Papers by Author: Hyun Cheol Oh

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.