• 대한금속재료학회지
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• 제48권4호
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• pp.326-334
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• 2010

Porous and net-shaped tantalum powder for a capacitor was formulated in a SHS (self-propagating high-temperature synthesis) process. However, this powder, which has weak strength among its particles and low flow ability, cannot be used for a capacitor. Therefore, this powder was sintered in a high-vacuum furnace to increase agglomeration to improve the flow ability, bonding strength among the particles, and shrinkage during pellet sintering. Finally, it was deoxidated with 2 wt% Mg powder to remove the increased surface oxygen that arose during the sintering process. The final product was analyzed in terms of its chemical and physical properties and was compared with a commercial powder used by a capacitor manufacturer.

• 한국재료학회지
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• 제12권10호
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• pp.784-790
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• 2002

For mass product of nanocrystalline ZnO ultrafine powders, self-sustaining combustion process(SCP) and ultrasonic spray combustion method(USCM) were applied at the same time. Ultrasonic spray gun was attached on top of the vertical type furnace. The droplet was sprayed into reaction zone of the furnace to form SCP which produces spherical shape with soft agglomerate crystalline ZnO particles. To characterize formed particles, fuel and oxidizing agent for SCP were used glycine and zinc nitrate or zinc hydroxide. Respectively, with changing combustion temperature and mixture ratio of oxidizing agent and fuel, the best ultrasonic spray conditions were obtained. To observe ultrasonic spray effect, two types of powder synthesis processes were compared. One was directly sprayed into furnace from the precursor solution (Type A), the other directly was heated on the hot plate without using spray gun (Type B). Powder obtained by type A was porous sponge shape with heavy agglomeration, but powder obtained using type B was finer primary particle size, spherical shape with weak agglomeration and bigger value of specific surface area. 9/ This can be due to much lower reaction temperature of type B at ignition time than type A. Synthesized nanocrystalline ZnO powders at the best ultrasonic spray conditions have primary particle size in range 20~30nm and specific surface area is about 20m$^2$/g.

• 한국재료학회지
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• 제15권5호
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• pp.334-339
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• 2005

Nickel Powders were synthesized by the reduction of $Ni(OH)_2$ reactant slurries from nonaqueous media, and the morphological characteristics of nickel powders with the addition of NaOH, the composition of mixed solvents, reaction temperature and reaction time were investigated. The NaOH addition changed the structure of agglomeration in the submicron range. As the volume ratio of TEA to DEA increased, the powders slightly suppressed the agglomeration between particles and their size increased. The reaction temperature on size and shape of nickel powders was significant. As reaction time was shortened from 40 min to 0.3 min at $220^{\circ}C$, size distribution of nickel powders was transferred to a narrow size distribution owing to the presence of smaller particles with below $1.0\;{\mu}m$.

• Geomechanics and Engineering
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• 제34권5호
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• pp.473-480
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• 2023

Acid rain of soils has a significant impact on mechanical properties. An X-ray diffraction test, scanning electron microscope (SEM) test, laser particle size analysis test, and triaxial unconsolidated undrained (UU) test were carried out in red clay soils with different compaction degrees under the effect of different concentrations of acid. The experiments demonstrated that: the dissolution effect of acid rain on colluvium weakened with the increase in the compacting degree under the condition of certain pH values, i.e., the damage to the structure of red clay soil was relatively light, where the number of newly increased pores in the soil decreased and the agglomeration of soil particles increased; for the same compacting degree, the structural gap decreased, and the agglomeration increased with the increase in the pH value (acidity decreases) of the acid rain; the dissolution rate of Si, Al, Fe, and other elemental minerals and cement in red clay soil was found to be higher under the effect of acid rain, in turn destroying the original structure of the soil body and producing a large number of pores. This is macroscopically expressed as the decrease of the soil cohesion and internal friction angle, thereby reducing the shear strength of the soil body.

• 한국전기전자재료학회논문지
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• 제17권2호
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• pp.138-143
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• 2004

CMP (Chemical Mechanical Polishing) technology for global planarization of multilevel interconnection structure has been widely studied for the next generation devices. Among the consumables for CMP process, especially, slurry and their chemical compositions play a very important role in the removal rates and within-wafer non-uniformity (WIWNU) for global planarization ability of CMP process. However, CMP slurries contain abrasive particles exceeding 1 ${\mu}{\textrm}{m}$ size, which can cause micro-scratch on the wafer surface after CMP process. Such a large size particle in these slurries may be caused by particle agglomeration in slurry supply-line. In this work, to investigate the effects of agglomeration on the performance of oxide CMP slurry, we have studied an aging effect of silica slurry as a function of particle size distribution and aging time during one month. We Prepared and compared the self-developed silica slurry by adding of alumina powders. Also, we have investigated the oxide CMP characteristics. As an experimental result, we could be obtained the relatively stable slurry characteristics comparable to aging effect of original silica slurry. Consequently, we can expect the saving of high-cost slurry.

• Applied Science and Convergence Technology
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• 제26권6호
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• pp.208-213
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• 2017

Flexible opto-electronic devices are developed on the insulating layer deposited stainless steel (STS) substrates. The silicon dioxide ($SiO_2$) material as the diffusion barrier of Fe and Cr atoms in addition to the electrical insulation between the electronic device and STS is processed using the plasma enhanced chemical vapor deposition method. Noble silver (Ag) films of approximately 100 nm thickness have been formed on $SiO_2$ deposited STS substrates by E-beam evaporation technique. The films then were annealed at $650^{\circ}C$ for 20 min using the rapid thermal annealing (RTA) technique. It was investigated the variation of the surface morphology due to the interaction between Ag films and $SiO_2$ layers after the RTA treatment. The results showed the movement of Si atoms in silver film from $SiO_2$. In addition, the structural investigation of Ag annealed at $650^{\circ}C$ indicated that the Ag film has the material property of p-type semiconductor and the bandgap of approximately 1 eV. Also, the films annealed at $650^{\circ}C$ showed reflection with sinusoidal oscillations due to optical interference of multiple reflections originated from films and substrate surfaces. Such changes can be attributed to both formation of $SiO_2$ on Ag film surface and agglomeration of silver film between particles due to annealing.

