Aerosol reactors

Tiwari, V., Jiang, J., Sethi, V. and Biswas, P. (2008) One-step synthesis of noble metal titanium dioxide nanocomposites in a flame aerosol reactor. Applied Catalysis A General, 345, 241-246. 

Pratsinis, SE. and S.V.R. Mastrangelo Material Synthesis In Aerosol Reactors (Optical Fiber Manufacture), Chem. Eng. Progress 65 (May 1989). 

To study the chemistry of highly concentrated particles in bulk solution one must avoid mass transfer limitations and the effects of container surfaces. Both of these problems are eliminated by directly using aerosol particles. Two approaches have been used to study aerosol chemistry (1) aerosol reactors in which the evolution of a suspension of particles is followed, and (2) experiments in which the changes occurring in a single particle can be followed. 

FIGURE 7SI Quenching (a) Heat transfer quenching by double pipe heat exchanger in an aerosol reactor, (b) Dilution quenching by the addition of a cold gas. 

Biswas, P, Li, X.M., and Pratsinis, S.E., Optical wave-guide preform fabrication— silica formation and growth in a high-temperature aerosol reactor, J. Appl. Phys., 65, 2445, 1989. 

Kammler, H.K., Mueller, R., Senn, O., and Pratsinis, S.E., Synthesis of silica-carbon particles in a turbulent Hj-air flame aerosol reactor, AIChE J., 47, 1533, 2001. 

A mathematical model of a nanoparticles growth during evaporation of a micron size droplet in a low pressure aerosol reactor is developed. The main factor is found to be evaporating cooling of droplets which affects formation of supersaturated solution in the droplet. The rate of cooling can reach 2T0 K/s. The final radius of nanoparticles was found to be independent on the precursor radius. Manifestation of Lifshitz-Slezov instability is illustrated by experimental data. Effects of Brownian motion of nanoparticles inside the droplet are discussed. 

Recently it was experimentally proven that the highest yield of nanoparticles of different substances, including semiconductor and magnetic ones, is obtained in low pressure spray pyrolysis of special multicomponent solutions [1], During this pyrolysis micron size droplets of the multicomponent aqueous solution evaporate in a low pressure aerosol reactor. Additionally these droplets often have solid precursors of nanometer size, so we can consider every droplet as a colloidal solution. 

The aim of our work is to present simulation results to give a clear physical picture of interference of complex processes in the evaporating droplet during the low pressure spray pyrolysis. For different conditions the drop of temperature of an evaporating droplet is displayed in Fig. 1. The volatile components are water and ammonia. Total pressure in the aerosol reactor is 60 Torr. The initial droplet temperature is 300 K and its initial radius is about 2 pm. For the gas flow... 

Figure 1. Droplet tenperature vs the path length in a low pressure aerosol reactor. (1) The ammonia molar fraction x=0.33 in a droplet and Xg=0.05 in the gas mixture, (2) x=0.05 and Xg=0.26, (3)...

In practice, coagulation almost always takes place in turbulent flows. Examples are industrial aerosol reactors, combustion systems, process gas flows, and the atmosphere. Turbulent... 

The experiments with MgO and ZnO agglomerates (Fig. 8.7a) lend qualitative support to this analysis. A transmission electron photomicrograph of the MgO aerosol showed large agglomerates composed of small primary particles about 5 nm in diameter. The appearance of the ZnO aerosol was quite different. The ZnO agglomerates were much smaller than the MgO particles but were composed of larger primary particles about 10 nm in diameter. Similar effects have been observed for the agglomerates produced by industrial aerosol reactors (Ulrich, 1984). 

According to Ulrich (1971), process conditions typical of pyrogenic silica aerosol reactors are silica mole fraction in vapor phase = 0.07, pressure = 1 atm. T = 1800 to 2100 K. 

Synthesis of Submicron Solid Particles Aerosol Reactors... 

The factors that determine the crystal structure of particles formed in aerosol reactors have not been studied systematically. In this section, we identify key theoretical concepts and review relevant experimental observations. Consideration is limited to single-component systems. Panicle crystal structure depends on a combination of thermodynamic (equilibrium) factors and rate processes. The equilibrium shape of a particle is detennined by the surface energies of its crystal face.s according to the Wulff construction (Chapter 8). Another factor that inay enter into the process is the excess pressure inside small particles according to the Laplace formula (Chapter 9). Thus the equilibrium form may vary with panicle size depending on the phase diagram,... 

The crystalline properties of silicon, silicon nitride, and silicon carbide nanoparticles produced in a laboratory aerosol reactor were measured by Cannon et al. (1982). Particles were produced using a COi laser to irradiate aerosol precursor gases. For example, silane (SiHj) u.sed to produce silicon particles could be healed adiabatically to the reaction temperature as long as the gas pressure wa.s maintained above 0,05 atm. At lower pressures, beat conduction to the cell walls balanced the heat absorbed by the gases, Silicon particles were generated at about 100() C by silane decomposition ... 

Revised and expanded, this second edition features new chapters on the kinetics of agglomeration of noncoale.seing particles and the fundamentals of aerosol reactor design. It covers the effecLs of turbulence on coagulation and gas-to-particle conversion and also di.scusses the formation of primary particles by the coltision-coale.scence niechani.sm. The chapter on the atmo.spheric aerosol has been completely rewritten within the aero.sol dynamics framework. Its basic approach and topicality make Smoke, Dust, and Haze Fundamentals of Aerosol Dynamics, 2le, an essential guide for both studenfs and researchers. 

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