Hyung Mi Lim

Effect of Catalyst on the Colloidal Silica Particle Growth in Direct Oxidation of Silicon

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.

Modification of Natural Zeolite Powder and Its Application to Interior Non-Woven Textile for Indoor Air Quality Control

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.

The Effect of Sodium Tripolyphosphate on Sodium Silicate-Cement Grout

Sodium silicate has been widely used as starting materials of chemical grout owing to its feasibility and short setting time with reasonable strength. Elution of sodium has been pointed out as the main reason of weak durability of homogel prepared with sodium silicate-cement grout. There are well known series of additives for controlling its setting time, fluidity, and compressive strength. We studied the structural change on the sodium silicate with additive of sodium tripolyphosphate (STPP) by 29Si nuclear magnetic resonance spectrum and viscosity. The homogel was prepared by mixing cement/water suspension and diluted sodium silicate/STPP mixtures, and aged in the water. The development of compressive strength and its structural change were observed using a universal test machine, X-ray diffraction, and scanning electron microscope. The additive changed the distribution of Si and rheological property of liquid sodium silicate, which caused more uniform distribution of Ca and Si in the homogel to lead to high initial strength and durability.

Characterization of surface charge and zeta potential of colloidal silica prepared by various methods

Colloidal silica is prepared by hydrolysis of TEOS, direct oxidation of Si powder, condensation of silicic acid, etc. There are differences in surface reactivity of silica particle due to the preparation routes. Therefore, it is useful to evaluate surface properties accurately in order to understand the physiochemical properties of the products. The surface charge density, site density and zeta potential with respect to three types of colloidal silica were estimated and discussed. The surface charge density was different depending on preparation method. It is decreasing in the order of direct oxidation, ion exchange, TEOS hydrolysis. The zeta potential is decreasing in the order of ion exchange, TEOS hydrolysis, direct oxidation. The order in surface charge density is different from that in zeta potential because of the difference in stability depending on the particle size and surface charge density.

Fe4[Fe(CN)6]3가 코팅된 Mica 또는 TiO2/Mica 적외선 반사용 청색안료 제조 및 이 도료의 차열 특성 평가

Fe4[Fe(CN)6]3 coated on a mica or TiO2/mica surface as infrared reflective blue pigment was prepared by a hydrothermal method. Fe4[Fe(CN)6]3, used as coloring agent, was uniformly coated on mica or TiO2/mica under the optimized condition of a 1.2 : 1 weight ratio between iron(III) chloride hexahydrate and potassium ferrocyanidetrihydrate at the initial pH level of 4.5 at 70˚C. The infrared (IR)-reflective pigments were characterized by SEM, Zeta-potenial, FT-IR, and UV-VIS NIR spectrophotometry. Especially the CIE color coordinate and total solar reflectance(TSR) properties of the pigments were investigated in relation to variation of the coating and coated substrate thicknesses. Isolation-heat paint was prepared with 20 wt% blue pigments fully dispersed in acryl-urethane resin and several additives to coat the film uniformly. The films were also measured with CIE color coordinate, TSR, and the surface temperature was recorded by an isolation-heat measuring system. The pigments and films of Fe4[Fe(CN)6]3 coated on mica and TiO2/mica showed high TSR values compared with the TSR value of Fe4[Fe(CN)6]3 itself. According to the increase of TSR value, the property of isolation-heat is effective. To realize the optimal blue color, we applied the the pigment to TiO2 coated mica(TM(b)) which has blueish interference color. The pigment of Fe4[Fe(CN)6]3 coated on TM(b) shows a strong blue color compared with that of Fe4[Fe(CN)6]3 coated on TiO2/Mmca(TM(w)), which has a whitish interference color.

