• 한국세라믹학회지
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• 제55권3호
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• pp.275-284
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• 2018

In the ball milling process of ceramic powders, according to economic considerations for industrial applications, it is very important to quickly determine the optimum process condition with the maximum grinding efficiency. However, it is still difficult to determine the optimum condition for a ball mill with respect to the various process parameters, such as the rotational speed and the milling time. Ball milling was carried out at the same starting conditions with given amounts of alumina powders, balls and water, and was conducted slower or faster or a critical rotational speed was just determined by observing the angular position of the slurry in a semi-translucent polyethylene laboratory container. With respect to the different rotational speeds, which were slower or faster than the critical rotational speed, the particle size distribution of the grained powders and the acoustic intensity caused by cascading of the balls led to various behaviors. From the results of the particle size distribution and the acoustic signal analysis in the ball milling, there was one rotational speed that made the finest milled powder with maximum acoustic intensity. As a result, there was a correlation between the ground particle size and the acoustic intensity, which yields the interpretation that it can be possible in-situ to determine the optimum condition of ball milling by acoustic signal without repeated measurement efforts.

• 한국자기학회지
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• 제5권6호
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• pp.928-936
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• 1995

원료$(NiO,\;CuO,\;ZnO,\;Fe_{2}O_{3})$를 사용하여 원하는 조성의 NiCuZn Ferrite 를 제조하기 위해서는, 가능한 고농도 원료슬러리를 균일 혼합 및 효율적인 분쇄를 하여야 한다. 본 연구에서는 습식 볼밀을 사용하여 혼합원료 입자들의 분산상태를 유지하며, 최적의 혼합 및 분쇄조건을 확립하고자 한다. 먼저 혼합원료의 분산특성을 조사한 후, 볼밀링시 사용하고자 하는 pH 영역을 결정하고, 이 때 사용 가능한 분산제를 선택하였다. 또한, 분산제의 양, 분쇄시간, 볼밀링 가능한 슬러리의 농도 등을 조사하였다. 혼합원료의 분산거동을 조사한 결과, 혼합 및 분쇄할 때 음이온성 고분자전해질(poly acrylic ammonium salt)이 적절한 분산제였으며, 분산제 양은 0.7 wt%가 적절하였다. 이 때 최적 볼밀링 시간은 18시간이었으며 볼밀링이 가능한 슬러리의 최대 농도는 약 55 vol%이었다. 혼합원료 30 vol%슬러리에 음이온성 고분자전해질을 0.7 wt% 첨가하여 18시간 볼밀링한 결과, 혼합원료의 평균입자경은 약 $0.54\mu\textrm{m}$, 비표면적은 $12.92m^{2}/cc$이었다. 이를 $700^{\circ}C$에서 3시간 동안 하소하면 단일상의 NiCuZn Ferrite가 얻어졌다.

• 펄프종이기술
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• 제43권4호
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• pp.40-48
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• 2011

In this study, we investigated the usability of new powdered additives in the paperboard industry. We manufactured the powdered additives from peanut husks and garlic stems by grinding. The chemical composition, particle size, particle size distribution, and particle shape were investigated to identify the basic properties of the powdered raw materials. To determine the effect of the powdered additives on paper properties, handsheets were prepared by adding the powdered additives to the pulp slurry. The chemical composition, such as the contents of holocellulose, lignin, and ash, showed similar values to those of other biomass materials. The particles of peanut husk powder were irregularly shaped, smaller, and had a broader particle size distribution than those of the garlic stem powder, which had the fibril form. The particles of the two powdered raw materials showed a positioning of expansion in the fiber network, resulting in increased bulk and a loss of strength. Handsheets containing garlic stem particles were stronger than handsheets containing peanut husk particles. Finally, the new powdered additives are beneficial to the bulk of paperboard.

• 한국분말재료학회지
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• 제13권5호
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• pp.336-339
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• 2006

Magnetic properties of nanostructured materials are affected in complicated manner by their microstructure such as pain size (or particle size), internal strain and crystal structure. Thus, studies on the synthesis of nanostructured materials with controlled microstructure are necessary fur a significant improvement in magnetic properties. In the present work, nanostructured Fe-Co alloy powders with a grain size of 50 nm were successfully fabricated from the powder mixtures of (99.9% purity) $FeCl_2$ and $CoCl_2$ by chemical solution mixing and hydrogen reduction.

• 한국터널지하공간학회 논문집
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• 제15권4호
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• pp.401-413
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• 2013

최근 연약지반 터널 현장에 활용되는 슬러리 쉴드 TBM은 굴진면으로 슬러리가 주입됨으로 그 안정성을 확보하는 공법이다. 하지만 간극이 과다하여 슬러리에 의한 폐색이 발생하지 않는 조립질 지반에서는 적용이 어렵기 때문에 첨가제를 혼입하여 사용하기도 한다. 본 연구에서는 첨가제의 역할로서 탄산가스를 주입함으로 슬러리가 주입되었을 때에 간극 내에 탄산가스가 흡착하여 폐색현상을 촉진시키는 효과를 규명하였다. 실내실험 결과 탄산 혼입에 따라 슬러리 쉴드 터널이 적용 가능한 유효입경이 1.0 mm에서 2.6 mm가량으로 증가하였고, 필터계수 ${\lambda}$가 $0.007sec^{-1}$이상인 경우에 탄산에 의한 효과가 발생함을 알 수 있었다.

