• 설비공학논문집
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• 제20권4호
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• pp.266-273
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• 2008

Natural gas hydrates are ice-like solid substances, which are composed of water and natural gas, mainly methane. They have three kinds of crystal structures of five polyhedra formed by hydrogen-bonded water molecules, and are stable at high pressures and low temperatures. They contain large amounts of organic carbon and widely occur in deep oceans and permafrost regions. Therefore, they are expected as a potential energy resource in the future. Especially, $1m^3$ natural gas hydrate contains up to $172Nm^3$ of methane gas, de pending on the pressure and temperature of production. Such large volumes make natural gas hydrates can be used to store and transport natural gas. In this study, three-phase equilibrium conditions for forming natural gas hydrate were numerically obtained in pure water and single electrolyte solution containing 3 wt% NaCl. The results show that the predictions match the previous experimental values very well, and it was found that NaCl acts as an inhibitor. Also, help gases such that ethane, propane, i-butane, and n-butane reduce the hydrate formation pressure at the same temperature.

• 대한화학회지
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• 제52권1호
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• pp.16-22
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• 2008

예비농축 및 분리를 위한 온라인 시스템을 소개하였다. 이 방법은 활성탄소에 흡착된 메틸티몰 블루로 납(II)의 착체형성을 기저로 한다. 간섭이온의 효과는 물론 수용액상의 산성도, 고상의 용량, 흐름변수와 같은 희석용액으로부터 납(II)의 정량회수와 고상 시약의 준비 상태에 대해 연구되었다. 예비농축 후에 금속이온은 0.5M HNO3 용액의 5 ml에 자동적으로 용출되고 납이온의 양은 불꽃원자 흡수 분광법로 측정하였다. 최적조건하에서, 수용액시료의 납이온은 컬럼에 의해 약 1000배 분리 및 농축되었다. 검출한계는 0.001mg mL-1였다. 납은 강과 수돗물시료에서 98에서 102% 회수율을 보였다.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2009년도 추계학술발표대회
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• pp.42.1-42.1
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• 2009

In recent years, it has been tried to develop the efficacy and bioactivity of Calcium Phosphate cements(CPC) as injectable bone substitute (IBS) by reinforcing them through varying the amount in its compositions and relative concentrations or adding other additives. In this study, the biocompatibility of are inforced Calcium Phosphate-Calcium Sulfate injectable bone substitute (IBS)containing poly ($\varepsilon$-caprolactone)PCL microspheres was evaluated which consisted of solution chitosan and Na-citrate as liquid phase and tetra calcium phosphate (TTCP), dicalciumphosphate anhydrous (DCPA) powder as the solid phase. The in vitrobiocompatibility of the IBS was done using MTT assay and Cellular adhesion and spreading studies. The in vitro experiments with simulated body fluid (SBF) confirmed the formation of apatite on sample surface after 7 and 14 days of incubation in SBF. SEM images for one cell morphologies showed that the cellular attachment was good. MG-63 cells were found to maintain their phenotype on samples and SEM micrograph confirmed that cellular attachment was well. In vitro cytotoxicity tests by an extract dilution method showed that the IBS was cytocompatible for fibroblast L-929.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2009년도 하계학술대회 논문집
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• pp.454-455
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• 2009

Selective emitter structure have an important research subject for crystalline silicon solar cells because it is used in production for high efficiency solar cells. A selective emitter structure with highly doped regions underneath the metal contacts is widely known to be one of the most promising high-efficiency solution in solar cell processing. Since most of the selective emitter processes require expensive extra masking and double steps process. Formation of selective emitters is not cost effective. One method that satisfies these requirements is the method of screen-printing with a phosphorus doping paste. In this paper we researched two groups of selective emitter structure process. One was using dopant paste, and the other was using solid source, in order to compare their uniformity, sheet resistance and performance condition time.

• 열처리공학회지
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• 제12권1호
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• pp.1-8
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• 1999

This study has investigated the effect of aging treatment on the microstructure and mechanical properties of Mg-6Al-xZn(x = 1.5, 2.5) alloys fabricated by the squeeze casting process. The microstructures of as-squeeze cast were composed of pro-eutectic ${\alpha}$, super saturated ${\alpha}$ and ${\beta}(Mg_{17}Al_{12})$ compound. Aged at both $200^{\circ}C$ and $240^{\circ}C$, Mg-6Al-xZn alloys showed the peak hardness due to the formation of ${\beta}(Mg_{17}Al_{12})$ precipitates. The discontinuous precipitates of the lamella type are predominant at $200^{\circ}C$ aging treatment, while the finely dispersed continuous precipitates were dominant at $240^{\circ}C$ aging treatment. Mg-6Al-xZn alloys fabricated by the squeeze casting process had the better combination of tensile strength and elongation compared to the conventionally cast alloys. As zinc contents increased, the tensile strength was increased by the solid solution strengthening effect of zinc.