• Food Science and Biotechnology
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• 제18권6호
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• pp.1439-1446
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• 2009

The surfaces of different-sized endosperm, bran, and husk rice powders were modified using carboxymethylation. Carboxymethylation was carried out using aqueous alkalization and neutralization. After the carboxymethylation process, the centrifuged products were milled and classified by size: particles passed through sieves of 45, 106, and $300-{\mu}m$ width. The effect of carboxymethylation on physical properties such as solubility and dispersibility of endosperm, bran, and husk particles were studied. Overall, carboxymethylation increased solubility of the particles, while size reduction increased dispersibility. In particular, carboxymethylation created good aqueous suspensions by minimizing interparticle agglomeration. Our results show that the combination of size reduction and carboxymethylation improves solubility and dispersibility, resulting in better stability of the suspension. This study may be helpful for expanding the use of rice and its byproducts as ingredients in a variety of food and beverage applications.

• 한국결정성장학회지
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• 제15권6호
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• pp.239-243
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• 2005

The effect of pH and particle size on the dispersion stability of ultra-fine $BaTiO_3$ suspensions in aqueous medium have been investigated by means of zeta potential, sediment experiments, and powder properties (particle analysis, specific surface area) etc. Zeta potential as a function of pH for two particles of different size increases from -75 to +10 mV with decreasing pH from 8.5 to 1.4. The curve of zeta potential for small particle (150 nm) has slow slope than that of large particle (900nm), giving IEP (isoelectric point) value of pH=1.6 for small particle and pH=1.9 for large particle respectively, which means that it is more difficult to control zeta potential with pH fur small particle than large particle. The dispersion stability of $BaTiO_3$ particles in aqueous medium was found to be strongly related with the agglomeration of colloidal suspensions with time through the sedimentation behaviors of colloidal particles with time and pH value.

• 한국전기전자재료학회논문지
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• 제14권7호
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• pp.557-561
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• 2001

Chemical mechanical polishing (CMP) process has been widely used to planarize dielectric layers, which can be applied to the integraded circuits for sub-micron technology. Despite the increased use of CMP process, it is difficult to accomplish the global planarization of in the defect-free inter-level dielectrics (ILD). Especially, defects such as micro-scratch lead to severe circuit failure which affect yield. CMP slurries can contain particles exceeding 1㎛ in size, which could cause micro-scratch on the wafer surface. The large particles in these slurries may be caused by particles agglomeration in slurry supply line. To reduce these defects, slurry filtration method has been recommended in oxide CMP. In this work, we have studied the effects of filtration and the defect trend as a function of polished wafer count using various filters in inter-metal dielectrics(IMD)-CMP process. The filter installation in CMP polisher could reduce defects after IMD-CMP process. As a result of micro-scratch formation, it is shown that slurry filter plays an important role in determining consumable pad lifetime. The filter lifetime is dominated by the defects. We have concluded that slurry filter lifetime is fixed by the degree of generating defects.

• Korean Chemical Engineering Research
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• 제58권4호
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• pp.642-650
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• 2020

순환유동층 보일러에서 유동 입자들의 순환 경로는 연소로에서 비산된 입자들이 사이클론에서 포집되어 비기계적 밸브인 실포트(Sealpot)를 거쳐 연소로로 재순환하는 일반적인 경로를 갖는다. 그러나, 유동 입자들로부터 열을 추가적으로 흡수하기 위해 유동층 외부열교환기(FBHE; Fluidized Bed Heat Exchanger)가 설치된 경우, 실포트의 일부 입자들은 FBHE를 거쳐 연소로로 재순환하는 경로를 갖게 된다. 이때 기포유동층 영역으로 운전되는 FBHE는 실포트로부터 유입되는 고온(800~950 ℃)의 입자들의 유동 특성에 따라 열교환 튜브의 국부적 가열로 인한 손상 및 hot spot에 의한 입자들의 고온 뭉침(agglomeration)이 발생할 수 있어 순환유동층의 안정적 조업에 영향을 미칠 수 있다. 본 연구에서는 국내 D 순환유동층 보일러의 FBHE에 대한 운전자료 분석 및 바라쿠다를 통한 CPFD(Computational Particle Fluid Dynamics) 해석을 통해 구조적 문제로부터 발생하는 열흐름의 불균일성을 밝혀내었다. 실제 D 순환유동층의 FBHE 열교환 튜브 온도는 실포트의 고체온도 변화와 가장 밀접한 상관관계를 나타내었으며, FBHE 내의 열흐름의 불균일성은 FBHE의 조업 유속의 증가(0.3→0.7 m/s)로는 그 불균일성을 해소하기 어려운 것으로 나타났다. 그러나, FBHE로 유입되는 고온 입자들에 대한 사전 혼합 영역(Premixing Zone)이 설치된 경우와, 연소로로 재순환되는 입자 배출 라인의 대칭화를 통한 구조변경 시, 입자 혼합의 증대와 더불어 열흐름의 불균일성은 상당 부분 감소하는 것으로 고찰되었다. 이에, FBHE의 구조 최적화가 열교환 성능 및 운전 안정성을 확보하는 대안임을 제시하였다.