Papers by Author: Hyung Mi Lim

Abstract: The ZrO₂ nanoparticles for highly refractive index nanocomposite are synthesized according to reaction temperature, zirconium precursor concentration, and kinds of precursor such as zirconium iso-propoxide (ZIP) and zirconium n-propoxide (ZNP). At lower reaction temperature the monoclinic phase is formed, whilst higher temperature favors the tetragonal and cubic phases. As the precursor concentration increased, the particle size of ZrO₂ nanoparticle slightly increased. TEM images prove that the ZrO₂ nanoparticles are spherical and monodisperse with a diameter of about 4 nm. The synthesized ZrO₂ was modified methacryloxy propyltrimethoxy silane (MPS) for dispersibility in organic solvent. Fourier transform infrared spectroscopy (FT-IR) and thermogravimetric analysis (TGA) illustrate that MPS are chemically attached to the surface of the ZrO₂. The ZrO₂ synthesized from ZNP and ZIP dispersed in o-phenylphenoxyethyl acrylate (OPPEA) is the highly transparent and the refractive index of this nanocomposite is 1.649 and 1.670, respectively.

Abstract: Highly crystalline and dispersible zirconia, synthesized by solvothermal reaction of zirconium (IV) isopropoxide isopropanol complex in benzyl alcohol, were functionalized with silane coupling agent and dispersed with o-phenylphenoxyethyl acrylate (OPPEA). Silane coupling agents such as 3-aminopropyltriethoxysilane (APTES) of amino functional silane, decyltrimethoxysilane (DTMS) of alkyl functional silane and 3-(trimethoxysilyl) propyl methacrylate (MPS) of acrylate functional silane have been used to modify nanoparticle surfaces and obtain dispersion of nanoparticles within OPPEA. The surface modified zirconia was compared according to silane coupling agent, FT-IR and TGA demonstrated that APTES, DMTS and MPS are chemically attached to the surface of the zirconia. The MPS-zirconia is dispersed as about 5 nm sized, whereas the APTES-zirconia, DTMS-zirconia are agglomerated. The MPS-zirconia/tetrahydrofuran (THF) sol at 15wt% loading shows high transmittance of 68 % at 550 cm^-1 and the 50wt% surface modified-zirconia/OPPEA sol show refractive index of 1.657.

Abstract: Zinc oxide(ZnO) has been widely applied in the fields of cosmetics, paint, coating and gas sensor. Size down of ZnO is essential for the preparation of sol or film of ZnO in the application. The size and shape of ZnO particles are controlled by varying drying method. The ZnO was prepared by mixing of zinc acetate and sodium hydroxide at 0°C. Then it was freeze dried or 20°C vacuum dried. After washing the residual ions, it was further compared by drying at 20°C vacuum drying or 200 °C oven drying. The ZnO powder was characterized by XRD, Brunauer-Emmet-Teller analysis(BET) and transmission electron microscope(TEM). The ZnO have wurzite structure with ~10 nm particle size when it was prepared by freeze drying and then 20°C vacuum drying after washing the residual ions. On the other hand, without freeze drying, the ZnO particles observed to be aggregated to 200~400 nm with primary particle size of ~20 nm. The smaller size of ZnO particle in freezing drying compared to 20°C vacuum drying may be explained by frozen water preventing the growth of ZnO particles.

Abstract: Nano size silica particles were produced by direct oxidation of silicon powder in the water with the base catalysts. The average size of 10~100 nm was successfully prepared from the starting material of silicon powder with variable procession parameters such as silicon solid content, choice of catalyst and amount, the order of mixing, etc. The sodium hydroxide and ammonium hydroxide was chosen for the base catalysts and their amount and addition order were found to control the size of silica particles in the oxidation reaction. The limited amount of NH4OH as the first catalyst seemed to limit the number of nucleus particles, and the limited amount of NaOH further feeded only for particle growing rather than nucleus formation, thereby it was observed to be able to control the average size of particles to be as large as 100 nm. The possible mechanism of particle growth was suggested by solubility of silica and relative affinity of NH4 + and Na+ ions to the surface of SiO2.

