Ungsoo Kim

Recovery of Metallurgical Silicon from Slurry Waste

Metallurgical grade silicon was recovered from slurry waste for ingot sawing process by acid leaching and thermal treatment. SiC abrasive was removed by gravity concentration and centrifugation. Metal impurities were removed by the acid leaching using HF/HCl. The remaining SiC was separated by the thermal treatment at 1600℃ in an inert atmosphere by the difference in melting points. The purity of the obtained silicon was found to be around 99.7%.

Hydrothermal synthesis of rod-like copper oxide crystals

A hyrdrothermal reaction process has been developed to prepare rod-like crystals of copper oxide using copper nitrate trihydrate as a function of synthesis temperature, stirring speed and solution pH value. The properties of the fabricated crystals were studied using scanning electron microscopy, X-ray diffraction and particle size analysis. The morphology of the synthesized CuO was dependent on both the pH value of the solution and the morphology of the seed materials. Synthesized particles have regular morphologies and a uniform size distribution.

On the Plasticity of Clay Mixtures with Bauxite Residue of the Bayer Process

“Bauxite Residue” (BR) is the main waste of alumina-producing Bayer process. With the aim to use BR in the heavy clay industry, the plasticity of clay mixtures with BR was studied by the “High Pressure Annular Shear Cell” (HPASC) technique. The information obtained is cohesion and pressure dependence values that enable the determination of optimal conditions for extrusion. The results for 30wt% BR addition, substituting the clay mixture, demonstrate that the maximum cohesion is increased. Nevertheless, the water demand is increased for achieving the appropriate cohesion and pressure dependence levels for extrusion, a factor that imposes increased demand for drying. By shifting the particle size distribution towards a higher mean particle size, redesigning the clay mixture or by polymer addition, the rheological behaviour of the paste can be adjusted.

Synthesis and characterization of LiMn 1.5 Ni 0.5 O 4 powders using polymerization complex method

The , substituting a part of Mn with Ni in the , the spinel structure has good charge-discharge cycle stability and high discharge capacity at 4.7 V. In this study powders were synthesized by polymerization complex method. The effect on the characteristics of synthesized powders was studied with citric acid (CA) : metal ion (ME) molar ratio (5 : 1, 10 : 1, 15 : 1, 30 : 1) and calcination temperature (). Single phase of was observed from XRD analysis on the powders calcined at low () and high temperatures (). The crystalline size and crystallinity increased with calcination temperature. At low calcination temperature the particle size decreased and specific surface area increased as the CA molar ratio increased. On the other hand, high particle growth rate at high calcination temperature interfered the particle size reduction and specific surface area increase induced by the increase of CA molar ratio.

Sintered body characteristics of LAS by addition of CaCO 3 and ZrO 2 using a solid-state reaction

LAS () ceramics were sintered by a solid-state reaction. and were added to the -spodumene () composition of the LAS system for enhancement of sintering behavior and mechanical strength, respectively. We have investigated the sintering characteristics, microstructures, mechanical properties and thermal expansion characteristics according to the change of the amount of additive and sintering temperature of the -spodumene. At 0.1 mol% , the densification of -spodumene was significantly improved. At 0.04 mol% , the strength of -spodumene was also improved. For all the selected all compositions, the thermal expansion coefficient was measured by a dilatometer, which revealed 1.2 to .

Synthesis of the orange color pigment in the system of TiO 2 -SnO-ZnO by solid state reaction

In this study, new composition of orange color pigment was developed by replacing formerly used lead and chromium with environment-friendly elements. TiO2-SnO-ZnO composite was synthesized using the solid state reaction under the reducing atmosphere with the LPG and air mixture gas. The synthesized pigments were characterized by spectrophotometer, X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and X-ray Photoelectron Spectroscopy (XPS). The colorimetric analysis of pigments exhibited color values ranging from yellow to orange-red. Five different crystalline phases were formed after the heat treatment for 4 and 6 hours. The color of pigments was strongly influenced by the crystalline structure of SnO 2 , having either cubic or tetragonal structure. The oxidation state study of elements revealed that the color of pigment is getting close to rYR with the increase of Sn 4+ ratio.

Characteristics of the sintered body of the Al 2 TiO 5 with addition of LAS (β-spodumene) and Fe 2 O 3

Al2TiO5 ceramics were sintered by a solid-state reaction. LAS (β-spodumene) and Fe2O3 were added to the Al2TiO5 composition for enhancement of sintering behavior such as mechanical strength and thermal shock resistance. The sintered body was much densified by addition of LAS and Fe2O3 because LAS formed the liquid-phase and Fe2O3 suppressed the grain growth. We have systematically investigated the sintering characteristics, microstructures, mechanical properties, and thermal shock resistance according to the change of the amount of additive. When the additive of LAS (20 wt%)-Fe2O3 was added to Al2TiO5, it confirmed that superior mechanical properties of the fracture strength of over 120 MPa and the thermal shock resistance of over 1,200 o C were achieved.

Effect of polymer compatibility on the binder migration during spray drying and compaction behavior

Granular feedstock for dry pressing is prepared by spray drying oxide powders with polymeric additives. The interactions between polymeric additives in suspension or during drying are usually considered negligible. However, recent studies demonstrate that interactions between polymers usually do occur and can adversely affect product performance. Flory-Huggins calculations predict phase separation of Na-PMAA and Na-PAA with PVA and homogeneous mixing of Na-silicate with PVA. These predictions were confirmed by the light scattering studies on polymer solutions and morphology studies on dried polymer solutions. This reveals that the interaction between polymers can lead to either a homogeneous or phase-separated solution, depending on the functional groups and chain length of polymers. PVA binder in spray-dried granules is stained and its location within the spray dried granule is observed verifying the effect of other polymers on binder migration and case-hardening of spray dried granules. The results indicate polymeric additives that prevent binder migration, potentially eliminating case-hardening in spray dried granules and the subsequent problems observed during compaction.