| This thesis characterizes the formation of a condensed phase, containing precursors to carbon, during the pyrolysis of ethane, through a combination of kinetic modeling, video analysis, scanning electron microscopy (SEM) and fluorescence spectroscopy. The results at short times were consistent with steady formation of precursors until a critical pressure was reached. Nucleation then occurred rapidly, followed by a steady growth of the volume of the particles. Aerosol nucleation and growth by condensation were determined to be controlled by processes following second order kinetics, in agreement with the theory of homogenous nucleation. The temperature dependence of the incubation period for formation of the aerosol indicated that the aerosol precursors examined in this study may also be relevant to soot formation from benzene. The heat of vaporization of the droplets was estimated to be 211+/-30 kJ mol -1. This was consistent with condensation of polycyclic aromatic hydrocarbons (PAHs) having molecular weights of about 439+/-79 g mol -1.;Previously developed sampling techniques were improved and used to collect aerosol samples that were analyzed by SEM and fluorescence spectroscopy. Emissions from collected samples were observed where emission from PAHs was expected. Spectra shifted to the right for longer times, which was consistent with growth of PAHs with time, as has been previously suggested. SEM revealed the presence of a polydisperse aerosol, consisting of small droplets and aggregates with particle sizes from 4 to 357 nm. Video analysis and image processing were shown to be effective methods for analyzing the dynamics of aerosol growth in two dimensions. Diffusion to the walls of the reactor was shown to be the main mechanism for aerosol removal in a static system.;Average particle diameters, calculated from the diffusion coefficients, increased with time. The time dependence of the average particle diameters could not be accounted for if the particles were growing by coagulation alone. Relative rate constants, for several processes involving aerosol removal and growth, indicated that nucleation and molecular condensation on the surface of the particles were dominant. |
