• 소성∙가공
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• 제31권5호
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• pp.290-295
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• 2022

Recently, the use of high-tech ceramic parts in functional electronic parts, automobile parts and semiconductor equipment parts is increasing. These ceramics materials are required to have high reproducibility, reliability, large size and complex shapes. The researchers initiated the work to develop a new shaping method called gel casting, which allows high performance ceramic materials with a complex shape to be produced. The manufacturing process parameters of gel casting include uniform mixing of the initiator, bubble removal, and slip injection. In this study, we analyzed the dispersion and gelation characteristics according to the change in the additive content of the alumina slurry in the gel casting process. The alumina slurry for gel casting was prepared by mixing a solvent, a monomer and a dispersant through a ball mill. Alumina powder and a gelation initiator were added to the mixed solution, and ball milling was performed for 24 hours. A viscosity of 6,435 cps and a stable zeta potential value were obtained under the conditions of alumina powder content of 55 vol% and dispersant 2.0 wt%. After curing for 12 hours by adding aps 0.1wt%, TEMED 0.2wt%, and Monomer 3, 5wt%, it was possible to separate from the molding cup, confirming that the gelation was completed.

• 한국세라믹학회지
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• 제39권11호
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• pp.1042-1047
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• 2002

$Al_2O_3-SiO_2$계 세라믹 화이버를 주원료로 하는 세라믹섬유지를 제조하기 위하여 스러리 점도변화에 따른 세라믹화이버의 침강특성과 pH 변화에 따른 제타전위의 변화와 세라믹화이버 분산특성과의 관계를 분석하였다. 슬러리에서 세라믹화이버의 해섬 및 분산을 위한 슬러리 적정 점도는 28~31 cps이었고, pH 변화에 따라 제타전위는 민감하게 변화하여 pH 7.5~9.5에서 -35~-36 mV로 최대치를 나타내었으며, 이때 세라믹화이버의 침강량도 가장 적게 나타나 슬러리의 제타전위가 증가함에 따라 세라믹화이버의 분산도 잘 이루어짐을 알 수 있었다. 습식초지공정 중 흡입탈수는 함수율 83 wt% 이상으로 유지시켜야 바인더 손실을 막을 수 있었으며, 압축탈수 후 함수율이 62wt% 미만이 되어야 습식회수가 가능하였다. 제조된 세라믹섬유지는 인장강도 $102 kgf/cm^2$, 평량 $98 g/m^2$를 나타내었다.

• 한국정밀공학회지
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• 제19권10호
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• pp.156-162
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• 2002

There are many factors affecting the results of CMP (Chemical Mechanical Polishing). Among them, the temperature is related to the removal rate and WIWNU (Within Wafer Non-Uniformity). In other words, the removal rate is proportional to the temperature and the variation of temperature distribution on a pad affects the non-uniformity within a wafer. In the former case, the active chemistry improves the rate of chemical reaction and the removal rate becomes better. But, there are not many advanced studies. In the latter case, a kinematical analysis between work-piece and pad can be obtained. And such result analysed from the mechanical aspect can be directly related to the temperature distribution on a pad affecting WIWNU. Meanwhile, the temperature change affects the quantities of both slurry and pad. The change of a pH value of the slurry chemistry due to a temperature variation affects the surface state of an abrasive particle and hence the agglomeration of abrasives happens above the certain temperature. And the pH alteration also affects the zeta potential of a pad surface and therefore the electrical force between pad and abrasive changes. Such results could affect the removal rate and etc. Moreover, the temperature changes the 1st and 2nd elastic moduli of a pad which are closely related to the removal rate and the WIWNU.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2004년도 하계학술대회 논문집 Vol.5 No.1
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• pp.227-230
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• 2004

As the organic acids were added in the slurry, zeta potential of alumina was changed to negative value and IEP value was shifted from alkaline to acidic pH. In citric acid based slurry, Cu surface continuously dissolved and etching depth linearly increased. On the contrary, passivation layer was grown on Cu surface in oxalic acid based slurry. As the platen rotation speed increased, Preston coefficient decreased in both slurries. With oxalic acid based slurry, at low velocity, removal rate is high value because of high friction force compared to citric acid based slurry. As platen velocity increased, removal of Cu in citric acid based slurry became higher value than oxalic acid based slurry. Typical lubrication behaviors were observed in both slurries. As Sommerfeld number increased, COF values gradually decreased and then re-increased. It indicated that lubrication was changed to direct contact or semi-direct contact mode to hydro-lubrication mode.

