• Asian Journal of Atmospheric Environment
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• 제6권4호
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• pp.304-313
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• 2012

In this study, the ${\AA}$ngstrom exponent for polydispersed aerosol during dynamic processes was investigated. Log-normal aerosol size distribution was assumed, and a sensitivity analysis of the ${\AA}$ngstrom exponent with regards the coagulation and condensation process was performed. The ${\AA}$ngstrom exponent is expected to decrease because of the particle growth due to coagulation and condensation. However, it is difficult to quantify the degree of change. In order to understand quantitatively the change in the ${\AA}$ngstrom exponent during coagulation and condensation, different real and imaginary parts of the refractive index were considered. The results show that the ${\AA}$ngstrom exponent is sensitive to changes in size distribution and refractive index. The total number concentration decreases and the geometric mean diameter of aerosols increase during coagulation. On the while, the geometric standard deviation approaches monodispersed size distribution during the condensation process, and this change in size distribution affects the ${\AA}$ngstrom exponent. The degree of change in the ${\AA}$ngstrom exponent depends on the refractive index and initial size distribution, and the size parameter changes with the ${\AA}$ngstrom exponent for a given refractive index or chemical composition; this indicates that the size distribution plays an important role in determining the ${\AA}$ngstrom exponent as well as the chemical composition. Subsequently, this study shows how the ${\AA}$ngstrom exponent changes quantitatively during the aerosol dynamics processes for a log-normal aerosol size distribution for different refractive indices; the results showed good agreement with the results for simple analytic size distribution solutions.

• Carbon letters
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• 제5권2호
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• pp.51-54
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• 2004

Isotropic pitch-based carbon fiber was isothermally activated in $CO_2$ atmosphere. Structural parameters of the isotropic carbon fibers and activated carbon fibers (ACFs) were evaluated by X-ray diffraction (XRD). The $d_{002}$ and La of the carbon fibers were measured to be 4.04 ${\AA}$ and 23.6 ${\AA}$ and those of ACFs were 4.29 ${\AA}$ and 22.7 ${\AA}$, respectively, representing less ordered through activation process. The pores in the ACFs were characterized by BET, and they showed super-high specific surface area of maximum value 3,495 $m^2/g$ from average pore size of 8.3 ${\AA}$ at 59% burn-off. It was recognized that 8-9 ${\AA}$ was optimum range of pore size for efficient creation of high specific surface area. The average size of the pores formed at higher temperature ($1100^{\circ}C$) was larger than that of the pores formed at lower temperature ($900^{\circ}C$).

• 한국대기환경학회:학술대회논문집
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• 한국대기환경학회 2007년도 추계학술대회 논문집
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• pp.433-435
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• 2007

• 한국자기학회지
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• 제11권4호
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• pp.146-150
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• 2001

스퍼터 증착시 수소 첨가가 NiFe/FeMn의 교환결합 자계 (H$_{ex}$)에 미치는 영향에 대하여 연구하였다. Si(100)/Ta(50 $\AA$)/NiFe(60 $\AA$)/FeMn(250 $\AA$)Ta(50 $\AA$)의 경우는 하지층 NiFe 증착시 수소 첨가량이 8%에서 H$_{ex}$과 H$_{c}$ 최적 특성을 보였다. Si(100)/Ta(50 $\AA$)/NiFe(60 $\AA$)/FeMn(250 $\AA$)/NiFe(70 $\AA$)/Ta(50 $\AA$) 시편에서 FeMn 증착 시에는 5% 수소 혼합개스에서 H$_{ex}$가 148 Oe로서 최적 특성을 보였다. 이는 수소 첨가에 의해 하지층 NiFe의 (111) 우선배항성 향상, 결정립 크기의 증가 및 음력이 감소하였으며 그에 따라 FeMn의 (111) 우선 배향성 및 결정립의 크기가 증가한 결과이다.다.결과이다.

• Nano
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• 제13권12호
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• pp.1850137.1-1850137.9
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• 2018

A series of silica surface-capped with hexamethyldisilazane (denoted as $H-SiO_2$) were prepared by liquid-phase in-situ surface-modification method. The as-obtained $H-SiO_2$ was incorporated into acrylic amino (AA) baking paint to obtain AA/$H-SiO_2$ composite extinction paints and/or coatings. $N_2$ adsorption-desorption tests were conducted to determine the specific surface area as well as pore size and pore volume of $H-SiO_2$. Moreover, the effects of $H-SiO_2$ matting agents on the physical properties of AA paint as well as the gloss and transmittance of AA-based composite extinction coatings were investigated. Results show that $H-SiO_2$ matting agents possess a large specific surface area and pore volume than previously reported silica obtained by liquid-phase method. Besides, they have better dispersibility in AA baking paint than the unmodified silica. Particularly, $H-SiO_2$ with a silica particle size of $6.7{\mu}m$ and the dosage of 4% (mass fraction) provides an extinction rate of 95.2% and a transmittance of 79.3% for the AA-based composite extinction coating, showing advantages over OK520, a conventional silica matting agent. Along with the increase in the silica particle size, $H-SiO_2$ matting agents cause a certain degree of increase in the viscosity of AA paint as well as a noticeable decrease in the gloss of the AA-based composite extinction coating, but they have insignificant effects on the hardness and adhesion to substrate of the AA-based composite coatings. This means that $H-SiO_2$ matting agents could be well applicable to preparing low-viscosity and low-gloss AA-based matte coatings.

