Upward Thermal Diffusion Cloud Chamber

FIGURE 10.5 Upward thermal diffusion cloud chamber. Typical cloud chamber profiles of total gas-phase density, temperature, partial pressure p ( -nonane in this example), equilibrium vapor pressure p saturation ratio 5, and nucleation rate J. as a function of dimensionless chamber height at 7 = 308.4 K, S = 6.3, and total p = 108.5 kPa. (Reprinted with permission from Katz, J. L., Fisk, J. A. and Chakarov, V. M. Condensation of a Supersaturated Vapor IX. Nucleation of Ions, J. Chem. Phys. 101. Copyright 1994 American Institute of Physics.) 

1 cm s . As droplets form and grow they fall under the influence of gravity continued evaporation of the liquid pool serves to replenish the vapor molecules of the nucleating substance so that the experiment can be run in steady state. Nucleation rates that can be measured in the upward thermal diffusion cloud chamber vary roughly from 10 to 10 cm s .  

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The presence of ions has been shown experimentally to enhance the rate of nucleation of liquid drops in a supersaturated vapor. Katz et al. (1994) showed, for example, that the nucleation rate of n-nonane, measured in an upward thermal diffusion cloud chamber, at an ion density of 16 x 106 ions cm-3, increased by a factor of 2500 over that in the absence of ions. These investigators also confirmed experimentally that the nucleation rate is directly proportional to the ion density. The phenomenon of ion-induced nucleation plays an important role in atmospheric condensation, particularly in the ionosphere. While both positive and negative ions increase the nucleation rate, many substances exhibit a preference for ions of one sign over the other. 

In the experiments, a modified upward thermal diffusion cloud chamber is used for the synthesis of the nanoscale particles (10,31,32), A sketch of the chamber with the relevant components necessary for the synthesis of nanoparticles is shown in Figure 2. This chamber has been commonly used for the production of steady state supersaturated vapors for the measurements of homogeneous and photo-induced nucleation rates of a variety of substances (33). Detailed description of the chamber and its major components can be found in several references (33,34), Here we only offer a very brief description of the modifications relevant to the synthesis of the... 

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