• 한국응용과학기술학회지
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• 제30권4호
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• pp.635-648
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• 2013

This study was carried out to investigate the emulsifying properties of surface-active substances from defatted rapeseed cake by supercritical $CO_2$ extraction. Based on the interfacial tension data, a supercritical fluid extract (SFE) with the lowest value of 14.16 mN/m was chosen for evaluation which was obtained from No. 2 extraction condition (150 bar, $65^{\circ}C$, 250 g). For emulsions with SFE, some physicochemical properties (i.e., fat globule size, creaming stability, zeta potential etc) were investigated according to changes in SFE concentration, pH, and NaCl addition in an emulsion. It was found that fat globule size was decreased with increasing SFE concentration in emulsion, with showing a critical value at 0.5 wt%, thereby resulting in less susceptibility to creaming behavior. The SFE emulsion also showed instability at acidic conditions (pH<7.0) as well as by NaCl addition. This was coincided with zeta potential data of emulsion. In addition, SSL (sodium stearoyl lactylate) found to be suitable as a co-surfactant, as it helped considerably in decreasing fat globule size in emulsions and its optimum concentration to be over 0.03 wt%, based on 0.1 wt% SFE in emulsion.

• Journal of Pharmaceutical Investigation
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• 제38권3호
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• pp.163-169
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• 2008

Liposomes are spherical vesicles composed of lipid bilayer membranes. However, the conventional liposomes have been found to be plagued by rapid opsonization and taken up by the reticuloendothelial system (RES), resulting in shortened circulation time and limited intracellular uptake to target cell. In this study, polyethyleneglycol-cationic liposomes (PCL) containing cationic lipid and DSPE-mPEG were prepared by thin film cast-hydration method. The PEG liposomes had approximately $97.0{\pm}1.3\;nm$ of mean particle diameter and $-21.7{\pm}1.2\;mV$ of zeta potential value. PCL had $96.4{\pm}1.8\;nm$ of mean particle diameter and $-8.7{\pm}1.1\;mV$ of zeta potential value with a decrease of about 10 mV compared to the PEG liposomes. Loading of model drug, doxorubicin (DOX), in liposomes were carried out by using remote loading method and the loading efficiency of DOX in liposomes was about $95.0{\pm}1.9%$. Intracellular uptake and cytotoxicity of PCL were higher than that of PEG liposomes to murine B16F10 melanoma cells. In addition, anti-tumor activity of PCL was similar to that of PEG liposomes on growth of A549 human lung carcinoma in BALB/c mice. Consequently, PCL modified with cationic lipid may be applicable as anticancer drug carriers that can increase intracellular uptake and therapeutic efficacy.

• 한국응용과학기술학회지
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• 제30권4호
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• pp.779-789
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• 2013

This study aimed to investigate the emulsifying properties of bovine lactoferrin in food emulsion system. First, lactoferrin solution was prepared to study its surface activities, such as surface adsorption characteristics and ${\zeta}$-potential. Second, some physicochemical properties of lactoferrin emulsion which resulted from variations of environmental conditions (i.e., pH or NaCl addition) were determined. As for surface adsorption characteristics evaluated by surface tension, it was decreased with increasing lactoferrin concentration in solution ($1{\times}10^{-5}{\rightarrow}0.2wt%$) and showed a plateau (${\fallingdotseq}44$mN/m) above 0.01 wt%. It was also changed with pH and the minimum value of 53.8 mM/m was observed at pI of lactoferrin. This was related to changes in ${\zeta}$-potential of the lactoferrin solution with respect to pH. Fat globule size of lactoferrin emulsion was decreased with increasing lactoferrin concentration and a stable emulsion was formed above 0.5 wt% lactoferrin in emulsion with fat globule size $d_{32}$ of ca. 0.33 ${\mu}m$ as confirmed by creaming stability experiment (i.e., Turbiscan). As with surface tension, fat globule size of lactoferrin emulsion also changed with pH and showed a maximum value at pI. As evaluated by Turbiscan, in the presence of NaCl, the lactoferrin emulsion showed instability in particular above 10 mM.

