• Journal of the Korean Magnetics Society
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• v.6 no.3
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• pp.145-150
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• 1996

The magnetic thin films can be prepared without vacuum process and under the low temperature ( < $100^{\circ}C$) by ferrite plating. We have performed ferrite plating of $Fe_{3-x}Mn_{x}O_4(x=0.0~0.023)$ films on glass plate at $80^{\circ}C$. We got the film $9000\AA$ in thickness, having a mirror-like luster. The composition parameter, x, in the $Fe_{3-x}Mn_{x}O_4$ films is much smaller then the corresponding on, x', in the reaction solution(x/x'=O.04). The saturation magnetization($M_{s}$) of $Fe_{3}O_{4}$ ferrite film as measured by a VSM was $M_{s}$=480 emu/cc which agrees with $Fe_{3}O_{4}$ bulk samples.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.52 no.4
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• pp.153-158
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• 2003

This thesis deal with ferroelectric and ferromagnetic materials. PZT/Ferrite ceramics were made by the making process using PZT powder and garnet ferrite powder. PZT and ferrite are mixed as much 90%-10%, 50%-50%, and so on. After making samples, we are polishing samples until thickness is 0.1~0.2mm. We measured all kinds of samples in room temperature and applied magnetic field from -4500 to 4500 Oersted and conducted test of magnetical and electrical measurement using VSM and lpC resolution electrometer calibrated with RT66A pulsed tester. From this measurement, we can calculate tunability of these samples using C value obtained from P-E loop. As a result, it was able to measure magnetic characteristic when two matter had each other component ratio, and it was compound. However, it confirmed the possibility that was able to have ferroelectric characteristic with you in PZT 90% and ferrite 10%. Therefore, If this thing comes for PZT 50% and ferrite 50% have ferroelectric characteristic as him in a compound sample ore, can use this in an oscillator, supersonic waves detector in addition to a piezoelectric element. It may contribute to multipurpose of an element and demands such as a miniaturization of equipment, efficiency, reduce of a price which can use a characteristic of two components.

• Journal of the Korean Ceramic Society
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• v.32 no.3
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• pp.313-320
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• 1995

We investigated the preferred orientation, electrical and magnetic properties of the Mn-Zn ferrite thin films deposited on SiO2/Si(100) by ion beam sputtering. The Cu-added Mn-Zn ferrite thin films had a preferred orientation of (111) with a weak orientation, (311). While the Zn-added one had a strong (111) preferred orientation. The saturation magnetization of the Cu- or Zn-doped Mn-Zn ferrite films increased with increasing substrate temperature (Ts) due to the increase of grain size and the enhancement of crystallinity. For the same reason the coercivity of Cu- or Zn-doped Mn-Zn ferrite films deposited at low Ts increased with increasing Ts, but those of the films deposited at high Ts slightly decreased not only because the defect density of the films decreases but because more grains have multi-domains with increasing Ts. The resistivity of Cu- or Zn-added Mn-Zn ferrite thin fims measured by complex impedance method decreased with increasing Ts due to the ehhancement of crystallinity as well as due to the increase of grain size.

• Journal of the Korean Society for Heat Treatment
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• v.12 no.1
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• pp.21-30
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• 1999

The present study were investigated changes of precipitation behaviour of laves phase in ferrite single phase and ferrite-martensite dual phase and precipitation of laves phase under stress. Hardness changes in ferrite phase appeared two hardness peaks by precipitation of initial fine precipitator and laves phase in 3Mo-0.3Si and 3Mo-0.3Si-C specimens, respectively. Hardness changes in martensite phase of 3Mo-0.3Si-C specimen was lower in the initial stage of aging by carbide precipitation and after this, increased by re-hardening due to precipitation of laves phase. In the ferrite phase, laves phase was mainly precipitated, whereas in the martensite phase, carbide was preferentially formed during the initial stage of aging and with increasing aging time, laves phase and carbide were simultaneously precipitated by precipitation of laves phase at around carbide. In the ferrite-martensite interface, laves phase was mainly precipitated and carbide was mainly formed at boundary of lath martensite than grain boundary. Adding the stress in aging, fine precipitator of inital precipitation of laves phase precipitated in (100) of perpendicular to tensile direction and has grown to only followed<010>direction and also, volume fraction of laves phase increased. Consequently, the stress added was accelerated initial precipitation of laves phase.

