• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.399-399
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• 2008

Synthesis and characterization of ZnO structure such as nanowires, nanorods, nanotube, nanowall, etc. have been studied to multifunctional application such as optical, nanoscale electronic and chemical devices because it has a room-temperature wide band gap of 3.37eV, large exiton binding energy(60meV) and various properties. Various synthesis methods including chemical vapor deposition (CVD), physical vapor deposition, electrochemical deposition, micro-emulsion, and hydrothermal approach have been reported to fabricate various kinds of ZnO nanostructures. But some of these synthesis methods are expensive and difficult of mass production. Wet chemical method has several advantage such as simple process, mass production, low temperature process, and low cost. In the present work, ZnO nanorods are deposited on ITO/glass substrate by simple wet chemical method. The process is perfomed by two steps. One-step is deposition of ZnO seeds and two-step is growth of ZnO nanorods on substrates. In order to form ZnO seeds on substrates, mixture solution of Zn acetate and Methanol was prepared.(one-step) Seed layers were deposited for control of morpholgy of ZnO seed layers by spin coating process because ZnO seeds is deposited uniformly by centrifugal force of spin coating. The seed-deposited samples were pre-annealed for 30min at $180^{\circ}C$ to enhance adhesion and crystallinnity of ZnO seed layer on substrate. Vertically well-aligned ZnO nanorods were grown by the "dipping-and-holding" process of the substrates into the mixture solution consisting of the mixture solution of DI water, Zinc nitrate and hexamethylenetetramine for 4 hours at $90^{\circ}C$.(two-step) It was found that density and morphology of ZnO nanorods were controlled by manipulation of ZnO seeds through rpm of spin coating. The morphology, crystallinity, optical properties of the grown ZnO nanostructures were carried out by field-emission scanning electron microscopy, high-resolution electron microscopy, photoluminescence, respectively. We are convinced that this method is complementing problems of main techniques of existing reports.

• Journal of the Korea Concrete Institute
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• v.25 no.3
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• pp.261-269
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• 2013

In this study, it was developed eco-friendly inorganic binding material concrete using ground granulated blast furnace slag and alkali activator (water glass, sodium hydroxides). Eight reinforced concrete beam using inoganic binding material concrete were constructed and tested under monotonic loading. The major variables were mixture ratio of alkali activator, type of admixture and admixture. Experimental programs were carried out to improve and evaluate the flexural performance of such test specimens, such as the load-displacement, the failure mode, the maximum load carrying capacity, and ductility capacity. All the specimens were modeled in scale-down size. The eco-friendly concrete using inorganic binding material encouraged alkali activation reaction was rapidly hardening speed and showed possibility as a high strength concrete. Also, the RC beams using new materials showed similar behavior and failed similarly with RC beam used portland cement. It is thought that eco-friendly inorganic binding material concrete can be used with construction material and product as a basic research to replace cement concrete. If there is application to structures in PC member as well as production of 2nd concrete product, it could be improved the productivity and reduction of construction duration etc.

• Journal of the korean academy of Pediatric Dentistry
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• v.28 no.1
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• pp.118-128
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• 2001

This study was performed to evaluate the toothbrush abrasion characteristics of seven commercially available light-cured cervical restorative materials one resin-modified glass-ionomer material(Fuji II LC) three polyacid-modified composites(Compoglass, Dyract, F2000), and three light-cured composites(Heliomolar, Palpique Estelite, UniFil F). All samples were stored in distilled water at $37^{\circ}C$ for 10 days. 2.0N of weight was loaded during the test and the abraded surfaces were examined with profilometer and SEM after 100,000 cycles. The results obtained were summarized as follows; 1. The highest hardness value of 79.7 was observed in the FT group and the lowest value of 20.0 was observed in the HM group. Results of Tukey test showed that an overall significant difference was indicated except the CG and DR groups(p<0.05). 2. The highest surface roughness was observed in the FL group and the lowest was observed in the UF group. Results of Tukey test showed the significant difference between the FL or FT and UF groups(p<0.05). 3. Statistically higher abrasion and surface roughness were observed for the dentifrice of paste type, Perio A+, than for that of gel paste type, Tom & Jerry. 4. The surface roughness values increased on the abraded surfaces because of the protrusion of filler particles due to selective removal of matrix resin.