• 한국재료학회지
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• 제26권3호
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• pp.136-142
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• 2016

To study the dispersion factors of silica sol prepared from fumed silica powder, we prepared silica sol under an aqueous system using a batch type bead mill. The dispersion properties of silica sol have a close relationship to dispersion factors such as pH, milling time and speed, the size and amount of zirconia beads, the solid content of fumed silica, and the shape and diameter of the milling impellers. Especially, the silica particles in silica sol were found to show dispersion stability on a pH value above 7, due to the electrostatic repulsion between the particles having a high zeta potential value. The shape and diameter of the impellers installed in the bead mill for the dispersion of fumed silica was very important in reducing the particle size of the aggregated silica. The median particle size ($D_{50}$) of silica sol obtained after milling was also optimized according to the variation of the size and amount of the zirconia beads that were used as the grinding medium, and according to the solid content of fumed silica. The dispersion properties of silica sol were investigated using zeta potential, turbiscan, particle size analyzer, and transmission electron microscopy.

• 폴리머
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• 제35권6호
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• pp.548-552
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• 2011

본 연구에서는 기능화된 다중벽탄소나노튜브를 준비하기 위해서 두 가지 기능화 방법인 산처리와 화학적 아미드화 방법이 수행되었다. 그리고 에폭시/기능화된 다중벽탄소나노튜브 복합재료의 특성이 연구되고 비교되었다. 기능화 방법에 따른 다중벽탄소나노튜브의 표면 관능기를 확인하기 위해 푸리에 변환 적외선 분광기(FTIR)를 사용하였다. 계면 및 열전도도에 미치는 다중벽탄소나노튜브 기능화의 효과는 제타전위차 분석기, 전자주사현미경 그리고 열전도도 분석기에 의해서 연구되었다. 이러한 결과들로 에폭시/기능화된 다중벽탄소나노튜브 복합재료의 열전도도는 dodecylamine과의 그래프팅을 통해 증가될 수 있다는 것을 알 수 있었다. 이것은 DGEBF 에폭시 수지 내에서 dodecylamine과 그래프팅한 다중벽탄소나노튜브의 상대적으로 강한 분산력에 의한 것으로 설명될 수 있었다. 이러한 결과들은 그래프팅한 다중벽탄소나노튜브의 제타전위차 값이 산처리한 다중벽탄소나노튜브의 값보다 더 높은 음의 값을 가지는 결과와 일치하였다.

• 설비공학논문집
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• 제24권5호
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• pp.454-460
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• 2012

The purpose of the present work is to investigate the removal characteristics of positively charged filters for capturing negatively charged particles such as bacteria and virus in water. In order to reduce the pressure drop and increase the filtration efficiency, the filter media, modified by charge modifier having positive functional groups, is developed and evaluated. Improved liquid filters have been developed with the modified surface charge to capture and adsorb particles by electrokinetic interaction between the filter surface and particles contained in an aqueous liquid. The positively charged filter media is composed of glass fiber, cellulose and poly-ethylenimine resin for positively charging with the variation of volume ratio. The zeta potential value of the positively charged filter is +37.92 mV at the glass fiber and cellulose content ratio of 50 : 50 with resin content of 100%, while that of the PSL test particle is -23.5 mV at pH 7. The removal efficiency of the electro-positively charged filter is 98% for PSL particles of 0.11 ${\mu}m$, while that of the negatively charged filter is 7%. The positively charged filter media showed the potential to be an effective method for removing fine particles from the contaminated water for liquid filtration.