• Journal of the Korea Concrete Institute
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• v.14 no.6
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• pp.813-822
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• 2002

The purpose of the present study is first to refine the mathematical material models for moisture and temperature distributions in early-age concrete and then to incorporate those models into finite element procedure. The three dimensional finite element program developed in the present study can determine the degree of hydration, temperature and moisture distribution in hardening concrete. It is assumed that temperature and humidity fields are fully uncoupled and only the degree of hydration is coupled with two state variables. Mathematical formulation of degree of hydration Is based on the combination of three rate functions of reaction. The effect of moisture condition as well as temperature on the rate of reaction is considered in the degree of hydration model. In moisture transfer, diffusion coefficient is strongly dependent on the moisture content in pore system. Many existing models describe this phenomenon according to the composition of mixture, especially water to cement ratio, but do not consider the age dependency. Microstructure is changing with the hydration and thus transport coefficients at early ages are significantly higher because the pore structure in the cement matrix is more open. The moisture capacity and sink are derived from age-dependent desorption isotherm. Prediction of a moisture sink due to the hydration process, i.e. self-desiccation, is related to autogenous shrinkage, which may cause early-age cracking in high strength and high performance concrete. The realistic models and finite element program developed in this study provide fairly good results on the temperature and moisture distribution for early-age concrete and correlate very well with actual test data.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.180-180
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• 2012

Heteroepitaxial GaN nano- and micro-rods (NMRs) are one of the most promising structures for high performance optoelectronic devices such as light emitting diodes, lasers, solar cells integrated with Si-based electric circuits due to their low dislocation density and high surface to volume ratio. However, heteroepitaxial GaN NMRs growth using a metal-organic vapor phase epitaxy (MOVPE) machine is not easy due to their long surface diffusion length at high growth temperature of MOVPE above $1000^{\circ}C$. Recently some research groups reported the fabrication of the heteroepitaxial GaN NMRs by using MOVPE with vapor-liquid-solid (VLS) technique assisted by metal catalyst. However, in the case of the VLS technique, metal catalysts may act as impurities, and the GaN NMRs produced in this mathod have poor directionallity. We have successfully grown the vertically well aligned GaN NMRs on Si (111) substrate by means of self-catalystic growth methods with pulsed-flow injection of precursors. To grow the GaN NMRs with high aspect ratio, we veried the growth conditions such as the growth temperature, reactor pressure, and V/III molar ratio. We confirmed that the surface morphology of GaN was strongly influenced by the surface diffusion of Ga and N adatoms related to the surrounding environment during growth, and we carried out theoretical studies about the relation between the reactor pressure and the growth rate of GaN NMRs. From these results, we successfully explained the growth mechanism of catalyst-free and mask-free heteroepitaxial GaN NMRs on Si (111) substrates. Detailed experimental results will be discussed.

• Journal of the Korean Chemical Society
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• v.50 no.6
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• pp.464-470
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• 2006

the coricosteroid drug dexamethasone is an efficacious antiinflammatory drug, it is difficult to formulate in an injectable formulation due to its poor aqueous solubility. A lipid-based nanosphere formulation containing dexamethasone was designed for solubilization of the drug in aqueous solution and sustained release of the drug from the nanosphere. The lipid nanospheres, composed of phospholipid, cholesterol and cationic lipid, were prepared by self emulsification-solvent diffusion method followed by diafiltration. Physicochemical characteristics such as mean particle diameter, zeta potential and drug loading efficiency of the lipid nanospheres were investigated according to the variation of either the kind of lipid or the lipid composition. The lipid nanospheres had a mean diameter 80-120 nm and dexamethasone loading efficiency of greater than 80%. The drug loading efficiency increased with the increase of the length of aliphatic chain attached to the phospholipid. However, the drug loading efficiency was inversely proportional to the increase of cholesterol content in the lipid composition. The lipid nanosphere could not be prepared without the use of cationic lipid and the drug loading efficiency was proportional to the increase of cationic lipid content. The lipid nanospheres containing dexamethasone are a promising novel drug carrier for an injectable formulation of the poorly water-soluble drugs.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.6
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• pp.3442-3447
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• 2014

A simple method to evaluate the hygroscopic characteristics of polymer of microelectronic plastic package is suggested. To evaluate the characteristics, specimens were prepared, and the internally absorbed moisture masses were measured as a function of the absorbing time and calculated numerically. The hygroscopic pressure ratio was calculated by heat transfer analysis supported by commercial FEM code because the hygroscopic diffusion equation has the same form as the heat transfer equation. The moisture masses were then summed by the self developed code. The nonconductive polymers had quite different characteristics for the different lots, even though they were the same products. The absorbed moisture mass variations were calculated for several different characteristics, and the optimal curve of the mass variation close to experimental data was selected, whose solubility and diffusivity were affected by the hygroscopic characteristics of the material. The method can be useful in the industrial fields to quickly characterize the polymer material of the semiconductor package because the fast correspondence is normally required in industry. The weight changes in the aluminum-nonconductive-polymer joint due to moisture absorption were measured. The deformed system was also measured using the Moire Interferometry system and compared with the results of finite element analysis.

