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RISS 인기검색어
- 검색키워드
- 저자 : ( Ga Yeong Kim ) (검색결과 241 건)
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Ga-Yeong Kim,Tae-Hoon Kim,Hee-Ryoung Cha,Yang-Do Kim,Jung-Goo Lee 한국자기학회 2021 한국자기학회 학술연구발표회 논문개요집 Vol.31 No.1
Heavy rare earth elements such as Dy and Tb should be added for coercivity enhancement of Nd-Fe-B magnets. However, cost problem become more serious because the natural abundance of Dy and Tb comparing with Nd is lower than 10%. Therefore, many research was focused on modifying the microstructure to reduce the use of Heavy rare earth elements. On the other hand, Ce and La is the most abundant rare earth elements and constitute is more than 70% of the total rare earth element, and the price of Ce is about 10 times lower than Nd. Hence, it is a technologically interesting challenge to develop high-performance Nd-lean Nd-Fe-B magnets by substitution of Ce and La for Nd, which is also quite important from an industrial viewpoint. However, the magnetic properties of Nd-Fe-B magnets could be drastically deteriorated after replacing Nd with Ce and La due to inferior intrinsic magnetic properties of Ce<sub>2</sub>Fe<sub>14</sub>B (4πM = 11.7 kG, Ha = 26 kOe) and La<sub>2</sub>Fe<sub>14</sub>B (4πM = 13.8 kG, Ha = 20 kOe) compared to Nd<sub>2</sub>Fe<sub>14</sub>B (4πM = 16 kG, Ha = 73 kOe). Melt-spinning technique has been employed to obtain ultrafine-grained magnetic powders which have high coercivity due to the ultrafine grains. The melt-spun powder, which has Isotropic nanocrystalline, is subjected to hot-deformation (hot-pressing and subsequent die-upset) process in order to induce grain alignment along the c-axis parallel to the pressing direction, increasing the (BH)max. The mechanism of texture formation was well known that grains grew along the [010] and [100] axis into platelet shape and the [001] axis of platelet grains were oriented parallel to the pressing direction by the interface-controlled solution-precipitation-creep process and grain boundary sliding during hot-deformation process. So, grain boundary characteristics could significantly affect the texture formation during hot-deformation process. In this study, effect of Nd-Cu infiltration of (Nd, M)-Fe-B initial powder on hot-deformation behavior was investigated. Initial ribbons with the nominal compositions of (Nd1-xMx)<sub>13.6</sub>Fe<sub>bal</sub> B<sub>5.6</sub>Ga<sub>0.6</sub>Co<sub>6.6</sub> (x=0, x=0.2/M=Ce, x=0.3/M=Ce and x=0.3/M=Ce+La, wt.%, named as ND, CE0.2, CE0.3 and CELA0.3, respectively) were prepared by a single-roller melt-spinning technique and then pulverized into powders. The melt-spun powders were then hot-pressed and subsequently die-upsetted. In our previous study, the grain boundary phase of ND magnet was quite uniformly distributed along grain boundaries. However, the grain boundary phase became unclear and the triple junction phase increased with Ce and La content. Especially, the grain boundary phase of CELA0.3 magnet was quite unclear in almost area, whereas a lot of big-sized triple junction phase was formed. The RE-rich phase acts as a lubricant promoting the grain boundary sliding to form c-axis textured anisotropic magnets during the hot deformation process. When the RE-rich phase is not evenly distributed across the grain boundaries, grain boundary sliding could be suppressed and the degree of alignment decreases. It was confirmed that the degree of alignment was decreased with increasing Ce and La content. However, the grain boundary diffusion process in initial powder was favorable to the improvement of alignment of (Nd,M)-Fe-B hot-deformed magnets. Based upon these results, effect of grain boundary diffusion process of grain alignment and magnetic properties of Nd-lean Nd-Fe-B hot-deformed magnets will be discussed.
