• 한국재료학회:학술대회논문집
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• 한국재료학회 2011년도 춘계학술발표대회
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• pp.58.1-58.1
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• 2011

WC-Co and other similar cemented carbides have been widely used as hard materials in industrial cutting tools and as mould metals; and a number of techniques have been applied to improve its microstructural characteristics, hardness and ear resistance. Cobalt is used primarily to facilitate liquid phase sintering and acts as a matrix, i.e. a cementing phase between WC grains. A uniform distribution of metal phase in a ceramic is beneficial for improved mechanical properties of the composite. WC-Co, starting from initial powders, is vastly used for a variety of machining, cutting, drilling, and other applications because of its unique combination of high strength, high hardness, high toughness, and moderate modulus of elasticity, especially with fine grained WC and finely distributed cobalt. In this study, that started with two different compositions of initial powders, WC-7.5wt%Co and WC-12wt%Co with initial powder size being 1~3 ${\mu}m$, magnetic pulsed compaction followed by subsequent vacuum sintering were carried out to produce consolidated preforms. Magnetic Pulsed Compaction (MPC), a very short duration (~600 ${\mu}s$), high pressure (~4 Gpa), high-density preform molding method was used with varied pressure between 0.5 and 3.0 Gpa, in order to reach an initial high density that would help improve the sintering behavior. For both compositions and varied MPC pressure, before and after sintering, changes in microstructural behavior and mechanical properties were analyzed. With proper combination of MPC pressure and sintering, samples were obtained with better mechanical properties, densification and microstructural behavior, and considerably improved than other conventional processes.

• Journal of Electrochemical Science and Technology
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• 제6권4호
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• pp.121-130
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• 2015

The micro emulsion method has been successfully used for preparing perovskite LaCoO₃ with uniform, fine-shaped nanoparticles showing high activity as electro catalysts in oxygen reduction reactions (ORRs). They are, therefore, promising candidates for the air-cathode in metal-air rechargeable batteries. Since the activity of a catalyst is highly dependent on its specific surface area, nanoparticles of the perovskite catalyst are desirable for catalyzing both oxygen reduction and evolution reactions. Herein, LaCoO₃ powder was also prepared by sol-gel method for comparison, with a broad particle distribution and high agglomeration. The electro catalytic properties of LaCoO₃ and LaCoO₃-carbon Super P mixture layers toward the ORR were studied comparatively using the rotating disk electrode technique in 0.1 M KOH electrolyte to elucidate the effect of carbon Super P. Koutecky-Levich theory was applied to acquire the overall electron transfer number (n) during the ORR, calculated to be ~3.74 for the LaCoO₃-Super P mixture, quite close to the theoretical value (4.0), and ~2.7 for carbon-free LaCoO₃. A synergistic effect toward the ORR is observed when carbon is present in the LaCoO₃ layer. Carbon is assumed to be more than an additive, enhancing the electronic conductivity of the oxide catalyst. It is suggested that ORRs, catalyzed by the LaCoO₃-Super P mixture, are dominated by a 2+2-electron transfer pathway to form the final, hydroxyl ion product.

• 한국결정성장학회지
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• 제13권3호
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• pp.111-116
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• 2003

FED용 적색형광체인 $(Y,Gd)_2O_2$S : Eu 분말의 합성과 부활성제로서의 $Gd^{3+}$ 의 영향과 이에 따른 미세조직의 변화및 저전압 발광특성등이 다양한 소결온도에서 조사되었다. 311 nm의 여기파장을 이용시 발광은 627nm에서 $^{5}D_0 \$\longrightarrow$ $$^7F_2$ 천이에 의해 일어남이 관찰되었고 $Gd^{3+}$ 5 mole%, $950^{\circ}C$ 소결에서 가장 높은 발광휘도를 나타냈으며 $Gd^{3+}$ 5 mole% 이상에서는 농도소광현상이 일어났다. 소결 후의 평균입자크기는 약 1 $\mu$m이었으며 $(Y,Gd)_2O_2$S : Eu의 발광효율이 $Y_2O_2$S : Eu 보다우수한 것으로 나타났다.

