a Flow Chamber for Quantitative Nucleation Investigations and Ultrafine Particle Production and Capture.

A flow diffusion nucleation chamber to be used for homogeneous nucleation studies and particle production and capture was designed, characterized, constructed, and tested. A mathematical model was developed to predict the temperature, concentration, supersaturation, and nucleation rate profiles throughout the nucleation chamber. Fluid dynamic modeling was used to better understand the flow characteristics in the chamber. Critical supersaturation versus temperature data for the 1-propanol/helium system obtained using the flow diffusion nucleation chamber was compared to data obtained with the same system using a thermal diffusion cloud chamber. Excellent agreement was observed between these sets of data. We have observed dependence of the homogeneous nucleation process on the nature of background gas using 1-propanol as the nucleating vapor and helium, argon, nitrogen and hydrogen as the background gases. Critical supersaturation data as a function of temperature obtained from experiments using helium or hydrogen as background gases are in agreement. Also, data obtained using nitrogen and argon as background gases are in agreement. However, the data from experiments with the heavier gases (argon and nitrogen) are different from data obtained using the lighter gases (helium and hydrogen). The phenomenon of photo-induced nucleation (PIN) of CS_2 in various concentrations with 1-propanol was studied and the collected particle samples were examined using various analytical techniques such as energy dispersive x-ray analysis, scanning electron microscopy, and transmission electron microscopy. We were able to probe the size and structure of the ultrafine particle clusters formed as a result of the PIN process under different conditions. We observed that in this system sulfur was the dominant product of the PIN process under all conditions, suggesting a resolution to a controversial issue concerning the mechanism of the PIN of CS_2.