Papers by Author: Kyung Nam Kim

Abstract: In this study, a comparative investigation of the effect of two solvents on cadmium-doped zincoxide (Cd-ZnO) nanoparticles synthesized via the sol-gel method is presented and discussed. Zinc acetate was used as the precursor with ethanol and methanol as solvents, and cadmium nitrate tetrahydrate was used as the cadmium dopant source. The properties of the synthesized ZnO nanoparticles were examined by XRD, SEM, TEM,TG-DTA and UV-vis spectroscopy (UV-vis). It was found that the crystallite sizes of the ZnO nanoparticles ranged from 35 to 50nm and had spherical shapes, and that the particle size decreased with Cd doping. Consequently, absorbance spectra showed that the Cd-doped ZnO nanoparticles extended the light absorption properties of the material into the visible region. Furthermore, the ZnO nanoparticles synthesized with ethanol had a relatively smaller sizethan methanol which resulted in higher absorbance of ZnO synthesized with ethanol than methanol.

Abstract: In this study, the characteristics of porcelain body, glaze and inlay were analyzed, using Koryo celadon shard of 10^th-14^th century. The characterization of celadon shard were investigated by Scanning electron microscopy, X-ray fluriscence, X-ray diffractometer, and Dilatometer. The characteristics of celadon shard is similar in color to gray-green with the naked eye, and the thickness of glaze layer and body is about 149.5-200μm and 4.2-8.8mm. The chemical compositions of body is SiO₂ 70.9-74.8wt%, Al₂O₃ 19.4-20.5wt%, RO▪RO₂(R=Ca, Mg, K) 4.0-7.0wt% and Fe₂O₃1.3-2.7wt% in weight ratio. The high contents (12.5-24.6wt%) of calcium oxide in the glaze is considered lime type. In the chemical compositions of the white and black inlay Al₂O₃ is 33.2-37.1wt% and 19.7wt%, and Fe₂O₃ is 1.1wt% and 5.6wt% in weight ratio, respectively. The density of black inlay is higher than that of white inlay, and firing temperature for celadon may be about 1250°C.

Abstract: Thin films of various composition in the system of TiO2•SiO2 have been fabricated by the sol-gel process using Si(OC2H5) and Ti(OC3H7i)4 as precursors. TiO2•SiO2 films were formed on the glass substrate by spin-coating technique and heated at 500°C for 1 h. The relationship between hydrophilicity, photocatalytic properties and self-cleaning property with SiO2 addition and UV light irradiation were investigated. Photocatalytic activity of TiO2•SiO2 films showed decomposition of ~97% of acetaldehyde in 2 h and a water contact angle of ~10°. TiO2•SiO2 films can have more hydrophilic activity and less photocatalytic activity by increasing of SiO2 addition. XPS measurements revealed that the amount of organic compounds adsorbed on the films decreased with the UV light irradiation and SiO2 addition, because of the increased of both OH group contents in films and decomposed organic contaminants of the films surface.

Abstract: In this study, mine tailings obtained in a region near to Youngwol Sangdong(Korea) was used to investigate the contamination of heavy metal ions. Some amount of mine tailings and lignin(AE agent) were added in the general cement pastes, of which the compressive strength and leaching rate were investigated. X-ray fluorescence analysis shows that the major constituents of mine tailings are 56.9wt% of SiO2, 10.8wt% of Fe2O3, 11.2wt% of CaO and 11.4wt% of Al2O3, and the major phases are quartz and calcite. In the content of heavy metal ions, the concentration of As ion is the highest as 257.261mg/ℓ. When mine tailings and lignin were added in cement pastes, the compressive strength was higher in the cement pastes adding only lignin. Lignin addition significantly improved the compressive strength of cement pastes by approximately 15% when being cured in distilled water. The compressive strength was lower in the cement pastes adding mine tailings than in the cement pastes not adding. The leaching rates of Cr, Pb and As ion in distilled water were decreased in the cement pastes adding lignin, compared to in the cement pastes not adding. The leaching rates of all heavy metal ions in the cement pastes curing for 28 days were within the maximum permitted limits in KSLT and EPT method. Therefore, it is thought that mine tailings can be used as an ecological material.

