• 한국분말재료학회지
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• 제22권2호
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• pp.105-110
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• 2015

In this study, effect of core-shell structure on compaction behavior of harmonic powder is investigated. Harmonic powders are made by electroless plating method on Fe powders. Softer Cu shell encloses harder Fe core, and the average size of Fe core and thickness of Cu shell are $34.3{\mu}m$ and $3.2{\mu}m$, respectively. The powder compaction procedure is processed with pressure of 600 MPa in a cylindrical die. Due to the low strength of Cu shell regions, the harmonic powders show better densification behavior compared with pure Fe powders. Finite element method (FEM) is performed to understand the roll of core-shell structure. Based on stress and strain distributions of FEM results, it is concluded that the early stage of powder compaction of harmonic powders mainly occurs at the shell region. FEM results also well predict porosity of compacted materials.

• 한국분말재료학회지
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• 제24권2호
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• pp.128-132
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• 2017

Harmonic structure materials are materials with a core-shell structure having a shell with a small grain size and a core with a relatively large grain size. They are in the spotlight because their mechanical properties reportedly feature strength similar to that of a sintered powder with a fine grain size and elongation similar to that of a sintered powder with a coarse grain size at the same time. In this study, the tensile properties, microstructure, and stretch-flangeability of harmonic structure SUS304L made using powder metallurgy are investigated to check its suitability for automotive applications. The harmonic powders are made by mechanical milling and sintered using a spark plasma sintering method at 1173 K and a pressure of 50 MPa in a cylindrical die. The sintered powders of SUS304L having harmonic structure (harmonic SUS304L) exhibit excellent tensile properties compared with sintered powders of SUS304L having homogeneous microstructure. In addition, the harmonic SUS304L has excellent stretch-flangeability compared with commercial advanced high-strength steels (AHSSs) at a similar strength grade. Thus, the harmonic SUS304L is more suitable for automotive applications than conventional AHSSs because it exhibits both excellent tensile properties and stretch-flangeability.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1999년도 춘계학술대회 논문집
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• pp.99-102
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• 1999

A mixture which was made from organic gel, glass powder and ceramic powder was masklessly etched for fabrication of barrier rib of PDP(Plasma Display Panel) by focused Ar$^{+}$ laser( λ =514 nm) and Nd:YAG(λ =532, 266 nm) laser irradiation at the atmosphere. The depth of the etched grooves increases with increasing a laser fluence and decreasing a scan speed. Using second harmonic of Nd:YAG laser, the threshold laser fluence was 6.5 mJ/$\textrm{cm}^2$ for the sample of PDP barrier rib softened at 12$0^{\circ}C$. The thickness of 130 ${\mu}{\textrm}{m}$ of the sample on the glass was clearly removed without any damage on the glass substrate by fluence of 19.5 J/$\textrm{cm}^2$....

• 대한전기학회:학술대회논문집
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• 대한전기학회 2006년도 추계학술대회 논문집 전기물성,응용부문
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• pp.18-19
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• 2006

In this study, dielectric properties of the ${Mg_5}{B_4}{O_{15}}$ (B=Ta, Nb) cation-deficient perovskite ceramics and its oscillator application are investigated. The cation-deficient perovskite ceramics are prepared through the solid-state route. According to the XRD pattern, ${Mg_4}{Ta_2}{O_9}$ and $Mg{Ta_2}{O_6}$ phase existed in calcined and sintered ${Mg_5}{Ta_4}{O_15}$ powder. Also ${Mg_5}{Ta_4}{O_{15}}$ phase added with increasing sintering temperature. In the case of calcined and sintered ${Mg_5}{Nb_4}{O_{15}}$ powder, single phase of ${Mg_5}{Nb_4}{O_{15}}$ is appeared. In the case of the ${Mg_5}{Ta_4}{O_{15}}$ and ${Mg_5}{Nb_4}{O_{15}}$ ceramics sintered at $1450^{\circ}C$ for 5h, the dielectric constant, quality factor, and temperature coefficient of the resonant frequency (TCRF) were 8.2, 259,473 GHz, $-10.91ppm/^{\circ}C$ and 14, 37,350 GHz, $-52.3\;ppm/^{\circ}C$, respectively. Simulated DR with ${Mg_5}{Ta_4}{O_{15}}$ ceramics had the operating frequency of 10.99 GHz and S(2,1) of -29.795 dB. Size of manufactured oscillator was $56{\times}48{\times}34\;mm^3 and operated at 11.93 GHz. Power output and second harmonic of oscillator were +13.61 dBm and -23.81 dBc at 23.85 GHz, respectively.

