• 한국초전도ㆍ저온공학회논문지
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• 제25권3호
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• pp.18-21
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• 2023

Pollution of the environment by micro-plastics is now a worldwide problem. Plastics are difficult to decompose and put a great load on the marine environment. Especially a plastic with a size of 5 mm or less is defined as micro-plastic and are carried by ocean currents over long distances, causing global pollution. These are not easily decomposed in the natural environment. In this paper, we aimed to experimentally demonstrate that micro-plastics in seawater can be continuously separated by electromagnetic Archimedes force. Using polyethylene particles of 3 mm in diameter as the separation target, a flow channel was fabricated and separation conditions were investigated by particle trajectory calculations for separation experiments. Based on the calculation results, a solenoid-type superconducting magnet was used as a source of magnetic field to conduct separation experiments of micro-plastics in seawater. Although a high separation rate was assumed in the simulation results, the experimental results did not show any significant improvement in the separation rate due to the electromagnetic Archimedes force. It was found that the gas generated by the electrolytic reaction may have inhibited the migration of the particles.

• 한국대기환경학회지
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• 제29권3호
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• pp.325-337
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• 2013

The size-fractionated aerosol samples have been collected at Gosan Site of Jeju Island during the spring season of 2010, in order to examine the chemical composition characteristics of the Asian Dust and Non-Asian Dust particles. The concentrations of ${HCO_3}^-$, Al, and nss-$Ca^{2+}$ in $PM_{10}$ had tremendously increased during the heavy Asian Dust (March 20, 2010). The concentration ratios of Asian Dust to Non-Asian Dust for the soil species (nss-$Ca^{2+}$, ${HCO_3}^-$, Al, Fe, Ti, Mn) were 12.2~30.7, meanwhile those for the anthropogenic species (nss-${SO_4}^{2-}$, ${NH_4}^+$, ${NO_3}^-$, $K^+$, Zn, Pb, and Cu) were 2.9~7.8. During the heavy Asian Dust event, the concentration increase of ${NO_3}^-$ in $PM_{2.5}$ were much more apparent than those of nss-${SO_4}^{2-}$ and ${NH_4}^+$, and the soil species (nss-$Ca^{2+}$ and ${HCO_3}^-$) showed much higher concentration increase. The neutralization factor of $NH_3$ was higher than that of $CaCO_3$. However, the neutralization factor of $CaCO_3$ in $PM_{10}$ was exceptionally high during the heavy Asian Dust, showing the evidence of heavy migration of soil particles. From the study for size fractionated particles, it was found that nss-${SO_4}^{2-}$ and ${NH_4}^+$ were mostly distributed in fine particle mode, on the other hand, ${NO_3}^-$ existed evenly in both fine and coarse particle modes, and the soil species (nss-$Ca^{2+}$, Al, Fe, etc.) were mainly in the latter mode. During the heavy Asian Dust, in particular, the concentrations of ${NH_4}^+$, nss-${SO_4}^{2-}$, $K^+$, Zn, and Pb had increased in coarse particle mode as well.

• Nuclear Engineering and Technology
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• 제26권4호
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• pp.461-470
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• 1994

방사성 코발트, 스트론 , 세슘의 사암에 대한 수착특성평가 실험을 수행하였다. 수착반응속도론적 평가와 더불어 수착유형 및 가역성 등을파악하였다. 수착반응은 크게 두 단계로 나눌 수 있는데, 초기 10시간 이내에 사암외부표면에 대부분의 수착이 일어나고, 이후에는 사암입자내 미세공극을 통한 내부수착 표면으로의 확산이 수착속도 결정단계로 작용하는 과정이다. 방사성핵종이 지하매질에 수착하는 주된 수착유형을 정량적으로 평가하기 위한 방법으로서 순차적화학추출법을 도입하여 방사성핵종이 수착되어 있는 사암에 대해 탈착 실험을 수행하였다. 특히 이온교환되어 있는 세슘을 탈착시키기 위해 염화칼륨 용액으로 추출하는 공정을 도입하였다. 본 연구에서 고려한 수착유형은 지하수조건에서 가역적 수착, 이온 교환, 철망간산화 /산수소화물과의 결합, 비가역적 고착등이다. 스트론튬은 사암표면에 상대적으로 반응이 빠르고 가역적인 이온교환반응을 하였다. 코발트와 세슘은 복합적인 수착반응 양상을 보였다. 코발트의 경우, 주된 수착유형은 철망간산화 /산수소화물과의 결합이고, 비가역적인 고착도 상당비율 일어났다. 세슘의 경우, 비가역적 고착이 주된 수착유형이였으며, 이온교환도 상당비율 일어났다. 그러므로, 수착반응의 가역성 및 이동성은 스트론튬 ＞ 코발트 ＞ 세슘 순이였다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2008년도 하계학술대회 논문집 Vol.9
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• pp.546-546
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• 2008