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Ga-Yeong Kim,Hee-Ryoung Cha,Youn-Kyoung Baek,Young-Kuk Kim,Dong-Hwan Kim,Yang-Do Kim,Jung-Goo Lee 한국자기학회 2020 Journal of Magnetics Vol.25 No.2
Nd in hot-deformed Nd-Fe-B magnets was partially substituted by Ce and La for the purpose of reducing the materials cost and balancing the utilization of rare earth resources. Initial melt-spun ribbons with the nominal compositions of (Nd1-xMx)13.6FebalB5.6Ga0.6Co6.6 (x = 0, x = 0.2/M=Ce, x = 0.3/M=Ce, Ce+La, wt.%) were prepared by a single-roller melt-spinning method, and pulverized into powders. The powders were then hot-pressed at 973 K under 100 MPa, and deformed at 973 K until 75 % of height reduction was achieved. The magnetic properties of hot-deformed magnets were decreased with the substitution of Ce for Nd. In addition, simultaneous substitution of Ce and La for Nd resulted in much lower magnetic properties. This tendency was almost the same as initial melt-spun powders. The deterioration on magnetic properties by substation of Ce and La for Nd in hot-deformed Nd-Fe-B magnets could be attributed to not only inferior intrinsic properties of (Ce/La)₂Fe14B to Nd₂Fe14B phase but also the effect of Ce/La substitution on microstructure such as density and grain alignment during hot-deformation. Although the magnetic properties were deteriorated by substitution of Ce and La for Nd in hot-deformed Nd-Fe-B magnets, the cost performance was largely enhanced from 2.32 to 2.62 MGOe×kg/$ by 13 % when increasing the content of Ce substituted for Nd from 0 to 0.3 wt.%.
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High-performance Ce-substituted Nd-Fe-B hot-deformed magnets produced by dual alloy method
Ga-Yeong Kim,Tae-Hoon Kim,Hee-Ryoung Cha,Yang-Do Kim,Jung-Goo Lee 한국자기학회 2021 한국자기학회 학술연구발표회 논문개요집 Vol.31 No.2
Nd-Fe-B magnets have been used for the traction motor of hybrid or electric vehicles due to its excellent magnetic properties. With increasing demand on Nd-Fe-B magnets, the shortage of Nd resource is becoming more serious. Ce and La is the most abundant rare earth elements and constitute more than 70% of the total rare earth element, and the price of Ce is about 10 times lower than Nd. Hence, from both industrial and academic viewpoints, it is a technologically important to develop high-performance Ce or La substituted Nd-Fe-B magnets. However, the magnetic properties of Nd-Fe-B magnets could be drastically deteriorated after replacing Nd with Ce and La due to inferior intrinsic magnetic properties of Ce₂Fe14B (4πMs = 11.7 kG, Ha = 26 kOe) and La₂Fe14B (4πMs = 13.8 kG, Ha = 20 kOe) compared to Nd₂Fe14B (4πMs = 16 kG, Ha = 73 kOe). Despite of the inferior intrinsic magnetic properties of Ce₂Fe14B and La₂Fe14B to Nd₂Fe14B, it is reported that deterioration of magnetic properties due to Ce and La substitution could be largely suppressed by constructing a multi-main-phase (MMP) structure in Nd-Fe-B sintered magnets. RE elements are inhomogeneously distributed within a 2:14:1 grains when sintering a mixture of Ce, La-free and Ce, La-containing RE₂Fe14B powders. Compared to single-main-phase (SMP) magnets, where Ce and La is homogeneously substituted Nd in the 2:14:1 phase, MMP magnets show much better magnetic performance. In this study, effect of dual-phase of Nd-Ce-Fe-B hot-deformed magnets using melt-spun powder was investigated. Initial ribbons with the nominal compositions of Nd13.6FebalB5.6Ga0.6Co6.6 and (Nd0.6Ce0.4)13.6FebalB5.6Ga0.6Co6.6 were prepared by a single-roller melt-spinning technique and then pulverized into powders. By tuning the mass ratios of the Ce-free and Ce-containing powder, Ce-containing magnets with 0-30 wt.% (named as ND, CE0.2 and CE0.3, respectively) Ce content were prepared by dual alloy method. The melt-spun powders were then hot-pressed and subsequently die-upsetted. In our previous study, the remanence and coercivity gradually decreased with increasing Ce content. This dependence of magnetic properties on Ce content could be ascribed to the magnetic dilution effect that Ce substitution for Nd in the 2:14:1 phase decreased the intrinsic magnetic properties. However, dual-phase hot-deformed magnets shows higher magnetic properties than single-phase hot-deformed magnets at the same composition. From SEM observation, it was confirmed that the Ce-free and Ce-containing area is quite different, the crystallographic alignment of Ce-containing area is inferior to that of Ce-free area. After annealing at 973 K, the composition of the flake interface changes due to interdiffusion during the annealing process. In sintered magnet, it has been reported that the peculiar chemical heterogeneity of dual-phase magnet is that the short-range exchange coupling and long-range magnetostatic interaction can induce higher remanence and coercivity simultaneously than those of single-phase magnets with the same composition. In this study as well, it is thought that the coercivity and remanence were improved due to the interdiffusion of elements between the flake interface by annealing. Compared to the Nd-Fe-B magnet (4πMr = 13.1 kG, Hc = 17.3 kOe), with CE0.3, Hc decreases drastically to 15.6 kOe, accompanied with significant falls in 4πMr to 11.5 kG. In contrast, for the dual-phase magnet with CE0.3, Hc reaches 16.74 kOe and 4πMr is 12.1kG, which are 7.3% and 9.2% higher than those of single-phase magnet, respectively. Based upon these results, effect of interdiffusion conditions of ma
