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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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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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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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일부 고등학생의 자기 통제력이 스트레스와 구강건강 관련 삶의 질에 대한 조절효과 연구
이가령 ( Ga Ryoung Lee ) 한국치위생학회(구 한국치위생교육학회) 2016 한국치위생학회지 Vol.16 No.2
Objectives: The purpose of the study is to investigate the influence of self-control on stress management and oral health related quality of life in high school students. Methods: A self-reported questionnaire was completed by 422 high school students in Ulsan from December 1, 2014 to February 20, 2015. The study instrument consisted of stress and self-control. The stress instrument included 17 items modified by Kim and Lee. The self-control instrument was modified by Kim and had 20 items. Pearson``s correlation analysis was conducted to analyze the relationship between stress, self-control and oral health related quality of life. Regression analysis was used to analyze the effect of the stress on oral heal related quality of life. Hierarchical regression analysis was done to analyze the control effect of self-control in the relationship between the stress and oral health related quality of life. Results: The higher stress level resulted in the lower oral heal related quality of life. The higher self-control maintained the higher oral health related quality of life. The higher long term pursuit of satisfaction led to higher oral health related quality of life. The immediate suppression of satisfaction had a positive influence on the higher oral health related quality of life. Conclusions: There were significant correlations in self-control on stress management and oral health related quality of life.
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이가령 ( Ga Ryoung Lee ) 한국치위생학회(구 한국치위생교육학회) 2013 한국치위생학회지 Vol.13 No.1
Objectives: The purpose of this study was to attempt to lay the foundation for the development of oral health programs geared toward promoting the oral health of low socioeconomic class children. Methods: The subjects of this study have been investigated for the use of children to 96 local children`s center. Questionnaire for research purposes are described in more detail under the coordination of child care teachers to students, students to be able to record. The survey was conducted at the Health center. Analyzed the data collected by SPSS 18.0. Results: The findings of the study were as follows: The children were influenced by habits of having a snack in dental caries experience. Higher intake of bread and a lot of children more probability of dental caries experience. I`ve found a lot of sweet-food intake eleven cakes or fruits and vegetables that children prefer higher dental caries experience was low. Conclusions: Education on dietary behavior for low-income children was necessary because of the high correlation of the relationship between dietary habits and dental caries and diet.
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이가령(Ga-Ryoung Lee),유왕근(Wang Keun Yoo) 한국농촌의학 지역보건학회 2010 농촌의학·지역보건 Vol.35 No.1
본 연구는 우리나라 일부 농촌지역 노인의 구강건강상태와 의치만족도의 관련성을 조사하여 의치 만족도에 관여하는 요인들을 분석하고자 경상북도 지역 내 2개군 지역을 선정하여 지역 내 만 65세 이상 노인들을 대상으로 구강검사를 실시하고, 이들 중 가철성 의치를 장착한 노인만을 대상으로 의치만족도에 대한 설문조사하였다. 최종 수합된 546명의 자료를 분석한 결과 다음과 같다. 첫째, 조사대상자들의 각 세부요인별 만족도 점수는 저작기능에 대한 만족도의 경우 3.20±1.08, 의치고정에 대한 만족도 3.45±0.96, 심미적인 만족도 3.73±0.99 그리고 일반적인 만족도는 3.56±1.04이었다. 둘째, 인구통계적 특성에 따른 의치만족도의 차이는 성별의 경우 여자에 비해 남자에서 저작기능, 의치고정, 심미 및 일반 만족도가 모두 높은 경향이 있었으며, 의치고정에 대한 만족도에서는 통계적으로 유의하였다. 연령에 따른 차이는 75세 이상인 군에서 모든 세부요인별 만족도가 가장 낮았으며, 저작기능 및 의치고정에 대한 만족도와 심미적인 만족도의 경우 통계적으로 유의하였다. 교육수준이 높을수록 만족도가 증가하는 경향이 있었으며, 저작기능 및 의치고정에 대한 만족도와 일반적인 만족도에서 통계적으로 유의하였다. 동거가족에 따른 차이는 배우자와 함께 거주하는 경우에 만족도가 가장 높았으며, 저작기능에 대한 만족도의 경우 통계적으로 유의하였다. 또한 직업유무의 경우 직업이 있는 군이 없는 군에 비해 모든 세부요인별 만족도가 통계적으로 유의하게 높았으며, 월소득에 따른 차이는 소득수준이 높을수록 만족도가 증가하는 경향이 있었으며, 저작기능에 대한 만족도를 제외한 의치고정 만족도, 심미적인 만족도, 일반적인 만족도에서 각각 통계적으로 유의하였다. 셋째, 구강건강상태 및 사용의치에 따른 의치만족도의 차이는 우식경험영구치수의 경우 우식경험영구치수가 10개 미만인 군의 만족도가 가장 높았고, 잔존치아 수에 따른 차이는 잔존치아 수가 10개 이상인 군들의 만족도가 상대적으로 높았으며, 특히 의치고정에 대한 만족도와 심미적인 만족도에서는 통계적으로 유의하였다. 또한 음식을 먹을 때 의치를 사용하는 군이 사용하지 않는 군에 비해 저작기능 만족도, 의치고정 만족도, 심미적인 만족도, 일반적인 만족도가 모두 통계적으로 유의하게 높았다. 하루 종일 의치를 사용하는 군의 만족도는 사용하지 않는 군에 비하여 상대적으로 높은 경향을 보였으며 의치고정 만족도를 제외한 저작기능 만족도, 심미적인 만족도, 일반적인 만족도에서 각각 통계적으로 유의하였다. 이러한 연구결과를 종합해 볼 때 농촌지역 노인들의 구강건강상태 및 의치만족도는 전반적으로 낮은 것으로 조사 되었으며 이들 농촌지역 노인들의 구강보건을 증진시킬 수 있는 효과적인 노인구강보건 관리 및 교육프로그램이 시행되어야 할 것이다. Objectives: The study aimed to explore dental status and denture satisfaction in some rural elderly people. Methods: A total of 546 participants aged over 65 years was surveyed cross-sectionally. The subjects were surveyed with regard to their denture satisfaction by a structured questionnaire. The Wilcoxon or Kruskal-Wallis test was used for analysis. Results: As for respondents" satisfaction for dentures by the Likert scale of 5 score, aesthetic satisfaction(3.73) was highest, followed by general satisfaction (3.56) and masticatory functions satisfaction (3.45). In addition, the educational level, occupation, monthly income, the number of remaining teeth, use of denture variables have statistically significant difference in the denture satisfaction of those elderly people interviewed. Conclusions: The results showed that denture satisfaction in some rural elderly people was different in each categories. Consequently, providing tailor-made oral health education programs for the effective denture management of the elderly people should be needed in order to improve the quality of life of the aged.
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