• Proceedings of the Korea Association of Crystal Growth Conference
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• 1996.06b
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• pp.87-107
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• 1996

The fine Co powder with an average particle sie of less than 1$\mu\textrm{m}$ was prepared by hydrothermal reduction with hydrogen from Co(OH)2 slurry obtained by mixing the solutons of CoSO4$.$7H2O and NaOH. A method to control pH of the end solution around neutrality was proposed. The reduction rate was found to be a function of pH, temperature, hydrogen pressure and the amount of catalyst.

• Journal of the Korean Ceramic Society
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• v.20 no.1
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• pp.49-54
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• 1983

The main object of this study is to investigate the effect of Al powder as an additive on the sintering of calcined alumina comparing with that of calcined alumina alone. The degree of Al oxidation is calculated by measuring the weight increase during the firing Water absorption bulk density and compressive strength of the $Al_2O_3+Al$ system at each temperature are compared with those of $Al_2O_4$ alone. The $Al_2O_3+Al$ system shows better physical propeties than Al2O3 alone and it seems by the SEM observation that the fine oxidized Al particles(fine $Al_2O_3$ particles submicron unit) fill the interstices of the original $Al_2O_3$ par-ticles and thus result in the well-close-packed arrangement of the particles.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.195-196
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• 2006

In recent years, demands for sintered ferrous material with higher strength are increasing. To satisfy these demands, studies and commercial use of the die wall lubrication method, the warm compaction method and the combination of both methods are widely carried out to achieve high density. The die wall lubrication warm compaction method makes it possible to achieve high density by reducing internal lubricant through die wall lubrication, although the method involves several issues such as prolonged cycle time due to lubricant spraying and difficulty in spraying lubricant in the case of compacting with complicated geometry. Meanwhile, the conventional warm compaction method requiring no die wall lubricant application cannot achieve such a high density as in the case of die wall lubrication warm compaction due to higher volume of internal lubricant. However, this report discloses our study result in which the possibility of improving density is exhibited by using a lubricant type with superior dynamic ejection property that can reduce volume of lubricant additive.

• Journal of Powder Materials
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• v.7 no.3
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• pp.154-160
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• 2000

In order to enhance sinterability of W-Cu composites used for heat sink materials, mechanical alloying process where both homogeneous mixing of component powders and fine dispersion of minor phase can be easily attained was employed. Nanostructured W-Cu powders prepared by mechanical alloying showed W grain size ranged of 20-50 nm and were able to be efficiently sintered owing to the fine particle size as well as uniform distribution of Cu phase. The thermal properties such as electrical resistivity, coefficient of thermal expansion and thermal conductivity were evaluated as functions of temperature and Cu content. It was found that the coefficient of thermal expansion could be controlled by changing Cu content. The measured electrical resistivities and thermal diffusivities were also varied with Cu content. The thermal conductivities calculated from the values of resistivities and diffusivities showed similar tendency as a function of temperatures. However, this is in contradiction with thermal conductivities of pure W and Cu which decrease with increasing temperature.

• Journal of Powder Materials
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• v.15 no.2
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• pp.81-86
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• 2008

최근프린팅기술은 전자부품소재 산업의 대형화 및 저가격화의 해법으로 기대되고 있다. 특히 전자부품소재 프린팅 기술 중 잉크젯공정은 최신 디스플레이용 전극소재, PCB, FPCB 및 기타 소재공정에 이용하려는 움직임이 활발히 진행되고 있다. 그러나 잉크젯 기술은 재료의존도 비중이 높은 기술로서 소재(금속잉크)의 개발이 최우선시 되어야한다. 전자부품소재용 금속잉크에 사용되는 금속 나노입자는 우수한 전기전도성과 산업적응용이 가능해야 한다. 따라서 최근 연구되고 있는 금속 나노입자의 연구결과 중 전자잉크에 적용 가능한 연구결과와 응용분야에 대하여 서술하였다.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2013.05a
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• pp.85-86
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• 2013

Weakness of fine powder of blast furnace slags includes the decrease of initial intensity and delay of setting time. To solve this problem, there has been research on the alkali activation to induce hardening using alkaline chemical. However, the use of chemicals is dangerous and not cost effective, which can be solved by using recycled aggregates, one of construction wastes. The role of alkali activator can be substituted by alkali of non-hydrated cement included in recycled aggregates. In this study, the alkaline value of recycled aggregates will be evaluated through the comparison of molarity of sodium hydroxide (NaOH).

