• Asian Journal of Atmospheric Environment
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• 제4권2호
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• pp.106-114
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• 2010

By the application of novel double detector system of micro-PIXE that can detect light elements (Z<14), we made an attempt to provide a thorough discussion on the aging processes of Asian dust (hereafter called "AD") particle by reaction with sea-slat. The elemental spectra and maps obtained from the microbeam radiation of micro-PIXE to individual AD particles were useful for fractionating AD particles into both internally and externally mixed particles. A spatial distribution of elements in a minute domain of single particle obtained by scanning the microbeam irradiation enabled us not only to estimate the chemical mixing state of individual AD particles but also to presume their aging processes in both ambient air and cloud. By calculating the normalized micro-PIXE net count of elements, it was possible to classify individual AD particles into three distinct groups (i.e., (1) Aging type 1: AD particle coated by the gaseous Cl evaporated by the reaction between artificial acids and sea salt; (2) Aging type 2: AD particle mixed with sea salt but no additional reaction with artificial acids; and (3) Non-aged type) A relatively high transformation rate (63.3-75.9%) was shown in large particles (greater than $5.1\;{\mu}m$ in diameter).

• Elastomers and Composites
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• 제43권4호
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• pp.230-240
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• 2008

분산중합법에 의해 무기물을 포함하는 고분자 미립자를 합성하기 위해 styrene과 n-butyl methacrylate가 알루미나와 함께 중합되었다. Styrene과 n-butylmethacrylate의 무게 비는 3:1이었고, 입자안정제는 poly(N-vinyl pyrrolidon), 중합 개시제로는 2,2'-azobis(isobutyronitrile)를 사용하여 개시제의 농도, 분산매의 종류, 분산매의 혼합 용해도 상수 (${\delta}_{mix}$), 커플링제의 종류와 농도에 따른 입자경을 조사하였다. 개시제의 농도가 증가함에 따라 입자경이 소폭 상승하였고 분산매의 극성이 증가할수록 입경이 증가하였고, 분산매로서, 이소프로판올과 이온교환수를 조성비에 따라 사용한 경우, $[{\delta}_{mix}]^{-4.01}\;{\propto}$ 평균 입자경과 $[{\delta]_{mix}]^{-0.83}\;{\propto}$ 입경 분포의 관계를 얻을 수 있었다. 커플링제의 종류와 농도변화에 따른 입자경 및 입자경 분포는 뚜렷한 차이가 없었다.

• Asian-Australasian Journal of Animal Sciences
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• 제23권4호
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• pp.483-490
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• 2010

The objectives of this study were to measure particle size and evaluate the effect of increasing alfalfa hay particle size on production characteristics in lactating Holstein dairy cows. Ninety multiparous Holstein cows in early to mid-lactation were randomly assigned in a complete randomized design for a 30-day period. Animals were offered one of the three diets, which were identical in energy, protein, and chemical composition, but differed only in particle size of alfalfa hay. The treatments were A) total mixed ration (TMR) in which only fine chopped alfalfa hay was incorporated in the ration, B) the same diet in which half of the alfalfa hay was fine chopped and incorporated in the mixed ration and half was long hay and offered as a top dressing, and C) the same diet with long hay alfalfa offered as a top dressing. Distribution of particle size of rations was determined through 20,000, 8,000 and 1,000 ${\mu}m$ sieves. The new method of quantitative determination of manure index was examined for each cow on different treatments. The geometric mean length of particle size in the rations was 5,666, 9,900 and 11,549 ${\mu}m$ for treatments A, B and C, respectively. Fat corrected milk (4%), milk fat percentage and production were significantly different (p<0.05) in treatment A versus B and C (fat corrected milk (FCM, 4%)) 28.3 vs. 35.2 and 32.3 kg/d, fat percentage 2.89, 4.04 and 3.62; but the change of ration particle size had no significant effect on milk production (p>0.05). Blood concentration of cholesterol in treatment A was significantly higher (p<0.05) than treatment B and C (181.0 vs. 150.0 and 155.2 mg/dl). Manure index in treatment C was significantly different (p<0.05) from treatment B (15.86 vs. 17.67). Based on these experimental findings, it is concluded that an increase in the ration particle size can increase milk fat percentage due to providing more physically effective fiber, which in turn could effect changes in manure consistency.