• 한국통신학회논문지
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• 제25권9B호
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• pp.1635-1640
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• 2000

본 논문에서는 기본파를 억제시키고 2차 고조파가 주 발진신호로 동작되는 18GHz 대역의 push-push 발진기를 semi-MMIC 형태로 설계 및 제작하였다. 마이크로스트립 선로를 포함하는 passive component는 semi-insulating GaAs 기판위에 MMIC 공정을 이용하여 구현하고, Chip 형태의 P-HEMT, 저항, 캐패시터를 Au wire-bonding에의해 연결하였으며, via-hole 대신 접지면을 회로 주변에 구성하여, back-side와 wire-bonding하였다. 실험 결과 -10.5 dBm의 출력 전력 특성을 얻었으며, 기본 주파수 억압은 -17.3 dBc/Hz의 특성을 보였다. 위상 잡음은 100kHz offset에서 -97.7 dBc/Hz를 얻었다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2000년도 제18회 학술발표회 논문개요집
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• pp.213-213
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• 2000

Direct laser vaporization of transition-metal(Co, Ni)/graphite composite pellet produced single wall carbon naotubes(SWNT) in the condensing vapor in a heated flow cylinder-type tube furnace, Transition metal/graphite composite pellet target was made by mixing graphite, Co, and Ni in 98:1:1 atomic weight ratios, pressing the mixed powder, and curing it. The target was placed in a tube furnace maintained at 1200$^{\circ}C$ and Ar inert collision gas continuously flowed into the tube. The 2nd harmonic, 532nm wavelength light from Nd-YAG laser was used to vaporize the tube. The carbon nanotubes produced by the laser vaporization were accumulated on quartz tube wall. The raw carbon nanotube materials were purified with surfactants(Triton X-100) in a ultrasonicator. These carbon nanotubes were analyzed using SEM, XRD, and Raman spectroscopic method. The carbon nanotube growth on the Ni-patterned Si substrate was investigated by the CVD process. Transition-metal, Ni and CH4 gas were used as a catalyst and a reactant gas, respectively. The structure and the phonon frequencies of the carbon nanotubes formed on the patterned Si substrate were measured by SEM and Raman spectrometer.

• 공업화학
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• 제9권2호
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• pp.177-184
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• 1998

분체 형태의 소수성 고분자 polymethylmethacrylate(PMMA), poly vinyl chloride(PVC)와 친수성 금속 aluminium에 대한 water, glycerol, formamide, diiodomethane, 1,1,2,2-tetrabromoethane, 1-bromonaphthalene, acetone, chloroform, benzene, ethanol과 methanol과의 접촉각을 Washburn식을 기본으로 한 wicking법으로 측정하였다. 또한, 농도에 따른 음이온 계면활성제 SDS(sodium dodecyl sulfate)와 양이온 계면활성제 CTAB(cetyl trimethylamonium bromide) 수용액과의 접촉각을 측정하였다. 유기액체들과의 측정된 접촉각으로부터 Zisman plot을 사용하여 임계표면장력, ${\gamma}_c$를 예측하였으며, 농도에 따른 계면활성제 SDS와 CTAB수용액과의 접촉각으로부터 adhesion tension plot을 사용하여 ${\gamma}_c$를 예측하였다. 유기액체, 계면활성제 SDS와 CTAB수용액에 대해서 분체 PMMA의 ${\gamma}_c$는 각각 43.5, 28.3과 $36.2mNm^{-1}$이며, 분체 PVC의 ${\gamma}_c$는 각각 44.2, 28.0과 $34.8mNm^{-1}$값을 얻었다. 이로부터, 고체 표면의 적심성과 성질이 계면활성제의 첨가에 의해 변화됨을 알 수 있었다. 또한, 측정된 접촉각으로부터 조화평균식을 사용하여 각 고체의 표면자유에너지. ${\gamma}_s$와 그 성분 값들을 결정하였다.

• Journal of Electrical Engineering and Technology
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• 제10권4호
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• pp.1621-1625
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• 2015

Power quality has always been a concern of power engineers. Certainly an argument can be successfully made that most parts of power engineering have the ultimate objective to improve power quality. AC motors were widely used in industrial and domestic applications. Generally, AC motors were of two types: Induction and Synchronous motors. In motor many parameters like different load cycling, switching, working in hot weather and unbalances creates harmonics which creates major reasons for temperature rise of the motors. Due to high peak value of voltage, harmonics can weaken insulation in cables, windings and capacitors and different electronic components. Higher value of harmonics increase the motor current and decrease the power factor which will reduce the life time of the motor and increase the overall rating of all electrical equipments. Harmonics reduction of all the motors in India will save more power. Coating of windings of the motor with nano fillers will reduce the amount of harmonics in the motor. Based on the previous project works, actions were taken to use the enamel filled with various nano fillers for the coating of the windings of the different AC motors. Ball mill method was used to convert the micro particles of Al₂O₃, SiO₂, TiO₂, ZrO₂ and ZnO into nano particles. SEM, TEM and XRD were used to augment the particle size of the powder. The synthesized nano powders were mixed with the enamel by using ultrasonic vibrator. Then the enamel mixed with the nano fillers was coated to the windings of the several AC motors. Harmonics were measured in terms of various indices like THD, VHD, CHD and DIN by using Harmonic analyzer. There are many other measures and indices to describe power quality, but none is applicable in all cases and in many instances, these indices may hide more than they show. Sometimes power quality indices were used as a basis of comparison and standardization. The efficiency of the motors was increased by 5 – 10 %. The thermal withstanding capacity of the motor was increased by 5º to 15º C. The harmonics of the motors were reduced by 10 – 50%.