Papers by Author: Sung Jin Kim

Abstract: Two types of welding methods were performed on austenitic 304 stainless steel: laser welding and TIG welding. The differences of the corrosion characteristics of the welded zones from the two welding methods were investigated with electrochemical methods, such as measurement of the corrosion potential, polarization curves, cyclic voltammogram, etc. The Vickers hardness of all laser-welded zones (WM:Weld Metal, HAZ:Heat-Affected Zone, BM:Base Metal) was relatively higher while their corrosion current densities exhibited a comparatively lower value than those which were TIG welded. In particular, the corrosion current density of the TIG-welded HAZ had the highest value among all other welding zones, which suggests that chromium depletion due to the formation of chromium carbide occurs in the HAZ, which is in the sensitization temperature range, thus it can easily be corroded with an active anode. Intergrenular corrosion was also observed at the TIG-welded HAZ and WM zones. Consequently, we can see that corrosion resistance of all austenitic 304 stainless steel welding zones can be improved via the use of laser welding.

Abstract: The enhancement of physical properties of porous honeycomb filter for air purification was investigated using cordierite with the addition of pore former and zirconia additive. Because cordierite honeycomb has porous body, binder formulation was varied using graphite for a pore forming agent as well as lubricating agent during the extrusion process. Also, the effect of zirconia additives on the resultant physical properties of honeycomb filter such as porosity, thermal expansion coefficient and mechanical strength was investigated.

Abstract: In the study, we attempted to synthesize the cordierite by the reaction of fly-ash and alumina, silicon dioxide, magnesia powders. And also porous cordierite honeycomb filte r for air purification was fabricated from the combination of synthetic cordierite using fly as h and pore forming agent. As the extrusion processing parameters of honeycomb, binder formul ation and extrusion conditions were investigated. Graphite addition was effective for the reduce ment of extrusion pressures. Porous cordierite honeycomb was fabricated with high porosity ( 58%), and good compressive strength (69MPa) with 30wt% graphite at low sintering tempera ture(1150oC).

Abstract: Cordierite is known as three different crystalline forms, such as metastable form (µ- cordierite), high temperature form (α–cordierite; indialite), and low temperature form (β-cordierite). In general, cordierite has a phase transition behavior from metastable form to high temperature form. In this study, we focused to synthesize the porous cordierite at low temperature using reaction method without metastable form. When we used a pure starting powders (Al2O3, MgO, and SiO2), metastable cordierite and Mg spinel phase was obtained during the heat treatment. However, fly ash based mixture used as a starting powder, we obtained a porous α–cordierite at low synthesis temperature through transition from sapphirine/spinel and mullite/spinel

Abstract: Cordierite was synthesized by the reaction sintering using a high-energy ball milling process. After a high-energy ball milling for 32hr, the reaction temperature of cordierite was reduced to 1350oC from the conventional synthesis temperature of 1460oC. High-energy ball milling process was effective for the formation of amorphous silica layer to provide a low reaction temperature of cordierite.

Abstract: To find a novel exopolysaccharide, marine bacterial strains were isolated from coastal regions of Korea. Strain 00SS11568 was then selected as it produced a mucous exopolysaccharide during the stationary phase in a batch culture. The isolate was identified as Alteromonas sp. based on its 16S rDNA sequence, morphological, and biochemical properties. The exopolysaccharide, designated as p-11568, exhibited an emulsifying ability. The Emulsification Index (E24) of 0.1% p- 11568 was 77.4% with an emulsified kerosene content, and was higher than those of commercial polysaccharides, such as xanthan gum (26.1%), gellan gum (1.3%), and sodium alginate (2.0%). p- 11568 was found to be composed of glucose and galactose as the main natural sugars in a molar ratio of 1.3:1, along with uronic acid (18.9%, w/w) and sulfate groups (1.2% w/w). The average molecular mass was 4.4 x 105 daltons by gel filtration chromatography. The effects of pH, temperature, inorganic compounds, and C and N sources were tested to obtain the optimal medium composition for the production of p-11568. Under optimal growth conditions with the M-11568 medium, 14.9 g of crude p-11568 per liter was obtained.

Abstract: In order to control the grain size of Cu-15.0Zn-8.1Al shape memory alloy, the spark plasma sintering (SPS) technique was applied. The sintering processes were carried out under different atmospheres with a different powder size. The sintered bodies were denser under the Ar+4%H2 gas atmosphere than under the 100% Ar gas. By using the small-sized powders, the fine microstructure with average grain size of 2~3􀀀 was obtained. With the large-sized powders, the single martensitic phase was observed with the average grain size of 70~72􀀀 . When the starting powders with different sizes were mixed, it is confirmed that the average grain size of the manufactured alloys was 15􀀀 , but the distribution of grain size was not uniform.