• 한국염색가공학회지
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• 제21권1호
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• pp.30-37
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• 2009

Studies on plants such as lotus leaf suggested that dual-scale structure could contribute to super-hydrophobicity. We introduced super-hydrophobicity onto poly(ethylene terephthalate)(PET) fabric with dual-scale structure by assembling $TiO_2$ nano sol. PET fabric was treated with $TiO_2$ sol, water-repellent agent using various parameters such as particle size, concentration. Morphological changes by particle size were observed using field emmission scanning electron microscopy(FE-SEM) and AFM measurement, contact angle measurement equipment. The contact angle of water was about 138.5$^{\circ}$, 125.8$^{\circ}$, 125.5$^{\circ}$ and 108.9$^{\circ}$ for PET fabric coated with 60.2nm, 120.1nm, 200nm and 410.5nm $TiO_2$ particles, compared with about 111.5$^{\circ}$ for PET fabric coated with water repellent. When we mixed particle sizes of 60.2nm and 120.1nm by 7:3 volume ratio, the contact angle of water was about 132.5$^{\circ}$. And we mixed particle sizes of 60.2nm and 200nm by 7:3 volume ratio, the contact angle of water was about 141.8$^{\circ}$. Also we mixed particle sizes of 60.2nm and 410.5nm by 7:3 volume ratio, the best super-hydrophobicity was obtained. In this paper, we fabricated various surface structures to the water-repellent surfaces by using four types of $TiO_2$ nano-particles, and we found that the nanoscale structure was very important for the super-hydrophobicity.

• Tribology and Lubricants
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• 제39권2호
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• pp.72-75
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• 2023

Silicon carbide (SiC) is used as a substrate material for power semiconductors; however, SiC chemical mechanical polishing (CMP) requires considerable time owing to its chemical stability and high hardness. Therefore, researchers are attempting to increase the material removal rate (MRR) of SiC CMP using various methods. Mixed-abrasive CMP (MAS CMP) is one method of increasing the material removal efficiency of CMP by mixing two or more particles. The aim of this research is to study the mathematical modeling of the MRR of MAS CMP of SiC with SiO₂ and TiO₂ particles. With a total particle concentration of 32 wt, using 80-nm SiO₂ particles and 25-nm TiO₂ particles maximizes the MRR at 8 wt of the TiO₂ particle concentration. In the case of 5 nm TiO₂ particles, the MRR tends to increase with an increase in TiO₂ concentration. In the case of particle size 10-25 nm TiO₂, as the particle concentration increases, the MRR increases to a certain level and then decreases again. TiO₂ particles of 25 nm or more continuously decreased MRR as the particle concentration increased. In the model proposed in this study, the MRR of MAS CMP of SiC increases linearly with changes in pressure and relative speed, which shows the same result as the Preston's equation. These results can contribute to the future design of MAS; however, the model needs to be verified and improved in future experiments.

• Applied Science and Convergence Technology
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• 제25권6호
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• pp.162-165
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• 2016

APhotocatalysis process uses ambient oxygen from air and irradiation, fundamentally UV light, to generate oxidation and reduction which can degrade almost all harmful organic and inorganic compounds to nontoxic substances. This study was focused on enhancement of photocatalytic activity which improves the photocatlytic efficiency with $TiO_2$ particle by mixing of certain amounts of Zn particles. We analyzed degradation of organic pollutant materials such as toluene and phenol with the mixed photocatalysis by using UV-visible spectrophotometer and obtained a result that photocatalytic activity is increased with increasing amount of Zn particle. Especially, in the case of $TiO_2$ (1 mmol) and Zn (0.1 mmol) mixture photocatalyst, we obtained at least 2 times higher photocatalytic activity compared with the commercially available $TiO_2$ photocatalyst (Degussa P-25), indicating that our mixed photocatalyts (Zn-doped $TiO_2$) is very effective of removing both organic dye and pollutants and the conversion rate of toluene is much faster than that of phenol.

