Size-selected nanoparticle chemistry: Kinetics of soot oxidation

Use of a Differential Mobility Analyzer (DMA) for size selection of monodisperse (or mono-area) nanoparticles can provide useful information for determining chemical and physical properties of those nanoparticles. Taking advantage of this, new experimental protocols, i.e. on line and offline methods, have been developed to conduct surface chemistry and to extract surface kinetic rates on size-selected (or mono-area) nanoparticles. The online method utilizes a High Temperature Oxidation-Tandem Differential Mobility Analyzer (HTO-TDMA) technique, in which monodisperse particles are selected from a polydisperse aerosol input stream and then subjected to chemical processing. The change in particle size is measured and used to determine kinetic information for the relevant surface reaction. This online method has been applied to measure the oxidation rate of flame soot and Diesel particles in air over temperatures ranging from 500 to 1200°C. The offline method uses Transmission Electron Microscopy (TEM). Mono-area particles are sampled on TEM grids using the particles on such TEM grid samples. The relationship between mobility equivalent diameter and projected area equivalent diameter was investigated using those particle samples on the TEM grids. The particles on the TEM grids underwent the oxidation process in a separate furnace. Individual soot particles were tracked to investigate the change in morphology, and groups of mono-area particles were visualized before and after the oxidation process. The oxidation rates were determined from the change in projected area equivalent diameter by image-processing a series of TEM images. The offline method has been used to measure the oxidation rates at low temperatures (<∼500°C). The protocols developed in this thesis work present significant advances compared to the conventional techniques in determining kinetics of particle oxidation at high and low temperatures.