• Journal of the Korean Magnetics Society
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• v.3 no.2
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• pp.108-114
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• 1993

This paper presents a study on the effects of silica coating in the production of ${\gamma}-Fe_{2}O_{3}$ powders suitable for magnetic recording media. Emphasis has been put on investigating the relationship between the powder characteristics and the effects of silica coating in the heat-treatment stage of ${\gamma}-Fe_{2}O_{3}$ production. After we prepared non-coated ${\gamma}-Fe_{2}O_{3}$ and silica coated ${\gamma}-Fe_{2}O_{3}$ with coating water glass on the surface of goethite and heattreatment process, we compared and investigated powder characteristics. As silica coated layer played a role of preventing the powders from overreduction to metal iron and rapid oxidation, silica coated ${\gamma}-Fe_{2}O_{3}$ showed superior magnetization value due to inhibiting t!1e adulteration of ${\alpha}-Fe_{2}O_{3}$ into the final product. When silica coated layer acted as a sintering restrainer, silica coated ${\gamma}-Fe_{2}O_{3}$ showed high coercivity and specific sur-face area due to good acicularity.

• Elastomers and Composites
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• v.47 no.1
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• pp.43-53
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• 2012

A suspension copolymerization of styrene and butyl methacrylate (BMA) in the aqueous phase was conducted at a selected temperature between 65 and $95^{\circ}C$. Hydrophobic silica was selected as a stabilizer and azobisisobutyronitrile (AIBN) as an initiator. Optimum dispersion of silica in water was obtained at pH 10 while polymerization reaction was run at pH 7. TGA and EDS measurements revealed that 90% of silica functioned as a stabilizer and 10% were incorporated into polymeric particles. Average particle diameter decreased with increasing amounts of stabilizer. Molecular weights displayed an increase when the stabilizer concentration reached 1.67 wt%. An increase in the initiator concentration and/or reaction temperature raised the reaction rate but decreased molecular weights. Particle diameter was nearly independent of the initiator concentration and reaction temperature. An increase in the BMA proportion decreased the glass transition temperature and increased the particle diameter with irregularity in shape. Incorporation of carbon black into the particles composed of styrene and BMA prolonged the reaction time before reaching completion. We have confirmed that a suspension copolymerization of styrene and BMA with hydrophobic silica as a stabilizer can produce spherical composite particles with $1-30{\mu}m$ in diameter containing carbon black.

• Korean Journal of Environmental Agriculture
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• v.28 no.3
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• pp.281-288
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• 2009

The strobilurin fungicides, azoxystrobin and kresoxim-methyl, were investigated to know the biological half-lives and dissipation patterns in Korean melon under plastic film house condition. Used pesticides for field application were 20% azoxystrobin of suspension concentrate and 47% kresoxim-methyl of water dispersible granule. Two pesticides were sprayed at recommended and double dose rate. Pesticide residues in Korean melon were analyzed until 14 days after application. The azoxystrobin was analyzed by HPLC equipped with UV detector after cleanup with florisil glass column. Initial residue concentrations of azoxystrobin in Korean melon at recommended and double dose rate were 0.09 mg/kg and 0.14 mg/kg, respectively. Those were less than 0.2 mg/kg maximum residue limit of Korean melon established by KFDA. The biological half-lives of azoxystrobin in Korean melon were 4.7 days at recommended dose rate and 7.8 days at double dose rate. Initial concentrations of kresoxim-methyl which was analyzed by GLC-ECD in Korean melon at recommended and double dose rate were 0.10 mg/kg and 0.23 mg/kg, respectively. Those were less than 1.0 mg/kg, MRL. The biological half-lives of kresoxim-methyl in Korean melon were 4.1 days at recommended dose rate and 4.8 days at double dose rate. The residue amounts of both pesticide was lower than MRL and biological half-lives were not so long. Because the weight of Korean melon under plastic film house condition was fast increased during cultivation.

• Journal of the Korean Wood Science and Technology
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• v.43 no.6
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• pp.868-875
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• 2015