• 한국재료학회지
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• 제23권9호
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• pp.525-530
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• 2013

This study investigated the continuous cooling transformation, microstructure, and mechanical properties of highstrength low-alloy steels containing B and Cu. Continuous cooling transformation diagrams under non-deformed and deformed conditions were constructed by means of dilatometry, metallographic methods, and hardness data. Based on the continuous cooling transformation behaviors, six kinds of steel specimens with different B and Cu contents were fabricated by a thermomechanical control process comprising controlled rolling and accelerated cooling. Then, tensile and Charpy impact tests were conducted to examine the correlation of the microstructure with mechanical properties. Deformation in the austenite region promoted the formation of quasi-polygonal ferrite and granular bainite with a significant increase in transformation start temperatures. The mechanical test results indicate that the B-added steel specimens had higher strength and lower upper-shelf energy than the B-free steel specimens without deterioration in low-temperature toughness because their microstructures were mostly composed of lower bainite and lath martensite with a small amount of degenerate upper bainite. On the other hand, the increase of Cu content from 0.5 wt.% to 1.5 wt.% noticeably increased yield and tensile strengths by 100 MPa without loss of ductility, which may be attributed to the enhanced solid solution hardening and precipitation hardening resulting from veryfine Cu precipitates formed during accelerated cooling.

• 열처리공학회지
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• 제9권4호
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• pp.252-260
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• 1996

A study was conducted to examine the precipitation phenomena of Al-2.1Li-2.9Cu alloy by differential scanning calorimetry and transmission electron microscopy. DSC curves were measured over the temperature range of $25{\sim}550^{\circ}C$ at a heating rate of $2{\sim}20^{\circ}C$/min.. Three heat evolution peaks and three heat absorption peaks were observed in the DSC curve for the as-quenched specimen. From DSC results and TEM analysis, it was proved that the precipitation sequence in the as-quenched specimen is supersaturated solid solution ${\rightarrow}$ GP zone ${\rightarrow}{\delta}^{\prime}{\rightarrow}T_1{\rightarrow}T_2$ and ${\theta}^{\prime}$ was detected in the peak aged specimen at $160^{\circ}C$. The major phase formed at peak hardeness in the aging at $160^{\circ}C$ was ${\delta}^{\prime}$ phase. The activation energies for the formation of ${\delta}^{\prime}$ and $T_1$ phases were 22.3kcal/mole and 24.3kcal/mole, respectively. These lower activation energies than those for diffusion of Cu and Li in Al are ascribed to the quenched-in excess vacancies.

• 한국재료학회지
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• 제14권10호
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• pp.737-742
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• 2004

$CuInSe_2$ (CIS) nanoparticles of chalcopyrite structure were directly synthesized by a solvothemal method in an autoclave with diethylamine as a solvent. A morphology change of the nanoparticles was observed as a function of reaction temperatures and times. Dense rod-type CIS nanoparticles with width of $5\sim10mm$ and length in the range of 30-80 nm were obtained at $180^{\circ}C$ for 36 hrs whereas spherical particles with diameter in the range of 5-10 nm were observed at $250^{\circ}C$ for 36 hrs. The formation of the rod-like nanoparticles in diethylamine, without double N-chelation, was explained by the Solution-Liquid-Solid (SLS) mechanism.

• Tribology and Lubricants
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• 제23권1호
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• pp.14-18
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• 2007

SCM415 alloy was implanted with nitrogen ions using plasma source ion implantation (PSII), at a dose range of $1{\times}10^{17}\;to\;6{\times}10^{17}N^{+}cm^{-2}$. Auger electron spectrometry (AES) was used to investigate the depth profile of the implanted layer. Friction and wear tests were carried out on a block-on-ring wear tester. Scanning electron microscopy (SEM) was used to observe the micro-morphology of the worn surface. The results revealed that after being implanted with nitrogen ions, the frictional coefficient of the surface layer decreased, and the wear resistance increased with the nitrogen dose. The tribological mechanism was mainly adhesive, and the adhesive wear tended to become weaker oxidative wear with the increase in the nitrogen dose. The effects were mainly attributed to the formation of a hard nitride precipitate and a supersaturated solid solution of nitrogen in the surface layer.

• Bulletin of the Korean Chemical Society
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• 제28권12호
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• pp.2459-2465
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• 2007

V2O5/TiO2-ZrO2 catalyst modified with V2O5 was prepared by adding Ti(OH)4-Zr(OH)4 powder into an aqueous solution of ammonium metavanadate followed by drying and calcining at high temperatures. The characterization of prepared catalysts was performed using XRD, DSC, solid-state 51V NMR, and FTIR. In the case of calcination temperature of 500 oC, for the catalysts containing low loading V2O5 below 25 wt % vanadium oxide was in a highly dispersed state, while for catalysts containing high loading V2O5 equal to or above 25 wt % vanadium oxide was well crystallized due to the V2O5 loading exceeding the formation of monolayer on the surface of TiO2-ZrO2. The strong acid sites were formed through the bonding between dispersed V2O5 and TiO2-ZrO2. The larger the dispersed V2O5 amount, the higher both the acidity and catalytic activities for acid catalysis.