• 한국세라믹학회지
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• 제50권3호
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• pp.218-225
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• 2013

The densification behavior and strength of sintered reaction bonded silicon nitrides (SRBSN) that contain $Lu_2O_3-SiO_2$ additives were improved by the addition of fine Si powder. Dense specimens (relative density: 99.5%) were obtained by gas-pressure sintering (GPS) at $1850^{\circ}C$ through the addition of fine Si. In contrast, the densification of conventional specimens did not complete at $1950^{\circ}C$. The fine Si decreased the onset temperature of shrinkage and increased the shrinkage rate because the additive helped the compaction of green bodies and induced the formation of fine $Si_3N_4$ particles after nitridation and sintering at and above $1600^{\circ}C$. The amount of residual $SiO_2$ within the specimens was not strongly affected by adding fine Si powder because most of the $SiO_2$ layer that had formed on the fine Si particles decomposed during nitridation. The maximum strength and fracture toughness of the specimens were 991 MPa and $8.0MPa{\cdot}m^{1/2}$, respectively.

• Bulletin of the Korean Chemical Society
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• 제35권5호
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• pp.1379-1384
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• 2014

${\alpha}-Fe_2O_3$ spherical particles having an average diameter of ca. 420 nm and ${\alpha}-Fe_2O_3$ fine particles (< 10 ${\mu}m$ particle size) were prepared to examine as catalysts for CO oxidation. Kinetic studies on the catalytic reactions were performed in a flow reactor using an on-line gas chromatography system operated at 1 atm. The apparent activation energies and the partial orders with respect to CO and $O_2$ were determined from the rates of CO disappearance in the reaction stage showing a constant catalytic activity. In the temperature range of $150-275^{\circ}C$, the apparent activation energies were calculated to be 13.7 kcal/mol on the ${\alpha}-Fe_2O_3$ spherical submicron clusters and 15.0 kcal/mol on the ${\alpha}-Fe_2O_3$ fine powder. The Pco and $Po_2$ dependencies of rate were investigated at various partial pressures of CO and $O_2$ at $250^{\circ}C$. Zero-order kinetics were observed for $O_2$ on both the catalysts, but the reaction order for CO was observed as first-order on the ${\alpha}-Fe_2O_3$ fine powder and 0.75-order on the ${\alpha}-Fe_2O_3$ spherical submicron clusters. The catalytic processes including the inhibition process by $CO_2$ on the ${\alpha}-Fe_2O_3$ spherical submicron powder are discussed according to the kinetic results. The catalysts were characterized using XRD (X-ray powder diffraction), FE-SEM (field emission-scanning electron microscopy), HR-TEM (high resolution-transmission electron microscopy), and $N_2$ sorption measurements.

• 대한화학회지
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• 제38권6호
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• pp.411-417
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• 1994

난용성 신소재 중의 하나인 파인 세라믹의 분석을 위하여, 알칼리 용융법과 고압 산분해법 등의 시료 전처리법을 유도결합원자발광분석기(ICP-AES)를 이용하여 연구하였다. Al2O3 분말을 분석하여 본 결과, 고압 산분해법이 알칼리 용융법보다 재현성 있는 측정치를 얻을 수 있었다. SiC분말의 경우에서는 고압산분해법으로 처리한 후 Si매트릭스를 Si-F형태로 증발시켜서 분석하여 본 결과 분말 중의 ppm 농도 범위의 불순물들이 매트릭스에 의한 간섭없이 분석되었다. 일본 인증기준물인 JCRM022, JCRM023 초미립 분말을 고압 산분해법으로 분석하여 본 결과, 좋은 재현성과 높은 정확성을 나타내었다.

• 마이크로전자및패키징학회지
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• 제20권4호
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• pp.65-68
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• 2013

A novel bumping process using solder bump maker (SBM) is developed for fine-pitch flip chip bonding. It features maskless screen printing process. A selective solder bumping mechanism without the mask is based on the material design of SBM. Maskless screen printing process can implement easily a fine-pitch, low-cost, and lead-free solder-on-pad (SoP) technology. Its another advantage is ternary or quaternary lead-free SoP can be formed easily. The process includes two main steps: one is the thermally activated aggregation of solder powder on the metal pads on a substrate and the other is the reflow of the deposited powder on the pads. Only a small quantity of solder powder adjacent to the pads can join the first step, so a quite uniform SoP array on the substrate can be easily obtained regardless of the pad configurations. Through this process, an SoP array on an organic substrate with a pitch of 130 ${\mu}m$ is, successfully, formed.