Abstract: The coatings composed of colloidal silica, methyltrimethoxy silane (MTMS), water, and acid catalysts have been prepared with variation of colloidal silica contents from 0 to 20 %. All the coatings were prepared and coated on the aluminum plate under the same condition except the contents of colloidal silica, and the compensating contents of MTMS and water with fixed molar ratio of MTMS and water to be 3. The physical properties were compared in terms of hardness, adhesion strength, corrosion, wear resistance, and thermo gravimetry analysis, etc. The pencil hardness was drastically increased with the addition of 5% colloidal silica particles and was further increased slightly by increase of additional silica. The corrosion resistance of the coating film against alkali solution was improved by increasing colloidal silica content, however, the acid resistance was less affected by the content of colloidal silica.

Abstract: TiO2/SiO2 hybrid film, having water resistance, for water purification photocatalyst was successfully and firmly coated on stainless steel with one dip coating and heat curing method. By controlling relative content of the TiO2 sol and the SiO2 based binder, these films were found to have a significant influence on the hardness, water-resistance, and photocatalytic activity.

Abstract: Physical properties of various inorganic materials have been measured in terms of pore size distribution and porosity, BET surface area by nitrogen adsorption, pH, ion conductivity, and concentration of ions after elution test. The microbial survival rate and their stability have been monitored in every 10 days during 120 days by dilution plating method. The correlations between physical property of the inorganic carrier and microbial survival rate have been examined for the better preparation of microbial fertilizer. Average size of pore, and concentration of soluble ions were unequivocal factors affecting on microbial survival rate but BET surface area, average porosity, and ion conductivity revealed the equivocal correlation with microbial survival rate. Higher concentration of soluble ions gives lower survival rate and inorganic carriers with high microbial survival rate seemed to have preferred range of pore size.

Abstract: Zeolites with different sizes and structures were applied on the surface of cellulose fibers with organic and inorganic binders. The effects of zeolite structure and size and choice of binder on the deodorization rate have been studied. The smaller the particle size, the more effective the deodorization rate of both the zeolite coated cellulose fibers and the powder itself. The deodorization rate depends on both the type and amount of inorganic binder. A silica based inorganic binder revealed higher efficiency on deodorization than silicate based inorganic binder and also higher than organic binders.

Abstract: The application of VOC-free materials for building interior is the first step to reduce the contamination level, however, it is practically unavoidable to find a way to eliminate existing pollutants from furniture, adhesives, etc. As a positive way of controlling the air indooors, the air conditioner may be applied with high functional filter, which uses electricity for compulsory air circulation. As an alternative, we modified natural zeolite powder by ion exchange and also by addition of TiO2 photo-catalyst for multifunctional powder to contribute to controlling the indoor air quality. The modified zeolites were applied on the interior non-woven polypropylene sheet to reduce indoor air pollutants not only by adsorption mechanism but also by decomposition mechanism. We studied deodorization of the multi-functional powders and also their coating on non-woven textiles by a Gastec method.

Abstract: Layered double hydroxide(LDH) was synthesized from the mixture of magnesium hydroxide and aluminum hydroxide with microwave irradiation. It has been compared with that of conventional heating method in the respect of crystallization time, structure, morphology, particle size, and its anion exchange capacity. The microwave speeded up the crystallization rate of Mg-Al- LDH so that the XRD patterns of LDH was observed from the sample after microwave hydrothermal treatment, while the crystal phase was hardly observed from that prepared by conventional hydrothermal method before drying process. Mg-Al-LDH prepared with microwave irradiation seemed to have slightly higher Mg/Al molar ratio even with the same compositions of starting materials and the lower anion exchange capacity after 1 day exposure in 0.1N NaCl solution compared to the conventionally prepared one.