Papers by Author: Won Sik Seo

Abstract: Feasibility of producing porous gradient structure by spark plasma sintering (SPS) process was examined. Adequate combination of porosity gradient and pore size distribution could be obtained by appropriately controlling the SPS parameter such as sintering temperature, sintering time, applied pressure, and stopper length. For the longitudinal porous gradient structure, pure W sample was prepared by specially shaped graphite mold. Stainless steel powder was employed for the radially layered porous structure with different pore size. The graded porous structure could be applied for the fabrication of W-Cu FGM by Cu-infiltration and high temperature filter with high filtration efficiency.

Abstract: Nanosize nickel powders were successfully produced by electrical explosion of wire (EEW). In EEW, the nickel wire was discharged in a chamber filled with nitrogen or argon gas, and the produced powders were subsequently stabilized by air-passivation at room temperature for 2 h. X-ray diffraction only showed the nickel phase of FCC crystal structure, whereas TEM and XPS analyses showed the formation of a very thin oxide layer of NiO on the surface of particles. Particles were spherical in shape, and the mean particle size calculated by specific surface area was about 100 nm. The particle size decreased with increasing charging voltage and with increasing ambient gas pressure. Argon gas was more effective in producing finer particles than nitrogen gas.