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Microfabrication and optical properties of highly ordered silver nanostructures
Cha, Hee-Ryoung,Lee, Jaeseon,Lee, Jae-Wook,Kim, Jong-Man,Lee, Jaebeom,Gwak, Jihye,Yun, Jae Ho,Kim, Yangdo,Lee, Dongyun Springer 2012 Nanoscale research letters Vol.7 No.1
<P>Using thermal evaporation, we fabricated five uniform and regular arrays of Ag nanostructures with different shapes that were based on an anodized aluminum oxide template and analyzed their optical properties. Round-top-shaped structures are obtained readily, whereas to obtain needle-on-round-top-shaped and needle-shaped structures, control of the directionality of evaporation, pore size, length, temperature of the substrate, etc., was required. We then observed optical sensitivity of the nanostructures by using surface-enhanced Raman scattering, and we preliminarily investigated the dependency of Raman signal to the roughness and shape of the nanostructures.</P>
Hee-Ryoung Cha,Ji-Hun Yu,Youn-Kyoung Baek,Hae-Woong Kwon,Yang-Do Kim,Jung-Goo Lee 한국자기학회 2014 Journal of Magnetics Vol.19 No.1
The influence regarding the dehydrogenation speed, at the desorption-recombination state during the hydrogenation-disproportionation-desorption-recombination (HDDR) process, on the microstructure and magnetic properties of Nd-Fe-B magnetic powders has been studied. Strip cast Nd-Fe-B-based alloys were subjected to the HDDR process after the homogenization heat treatment. During the desorption-recombination stage, both the pumping speed and time of hydrogen were systematically changed in order to control the speed of the desorption-recombination reaction. The magnetic properties of HDDR powders were improved as the pumping speed of hydrogen at the desorption-recombination stage was decreased. The lower pumping speed resulted in a smaller grain size and higher DoA. The coercivity and the remanence of the 200-300 μm sized HDDR powder increased from 12.7 to 14.6 kOe and from 8.9 to 10.0 kG, respectively. In addition, the remanence was further increased to 11.8 kG by milling the powders down to about 25-90 μm, resulting in (BH)max of 28.8 MGOe.
희토류 자원문제 해결을 위한 Nd 저감형 Nd-Fe-B계 영구자석 소재 기술 개발 동향
차희령(Hee-Ryoung Cha),백연경(Youn-Kyoung Baek),이정구(Jung-Goo Lee),김동환(Dong-Hwan Kim) 한국자기학회 2019 韓國磁氣學會誌 Vol.29 No.3
Recently, the demand of high efficient/miniaturized parts is increasing with the development of industry. Especially, the hybrid/electric vehicle market is rapidly growing because of the energy saving and environmental problems. The Nd-Fe-B magnet is one of the most important material in the automobile industry, which determines the efficiency and performance of traction motors. However, the issues on the resource and the price of heavy rare-earth (HRE) metals which are used to improve thermal stability of the magnet are constantly emerging. In addition, as the demand for Nd-Fe-B magnets is rapidly increasing with the growth of the electric vehicle market, Nd is also expected to be in short supply to meet the demand. Thus, there is a growing interest in research to replace Nd/Pr with Ce/La which is more abundant and cheaper than Nd along with the development of HRE lean/free magnets. The present article introduces the trend in research and development of a Nd-reduced rare-earth magnet to solve the problem of rare-earth resources.
MS-HDDR 프로세스의 DR 속도 제어를 통한 초미세 결정립 Nd2Fe14B계 자성분말 제조
차희령 ( Hee Ryoung Cha ),이정구 ( Jung Goo Lee ),백연경 ( Youn Kyoung Baek ),유지훈 ( Ji Hun Yu ),권해웅 ( Hae Woong Kwon ),김양도 ( Yang Do Kim ) 대한금속재료학회(구 대한금속학회) 2013 대한금속·재료학회지 Vol.51 No.5
In the present study, the influence of desorption-recombination (DR) speed during hydrogenation- decomposition-desorption-recombination (HDDR) process on the microstructure and magnetic properties of Nd-Fe-B based magnetic powders has been studied. Nd-Fe-B based alloys were made by mold casting and homogenization heat treatment. They were then subjected to HDDR treatment. During DR reaction, pumping speed and time of hydrogenation were systematically changed to control the speed of DR reaction. It was found that the slower hydrogen desorption during DR reaction can result in a smaller grain size and significantly increases the magnetic properties of the powder. The coercivity and the remanence of the HDDR powders in the size range of 200-300 μm was 12.4 kOe and 11.4 kG, respectively. In addition, the remanence was further increased to 12.0 kG by milling the powders down to 25-90 μm, which resulted in (BH)max of 26.5 MGOe.
차희령(Hee-Ryoung Cha),김태훈(Tae-Hoon Kim),이정구(Jung-Goo Lee) 한국자기학회 2022 韓國磁氣學會誌 Vol.32 No.2
Nd-Fe-B based permanent magnets are widely used for various applications due to their excellent magnetic properties. However, the increasing demand for Nd-Fe-B based permanent magnet with growth of the eco-friendly vehicle market is accelerating the imbalance between the supply and demand of rare-earth elements such as Dy, Tb, and Nd. For heavy rare earth (HRE)-free or Nd-lean magnets, it is necessary to refine the crystal grains to the single domain size of Nd2Fe14B phase (~300 ㎚), and to form the uniform and continuous grain boundaries phase as a non-magnetic phase. The hot-deformed Nd-Fe-B magnet have a very high potential as a HRE-free or Nd-reduced permanent magnet due to its ultra-fine grain size of ~300 ㎚. In this paper, we introduce overall research and development trend for the hot-deformation process of Nd-Fe-B based permanent magnets to develop the high performance HRE-free or Nd-lean permanent magnets.