Preparation of Mg(OH) 2 -Melamine Core-Shell Particle and Its Flame Retardant Property

Magnesium hydroxide-melamine core-shell particles were prepared through the coating of melamine monomer on the surface of magnesium hydroxide in the presence of phosphoric acid. The melamine monomer was dissolved in hot water but recrystallized on the surface of magnesium hydroxide by quenching to room temperature in the presence of phosphoric acid. The core-shell particle was applied to low-density polyethylene/ ethylene vinyl acetate (LDPE/EVA) resin by melt-compounding at as flame retardant. The effect of magnesium hydroxide and melamine content has been studied on the flame retardancy of the core-shell particles in LDPE/EVA resin according to the preparation process and purity of magnesium hydroxide. Magnesium hydroxide prepared with sodium hydroxide rather than with ammonia solution revealed higher flame retardancy in core-shell particles with LDPE/EVA resin. At 50 wt% loading of flame retardant, core-shell particles revealed higher flame retardancy compared to that of the exclusive magnesium hydroxide in LDPE/EVA composite, and it was possible to satisfy the V0 grade in the UL-94 vertical test. The synergistic flame retardant effect of magnesium hydroxide and melamine core-shell particles was explained as being due to the endothermic decomposition of magnesium hydroxide and melamine, which was followed by the evolution of water from the magnesium hydroxide and porous char formation due to reactive nitrogen compounds, and carbon dioxide generated from melamine.

Effect of Particle Size of Ceria Coated Silica and Polishing Pressure on Chemical Mechanical Polishing of Oxide Film

Submicron colloidal silica coated with ceria were prepared by mixing of silica and nano ceria particles and modified by hydrothermal reaction. The polishing efficiency of the ceria coated silica slurry was tested over oxide film on silicon wafer. By changing the polishing pressure in the range of with the ceria coated silica slurries in , rates, WIWNU and friction force were measured. The removal rate was in the order of 200, 100, and 300 nm size silica coated with ceria. It was known that the smaller particle size gives the higher removal rate with higher contact area in Cu slurry. In the case of oxide film, the indentation volume as well as contact area gives effect on the removal rate depending on the size of abrasives. The indentation volume increase with the size of abrasive particles, which results to higher removal rate. The highest removal rate in 200 nm silica core coated with ceria is discussed as proper combination of indentation and contact area effect.

Highly Thermal Conductive Alumina Plate/Epoxy Composite for Electronic Packaging

In this study, alumina plates 9~25 μm in size were used as thermal fillers, and epoxy resin was used as a polymer matrix. Oriented alumina plate/epoxy composites were prepared using a rolling method. The effect of ordering alumina plates increased with alumina plate size. The thermal conductivity and flexural strength of the composites were investigated. The horizontal thermal conductivity of the oriented composite was significantly higher than the vertical thermal conductivity. The horizontal thermal conductivity of the 75 wt% alumina content was 8.78 W/mk, although the vertical thermal conductivity was 1.04 W/mk. Ordering of the alumina plate using a rolling method significantly improved the thermal conductivity in the horizontal direction. The flexural strengths of the ordered alumina/epoxy composites prepared at different curing temperatures were measured.

Preparation and Characterizations of Polymethylmethacrylate (PMMA)/Acrylate Rubber (ACM) Blend for Light Diffuser Applications

Dynamically vulcanized PMMA/ACM (80 wt%/20 wt%) blend using DCP as a curing agent was prepared using internal mixer. The morphology, mechanical properties, optical properties, melt viscosity and die swell were characterized by using FE-SEM, tensile test, Izod impact test, dynamic mechanical analysis, ARES and capillary rheometer, respectively. The blends show a phase-separated morphology in which ACM are dispersed in PMMA matrix. Dynamically vulcanized blend exhibits higher mechanical properties, higher melt viscosity, and die swell as compared to simple blend. And, the dynamically vulcanized blend showed total transmittance of more than 75% and haze of higher than 90%, which enable it to find potential applications to fabricate an optical diffuser by extrusion process.

Application of Zeolites on Cellulose Fiber

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.