Kyong H. Lee

Characterization of Carbon Nanotubes/Cu Nanocomposites Processed by Using Nano-sized Cu Powders

Carbon nanotubes (CNTs) have attracted remarkable attention as reinforcement for composites owing to their outstanding properties. CNT/Cu nanocomposites were fabricated by mixing the nano-sized Cu powders with multi-wall carbon nanotubes and followed by the spark plasma sintering process. The CNT/Cu nanocomposite fabricated from nano-sized Cu powders shows more homogeneous distribution of CNTs in matrix compared to that fabricated from macro-sized Cu powders. The hardness of CNT/Cu nanocomposite fabricated from nano-sized Cu powders increases with increasing the volume fraction of CNTs, while the hardness of that fabricated from macro-sized Cu powders decreases with the addition of CNTs.

POST-IRRADIATION ANALYSES OF U-MO DISPERSION FUEL RODS OF KOMO TESTS AT HANARO

Since 2001, a series of five irradiation test campaigns for atomized U-Mo dispersion fuel rods, KOMO-1, -2, -3, -4, and -5, has been conducted at HANARO (Korea) in order to develop high performance low enriched uranium dispersion fuel for research reactors. The KOMO irradiation tests provided valuable information on the irradiation behavior of U-Mo fuel that results from the distinct fuel design and irradiation conditions of the rod fuel for HANARO. Full size U-Mo dispersion fuel rods of 4-5 g-U/cm3 were irradiated at a maximum linear power of approximately 105 kW/m up to 85% of the initial U-235 depletion burnup without breakaway swelling or fuel cladding failure. Electron probe microanalyses of the irradiated samples showed localized distribution of the silicon that was added in the matrix during fuel fabrication and confirmed its beneficial effect on interaction layer growth during irradiation. The modifications of U-Mo fuel particles by the addition of a ternary alloying element (Ti or Zr), additional protective coatings (silicide or nitride), and the use of larger fuel particles resulted in significantly reduced interaction layers between fuel particles and Al.

Amalgamation mechanism in dental amalgam alloys

Model experiments to explore the amalgation mechanism in conventional Ag3Sn and high copper single-composition dental alloys have been conducted by rotating alloy roda in liquid mercury at different speeds and for different durations. After removing the rod from the mercury, the vacuum volatilization technique was used to accelerate the supersaturation of dissolved elements in the liquid mercury. The surface and sectional scanning electron microscope (SEM) views give direct evidence for new amalgamation mechanism in high copper dental alloys. The amalgamation reaction begins with the selective dissolution of the Ag3Sn phase in mercury, tin gettering to the crumbled-off Cu3Sn phase, heterogeneous nucleation of the Cu6Sn5 phase on the seed of the crumbled-off Cu3Sn phase and was followed by the nucleation of the Ag2Hg3 phase. The unexplained phenomena, the formation of the γ-2 phase (Sn7-8Hg) in higher content of mercury and the nonexistence of the γ-2 phase in higher content of copper alloys such as Sybralloy, were clearly understood by applying the new model.