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분무건조된 Nd-Fe-B 전구체 입자의 크기조절 및 환원-확산 후 자기 특성에 미치는 영향
백연경,서영택,이정구,김동수,배동식,최철진,Baek, Youn-Kyoung,Seo, Young-Taek,Lee, Jung-Goo,Kim, Dong Su,Bae, Dong Sik,Choi, Chul-Jin 한국분말야금학회 2013 한국분말재료학회지 (KPMI) Vol.20 No.5
In this study, we fabricated $Nd_2Fe_{14}B$ hard magnetic powders with various sizes via spray drying combined with reduction-diffusion process. Spray drying is widely used to produce nearly spherical particles that are relatively homogeneous. Thus, the precursor particles were prepared by spray drying using the aqueous solution containing Nd salts, Fe salts and boric acid with the target stoichiometric composition of $Nd_2Fe_{14}B$. The mean particle sizes of the spray-dried powders are in the range from one to seven micrometer, which are adjusted by controlling the concentrations of precursor solutions. After debinding the as-prepared precursor particles, ball milling was also conducted to control the particle sizes of Nd-Fe-B oxide powders. The resulting particles with different sizes were subjected to subsequent treatments including hydrogen reduction, Ca reduction and washing for CaO removal. The size effect of Nd-Fe-B oxide particles on the formation of $Nd_2Fe_{14}B$ phase and magnetic properties was investigated.
거대기공 구조-역오팔 또는 중공 구조를 갖는 KIT-1 메조포러스 실리케이트의 제조
백연경,이정구,김영국,Baek, Youn-Kyoung,Lee, Jung-Goo,Kim, Young Kuk 한국분말야금학회 2016 한국분말재료학회지 (KPMI) Vol.23 No.3
We report a facile method for preparing KIT-1 mesoporous silicates with two different macroporous structures by dual templating. As a template for macropores, polystyrene (PS) beads are assembled into uniform three dimensional arrays by ice templating, i.e., by growing ice crystals during the freezing process of the particle suspension. Then, the polymeric templates are directly introduced into the precursor-gel solution with cationic surfactants for templating the mesopores, which is followed by hydrothermal crystallization and calcination. Later, by burning out the PS beads and the surfactants, KIT-1 mesoporous silicates with macropores are produced in a powder form. The macroporous structures of the silicates can be controlled by changing the amount of EDTANa4 salt under the same templating conditions using the PS beads and inverse-opal or hollow structures can be obtained. This strategy to prepare mesoporous powders with controllable macrostructures is potentially useful for various applications especially those dealing with bulky molecules such as, catalysis, separation, drug carriers and environmental adsorbents.
환원-확산법에 의해 제조된 Sm-Fe 합금분말의 질화거동 및 자기특성에 미치는 Mn첨가 효과
서영택,백연경,이정구,최철진,Seo, Young-Taek,Baek, Youn-Kyoung,Lee, Jung-Goo,Choi, Chul-Jin 한국분말야금학회 2013 한국분말재료학회지 (KPMI) Vol.20 No.1
In the present study, we systematically investigated the effect of Mn addition on nitrogenation behavior and magnetic properties of Sm-Fe powders produced by reduction-diffusion process. Alloy powders with only $Sm_2(Fe,Mn)_{17}$ single phase were successfully produced by the reduction-diffusion process. The coercivity of $Sm_2(Fe,Mn)_{17}$ powder rapidly increased during nitrogenation and reached the maximum of 637 Oe after 16 hours. After further nitrogenation, it decreased. In contrast, the coercivity of $Sm_2Fe_{17}$ powder gradually increased during nitrogenation for 24 hours. The coercivity of $Sm_2(Fe,Mn)_{17}$ powder was higher than that of $Sm_2Fe_{17}$ powder at the same condition of nitrogenation. It was considered that the Mn addition facilitates the nitrogenation of $Sm_2Fe_{17}$ powder and enhances the coercivity.