Copper (Cu) Chemical mechanical polishing (CMP) has been an essential process for Cu wifing of DRAM and NAND flash memory beyond 45nm. Copper has been employed as ideal material for interconnect and metal line due to the low resistivity and high resistant to electro-migration. Damascene process is currently used in conjunction with CMP in the fabrication of multi-level copper interconnects for advanced logic and memory devices. Cu CMP involves removal of material by the combination of chemical and mechanical action. Chemicals in slurry aid in material removal by modifying the surface film while abrasion between the particles, pad, and the modified film facilitates mechanical removal. In our research, we emphasized on the role of chemical effect of slurry on Cu CMP, especially on the effect of amine functional group on removal rate selectivity between Cu and Tantalum-nitride (TaN) film. We investigated the two different kinds of complexing agent both with amine functional group. On the one hand, Polyacrylamide as a polymer affected the stability of abrasive, viscosity of slurry and the corrosion current of copper film especially at high concentration. At higher concentration, the aggregation of abrasive particles was suppressed by the steric effect of PAM, thus showed higher fraction of small particle distribution. It also showed a fluctuation behavior of the viscosity of slurry at high shear rate due to transformation of polymer chain. Also, because of forming thick passivation layer on the surface of Cu film, the diffusion of oxidant to the Cu surface was inhibited; therefore, the corrosion current with 0.7wt% PAM was smaller than that without PAM. the polishing rate of Cu film slightly increased up to 0.3wt%, then decreased with increasing of PAM concentration. On the contrary, the polishing rate of TaN film was strongly suppressed and saturated with increasing of PAM concentration at 0.3wt%. We also studied the electrostatic interaction between abrasive particle and Cu/TaN film with different PAM concentration. On the other hand, amino-methyl-propanol (AMP) as a single molecule does not affect the stability, rheological and corrosion behavior of the slurry as the polymer PAM. The polishing behavior of TaN film and selectivity with AMP appeared the similar trend to the slurry with PAM. The polishing behavior of Cu film with AMP, however, was quite different with that of PAM. We assume this difference was originated from different compactness of surface passivation layer on the Cu film under the same concentration due to the different molecular weight of PAM and AMP.

• Journal of Electrical Engineering and Technology
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• 제12권1호
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• pp.161-172
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• 2017

In the paper, a hybrid technique is proposed for detecting the location and capacity of distributed generation (DG) sources like wind and photovoltaic (PV) in power system. The novelty of the proposed method is the combined performance of both the Biography Based Optimization (BBO) and Particle Swarm Optimization (PSO) techniques. The mentioned techniques are the optimization techniques, which are used for optimizing the optimum location and capacity of the DG sources for radial distribution network. Initially, the Artificial Neural Network (ANN) is applied to obtain the available capacity of DG sources like wind and PV for 24 hours. The BBO algorithm requires radial distribution network voltage, real and power loss for determining the optimum location and capacity of the DG. Here, the BBO input parameters are classified into sub parameters and allowed as the PSO algorithm optimization process. The PSO synthesis the problem and develops the sub solution with the help of sub parameters. The BBO migration and mutation process is applied for the sub solution of PSO for identifying the optimum location and capacity of DG. For the analysis of the proposed method, the test case is considered. The IEEE standard bench mark 33 bus system is utilized for analyzing the effectiveness of the proposed method. Then the proposed technique is implemented in the MATLAB/simulink platform and the effectiveness is analyzed by comparing it with the BBO and PSO techniques. The comparison results demonstrate the superiority of the proposed approach and confirm its potential to solve the problem.

• 한국지하수토양환경학회지:지하수토양환경
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• 제18권3호
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• pp.109-118
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• 2013

Characteristics of the transport of zero-valent iron nanoparticles (nZVI) in an aquifer were investigated to evaluate an application of nZVI-based reactive zone technology. Main flow direction of groundwater was north. Preferential flow paths of the groundwater identified by natural gradient tracer test were shown northeast and northwest. The highest groundwater velocity was $4.86{\times}10^{-5}$ m/s toward northwest. When the breakthrough curves obtained from the gravity injection of nZVI were compared with the tracer curves, the transport of nZVI was retarded and retardation factors were 1.17 and 1.34 at monitoring wells located on the northeast and northwest, respectively. The ratios of the amount of nZVI delivered to the amount of tracer delivered at the two wells mentioned above were 24 and 28 times greater than that of the well on the main flow direction, respectively. Attachment efficiency based on a filtration theory was $4.08{\times}10^{-2}$ along the northwest direction that was the main migration route of nZVI. Our results, compared to attachment efficiencies obtained in other studies, demonstrate that the mobility of nZVI was higher than that of results reported in previous studies, regardless of large iron particle sizes of the current study. Based on distribution of nZVI estimated by the attachment efficiency, it was found that nZVI present within 1.05 m from injection well could remove 99% of TCE within 6 months.

