-elements have to be specified (Grof and Kosek, 2005 Grof et al., 2005a). 

During their displacement, elementary particles are constantly encountering obstacles, other moving elements, oscillation states etc. The particle evolution is randomly chosen among the different presented possibilities ( process components ). 

This means that the process exchange characterizes the particle evolution. The process occurring before and after the transformation is called the process componenf , whereas the transformation itself which represents the stochastic evolution is called the connection process . 

Bensberg, a., Roth, P., Brink, R. Lange, H. 1999 Modeling of particle evolution in aerosol reactors with coflowing gaseous reactants. AIChE Journal 45, 2097-2107. 

The AA series shows the same particle evolution with a slightly different ze distribution. The fresh catalyst has particles of ze between 20 and 300 A, most of them around 20 A The AA-SR has basically the same size distribution but large particles begin to appear (2S0-S00 A). In the AA-700 catalyst, particles with size lower than 40 A disappear and sintering is observed with particles up to 900 A. Finally in the AA-900 only big particles are observed. 

Lyons (Ref 4) reports on a Universal Match Corp program to develop igniter-proplnt compns using an M-7 proplnt base viz, NG 24.8, NC 36.6, ethyl centralite 0.56, Mg 0.04 and Mg stearate 0.04%, plus either AP or K perchlorate 10%. To these two matrixes 30% of powdered Ti was added giving the parameters shown in Table 1. The authors noted that the advantages of these compns are that they are reproducible, have a h rate of hot particle evolution with reliable high energy output, and are safe to handle... 

Figure 2.13 Apparatus for aerosol formation of particles via the EISA route. Particle evolution indicated in dashed box. Reprinted from 11/579-585 Evaporation-Induced Self-Assembly Nanostructures made easy by Brinker, C.J. Lu, Y. Sellinger, A. Fan, H. 9, 7 No 12, 13. Copyright (1999) Wiley-VCH Verlag GmbH 8c Co. KGaA.

M. Eslamian, M. Ahmed, N. Ashgriz Modeling of solution droplet evaporation and particle evolution in droplet-to-particle spray methods, Drying Technology 27(3), 3-13, (2009). 

In total 12 experiments were carried out. Three volumetric feed flows were used (1.3, 3.3 and 5.3 ml/s) with two reactor volumes (10 ml and 6.5 ml). Each experiment was realized without and with an ultrasonic field of 40 Watt/cm. The precipitate was filtrated at room temperature and washed several times with deionizated water. The filtrate was dried for 12 h in a furnace at 65 °C. As a test for the catalytic activity of the Mn02 particles evolution of O2 from H2O2 was used. For these tests a sieve fraction between 63 pm and 80 pm of dried Mn02 was used. An amount of 0.05 g of manganese dioxide was given into a beaker with a solution of hydrochloric acid and hydrogen peroxide in water. The solid acts as a catalyst for the formation of oxygen (4a) and dissolutes simultaneously in the reaction (4b). 

Additionally, this approach offers, in the case of emulsion polymerization, a unified means of monitoring colloid/ polymer characteristics giving information about both the polymer and particle evolution, and thus allowing one to make correlations between key features of the two aspects of the emulsion polymerization process. Online monitoring of both particle and polymer characteristics should allow for studies of reaction kinetics, predictive and active reaction control, and also the ability to observe deviations and unexpected phenomena. 

Dally, B.B., Alwahabi, Z.T., Krishnamoorthy, L.V., Redman, L.D. and Christo, F.C. (2001) Measurements of particles evolution in the near combustion field of MTV formulation using mie scattering technique. 28th International Pyrotechnics Seminar, pp. 219-226. 

---