• Proceedings of the KIEE Conference
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• 2011.07a
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• pp.477-478
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• 2011

전기, 전자분야에 반도체가 폭넓게 사용됨에 따라 발 변전소에서 Noise에 의한 보호계전기 오동작 사례가 늘어나고 있어, 이것을 효과적으로 차단하고 설비의 오동작을 예방할 수 있는 필터개발이 필요 하였다. 현재 시중에서 사용하고 있는 Ferrite Filter는 일반 가전 및 OA를 대상으로 개발하였기 때문에 송변전계통의 변전소에서 발생하는 Noise와 차단 영역이 다르다. 따라서 송변전설비 보호계전기의 오동작원인을 분석하고, 변전소에서 발생하는 Noise의 형태를 측정하여 그것을 차단하기에 적합한 Clamp형의 Ferrite Filter를 개발하였다. Ferrite Filter는 재질에 따라 고주파 차단 영역이 결정된다. 일반적인 전자설비에 사용하는 니켈계(Ni-Zn) 재질의 Filter는 수MHz~수GHz 영역이며, 변전소에 주로 발생하는 고주파 수KHz~수MHz 영역은 망간계(Mn-Zn) 재질을 혼합하여 만들었다. 개발한 Filter의 성능 확인을 위해 공인시험기관인 KERI(한국전기연구원)에서 다양한 형태로 고주파 차단 특성 시험을 시행한 결과, 망간계와 니켈계 Ferrite Filter를 직렬로 설치함으로서 Noise를 효과적으로 차단함을 확인 하였고 5개소에 2개월간시범적용을 통하여 그 성능을 검증하였다. 본 연구결과는 Clamp형 Ferrite Filter의 기술적 한계로 여겨졌던 고주파 차단특성을 발변전소 등의 전력설비에서 발생하는 대역까지 확대하였으며, 경제적으로도 기존의 L-C Filter 대비 약 4%의 비용으로 설치할 수 있어 그 비용을 획기적으로 절감하였고, 설비의 정지 없이 언제든지 간편하게 설치할 수 있어 현장에서 적용하기에 매우 유용하다. 그 성능을 지속적으로 향상시켜 많은 분야에서 활용할 수 있도록 추가적인 연구개발이 필요할 것으로 판단된다.

• Journal of Powder Materials
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• v.15 no.4
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• pp.292-296
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• 2008

The electromagnetic (EM) wave absorption properties of the $Fe_{73}Si_{16}B_7Nb_3Cu_1$ nanocrystalline powder mixed with 5 to 20 vol% of Ni-Zn ferrites has been investigated in a frequency range from 100MHz to 10GHz. Amorphous ribbons prepared by a planar flow casting process were pulverized and milled after annealing at 425 for 1 hour. The powder was mixed with a ferrite powder at various volume ratios to tape-cast into a 1.0mm thick sheet. Results showed that the EM wave absorption sheet with Ni-Zn ferrite powder reduced complex permittivity due to low dielectric constant of ferrite compared with nanocrystalline powder, while that with 5 vol% of ferrite showed relatively higher imaginary part of permeability. The sheet mixed with 5 vol% ferrite powder showed the best electromagnetic wave absorption properties at high frequency ranges, which resulted from the increased imaginary part of permeability due to reduced eddy current.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.11a
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• pp.201-201
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• 2006