• Asian Journal of Atmospheric Environment
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• v.12 no.1
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• pp.78-86
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• 2018

Filter-based sampling techniques are the conventional way to collect particulate matter, but particles collected and entangled in the filter fibers are difficult to be removed and thus not suited for the following cell- and animal-based exposure experiments. Collecting aerosol particles in powder form using a cyclone instead of a filter would be a possible way to solve this problem. We developed a hybrid virtual-impactor/cyclone high-volume fine and coarse particle sampler and assessed its performance. The developed system achieved 50% collection efficiency with components having the following aerodynamic cut-off diameters: virtual impactor, $2.4{\mu}m$; fine-particle cyclone, $0.18-0.30{\mu}m$; and coarse-particle cyclone, $0.7{\mu}m$. The virtual impactor used in our set-up had good $PM_{2.5}$ separation performance, comparable to that reported for a conventional real impactor. The newly developed sampler can collect fine and coarse particles simultaneously, in combination with exposure testing with collected fine- and coarse-particulate matter samples, should help researchers to elucidate the mechanism by which airborne particles result in adverse health effect in detail.

• Journal of the Microelectronics and Packaging Society
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• v.9 no.4
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• pp.47-53
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• 2002

In this study, two different (NiCuZn)-ferrite which were fabricated by using ultra-fine powders synthesized by the wet processing and conventionally commercialized powder, were investigated and compared each other in terms of the low temperature sintering and electromagnetic properties. Composition of x and w in $(Ni_{0.4-x}Cu_xZn_{0.6})_{1+w}(Fe_2O_4)_{1-w}$ were controlled as 0.2 and 0.03, respectively. The sintering temperature were $900^{\circ}C$ for ultra-fine powders by way of initial heat treatment and $1150^{\circ}C$ for commercialized powders. The (NiCuZn)-ferrite by ultra-fine powders showed love. sintering temperature than that of commercialized powders by over $200^{\circ}C$, and excellent electromagnetic properties such as the quality factor which is a important factor in the multi-layered chip inductor. In addition, characteristics of B-H hysteresis, crystallinity, microstructure and powder morphology were analyzed by a vibrating sample method(VSM), x-ray diffractometer(XRD), transmission electron microscope (TEM) and scanning electron microscope(SEM).

• Proceedings of the Korea Association of Crystal Growth Conference
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• 2000.06a
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• pp.151-163
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• 2000

A polymerized organic-inorganic complexation route is introduced for the synthesis of oxide ceramic powders. Polyvinyl alcohol was used as the organic carrier for precursor ceramic gel. Porous and soft powders, which have a high specific surface area, were obtained after calcinating the aerated precursors. The PVA content and its degree of polymerization had a significant influence on the homogeneity of the final powder. In particular, attrition milling process with the porous powder resulted in ultra-fine particles. In the case of the preparation of cordierite powder, nano-size powder, which has a high specific surface area of 181 ㎡/g, was obtained by the milling process. The complexation route was also applied to the synthesis of unstable phase in room temperature like beta-cristobalite, high temperature form of silica.

• Proceedings of the Korea Concrete Institute Conference
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• 2002.10a
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• pp.549-554
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• 2002

In Powder System, SCC demands high dosage of superplasticizer and a lage amout of powder for suitable fluidity and viscosity. Okamura's method of most representative mixing design method in SCC of Powder-System is unfavorable economically because of using a large amount of powder. In addition, many ready-mixed concrete plants do not use his mix design method and procedure due to complexity for practical application. Therefore, Nan Su proposed more simple mix design method than Okamura's. It had an advantage in simplicity in practical application and required a smaller amount of powders compared with Okamura's method. This paper proposed an optimal mixture proportion of SCC with consideration of Nan Su's method. The new and modified mix design method required a smaller amount of powder than that of Nan Su's. To check the properties of SCC, considered with the requirements specified by the Japanese Society of Civil Engineering.(JSCE)