• 한국산업보건학회지
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• 제30권1호
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• pp.1-9
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• 2020

Objectives: The purpose of this case study is to assess workers' exposure to carbon nanotubes(CNTs) and characterize particles aerosolized during the process of producing CNT-enabled polytetrafuoroethylene(PTFE) composites at a worksite in Korea. Methods: Personal breathing zone and area samples were collected for determining respirable concentrations of elemental carbon(EC) using NIOSH(National Institute for Occupational Safety and Health) Method 5040. Personal exposure to nano-sized particles was measured as the number concentration and mean diameter using personal ultrafine particle monitors. The number concentration by particle size was measured using optical particle sizers(OPS) and scanning mobility particle sizers(SMPS). Transmission electron microscopy (TEM) area samples were collected on TEM grids and analyzed to characterize the size, morphology, and chemistry of the particles. Results: Respirable EC concentrations ranged from 0.04 to 0.24 ㎍/㎥, which were below 23% of the exposure limit recommended by NIOSH and lower than background concentrations. Number concentrations by particle size measured using OPS and SMPS were not noticeably elevated during CNT-PTFE composite work. Instant increase of number concentrations of nano-sized particles was observed during manual sanding of CNT-PTFE composites. Both number concentrations and mean diameters did not show a statistically significant difference between workers handing CNT-added and not-added materials. TEM analyses revealed the emission of free-standing CNTs and CNT-PTFE aggregate particles from the powder supply task and composite particles embedded with CNTs from the computer numerical control(CNC) machining task with more than tens of micrometers in diameter. No free-standing CNT particles were observed from the CNC machining task. Conclusions: Significant worker exposure to respirable CNTs was not found, but the aerosolization of CNTs and CNT-embedded composite particles were observed during handing of CNT-PTFE powders and CNC machining of CNT-PTFE composites. Considering the limited knowledge on the toxicity of CNTs and CNT composite particles to date, it seems prudent to take a precautionary approach for the protection of workers' health.

• 폴리머
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• 제26권3호
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• pp.367-374
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• 2002

본 연구에서는 나노 입자의 카본블랙을 결정성 고분자에 분산시켜 특정한 온도에서 저항이 급격하게 증가하는 positive temperature coefficient resistance (PTCR) 특성을 연구하였다. 열가소성 수지를 이용한 PTCR 소재를 열처리에 의하여 고분자의 큐리온도를 조절할 수 있었다. 나노입자 카본블랙이 고분자 구조내에 고르게 분산이 되지 않고, 카본블랙의 함량이 과다하면 negative temperature coefficient resistance (NTCR) 현상이 발생하였다. 카본블랙의 함량과 내부전압을 조절함에 따라 발열 온도를 선정할 수 있었다. 카본블랙의 함량에 따라 전기 전도성이 다르게 나타났으며, 20 wt% 이상에서는 저항이 거의 일정하게 나타난다는 것을 확인하였다. 본 연구에서 제조된 PTCR 소재는 반복적인 가열 냉각에 따른 상온에서의 초기 저항의 변화가 거의 없어 재현성을 확인하였으며, 초기의 낮은 저항에 의한 순간적인 발열에 의하여 저온에서의 PTCR 성능이 향상되었다.

• 전기학회논문지
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• 제57권4호
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• pp.625-628
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• 2008

Ba-Zn ferrite powders for electromagnetic insulator were synthesized by self-propagating high-temperature synthesis(SHS) with a reaction of $xBaO_2+(1-x)ZnO+0.5Fe_2O_3+Fe{\rightarrow}Ba_xZn_{1-x}Fe_2O_4$. In this study, phase indentification of SHS products was carried out by using x-ray diffractometry and quasi-nano sized Ba-Zn powders were prepared by a pulverizing process. SHS mechanism was studied by thermodynamical analysis about oxidation reaction among $BaO_2,\;ZnO,\;Fe_2O_3$, and Fe. As oxygen pressure increases from 0.25 MPa to 1.0 MPa, the SHS reactions occur well and make clearly the SHS products. X-ray analysis shows that final SHS products formed with the ratio of $BaO_2/ZnO$ of 0.25, 1.0 and 4.0, are mainly $Ba_xZn_{1-x}Fe_2O_4$. Based on thermodynamical evaluation, the heat of formation increases in the order of $ZnFe_2O_4,\;BaFe_2O_4$, and $Ba_xZn_{1-x}Fe_2O_4$. This supports that $Ba_xZn_{1-x}Fe_2O_4$ phase is predominately formed during SHS reaction. The SHS reactions to form $Ba_xZn_{1-x}Fe_2O_4$ depends on oxygen partial pressure, and the heat of formation during the SHS reaction. The SHS reactions tends to occur well with increasing the oxygen partial pressure and BaO2/ZnO ratio in the reactants This means that the SHS reaction for the formation of Ba-Zn ferrite includes the reduction of BaO2/ZnO and the oxidation of Fe. $Ba_xZn_{1-x}Fe_2O_4$ powders after pulverizing is agglomeratedwith a size of about $50{\mu}m$, in which quasi-nano sized particles with about 300nm are present.