• 한국초전도ㆍ저온공학회논문지
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• 제19권2호
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• pp.19-24
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• 2017

Cryogenic milling which is a combined process of low-temperature treatment and mechanical milling was applied to fabricate high critical current density $(J_c)MgB_2$ bulk superconductors. Liquid nitrogen was used as a coolant, and no solvent or lubricant was used. Spherical Mg ($6-12{\mu}m$, 99.9 % purity) and plate-like B powder (${\sim}1{\mu}m$, 97 % purity) were milled simultaneously for various time periods (0, 2, 4, 6 h) at a rotating speed of 500 rpm using $ZrO_2$ balls. The (Mg+2B) powders milled were pressed into pellets and heat-treated at $700^{\circ}C$ for 1 h in flowing argon. The use of cryomilled powders as raw materials promoted the formation reaction of superconducting $MgB_2$, reduced the grain size of $MgB_2$, and suppressed the formation of impurity MgO. The superconducting critical temperature ($T_c$) of $MgB_2$ was not influenced as the milling time (t) increased up to 6 h. Meanwhile, the critical current density ($J_c$) of $MgB_2$ increased significantly when t increased to 4 h. When t increased further to 6 h, however, $J_c$ decreased. The $J_c$ enhancement of $MgB_2$ by cryogenic milling is attributed to the formation of the fine grain $MgB_2$ and a suppression of the MgO formation.

• 한국건설순환자원학회논문집
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• 제5권4호
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• pp.389-394
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• 2017

본 연구는 콘크리트 블록을 생산하는 공장에서 경제적이면서 환경 친화적인 블록을 생산하기 위해 산업부산물 자원을 효과적으로 이용하는 방안에 관한 것이다. 즉, BS 3종에 일라이트, 탈황석고 및 폐내화물울 치환하여 종전에 연구되었던 결과에서 양호한 것으로 밝혀진 몇 개 변수를 Mock-up 시험성격으로 실제 생산라인에서 호안블록을 생산하여 그 특성을 분석하므로써 최적 조합을 확정하고자 한다. 실험결과 압축강도, 흡수율, 내동해성 및 수질영향의 pH 관점에서 고려하면 BS 3종에 정제 탈황석고 5% 치환 및 여기에 골재로서 일라이트를 1% 치환한 배합이 최적인 것으로 분석되었다. 그러나 일라이트는 시멘트 보다 고가이므로 경제적인 측면까지도 고려하면 BS 3종에 5%의 정제 탈황석고를 결합재로 치환하는 배합이 최적 조합인 것으로 밝혀졌다.

• 전자통신동향분석
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• 제35권4호
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• pp.1-10
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• 2020

Since the 1960s, semiconductor packaging technology has developed into electrical joining techniques using lead frames or C4 bumps using tin-lead solder compositions based on traditional reflow processes. To meet the demands of a highly integrated semiconductor device, high reliability, high productivity, and an eco-friendly simplified process, packaging technology was required to use new materials and processes such as lead-free solder, epoxy-based non cleaning interconnection material, and laser based high-speed processes. For next generation semiconductor packaging, the study status of two epoxy-based interconnection materials such as fluxing and hybrid underfills along with a laser-assisted bonding process were introduced for fine pitch semiconductor applications. The fluxing underfill is a solvent-free and non-washing epoxy-based material, which combines the underfill role and fluxing function of the Surface Mounting Technology (SMT) process. The hybrid underfill is a mixture of the above fluxing underfill and lead-free solder powder. For low-heat-resistant substrate applications such as polyethylene terephthalate (PET) and high productivity, laser-assisted bonding technology is introduced with two epoxy-based underfill materials. Fluxing and hybrid underfills as next-generation semiconductor packaging materials along with laser-assisted bonding as a new process are expected to play an active role in next-generation large displays and Augmented Reality (AR) and Virtual Reality (VR) markets.

• 한국소음진동공학회논문집
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• 제14권5호
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• pp.432-438
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• 2004

10 마이크로미터의 진폭을 갖는 28.4 KHz의 초음파 굽힘진동을 이용하여 초음파 진동판과 정지판 사이에서 다수의 소형 실린더 형태의 스티로폼를 진동판의 길이 방향으로 안정적으로 부양시켰다. 진동자와 정지판의 간격이 음향파장 (16.6 mm)의 1/2일 경우, 부양된 물체가 음향파장의 1/4 지점에서 안정적으로 부양되는 이유를 이론적으로 증명하였으며, 또한 실험적으로 검증하였다. 질량이 균형적으로 분포된 물체의 경우 부양시 고속으로 회전하게 되는데 이는 초음파 진동에 의해서 생성된 음향유동에 의한 것이다. 지름 1.8 mm, 길이 3 mm의 실린더 형태의 스티로폼의 경우 2400 rpm 으로 회전하는 것이 실험적으로 관찰되었다. 음향부양은 작은 세포나 혈액내의 구성체 혹은 미세 분진의 조작에 응용될 수 있다.