• Korean Chemical Engineering Research
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• v.48 no.3
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• pp.283-291
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• 2010

In this review, the studies on the electrochemical properties of $TiO_2$ nanotube as an anode material of lithium-ion battery, which was prepared by an alkaline hydrothermal reaction and anneling process, were investigated andanalyzed in terms of charge-dischage characteristics. Up to date, a maximum discharge capacity of $338mAh\;g^{-1}$(x=1.01) was achieved by the nanotube with $TiO_2(B)$ phase, whereas the theoretical capacity of $TiO_2$ anode was $335mAh\;g^{-1}$(x=1) in the basis of $Li_xTiO_2$ as a product of electrochemical reaction between $TiO_2$ and lithium. This was due to fast lithium transport by a shortened diffusion path provided by controlling the nanostructure of $TiO_2$, because the self-diffusion of lithium was slow in a basis of its activation energy as 0.48 eV. Due to an excellent ion storage capabilities in both the surface and the bulk phase, the $TiO_2$ nanotube could be a promising active material as both an anode of lithium-ion battery and an electrode of capacitor with high-rate performances.

• Elastomers and Composites
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• v.49 no.1
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• pp.43-52
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• 2014

The effect of nanoclay (Cloisite 20A) on the self-adhesion behavior of uncured brominated-isobutylene-isoprene rubber (BIIR) has been studied. The dispersion state of nanoclay into the rubber matrix was examined by SEM, TEM and XRD analysis. The thermal degradation behavior of the filled and unfilled samples was examined by TGA and improvement in the thermal stability of the nanocomposites occurred based on the weight loss (%) measurements. Also, addition of nanoclay enhanced the cohesive strength of the material by reinforcement action thereby reducing the degree of molecular diffusion across the interface of butyl rubber. However, the average depth of penetration of the inter-diffused chains was still adequate to form entanglement on either side of the interface, and thus offered greater resistance to peeling, resulting in high tack strength measurements. The improvement in tack strength was only achieved at critical nanoclay loading above 8 phr. Contact angle measurement was also made to examine the surface characteristics. There was no significant interfacial property change by employing the nanoclay.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.256-256
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• 2012

Cu가 기존 배선물질인 Al을 대체함에 따라 resistance-capacitance delay와 electromigration (EM) 등의 문제들이 어느 정도 해결되었다. 그러나 지속적인 배선 폭의 감소로 배선의 저항 증가, EM 현상 강화 그리고 stability 악화 등의 문제가 지속적으로 야기되고 있다. 이를 해결하기 위한 방법으로 Cu alloy seed layer를 이용한 barrier 자가형성 공정에 대한 연구를 진행하였다. 이 공정은 Cu 합금을 seed layer로 사용하여 도금을 한 후 열처리를 통해 $SiO_2$와의 계면에서 barrier를 자가 형성시키는 공정이다. 이 공정은 매우 균일하고 얇은 barrier를 형성할 수 있고 별도의 barrier와 glue layer를 형성하지 않아 seed layer를 위한 공간을 추가로 확보할 수 있는 장점을 가지고 있다. 또한, via bottom에 barrier가 형성되지 않아 배선 전체 저항을 급격히 낮출 수 있다. 합금 물질로는 초기 Al이나 Mg에 대한 연구가 진행되었으나, 낮은 oxide formation energy로 인해 SiO2에 과도한 손상을 주는 문제점이 제기되었다. 최근 Mn을 합금 물질로 사용한 안정적인 barrier 형성 공정이 보고 되고 있다. 하지만, barrier 형성을 하기 위해 300도 이상의 열처리 온도가 필요하고 열처리 시간 또한 긴 단점이 있다. 본 실험에서는 co-sputtering system을 사용하여 Cu-V 합금을 형성하였고, barrier를 자가 형성을 위해 300도에서 500도까지 열처리 온도를 변화시키며 1시간 동안 열처리를 실시하였다. Cu-V 공정 조건 확립을 위해 AFM, XRD, 4-point probe system을 이용하여 표면 거칠기, 결정성과 비저항을 평가하였다. Cu-V 박막 내 V의 함량은 V target의 plasma power density를 변화시켜 조절 하였으며 XPS를 통해 분석하였다. 열처리 후 시편의 단면을 TEM으로 분석하여 Cu-V 박막과 $SiO_2$ 사이에 interlayer가 형성된 것을 확인 하였으며 EDS를 이용한 element mapping을 통해 Cu-V 내 V의 거동과 interlayer의 성분을 확인하였다. PVD Cu-V 박막은 기판 온도에 큰 영향을 받았고, 200도 이상에서는 Cu의 높은 표면에너지에 의한 agglomeration 현상으로 거친 표면을 가지는 박막이 형성되었다. 7.61 at.%의 V함량을 가지는 Cu-V 박막을 300도에서 1시간 열처리 한 결과 4.5 nm의 V based oxide interlayer가 형성된 것을 확인하였다. 열처리에 의해 Cu-V 박막 내 V은 $SiO_2$와의 계면과 박막 표면으로 확산하며 oxide를 형성했으며 Cu-V 박막 내 V 함량은 줄어들었다. 300, 400, 500도에서 열처리 한 결과 동일 조성과 열처리 온도에서 Cu-Mn에 의해 형성된 interlayer의 두께 보다 두껍게 성장했다. 이는 V의 oxide formation energy가 Mn 보다 작으므로 SiO2와의 계면에서 산화막 형성이 쉽기 때문으로 판단된다. 또한, $V^{+5}$이온 반경이 $Mn^{+2}$이온 반경보다 작아 oxide 내부에서 확산이 용이하며 oxide 박막 내에 여기되는 전기장이 더 큰 산화수를 가지는 V의 경우 더 크기 때문으로 판단된다.