P3HT:PCBM 층 내 분산 가능한 금속 나노입자의 제조 및 이를 포함한 고분자 태양전지 소자의 특성에 관한 연구
김민지,최규채,김영국,김양도,백연경,Kim, Min-Ji,Choi, Gyu-Chae,Kim, Young-Kuk,Kim, Yang-Do,Baek, Youn-Kyoung 한국분말야금학회 2014 한국분말재료학회지 (KPMI) Vol.21 No.3
In this study, we prepare polymer solar cells incorporating organic ligand-modified Ag nanoparticles (O-AgNPs) highly dispersed in the P3HT:PCBM layer. Ag nanoparticles decorated with water-dispersible ligands (WAgNPs) were also utilized as a control sample. The existence of the ligands on the Ag surface was confirmed by FT-IR spectra. Metal nanoparticles with different surface chemistries exhibited different dispersion tendencies. O-AgNPs were highly dispersed even at high concentrations, whereas W-AgNPs exhibited significant aggregation in the polymer layer. Both dispersion and blending concentration of the Ag nanoparticles in P3HT:PCBM matrix had critical effects on the device performance as well as light absorption. The significant changes in short-circuit current density ($J_{SC}$) of the solar cells seemed to be related to the change in the polymer morphology according to the concentration of AgNPs introduced. These findings suggested the importance of uniform dispersion of plasmonic metal nanoparticles and their blending concentration conditions in order to boost the solar cell performance.
이정구 ( Jung Goo Lee ),백연경 ( Youn Kyoung Baek ),정국채 ( Kook Chae Chung ),최철진 ( Chul Jin Choi ) 대한금속재료학회(구 대한금속학회) 2011 대한금속·재료학회지 Vol.49 No.12
In the present study, the formation of hollow Cu oxide nanoparticles through the oxidation process at temperatures from 200 to 300℃ has been studied by transmission electron microscopy with Cu nanoparticles produced by the plasma arc discharge method. The Cu nanoparticles had a thin oxide layer on the surface at room temperature and the thickness of this oxide layer increased during oxidation in atmosphere at 200-300℃ However, the oxide layer consisted of Cu2O and CuO after oxidation at 200℃ whereas this layer was comprised of only CuO after oxidation at 300℃ On the other hand, hollow Cu oxide nanoparticles are obtained as a result of vacancy aggregation in the oxidation processes, resulting from the rapid outward diffusion of metal ions through the oxide layer during the oxidation process.
김경민,이정구,김경태,백연경,Kim, Kyung Min,Lee, Jung-Goo,Kim, Kyung Tae,Baek, Youn-Kyoung 한국분말야금학회 2019 한국분말재료학회지 (KPMI) Vol.26 No.2
Rare earth magnets are the strongest type of permanent magnets and are integral to the high tech industry, particularly in clean energies, such as electric vehicle motors and wind turbine generators. However, the cost of rare earth materials and the imbalance in supply and demand still remain big problems to solve for permanent magnet related industries. Thus, a magnet with abundant elements and moderate magnetic performance is required to replace rare-earth magnets. Recently, $a^{{\prime}{\prime}}-Fe_{16}N_2$ has attracted considerable attention as a promising candidate for next-generation non-rare-earth permanent magnets due to its gigantic magnetization (3.23 T). Also, metastable $a^{{\prime}{\prime}}-Fe_{16}N_2$ exhibits high tetragonality (c/a = 1.1) by interstitial introduction of N atoms, leading to a high magnetocrystalline anisotropy constant ($K_1=1.0MJ/m^3$). In addition, Fe has a large amount of reserves on the Earth compared to other magnetic materials, leading to low cost of raw materials and manufacturing for industrial production. In this paper, we review the synthetic methods of metastable $a^{{\prime}{\prime}}-Fe_{16}N_2$ with film, powder and bulk form and discuss the approaches to enhance magnetocrystalline anisotropy of $a^{{\prime}{\prime}}-Fe_{16}N_2$. Future research prospects are also offered with patent trends observed thus far.
실리카 코어 금 위성입자의 합성 및 표면 증강 라만 산란을 기반으로 한 센서로의 응용
최현지,김영국,윤석영,백연경,Choi, Hyun Ji,Kim, Young-Kuk,Yoon, Seok-Young,Baek, Youn-Kyoung 한국분말야금학회 2014 한국분말재료학회지 (KPMI) Vol.21 No.6
In this study, we synthesize silica-core gold-satellite nanoparticles (SGNPs) for the surface-enhanced Raman scattering (SERS) based sensing applications. They consist of gold satellite nanoparticles (AuNPs) fixed on the silica core nanoparticles, which sizes of AuNPs can be tunned by varying the amount of reactants (growth solution and reducing agent). Their surface plasmon resonance (SPR) properties were characterized by using UV-vis spectroscopy, showing that the growth of AuNPs on silica cores leads to the light absorption in the longer wavelength region. Furthermore, the size increase of AuNPs exhibited the dramatic change in SERS activity due to the formation of hot spots. The optimized SGNPs showing enhancement factor ${\sim}3.8{\times}10^6$ exhibited a detection limit of rhodamine 6G (R6G) as low as $10^{-8}M$. These findings suggest the importance of size control of SGNPs and their SPR properties to develop highly efficient SERS sensors.
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.