• 한국수소및신에너지학회논문집
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• 제15권2호
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• pp.98-107
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• 2004

Modified Ni/YSZ cermets for high temperature electrolysis were synthesized by dry or wet mechanical alloying methods. The Ni/YSZ composit particle was directly fabricated from the ball milling of Ni and YSZ powder or obtained from the reduction of NiO/YSZ particle after the ball milling of NiO and YSZ. In the case of the NiO/YSZ composite particle, the dry milling increased the average particle size whereas the wet milling decreased the size. The dry milling showed that fine YSZ particles were distributed over large Ni surfaces while Ni and YSZ particles similar in size were well mixed in the wet milling method. These features were the same in the Ni/YSZ composite particle prepared from Ni and YSZ powders. The electrical conductivity of the wet-milled Ni/YSZ cermet showed the highest value of $2{\times}10^2S/cm$ among the specimens and this value was increased to $1.4\times10^4S/cm$ after the sintering at $900^\circ{C}$ for 1 h.

• 한국건축시공학회지
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• 제4권2호
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• pp.129-136
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• 2004

High fluidity concrete(HFC) requires high dosage of superplasticizer to acquire sufficient fluidity, and high contents of fine powder and viscosity enhancing admixtures to resist segregation. The use of high amount of admixtures to make HFC at batcher plant in ready mixed concrete company is one of the reasons to raise the manufacturing cost of HFC. For this reason, new type of manufacturing method of HFC are described using both flowing concrete method and segregation reducing superplasticizer(SRS) in order to gain economical profit and offer the convenience for quality control.. As dosage of melamine based superplasticizer increases, it shows that fluidity and bleeding increase, while air contents and ratio of segregation resistance decrease. It also shows that addition of viscosity agent into superplasticizer reduce bleeding and improve segregation resistance of concrete. Dosage of AE agent into superplasticizer containing viscosity agent recovers loss of air contents during flowing procedure. Combination of proper contents of superplasticizer, viscosity agent and AE agent make possible to develope segregation reducing type superplasticizer. Compressive strength of high fluidity concrete applying flowing method with it is higher than that of base concrete. No differences of compressive strength between compacting methods are found. For the estimation of construction cost of high fluidity concreting using segregation reducing type superplasicizer, under same strength levels, although material cost of high fluidity concrete is somewhat higher than that of plain concrete due to segregation reducing type superplasticizer cost, labor cost and equipment cost of high fluidity concrete is cheaper than that of plain concrete. However, based on the strength differences, high fluidity concrete shows lower material cost, labor cost and equipment cost than that of plain concrete due to decreasing in size of member and re-bar caused by high strength development of concrete.

• Journal of Pharmaceutical Investigation
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• 제38권1호
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• pp.1-8
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• 2008

Planetary ball mill was used to decrease and control the particle size of excipients. The effects of the weight of sample and the revolution number of mill, and grinding time on the particle size of the ground sample were analyzed by response surface methodology. The optimum conditions for the milling of microcrystalline cellulose were 38.82 g of the weight of sample and 259 rpm of the revolution number of mill, and 45 minutes of grinding time. The predicted value of the particle size at the these conditions was $19.02{\mu}m$, of which the experimental value at the similar conditions was $18.68{\mu}m$. The tensile strength of tablets of single-component powders, such as microcrystalline cellulose, hydroxypropylmethyl cellulose and starch, binary mixtures and ground binary mixtures of these powder were measured at various relative densities. It was found that the logarithm of the tensile strength of the tablets was proportional to the relative density. A simple model, based upon Ryshkewitch-Duckworth equation that was originally proposed for porous materials, has been developed in order to predict the relationship between the tensile strength and relative density of ground binary tablets based on the properties of the constituent single-component powders. The validity of the model has been verified with experimental results for ground binary mixtures. It has demonstrated that this model can well predict the tensile strength of ground binary mixtures based upon the properties of single-component powders, such as true density, and the compositions. When the tensile strength of the mixture of microcrystalline cellulose hydroxypropylmethyl cellulose (90:10) and the ground mixture of them were compared, the tensile strength of the ground mixture decreased widely from 45.3 to 5.6% compared to the mixture in case the relative density of tablets was in the range of $0.7{\sim}0.9$. When the tensile strength of the mixture of microcrystalline cellulose starch (80:20) and the ground mixture of them were compared, the tensile strength of the ground mixture decreased widely from 31.0 to 11.6% compared to the mixture in case the relative density of tablets was in the range of $0.7{\sim}0.9$.