Papers by Author: Jae Hee Jung

Abstract: In diesel engine, generally, the removal of carbon nanoparticles has been based on a filtration system or oxidation reactor with O2 at high temperatures of above 800 °C. Recently, NO2 has been found to be a more efficient oxidant than O2 at lower temperatures in the range of 200~500 °C. Small amounts of NO2 in the range of a few hundreds of ppm by volume can promote the continuous oxidation of carbon particulates. Thus far, experiments involving diesel PM (particulate matter) oxidation by NO2 are only practiced as regards the soot deposited on filters or plates. However, in aerosol state, depending on the surrounding temperature and the NO2 concentration, the carbon nanoparticle removal rate is significantly different. Therefore, the study of nano-sized carbon aerosol oxidation in various gas circumstances is required. In this study, the oxidation characteristics of nano-sized carbon aerosol particles in NO2 condition are investigated.

Abstract: A generation method of in-situ gold nanoparticles using a small-sized ceramic heater with a local heating area is presented. The heater surface temperature was maintained uniformly. Gold nanoparticles with high concentration (> 107 particles/cm3) were produced and were stably generated for several hours because the heater surface temperature was maintained uniformly. Higher surface temperature yielded higher geometric mean diameter (GMD), geometric standard deviation (GSD), and total number concentration. Using this generator particle size distribution was easily controlled. Spherical and non-agglomerated nanoparticles were observed from TEM images, even at high concentration and high temperature. Although air was used as a carrier gas, the generated gold nanoparticles displayed pure crystallinity of the gold element, as determined by XRD analysis.

Abstract: A pulsed spark-discharge aerosol generator using air as a carrier gas was successfully applied to the titania nanoparticle production. The titanium vapor evaporated by spark discharge was subsequently supersaturated and condensed to titania nanoparticles by nucleation and condensation. The size and concentration of the particles can be controlled easily using air as a carrier gas by altering the repetition frequency, capacitance, gap distance, and flow rate of the spark-discharge system. TEM observation shows that the generated particles were aggregates, which primary particle sizes are a few nanometers. The element composition of the nanoparticles was titanium and the crystal phase was amorphous. XPS analysis shows that oxidation state of generated particles corresponded to TiO2. These XPS data indicates that some fraction of the evaporated titanium vapor could be oxidized in an air atmosphere by the oxidation with oxygen. However, enough time for crystallization was lacked because of raid cooling.