영구자석은 크게 Hard ferrite와 희토류계 자석, 그리고 Alnico 주조자석으로 구별되어진다. 그동안 Hard ferrite는 산업적으로 전자기 응용제품 또는 각종 구동 모터에 응용되어 왔지만, 최근 Nd계 희토류 자것이 고성능 모터의 소재로 급격히 대체되고 있다. 하지만, 희토류계 원료에 비해 동일 중량 대비 40~60배 가량 저렴한 Hard ferrite의 사용은 현재까지도 꾸준히 유지되고 있으며, 최근 자동차 고성능 모터용 Sr ferrite의 개발이 연구 중이다.[2] 본 연구에서는 제일원리 전산모사를 통하여 HCP 구조의 기본 Unit Cell 64개 원자를 가진 Sr-ferrite의 격자상수를 계산하여 기존 연구결과와 비교하였으며, 자화에너지와 자기모멘트를 계산하였다. 또한 향후 각종 첨가물의 영향에 대한 연구를 위해 기본 구조 및 치환 구조에 대해 고찰하였다. 그 결과 가장 안정한 에너지를 갖는 격자상수는 a=5.88, b=23.03으로 계산되어 Kimura et al의 측정 결과와 유사한 결과를 얻을 수 있었으며, $E_F$가 3.9171, $M_B$는 46.6481로 계산되었다. 항후 Sr-ferrite의 구조에서 Fe atom의 일부를 동일주기 원소인 Cr, Mn, Co, Ni, Cu로 치환하여 자기적 특성을 계산하여 본 연구결과와 비교하고자 한다.

• Journal of the Korean Chemical Society
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• v.56 no.5
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• pp.609-616
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• 2012

Ba-ferrite ($BaFe_{12}O_{19}$) nanoparticles were synthesized by chemical coprecipitation method in an aqueous solution. The particle size and the crystallization temperature of the Ba-ferrite nanoparticles were controlled varying the precipitation temperature. The precipitate that was prepared at $0^{\circ}C$ showed the crystal structure of Ba-ferrite in X-ray diffraction when it was calcined at the temperature above $580^{\circ}C$, whereas what was prepared at $50^{\circ}C$ showed the crystallinity when it was calcined at the temperature higher than about $700^{\circ}C$. The particle sizes of the synthesized Ba-ferrite were in a range of about 20-30 nm when it was prepared by being precipitated at $0^{\circ}C$ and calcined at $650^{\circ}C$. When the precipitation temperature increased, the particle size also increased even at the same calcination temperature. The magnetic properties of the Ba-ferrite nanoparticles were also controlled by the synthetic condition of precipitation and calcination temperature. The coercive force could be appreciably lowered without a loss of saturation magnetization when the Ba-ferrite nanoparticles were prepared by precipitation and calcination both at low temperatures.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.11b
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• pp.284-287
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• 2001

Multi-pole anisotropic Sr-ferrite sintered magnets has been studied by powder injection molding under applied magnetic field. The orientation of anisotropic Sr-ferrite powders higher than 80% during injection molding is achieved at the following conditions; apparent viscosity lower then 2500 poise in 1000 $sec^{-1}$ shear rate and applied magnetic field higher then 4 kOe. For the high fluidity and strength of injection molded compact, and the effective binder removal without defects during solvent extraction and thermal debinding, the optimum multi-binder composition is paraffin wax(PW)/carnauba wax(CW)/HDPE = 50/25/25 wt%. The rate of binder removal is proportional to the mean particle size of Sr-ferrite powders whereas it is inversely proportional to the content of Sr-ferrite powders and the sample thickness. The high magnetic properties of Sr-ferrite sintered magnets are; 3.8 kG of remanent flux density, 3.4 kOe of intrinsic coercivity, and 1.2 kG of surface flux density (l-mm-thick) in the direction of applied magnetic field.

• Journal of Welding and Joining
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• v.32 no.1
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• pp.22-27
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• 2014

In the past, cold crack was commonly observed in the HAZ(heat affected zone) of high-strength steels. Applying to TMCP(thermo-mechanical controlled process) and HSLA(high strength low alloy) steels, cold crack tends to increase the occurrence in the weld metal. It is generally understood that cold crack occurs when the following factors are present simultaneously : diffusible hydrogen in the weld metal, a susceptible microstructure and residual stress. In particular, many studies investigated the microstructural effect on the cold crack in HAZ and the cold crack in weld metals starts to receive the special attendance in modern times. The purpose of the study is to review the effect of weld microstructures (grain boundary ferrite, Widm$\ddot{a}$nstatten ferrite, acicular ferrite, bainite and martensite) on cold crack in the weld metals. Among various microstructures of weld metals, acicular ferrite produced the greatest resistance to the cold crack due to the fine interlocking nature and high-angle grain boundary of the microstructure.