• 한국분말재료학회지
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• 제18권3호
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• pp.290-296
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• 2011

Titanium carbonitride is more perspective materials compared to titanium carbide. It can be used in tool industry and special products because of its higher strength, abrasive wear-resistance and especially its strong chemical stability at high temperatures. We produced STS+TiCxNy composite by the spark plasma sintering for higher strength and studied the characteristics. The planar and cross-sectional microstructures of the specimens were observed by scanning electron microscopy. Characterizations of the carbon and nitride phases on the surface of composite were carried out using an X-ray diffractometer. During annealing TiCxNy particles diffusion into STS 430 was observed. After annealing, sintering isolations between particles were formed. It causes decreasing of mechanical strength. In addition when annealing temperature was increased hardness increased. Heterogeneous distribution of alloying elements particles was observed. After annealing composites, highest value of hardness was 738.1 MHV.

• Bulletin of the Korean Chemical Society
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• 제35권1호
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• pp.35-38
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• 2014

Herein, we report on the preparation of red fluorescent Si nanoparticles stabilized with styrene. Nano-sized Si particles emit fluorescence under UV excitation, which could be used to open up new applications in the fields of optics and semi-conductor research. Unfortunately, conventional methods for the preparation of red fluorescent Si nanoparticles suffer from the lack of a fully-established standard synthesis protocol. A common initial approach during the preparation of semi-conductors is the etching of crystalline Si wafers in a HF/ethanol/$H_2O$ bath, which provides a uniformly-etched surface of nanopores amenable for further nano-sized modifications via tuning of various parameters. Subsequent sonication of the etched surface crumbles the pores on the wafer, resulting in the dispersion of particles into the solution. In this study, we use styrene to occupy these platforms to stabilize the surface. We determine that the liberated silicon particles in ethanol solution interact with styrene, resulting in the substitution of Si-H bonds with those of Si-C as determined via UV photo-catalysis. The synthesized styrene-coated Si nanoparticles exhibit a stable, bright, red fluorescence under excitation with a 365 nm UV light, and yield approximately 100 mg per wafer with a synthesis time of 2 h. We believe this protocol could be further expanded as a cost-effective and high-throughput standard method in the preparation of red fluorescent Si nanoparticles.

• 폴리머
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• 제31권3호
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• pp.177-183
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• 2007

본 연구에서는 라벤더 오일을 심물질로 이용하여 나노크기의 폴리(비닐 아세테이트)(poly(vinyl acetate), PVAc) 방향 입자를 유화-확산법으로 제조하였다. 방향 물질의 방출 시기와 속도 조절로 방향 캡슐의 지속성과 내구성을 얻기 위하여 제조 조건에 따른 나노 방향 입자의 특성과 방출 거동을 주사 전자 현미경, 전기 영동 광산란 분광 분석기, 자외선-가시광선 분광 분석기 및 고성능 액체 크로마토그래피를 이용하여 고찰하였다. 제조된 방향 입자는 실험 조건을 조절함에 따라 평균 입자 크기가 224 nm인 구상 나노 입자로 제조하는 것이 가능하였으며, 170시간 동안의 방출 거동을 비교.평가한 결과 PVA로 코팅한 방향 입자가 더 지속적이고 안정적인 초기 방출 거동을 보임을 확인할 수 있었다. 본 연구의 PVAc 나노 방향 입자는 직물 및 피혁제품 등에 대한 내구성 방향가공에 적용될 수 있을 것으로 기대된다.

• 자원리싸이클링
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• 제23권6호
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• pp.22-29
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• 2014

네오디뮴 폐자석 침출액으로부터 희유금속인 네오디뮴을 회수하는 연구와 함께 네오디뮴과 같이 침출되는 철의 부가가치를 높이는 연구가 필요하다. 본 연구에서는 네오디뮴과 같이 침출되는 철의 유용자원화를 위한 기초연구로 철 나노분말을 제조하는 실험을 수행하였다. 본 연구는 $FeCl_3$ 용액을 철 분말 원료로, 분산제는 $Na_4P_2O_7$와 Polyvinylpyrrolidone를 이용하였고, 환원제로는 $NaBH_4$, 철 나노분말 핵생성 촉진제 seed로 염화팔라듐을 사용하였다. 제조한 철 나노분말을 XRD, SEM을 이용하여 분말의 형상 및 크기를 분석하였다. Fe와 $NaBH_4$의 몰 비를 1 : 5로 조절하여 철 분말을 제조하였으며, 이 때 철 분말은 구형이었으며, 입도는 약 50 ~ 100 nm 였다. 분산제 $Na_4P_2O_7$의 경우 100 mg/L에서 철 이온의 제타포텐셜이 음의 값을 가졌고, $FeCl_3$ 과 PVP와 Pd의 질량비 1 : 4 : 0.001에서 분산이 양호하고, 입도가 100 nm 인 철 나노분말을 합성하였다. 같은 반응 조건에서 폐 Nd 침출액의 Fe 이온을 pH를 조절하여 슬러리화한 후 실험을 진행한 결과, pH 9에서 구형의 철 분말을 합성할 수 있었으며, 20 L 이상의 Scale-up 공정에서는 분산제 없이 환원제로 175 nm 크기의 철 분말을 합성할 수 있었다.