• 한국정밀공학회지
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• 제21권10호
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• pp.34-41
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• 2004

A new method to fabricate the fine magnetic abrasives by using mechanical alloying is proposed. The mechanical alloying process is a solid powder process where the powder particles are subjected to high energetic impact by the balls in a vial. As the powder particles in the vial are continuously impacted by the balls, cold welding between particles and fracturing of the particles take place repeatedly during the ball milling process using a planetary mill. After the manufacturing process, fine magnetic abrasives which the guest abrasive particles c lung to the base metal matrix without bonding material can be obtained. The shape of the newly fabricated fine magnetic abrasives was investigated using SEM and its polishing performance was verified by experiment. It is very helpful to finishing the injection mold steel in final polishing stage. The areal ms surface roughness of the workpiece after several polishing processes has decreased to a few nanometer scales.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part2
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• pp.939-939
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• 2006

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2005년도 춘계학술대회
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• pp.310-313
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• 2005

The conical fluidizing system of a binary mixture of Geldart C powders and Geldart A particles was defined as the conical powder-particle fluidized bed. We used a cold conical powder-particle fluidized bed model having a 0.104m-I.D. and 0.6m-high with an apex angle of $10^{\circ}$ for fluidization of a binary powder-particle mixture of 50 $vol\%$ fine carbon black powders (HI-900L, Korea Carbon Black Co.) and coarse alumina particles $(90{\mu}m)$ under different superficial gas velocities (0-0.1 m/s). The differential bed pressure drop increases with increasing gas velocity, and it goes from zero to a maximum value with increasing or decreasing gas velocity. In the conical fluidized beds of fine powders, demarcation velocities of the partial fluidization, full fluidization, partial defluidization was not observed.

• Nuclear Engineering and Technology
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• 제52권8호
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• pp.1714-1723
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• 2020

This study aims at characterizing the rheological properties of uranium oxide powders for nuclear fuel pellets manufacturing. The flowability of these powders must be compatible with a reproducible filling of press molds. The particle size distribution is known to have an impact on the rheological properties and fine particles (<100 ㎛) are suspected to have a detrimental effect. In this study, the impact of the particle size distribution on the rheological properties of UO₂ powders was quantified, focusing on the influence of fine particles. Two complementary approaches were used. The first approach involved characterizing the powder in a static state: density, compressibility and shear test measurements were used to understand the behavior of the powder when it is transitioned from a static to a dynamic state (i.e., incipient flow conditions). The second approach involved characterizing the behavior of the powder in a dynamic state. Two zones, corresponding to two characteristic behaviors, were demonstrated for both types of measurements. The obtained results showed the amount of fines should be kept below 10 % wt to ensure a robust mold filling operation (i.e., constant mass and production rate).

• 콘크리트학회논문집
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• 제12권4호
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• pp.103-111
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• 2000

The influence of the improvement of grain shape of the coarse aggregate to the unit powder content of concrete and the fine aggregate ratio for the increase of the flowability and segregation resistance of high performance concrete was examined. According to the experimental results, flowability and compacting of concrete presents best states in the S/a which has the smallest 패야 ratio. The coarse aggregate after improvement of grain shape, that has changed from the 0.68 of spherical rate of disk shape to 0.73, led fine aggregate ratio to be down 6% (i.e from 47% to 41%). The improvement of grain shape of the coarse aggregate also led the lowest unit powder content to be down 60kg/㎥ (ie from 530kg/㎥ to 470kg/㎥). And approximate 10% of unit water content has been reduced as unit powder content was down. However, the compressive strength after the improvement of grain shape of the coarse aggregate decreased to 5% due to decrease of adhesiveness of the aggregate and cement paste.

• 한국분말재료학회지
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• 제13권1호
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• pp.46-51
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• 2006

Through the volume change of Sn in a low-temperature phase transformation, the Sn nanopowder with high, purity, was fabricated by an economic and eco-friendly process. The fine cracks were spontaneously generated. in, Sn ingot, which was reduced to powders in the repetition of phase transformation. The Sn nanopowder with 50 run in size was obtained by the 24th repetitions of phase transformation by low-temperature and ultrasonic treatments. Also, the $SnO_2$ powder was fabricated by the oxidation of the produced Sn powder to the ingot and milled by the ultrasonic milling method. The $SnO_2$ nanopowder of 20 nm in size was fabricated after the milling for 180 h.