• 한국세라믹학회지
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• 제46권3호
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• pp.282-287
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• 2009

Rod-shaped particle reinforced $LiAlO_2$ matrices for MCFC were fabricated by an aqueous tape-casting technique. The hydrolysis reaction and agglomeration of $\gamma-LiAlO_2$ particles in aqueous slurries were inhibited by additions of $LiOH{\cdot}H_2O$ and glycerin to the aqueous $\gamma-LiAlO_2$ slurry. The tape-casting, performed using the aqueous slurry containing protein albumin, was fast and led to an effective drying at casting temperature range of $60{\sim}65^{\circ}C$. The strength of the particle reinforced matrix was improved about 4 times compared to that of matrix without reinforcement. Pore size distribution ($0.1{\sim}0.4{\mu}m$) and porosity ($50{\sim}60%$) of the reinforced matrices were determined to be appropriate for the MCFC matrix. The aqueous tape casting process is not only environmental-friendly but also efficient for fabricating MCFC matrices compared to non-aqueous tape casting.

• 한국분말재료학회지
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• 제12권3호
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• pp.192-200
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• 2005

Ultrafine copper powder was prepared from $CuO-H_2O$ slurry with hydrazine, a reductant, under $70^{\circ}C$. The influence of various reaction parameters such as temperature, reaction time, molar ratio of $N_2H_4$, PvP and NaOH to Cu in aqueous solution had been studied on the morphology and powder phase of Cu powders obtained. The production ratio of Cu from CuO was increased with the ratio of $N_2H_4/Cu$ and the temperature. When the ratio of $N_2H_4/Cu$ was higher than 2.5 and the temperature was higher than $60^{\circ}C$, CuO was completely reduced into Cu within 40 min. The crystalline size of Cu obtained became fine as the temperature increase, whereas the aggregation degree of particles was increased with the reaction time. The morphology of Cu powder depended on that of the precursor of CuO and processing conditions. The average particle size was about $0.5{\mu}m$.

• 한국광물학회지
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• 제23권3호
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• pp.191-197
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• 2010

고순도 니켈 금속염으로부터 미세하고 입도가 균일한 니켈 분말 직접 제조 연구를 수행하였다. 구형의 형상을 갖는 미세한 니켈 분말을 제조하기 위하여 입도제어가 가능한 슬러리환원법을 사용하였다. 제조된 니켈 분말에 화학성분, 입도, X선회절, 주사전자현미경 분석을 실시하여 니켈 분말의 특성을 조사하였다. 환원제로 하이드라진(hydrazine)을 사용하고, 4.5 M NaOH에서 90분 반응시켜 약 100~200 nm의 입도를 가진 분산도가 양호한 구형의 니켈 분말을 제조할 수 있었다.

• Journal of the Korean Wood Science and Technology
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• 제22권1호
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• pp.85-90
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• 1994

The flow properties of binder latices for paper coating were investigated, together with dynamic viscoelastic properties of latex films and electron micrographs of latices, under various conditions. The amphoteric latex, binder pigment latex and anionic latex were used in this work. The amphoteric latex has both anionic and cationic functional group on its surface. The binder-pigment with a core-shell structure has dual functions : plastic pigment and binder. The low shear viscosity of binder latices and clay slurry were measured with Brookfield vis cometer. At low-shear rates. the viscosity decreased with increasing particle size of latex. On the amphoteric latex surface, the carboxyl groups are assumed to be fully dissociated over the region of pH 9~12, but the density of negative groups seems to be increased because of the gradual decrease in the degree of dissociation of amino groups. Since the apparent particle size of latex increases with surface charge, the electroviscous effect can be observed. On the anionic latex surface, the charge density is assumed to be nearly constant above pH 8. However, below pH 8 the coagulation of particles could be observed probably because of the decrease in the charge density.

• 한국입자에어로졸학회지
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• 제14권3호
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• pp.73-80
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• 2018

Recently, there has been much research on the effect of ultrafine dust on human body with increasing interest in the ultrafine dust. In the Republic of Korea, there are many old thermal power plants, and the amount of ultrafine dust emitted from the thermal power plants is reported to be about 14% of the total amount of domestic fine dust. Therefore, the amount of fine dust from the flue gas desulfurization facility in the thermal power plant needs be reduced. In this study, we made an experimental setup to simulate a flue gas desulfurization facility and analyzed the physical characteristics of the particles passing through a mist eliminator. Experiments were carried out to investigate the collection efficiency of the mist eliminator by using the Arizona Test Dust in a dry environment, and then spraying limestone slurry into the flue gas desulfurization system equipped with the mist eliminator to examine the size and morphology of limestone particles upstream and downstream of the mist eliminator. Cut-off size of the mist eliminator was formed at about $6{\mu}m$. The result of this study is expected to be helpful for designing an electrostatic precipitator for removing particles passing through the mist eliminator.