• 한국대기환경학회지
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• 제22권5호
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• pp.653-660
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• 2006

Due to the stronger exhaust emission regulations and the introduction of advanced technology in Diesel engine, the specific Diesel particulate matters have decreased by about one order of magnitude since the 1980's. In recent years, particle number emissions rather than particulate mass emissions have become the subject of controversial discussions. Recent results from health studies imply that it is possible that particulate mass does not properly correlated with the variety of health effects attributed to Diesel exhaust. Concern is instead now focusing on nano-sized particles. This study has been performed for the better understanding about the Diesel nano-particle measurement and size distribution characteristics in the exhaust system of a turbo charged Diesel engine. A scanning mobility particle sizer(SMPS) system was applied to measure the particle number and size concentration of Diesel exhaust particles. As the experimental results, the number concentrations in the particle size (Dp<200 nm) were very sensitive to dilution conditions. Specially the changes in nano-particle number concentrations(Dp<50 nm) increased along the downstream of exhaust flow. Also we found the dilution conditions were influencing the condensation of SOF and $H_2O$ during dilution and cooling of hot exhaust.

• 한국환경보건학회지
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• 제39권4호
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• pp.369-375
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• 2013

Objectives: This study was conducted to identify factors determining the toxicity of manufactured silver nano-particles (AgNPs) on aquatic organisms. Methods: For this purpose, we prepared several AgNPs with varied characteristics, including hydrodynamic size (nano-$^{ABC}Ag^{Cit}\;vs$-sized-$^{ABC}Ag^{Cit}$), impurities ($^{ABC}Ag$ stock vs $^{ABC}Ag$), and citrate capping ($^{ABC}Ag^{Cit}$), using a commercially available manufactured AgNP ($^{ABC}Ag$ stock). Acute tests were conducted using larval zebrafish (Danio rerioI). In addition, in order to determine the ecotoxicological potentials of various capping agents, toxicity tests were conducted with microbes, waterfleas, and fish for eight different capping agents that are used for NPs. Results: The toxicity of AgNPs in terms of 96 h fish $LC_{50}$ increased in the following order: $^{ABC}Ag$ stock < $^{ABC}Ag=^{ABC}Ag^{Cit}=nano-^{ABC}Ag^{Cit}$ < ${\mu}$-sized-$^{ABC}Ag^{Cit}$ < $AgNO_3$. After removing impurities by dialysis, 96 h $LC_{50}$ value decreased significantly from $126.6{\mu}g/L$ (95% confidence intervals [CI]: 107.0-146.2) ($^{ABC}Ag$ stock) to $78.6{\mu}g/L$ (CI: 72.7-84.8) ($^{ABC}Ag$). For ${\mu}$-sized-$^{ABC}Ag^{Cit}$ (ranging between 3.9 and 40.6 nm) and $^{ABC}Ag^{Cit}$ (40.6 nm and $9.1{\mu}m$), the 96 h $LC_{50}$ of the former ($43.9{\mu}g/L$, CI: 36.0-51.7) was approximately two-fold lower than that of the latter ($87.0{\mu}g/L$, CI: 73.5-100.3). Conclusions: In this study, we found that for acute lethality, the contribution of impurities and particle size was significant, but that of citrate was negligible.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.1417-1422
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• 2003

An electrical cascade impactor is a multistage impaction device to separate airborne particles into aerodynamic size classes using electrical method. We designed a real-time three-stage electrical low-pressure impactor, which is proper to nanometer sized environmental aerosols. Performance evaluation was carried out for stage 1 and 2. The monodisperse liquid dioctyl sebacate (DOS) particles were generated using condensation-evaporation followed by electrostatic classification using DMA (differential mobility analizer) for particles with diameters in the range of $0.04{\sim}0.8{\mu}m$. The evaluation of the electrical impactor is based on the use of two electrometers, one connected to the impaction plate of the impactor, and the other to the faraday cage as backup filter. The results showed that the experimental 50% cutoff diameters in the operation pressure were 0.53 and $0.12{\mu}m$ for stage 1 and stage 2. The effect of operation pressure on the cutoff diameter and the steepness of collection effcieicy curves is investigated.