• 한국재료학회지
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• 제17권9호
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• pp.453-457
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• 2007

Interest in use of ink-jet printing for pattern-on-demand fabrication of metal interconnects without complicated and wasteful etching process has been on rapid increase. However, ink-jet printing is a wet process and needs an additional thermal treatment such as an annealing process. Since a metal ink is a suspension containing metal nanoparticles and organic capping molecules to prevent aggregation of them, the microstructure of an ink-jet printed metal interconnect 'as dried' can be characterized as a stack of loosely packed nanoparticles. Therefore, during being treated thermally, an inkjet-printed interconnect is likely to evolve a characteristic microstructure, different from that of the conventionally vacuum-deposited metal films. Microstructure characteristics can significantly affect the corresponding electrical and mechanical properties. The characteristics of change in microstructure and electrical resistivity of inkjet-printed silver (Ag) films when annealed isothermally at a temperature between 170 and $240^{\circ}C$ were analyzed. The change in electrical resistivity was described using the first-order exponential decay kinetics. The corresponding activation energy of 0.44 eV was explained in terms of a thermally-activated mechanism, i.e., migration of point defects such as vacancy-oxygen pairs, rather than microstructure evolution such as grain growth or change in porosity.

• 한국지반공학회논문집
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• 제36권8호
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• pp.49-60
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• 2020

동상민감성 시료의 동상 거동을 평가하기 위해 완전히 결합된 열-수리-역학 연계해석을 수행하였다. 이를 위한 구성모델은 질량보존방정식, 에너지보존방정식, 힘평형방정식을 기반으로 유도되었다. 구성모델을 통해 간극수의 상변화, 간극수 유동 및 수반되는 기계적 변형 등 1차원 동결에 대한 다양한 물리적 현상을 정량적으로 고려할 수 있었다. 한편, 시료의 동상발생량 및 동상속도에 미치는 영향 인자들을 조사하기 위해 민감도 분석 연구가 수행되었다. 민감도 분석 결과에 따르면, 시료의 초기 간극비는 종속변수인 동상발생량과 동상속도에 독립적으로 큰 영향을 미치는 반면 흙 입자 열전도도 및 온도구배는 독립적으로 미치는 영향보다 두 변수 간 상호 작용을 통해 더 큰 영향을 미침을 확인하였다. 본 연구에서 고려된 인자들은 모두 동상발생량과 동상속도에 영향을 미치는 주요 인자이며, 표본시료의 동상민감성 여부를 결정하는 데에 활용될 수 있을 것이다.

• 펄프종이기술
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• 제30권3호
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• pp.74-83
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• 1998

The phenomenon of decrease in sizing efficiency when the stock temperature is increased is well recognized as summer sizing, and this is believed to be caused by uneven distribution of sizing agents on paper surface most often incurred by coagulation of sizing agents. When unevenly sized paper is used as coating base stock, nonuniform consolidation of the coating layer may result, which, in turn, causes uneven distribution of binder on coating surface. This causes nonuniform ink absorption to produce print mottle. In this study the effects of simple or polymeric electrolytes, storage temperature and time on the coagulation of cationic dispersed rosin size were investigated using a turbidity measurement method which was verified to correlate well with the particle size of rosin emulsion or its coagulates. Handsheets sized with rosin dispersions coagulated under various conditions were prepared and their sizing degree and coated paper properties including gloss and ink density were examined. The relationship between the sizing nonuniformity of coated papers and its ink absorption property was evaluated. Turbidity of rosin emulsion increased as the storage temperature and time were increased. Addition of simple or polymeric electrolytes caused reduction in $zeta$ -potential of the rosin dispersion and accelerated the coagulation tendency substantially. Reversion of the $zeta$ -potential of rosin dispersion, however, did not occur when coagulation was induced with simple electrolytes. On the other hand, addition of an anionic polyelectrolyte reversed the $zeta$ -potential of the flocculated rosin dispersion. This indicated that electrical double layer compaction and bridging flocculation were coagulation mechanisms for simple and polymeric electrolytes, respectively. Sizing degree decreased as coagulation of rosin was increased. Paper gloss, ink gloss and ink density were increased when sizing degree of base stock was increased most probably due to prevention of base paper swelling and increased binder migration to coating surface. This suggested that uneven printing ink density occurred when uneven sizing development was induced by coagulation of rosin particles.

• 한국재료학회지
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• 제28권11호
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• pp.646-652
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• 2018

During a long-term operation of polymer electrolyte membrane fuel cells(PEMFCs), the fuel cell performance may degrade due to severe agglomeration and dissolution of metal nanoparticles in the cathode. To enhance the electrochemical durability of metal catalysts and to prevent the particle agglomeration in PEMFC operation, this paper proposes a hybrid catalyst structure composed of PtCo alloy nanoparticles encapsulated by porous carbon layers. In the hybrid catalyst structure, the dissolution and migration of PtCo nanoparticles can be effectively prevented by protective carbon shells. In addition, $O_2$ can properly penetrate the porous carbon layers and react on the active Pt surface, which ensures high catalytic activity for the oxygen reduction reaction. Although the hybrid catalyst has a much smaller active surface area due to the carbon encapsulation compared to a commercial Pt catalyst without a carbon layer, it has a much higher specific activity and significantly improved durability than the Pt catalyst. Therefore, it is expected that the designed hybrid catalyst concept will provide an interesting strategy for development of high-performance fuel cell catalysts.