In order to replace existing slit type steel plate on the wooden structure joint, the FRP-reinforced laminated plates were produced. Four types of FRP-reinforced laminated plates were produced according to the type of reinforcement and adhesive, and before applying to the joint, the adhesion performance test according to KSF 3021 and KSF 2160 and the Compact Tension (CT) type fracture toughness test specified in ASTM D5045-99 were carried out. As a result of adhesion performance test, all GFRP textile, GFRP sheet, and GFRP Textile-Sheet type FRP-reinforced laminated plates satisfied the requirement of soaking delamination percentage with smaller than 5% based on KS standard. However, aramid type specimen satisfied the standard as the soaking delamination percentage of 4.8% but it did not satisfied the standard as the water proof soaking delamination percentage of 70%. As a result of fracture toughness test, the volume ratio of reinforcement to timber became 23% so that the strength of FRP-reinforced laminated plates increased by two to four times in comparison to the control specimen. It was confirmed that the GFRP Textile-Sheet type specimen was most resistant to the fracture most since the ratio of stress intensity factor compared with that of the control increased to 61% owing to the parallel arrangement of glass fiber to the load. As a result of tensile shear strength test using FRP-reinforced laminated plates and nonmetal dowels, it is about 12% lower than metal connectors.

• Journal of the Microelectronics and Packaging Society
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• v.10 no.2
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• pp.1-5
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• 2003

In this project, the efficiency of localized heating for micro systems packaging is developed by using a forced potential scheme microheater. Less than 0.2 Mpa contact pressure was used for bonding with a 200 mA current input for $50{\mu}m$ width, $2{\mu}m$ height and $8mm{\times}8mm$, $5mm{\times}5mm$, $3mm{\times}3mm$ sized phosphorus-doped poly-silicon microheater. The temperature can be raised at the bonding region to $800^{\circ}C$, and it was enough to achieve a strong and reliable bonding in 3 minutes. The IR camera test results show improved uniformity in heat distribution compared with conventional microheaters. For performing the gross leak check, IPA (Isopropanol Alcohol) was used. Since IPA has better wetability than water, it can easily penetrate small openings, and is more suitable for conducting a gross leak check. The pass ratio of bonded dies was 67%, for conventional localized heating, and 85% for our newly developed FP scheme. The bonding strength was more than 25Mpa for FP scheme packaging, which shows that FP scheme can be a good candidate for micro-scale hermetic packaging.

• Journal of the Korean Ceramic Society
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• v.25 no.3
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• pp.251-260
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• 1988

Ion-exchange porous glasses were prepared by heat treatment and subsequently hydro thermalor acid leaching treatment $10Li_2O$.$(90-x)B_2O_3$.$xSiO_2$ base glasses containing various amount of $Al_2O_3$ or $MoO_3$. It was investigated how the phase separation and the cation exchange capacity(CEC) were affected by the addition of $Al_2O_3$ or $MoO_3$. The optimum condition of phase separation in these glasses was about 48$0^{\circ}C$ for 10 hrs. The degree of phase separation was rapidly suppressed by the addition of $Al_2O_3$ up to 10 mol% and thereafter suppression effect was decreased. The maximum value of CEC, about 252meq/100g, was observed with the $1OLi_2O$.$45B_2O_3$.$45SiO_2＋7.5Al_2O_3$ porous glass prepared by hydrothermal treatment and its mean pore radius was about 16.3A. The addition of $MoO_3$ accelerated phase separation and leaching rate. Looking at the remakable increment of pore diameter and pore volume of these porous glasses by the addition of $MoO_3$, the effect of $MoO_3$ may be ascribed to the lowering of silica concentration in the borate phase and to the forming of water-soluble complex with silica during the leaching treatment.

• Journal of the Korean Geotechnical Society
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• v.29 no.1
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• pp.93-107
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• 2013

Thermal conduction of the particulate composites or granular materials can be widely used in porous materials and geotechnical engineering. And it has continued to develop "effective thermal conductivity" of medium by modeling energy relationship among particles in medium. This study focuses on the development of the effective thermal conductivity at the unsaturated conditions of soils using the modified network model approach assisted by synthetic 3D random packed systems (DEM method, Discrete Element Method) at the particle scale. To verify the network model, three kinds of glass beads and the Jumunjin sand are used to obtain experimental values at various unsaturated conditions. The PPE (Pressure Plate Extractor) test is then performed to obtain SWCC (Soil-Water Characteristic Curve) of soil samples. In the modified network model, SWCC is used to adjust the equivalent radius of thermal cylinder at contact area between particles. And cutoff range parameter to define the effective zone is also adjusted according to the SWCC at given conditions. From a series of laboratory tests and the proposed network model, the modified network model which adopts a SWCC shows a good agreement in modeling thermal conductivity of granular soils at given conditions. And an empirical correlation between the fraction of the mean radius (${\chi}$) and thermal conductivity at given saturated condition is provided, which can be used to expect thermal conductivity of the granular soils, to estimate thermal conductivity of granular soils.