Abstract: This study intends to increase the consumption of coal ash which is an industrial by-product from power plants. The coal ash used to be deposited in the ground and its recycling has been very poor comparing to the produced amount. This study aims to enhance practical application of coal ash as a shotcrete construction material. Derived were optimum mix proportions for high performance shotcrete using coal ash. In order to enhance long term performance, silica fume was also added. Experimental variables included replacement ratio of silica fume and coal ash. Compressive strength and potential hazardous contamination to soil were the primary factors in the performance evaluation. From the test results, when fly ash was replaced up to 10% of the cement, most required specifications were satisfied. Hazardous material content was shown to be well below the specifications. Therefore, when appropriate caution in handling is given in the field, it is strongly anticipated to increase the coal ash recycling as a shotcrete construction material.

Abstract: A green emitting SrAl2O4:Eu2+, Dy3+ phosphor with high brightness and long afterglow was synthesized by the sol-gel method. SrAl2O4: Eu2+, Dy3+ phosphor exhibited broad band extending from 450 to 650 nm and maximum emission spectra peaking at 520 nm. Three excited levels existed, two shoulders were observed at 270 and 330 nm in addition to the maximum at 360 nm on the excitation spectrum. After the removal of excitation light, the excellent after-glow characteristic of the phosphorescence was obtained as a result of low decay time, although the after-glow intensities of phosphor varied exponentially with the time.

Abstract: Municipal incinerator residue (MIR) was used as raw material to replace clay to manufacture bricks. Brick specimens were substituted from 0 to 50 wt% MIR by 10 wt% increment for clay. Clay-MIR brick specimens were fired at 800~1050°C for 2 h. Firing shrinkage, bulk density, water absorption rate and compressive strength were investigated. Leaching procedure tests were also conducted to characterize toxicity. Increasing MIR contents resulted in a decrease in water absorption rate, firing shrinkage and increase in compressive strength of bricks. It was found that when brick specimen with 50 wt% of MIR content was heat-treated at 1000°C for 2 h, a brick specimen could be generated, which was compressive strength of 1256 kg/cm2, water absorption ratio of 6.8% and firing shrinkage of 3.5%. This indicates that MIR is indeed suitable for the partial replacement of clay in bricks

Abstract: MgO thin film was deposited on soda lime glass substrate by sol-gel process. MgO thin film with the (200) preferred orientation were prepared by heat-treated at 300~500°C for 10 min. The crystallization, microstructure and electrical properties with various parameters of MgO thin films were investigated. Consequently, it was shows that the (200) preferred orientation of MgO thin film could be obtained as the heating temperature was increased. At heating temperature of 500°C, MgO thin film was composed of columnar crystals with a size of 120 nm. The dielectric constant of the (200) preferred orientation of MgO thin film at 1 kHz without the electric field was 7.2, with a dissipation factor of 4%. When the electric field was increased, the dielectric constant approaches to 7.9 with the dissipation factor of 2.1%. The refractive index of MgO thin film depended on the film thickness. The refractive index of 250 nm thickness was 1.70.

Abstract: Sericite has the intermediate nature of the muscovite and illite, which has been used as the additive of the cosmetics, the ceramic industry, welding rods, and other various pigments and the paint. In this study, the characteristics of sericite were examined using XRD(X-ray diffractometer), XRF(X-ray fluorescence spectrometer), TG-DTA(Thermal Analyzer), SEM(Scanning Electron Microscope) and PSA(Particle Size Analyzer). The raw ore is composed of 60.90wt% SiO2, 7.88wt% K2O, 0.36wt% TiO2, 24.80wt% Al2O3, 1.64wt% Fe2O3, 2.39wt% CaO, and 0.83wt% MgO. After sericite was purified, the content of SiO2 decreased from 60.9wt% to 51.4wt%, and in the crystal phase the intensity of quartz decreased significantly. For the high grade purification of sericite, the removal of iron and separation of quartz for the raw ore (sericite), the hydrocyclone were used with the magnetic separator. The content of iron was reduced from 1.64wt% to 0.91wt%.