Papers by Author: Gil Su Kim

Abstract: Inconel 617 is a candidate tube material for high temperature gas-cooled reactors (HTGR). The microstructure and mechanical properties of Inconel 617 were studied after exposure at high temperature of 1050oC. The dominant oxide layer was Cr-oxide. The internal oxide and Crdepleted region were observed below the Cr-oxide layer. The major second phases are M23C6 and M6C types of carbides. The composition of M23C6 and M6C were determined to be Cr21Mo2C6 and Mo3Cr2(Ni,Co)1C, respectively, by EDS. These carbides are coarsened during exposure. M6C carbide is more stable than M23C6 at high temperature. There was not much change in mechanical properties after exposure at 1050oC for 1000 h.

Abstract: The effect of Cu on the hydrogen reduction of molybdenum oxide powders was investigated by measuring the humidity change during a non-isothermal process of hydrogen reduction. The presence of Cu induced a shift in the reduction temperature and strongly affected the reduction processes of MoO3→Mo4O11→MoO2, which comprised the contained chemical vapor transport of MoOx(OH)2. This study suggests that the surface of the Cu grains acts as a nucleation site for the reduction of MoOx(OH)2 to MoO2 particles from MoO3 or Mo4O11 phases. Such an activated reduction process results in the deposition of metallic Mo and MoO2 particles on the surface of the Cu grains.

Abstract: Magnetic properties of nanostructured materials are affected by the microstructures such as grain size (or particle size), internal strain and crystal structure. Thus, it is necessary to study the synthesis of nanostructured materials to make significant improvements in their magnetic properties. In this study, nanostructured Fe-20at.%Co and Fe-50at.%Co alloy powders were prepared by hydrogen reduction from the two oxide powder mixtures, Fe2O3 and Co3O4. Furthermore, the effect of microstructure on the magnetic properties of hydrogen reduced Fe-Co alloy powders was examined using XRD, SEM, TEM, and VSM.

Abstract: The sintered microstructure homogeneity of W-15wt%Cu nanocomposite powders prepared from W-CuO mixture was investigated. The increment of heating rate considerably affected the homogeneity of sintered microstructure. In case of the higher heating rate, the microstructure was more homogeneous than that of the lower heating rate by reason of Cu- exudation during heating-up process.