• 한국분말재료학회지
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• 제16권4호
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• pp.249-253
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• 2009

3-D shape soft magnetic composite parts can be formed by general compaction method of powder metallurgy. In this study, the results on the high density nanostructured Fe-Si/Fe composite prepared by a warm compaction method were presented. Ball-milled Fe-25 wt.%Si powder, pure Fe powder and Si-polymer were mixed and then the powder mixture was compacted at various temperatures and pressures. Pore free density of samples up to 95% theoretical value has been obtained. The warm compacted sample prepared at 650 MPa and 240$^{\circ}C$ had highest compaction properties in comparison with other compacts prepared at 300, 400 MPa and room temperature and 120$^{\circ}C$. The magnetic properties such as core loss, magnetization saturation and coercivity were measured by B-H curve analyzer and vibration sample magnetometer.

• 한국분말재료학회지
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• 제22권5호
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• pp.362-366
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• 2015

The effect of sublimable vehicle composition in the camphor-naphthalene system on the pore structure of porous Cu-Ni alloy is investigated. The CuO-NiO mixed slurries with hypoeutectic, eutectic and hypereutectic compositions are frozen into a mold at $-25^{\circ}C$. Pores are generated by sublimation of the vehicles at room temperature. After hydrogen reduction at $300^{\circ}C$ and sintering at $850^{\circ}C$ for 1 h, the green body of CuO-NiO is completely converted to porous Cu-Ni alloy with various pore structures. The sintered samples show large pores which are aligned parallel to the sublimable vehicle growth direction. The pore size and porosity decrease with increase in powder content due to the degree of powder rearrangement in slurry. In the hypoeutectic composition slurry, small pores with dendritic morphology are observed in the sintered Cu-Ni, whereas the specimen of hypereutectic composition shows pore structure of plate shape. The change of pore structure is explained by growth behavior of primary camphor and naphthalene crystals during solidification of camphor-naphthalene alloys.

• 한국분말재료학회지
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• 제18권4호
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• pp.327-331
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• 2011

In order to fabricate the porous metal with controlled pore characteristics, unique processing by using metal oxide powder as the source and camphene as the sublimable material is introduced. CuO powder was selected as the source for the formation of Cu metal via hydrogen reduction. Camphene-based CuO slurry, prepared by milling at $47^{\circ}C$ with a small amount of dispersant, was frozen at $-25^{\circ}C$. Pores were generated subsequently by sublimation of the camphene. The green body was hydrogen-reduced at $200^{\circ}C$ for 30 min, and sintered at $500-700^{\circ}C$ for 1 h. Microstructural analysis revealed that the sintered Cu showed aligned large pore channels parallel to the camphene growth direction, and fine pores are formed around the large pore. Also, it showed that the pore size was controllable by the slurry concentration.

• 한국분말재료학회지
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• 제9권3호
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• pp.189-198
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• 2002

In this work, transient liquid phase (TLP) bonding of Ni-Cr heat resisted cast alloy (HP) was investigated. And also the behaviors of the solid particles distributed in the interlayer during TLP bonding were investigated. The MBF-60 and solid particles (Ni, Fe, and $Al_2O_3$ powders respectively) added MBF-60 which will be a liquid phase coexisting with solid particles at the bonding temperature were used as insert metal. The effective and sound bonding was possible by spark plasma sinter-bonding due to the differences of electric resistance between base metal and liquid insert layer which creates high temperature region. During the isothermal solidification, $Al_2O_3$ particles and solid particles of liquid phase sintered insert metal have shown no growth, while Ni and Fe particles grow rapidly. In this TLP bonding using the MBF-60 and distributed Fe, Ni particles as insert materials, the whole isothermal solidification process was dominated by the growth rate of the solid particles distributed in the interlayer.

• 한국분말재료학회지
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• 제21권5호
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• pp.366-370
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• 2014

The present study demonstrates the effect of solidification condition on the pore structure in freeze drying process using the slurries of CuO/sublimable vehicles. Camphene and Camphor-45 wt% naphthalene based slurries with 14 vol% CuO powder were frozen into a mold at $-25^{\circ}C$, followed by sublimation at room temperature. The green bodies were hydrogen-reduced and sintered at $500^{\circ}C$ for 1 h. The porous Cu specimen, frozen the CuO/camphene slurry into the heated mold of the upper part, showed large pores with unidirectional pore channels and small pores in their internal wall. Also, it was observed that the size of large pores was decreasing near the bottom part of specimen. The change of pore structure depending on the freezing condition was explained by the nucleation behavior of camphene crystals and rearrangement of solid powders during solidification. In case of porous Cu prepared from CuO/Camphor-naphthalene system, the pore structure exhibited plate shape as a replica of the original structure of crystallized vehicles with hypereutectic composition.