• Clean Technology
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• v.24 no.2
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• pp.105-111
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• 2018

This study presents a novel and eco-friendly process that can precisely control the location of the patches on the patch particles. The method of manufacturing these anisotropic hexagram patch particles consists of sequential combinations of two separate methods such as a sequential micromolding technique for fabricating patch particles and a selective localization method for controlling the location of patches on the patch particles. The micromolding technique was carried out using physicochemically stable material as a micromold. In order to fabricate the highly stable patch anisotropic hexagram particles, the perfluoropolyether (PFPE) micromold was used to the process of the micromolding technique because they could prevent the problem of diffusion of hydrophobic monomers while conventional poly(dimethylsiloxane) (PDMS) micromold is limited to prevent the problem of diffusion of hydrophobic monomers. Based on combination methods of the micromolding technique and the selective localization method, the reproducibility and stability have been improved to fabricate 12 different types of anisotropic hexagram patch particles. This fabrication method shows the unique advantages in eco-friend condition, easy and fast fabrication due to less number of process, the feasibility of a mass production. We believe that these anisotropic hexagram patch particles can be widely utilized to the field of the directional self-assembly.

• Korean Journal of Hazardous Materials
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• v.2 no.1
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• pp.18-26
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• 2014

We analyzed the demand of competent authorities requiring adequate technical information for initial investigation of chemical accidents. Reflecting technical reports on chemical accident response by environmental agencies in the U.S. and Canada, we presented information on environmental diffusion and toxic effects available for the first chemical accident response. Hydrogen fluoride may have the risk potential to corrode metals and cause serious burns and eye damages. In case of inhalation or intake, it could have severe health effects. The substance itself is inflammable, but once heated, it decomposes producing corrosive and toxic fume. In case of contact with water, it can produce toxic, corrosive, flammable or explosive gases and its solution, a strong acid, may react fiercely with a base. In case of hydrogen fluoride leak, the preventive measures are to decrease steam generation in exposed sites, prevent the transfer of vapor cloud and promptly respond using inflammable substances including calcium carbonate, sodium bicarbonate, ground limestone, dried soil, dry sand, vermiculite, fly ash and powder cement. The method for fire fighting is to suppress fire with manless hose stanchions or monitor nozzles by wearing the whole body protective clothing equipped with over-pressure self-contained breathing apparatus from distance. In case of transport accident accompanied with fire, evacuation distance is 1,600m radius. In cae of fire, fire suppression needs to be performed using dry chemicals, CO₂, water spray, water fog, and alcohol-resistance foam, etc. The major symptoms by exposure route are dyspnoea, bronchitis, chemical pneumonia and pulmonary edema for respiration, skin laceration, dermatitis, burn, frostbite and erythema for eyes, and nausea, diarrhea, stomachache, and tissue destruction for digestive organs. In atmosphere, its persistency is low, and its bioaccumulation in aquatic organism is also low.

• Journal of the Society of Disaster Information
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• v.16 no.2
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• pp.383-391
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• 2020

Purpose: To identify internal self ignition and ignition caused by external flames in energy storage rooms, and to analyze the difference between ignition due to overheating and ignition caused by external heat sources. Method: membrane melting point measurement, battery external hydrothermal experiment, battery overcharge experiment, comparative analysis of electrode plate during combustion by overcharge and external heat, overcharge combustion characteristics, external hydrothermal fire combustion characteristics, 3.4 (electrode plate comparison) / 3.5 (overcharge) /3.6 (external sequence) analysis experiment. Result: Since the temperature difference was very different depending on the position of the sensor until the fire occurred, it is judged that two temperature sensors per module are not enough to prevent the fire through temperature control in advance. Conclusion: The short circuit acts as an ignition source and ignites the mixed gas, causing a gas explosion. The electrode breaks finely due to the explosion pressure, and the powder-like lithium oxide is sparked like a firecracker by the flame reaction.