• 한국세라믹학회지
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• 제30권10호
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• pp.838-844
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• 1993

To control the pore size of silcia gel, formamide (FA), N,N-dimethyl formamide (DMF), polyethylene glycol (PEG) and polyacrylic acid (PAA) were added in the sol-gel process from starting solution with tetramethyl orthosilicate (TMOS). The gels were characterized using porosimeter, TG-DTA and SEM. As a result, the more contents of FA and PAA was increased the more gelation time was decreased, also the more contents of DMF and PEG was increased the more gelling time was increased. The mean pore size of gels was larger in the order of PAA, DMF, FA and PEG. And the mean pore size of porous silica glass was 59.0$\AA$, 31.5$\AA$, 29.9$\AA$ and 29.0$\AA$, respectively, heated at 75$0^{\circ}C$/100$0^{\circ}C$.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1997년도 춘계학술대회논문집
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• pp.81-84
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• 1997

The hot deformation behavior of SiCp/AA2024 composites reinforced with different sizes of SiCp reinforcements (1, 8, 15, 36, and 44${\mu}{\textrm}{m}$) was investigated by hot torsion tests. The hot restoration of the composites depending on the SiCp reinforcements particle size was studied from the effective stress - strain curves. Dynamic recrystallization (DRX) was occurred in the SiCp/AA2024 composites during the hot deformation at 320 - 43$0^{\circ}C$ under a strain rate of 1.0/sec. Also, the critical strain for DRX decreased with decreasing the reinforcement size of SiCp from 44 to 8${\mu}{\textrm}{m}$. The composite reinforced with SiCp of 8${\mu}{\textrm}{m}$ showed the highest flow stress (265 MPa) and the work hardening rate at 32$0^{\circ}C$ under a strain rate of 1.0/sec.

• 한국응용과학기술학회지
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• 제28권3호
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• pp.313-320
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• 2011

Encapsulation of L-ascorbic acid(AA) into BGsome was attempted to improve its stability. BGsome is a bio-compatible vesicular system prepared by dispersion of hydrated liquid crystalline phase formed through hydration of 1,3-butylene glycol(BG)-dissolved lecithin with an aqueous solution containing hydrophilic component. The characteristics of AA encapsulated BGsome, such as droplet size, surface charge, and solution appearance, was investigated. The concentration of AA solution had considerable effect on droplet size and surface charge of BGsome. Several tens nanometer droplet made by sonication treatment did not showed any change of size with storage time. Stability of AA was improved by encapsulation into BGsome, which was verified through DPPH test and HPLC assay.

• 공업화학
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• 제21권5호
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• pp.548-552
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• 2010

본 연구는 이소프렌에서 아세틸렌 불순물을 선택적으로 제거하기 위한 효과적인 흡착제의 개발이다. 흡착제로 기공의 크기가 $4{\AA}$에서 $5{\AA}$인 제올라이트를 이용하여 아세틸렌을 흡착하여 제거하는데 기공의 크기가 미치는 영향을 살펴보았다. 제올라이트 A의 기공크기는 Na와 Ca의 조성을 변화하여 조절하였다. 특히 아세틸렌의 주성분인 2-methyl-1-butyne-3-yen (IPA)와 2-butyne의 동역학적 지름의 차이 때문에 흡착제의 기공 크기는 흡착효과에 지대한 영향을 미치게 된다. 기공의 크기가 $5{\AA}$인 흡착제는 2-butyne의 높은 흡착력을 보였으나 IPA에는 낮은 흡착력을 보였다. 흡착등온선의 경우 개선된 Langmuir 모델이 2-butyne 흡착에 대해서 가장 좋은 fitting을 보였다. 이외에도 최적의 재생 조건을 찾기 위한 실험을 수행하였고 $300^{\circ}C$에서 12 h 동안 재생하였을 때 매우 효과적이었다.

• 한국표면공학회지
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• 제53권2호
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• pp.80-86
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• 2020

This paper is concerned with type of imperfections present within the anodic oxide films on AA2024 and surface hardness of the anodic film measured after ink-impregnation. The anodic oxide films were formed for 25 min at 40 mA/㎠ and 15±0.5℃ and 300 rpm of magnet stirring rate in 20% sulfuric acid solution. The ink-impregnation allows clear observations of not only the imperfections within the anodic oxide films but also an indentation mark on the oxide film surface made by a pyramidal-diamond penetrator for the hardness measurement. There were observed four different regions in the anodic oxide films on AA2024 and the surface hardness of the anodic oxide films appeared to be crucially dependent on the type of defects, showing 60~100 H_v on the oxide surface region I with large size black defect, 100~140 H_v on the oxide surface region II with large size grey defect, 140~170 H_v on the oxide surface region III with mall size black and/or grey defects and 170~190 H_v on the oxide surface region IV without defects. The pyramidal indentation marks were observed to be distorted in the regions with a large size black and grey defects, while no distortion of the indentation mark was observed in the regions with small size defects and without visible defects.