• 콘크리트학회논문집
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• 제23권6호
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• pp.757-763
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• 2011

콘크리트의 효율적인 조기강도 확보를 위해 시멘트의 성능 향상에 주안점을 두고 연구를 진행하였다. 이 연구는 선행 연구인 시멘트 생산 공정 중 부수적으로 발생되는 크기가 작은 시멘트(이하 미립자 시멘트, FC라 함)를 이용하는 콘크리트의 조기강도 발현 특성 연구에 대한 후속 연구로서 내구성 검토를 실시하였다. 실험 결과 굳지 않은 콘크리트에서는 각 배합별 목표 범위를 모두 만족하는 것으로 나타났고, 미립자 시멘트를 혼입하였을 때 응결시간은 촉진되었고 압축강도는 증진되었으며 수화열은 유사한 수준인 것으로 평가되었다. 특히, 내구성 측면에서는 미립자 시멘트 혼입 유 에 따라 모든 실험 항목에서 유사한 수준인 것으로 평가되었다.

• 대한화장품학회지
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• 제19권1호
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• pp.85-107
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• 1993

화장품에 사용되는 미분체의 혼합특성을 알기 위하여 화장품용 미분체 혼합기인 ribbon mixer, powder mixer micropulverizer, fine impact mill에 미립자, 구상 및 판상의 형태를 가진 bulk powders를 혼합시간을 변화 시키면서 혼합하는 실험을 하였다. 혼합분체의 혼합정도를 평가하기 위하여 산화철을 tracer로 사용하였으며, 원료 및 혼합물의 particle size distribution, specific surface area, density 및 표면색상을 측정하였다. 미분체 혼합물의 혼합시간과 표면색상변화, 입도분포 및 비표면적과의 사이에 대수적 1차 상관관계가 성립되었고, 색상의 변화로부터 혼합정도를 평가할 수 있는 간단한 식을 도출하였다. 사용된 혼합기에 대해 혼합기구별 modelling과 혼합에 따른 입도 분포 및 비표면적의 변화로부터 혼합기 impellar tip에서의 linear velocity별 혼합기는 대류혼합, 전단혼합 및 확산혼합으로 분류되었다.

• 한국재료학회지
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• 제22권7호
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• pp.352-357
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• 2012

$SnO_2$-mixed and Sn-doped $TiO_2$ nanoparticles were synthesized via a hydrothermal process. $SnO_2$-mixed $TiO_2$ nanoparticles prepared in a neutral condition consisted of anatase $TiO_2$ nanoparticles(diamond shape, ~25 nm) and cassiterite $SnO_2$ nanoparticles(spherical shape, ~10 nm). On the other hand, Sn-doped $TiO_2$ nanoparticles obtained under a high acidic condition showed a crystalline phase corresponding to rutile $TiO_2$. As the Sn content increased, the particle shape changed from rod-like(d~40 nm, 1~200 nm) to spherical(18 nm) with a decrease in the particle size. The peak shift in the XRD results and a change of the c-axis lattice parameter with the Sn content demonstrate that the $TiO_2$ in the rutile phase was doped with Sn. The photocatalytic activity of the $SnO_2$-mixed $TiO_2$ nanoparticles dramatically increased and then decreased when the $SnO_2$ content exceeded 4%. The increased photocatalytic activity is mainly attributed to the improved charge separation of the $TiO_2$ nanoparticles with the $SnO_2$. In the case of Sn-doped $TiO_2$ nanoparticles, the photocatalytic activity increased slightly with the Sn content due most likely to the larger energy bandgap caused by Sn-doping and the decrease in the particle size. The $SnO_2$-mixed $TiO_2$ nanoparticles generally exhibited higher photocatalytic activity than the Sn-doped $TiO_2$ nanoparticles. This was caused by the phase difference of $TiO_2$.

• 한국건축시공학회지
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• 제14권1호
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• pp.11-20
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• 2014

This research examined the effect of the quality of aggregate on concrete workability and compressive strength through an investigation into regional aggregate used in domestic ready mixed concrete plants. Through the research, it was found that aggregate for ready mixed concrete shows poor quality overall. The main factor of deterioration in the quality of the concrete is the particle size of fine aggregate and fine particle content in coarse aggregate. The quality of aggregate significantly influences concrete's workability, which is defined based on 0.08mm passage related with powder and absorption. In addition, poor aggregate quality leads to increased water content in concrete to secure workability, which is related with a decline in the compressive strength and durability of concrete.