• 한국분말재료학회지
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• 제9권1호
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• pp.50-60
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• 2002

SPS(Spark Plasma Sintering ) is known to be an excellent sintering method for porous materials. In the present work an attempt has been made of fabricating porous 316L Stainless steel with good mechanical properties by using controlled SPS process Porosity was 21%~53% at sintering temperature of $600^{\circ}C$~100$0^{\circ}C$ The limit of porosity with available mechanical strength was 30% at given experimental conditions. Porosity can be controlled by manipulating the intial height of the compact by means of the supporter and punch length. The applied pressure can be exerted entirely upon the supporter, giving no influence on the specimen. The specimen is then able to be sintered pressurelessly. In this case porosity could be controlled from 38 to 45% with good mechanical strength at sintering temperature of 90$0^{\circ}C$. As the holding time increased, neck between the particles grew progressively, but shrinkage of the specimen did not occur, implying that the porosity remained constant during the whole sintering process.

• 한국자동차공학회논문집
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• 제22권2호
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• pp.44-51
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• 2014

This paper describes system definition of the extended range EV and presents cruising strategy of EV mode and ER mode. Also high voltage battery strategic SOC could be indicated and compared depends on various generator working cycles. A C-segment SUV has been produced and carried out cruising test in order to validate on highway, city and hill climbing road. This paper shows advantages and disadvantages of SOC variation on each road environments and presents the strategies as the cruising test results. On the basis of the test result, this paper suggests future works and research directions for strategy of battery management to extended range EV.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2003년도 학술.기술논문발표회
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• pp.95-98
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• 2003

This paper presents the results of field experiment to apply the difference of setting tine method using super retarding agent for reducing hydration heat of mass concrete of foundation. According to the results, as the properties of fresh concrete, base concrete satisfies aimed slump and air content, and there is no difference of slump and air content with mixture of super retarding agent. The mixing ratio of super retarding agent is determined for setting time to be retarded by 12 hours in comparison with base concrete, but because the temperature of the air and concrete is low, the difference of setting time is retarded to 24 hours. In man concrete of foundation to which the difference of setting time method is applied, crack by hydration heat is not seen because the lower concrete of super retarding agent generates heat after generation of hydration heat of the upper concrete.

• 한국음향학회지
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• 제31권6호
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• pp.353-358
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• 2012

논문은 지식기반의 음성인식 시스템에서 비음 위치를 검출하기 위한 음향음성학적 파라미터를 제시하였다. 음향음성학적 파라미터는 앞선 연구자들의 연구내용을 토대로 비강을 통해 음성이 발성될 때 나타나는 특징을 기반으로 하여 선별하였다. 선별된 파라미터들은 대역별 에너지 비율, 대역별 에너지의 차이, 포먼트 그리고 포먼트의 차이로써, 비음 위치에 따라 변화하는 조음기관의 영향을 잘 나타내 주었다. 이러한 음향음성학 파라미터를 이용하여 비음을 순비음(/m/), 치경비음(/n/), 그리고 연구개비음(/ng/)으로 나누는 실험을 진행하였고, TIMIT 데이터베이스로 실험하였을 때 57.5%의 검출률을 얻을 수 있었다.

• 한국음향학회지
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• 제32권2호
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• pp.167-173
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• 2013

본 논문은 이중모음을 분류하기 위한 음향음성학적 파라메터를 연구하였다. 음향음성학적 파라메터는 성도를 통해 음성이 발성될 때 나타나는 특징을 기반으로 하여 분산분석(ANOVA) 방법을 통해 선별한 모음의 길이, 에너지 궤적, 그리고 포먼트의 차이를 이용하였다. TIMIT 데이터 베이스를 사용하였을 때, 단모음과 이중모음만을 구분하는 실험에서는 17.8% 의 밸런스 에러율(BER)을 얻을 수 있었고, /aw/, /ay/, 그리고 /oy/를 단모음과 분류하는 실험에서는 각각 32.9%, 29.9%, 그리고 20.2%의 에러율을 얻을 수 있었다. 추가적으로 진행한 실험에서, 음향음성학적 파라메터와 음성인식에 널리 쓰이고 있는 MFCC를 함께 사용하였을 경우 역시 성능향상이 나타나는 것을 확인하였다.