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Ga Yeong Kim,Sang Bin Lee,Ok Kon Moon,Ji Sung Kim,Jung Hyun Choi,Jung San Wang,Joo Hyun Park,Hong Rae Kim,Ju Hwan Lee,Kyung Ok Min 국제물리치료학회 2014 Journal of International Academy of Physical Ther Vol.5 No.2
This study investigated the effects of changes to the pulsation factor of pulsed direct currents on wound healing. Patients with a pressure ulcer at a care hospital for the elderly were randomly divided into three groups: Group 1 involved the application of 100㎲ in pulse duration, 10 ㎳ in pulse period, 100 pps in a pulsation factor, 15 ㎃ in pulse amplitude, and polarity red+ by using pulsed direct currents; Group 2 involved a change of pulse period to 8 ms; and Group 3 received general wound management. Although there were no statistically significant differences in the changing stages of pressure ulcers among the groups, all the groups dropped in numerical stages. In the two groups to which pulsed direct currents were applied, there was a statistically significant reduction in the stages of pressure ulcers from the initial assessment to the 12-week assessment (p<.05). Even though there were no statistically significant differences in changes to the area of pressure ulcers among the groups, a statistically significant decrease was found in pulsed direct current group 2 whose pulse period was shortened (p<.05). There was no difference in the healing rate of pressure ulcers among the groups, but it made a numerical increase in pulsed direct current group 1 and group 2 and a numerical decrease in group 3. There were no significant differences in the characteristics of those who had a full recovery among the groups. Those findings indicate that pulsed direct currents have positive effects on the wound healing of patients with a pressure ulcer and that a treatment with pulsed direct currents whose pulsation factor is raised by reducing the pulse duration is especially effective.
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Kim, Rae-Kwon,Kim, Min-Jung,Yoon, Chang-Hwan,Lim, Eun-Jung,Yoo, Ki-Chun,Lee, Ga-Haeng,Kim, Young-Heon,Kim, Hyeonmi,Jin, Yeung Bae,Lee, Yoon-Jin,Cho, Cheon-Gyu,Oh, Yeong Seok,Gye, Myung Chan,Suh, Yongj American Society for Pharmacology and Experimental 2012 Molecular pharmacology Vol.82 No.3
<P>Glioma cells with stem cell properties, termed glioma stem-like cells (GSCs), have been linked to tumor formation, maintenance, and progression and are responsible for the failure of chemotherapy and radiotherapy. Because conventional glioma treatments often fail to eliminate GSCs completely, residual surviving GSCs are able to repopulate the tumor. Compounds that target GSCs might be helpful in overcoming resistance to anticancer treatments in human brain tumors. In this study, we showed that 5-bromo-3-(3-hydroxyprop-1-ynyl)-2H-pyran-2-one (BHP), a new 2-pyrone derivative, suppressed the maintenance of the GSC population in both a glioma cell line and patient-derived glioma cells. Treatment of GSCs with BHP effectively inhibited sphere formation and suppressed the CD133(+) cell population. Treatment with BHP also suppressed expression of the stemness-regulating transcription factors Sox2, Notch2, and β-catenin in sphere-cultured glioma cells. Treatment of GSCs with BHP significantly suppressed two fundamental characteristics of cancer stem cells: self-renewal and tumorigenicity. BHP treatment dramatically inhibited clone-forming ability at the single-cell level and suppressed in vivo tumor formation. BHP markedly inhibited both phosphoinositide 3-kinase/Akt and Ras/Raf-1/extracellular signal-regulated kinase signaling, which suggests that one or both of these pathways are involved in BHP-induced suppression of GSCs. In addition, treatment with BHP effectively sensitized GSCs to chemotherapy and radiotherapy. Taken together, these results indicate that BHP targets GSCs and enhances their sensitivity to anticancer treatments and suggest that BHP treatment may be useful for treating brain tumors by eliminating GSCs.</P>
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