• 한국분말재료학회지
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• 제16권4호
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• pp.285-290
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• 2009

HDDR treated anisotropic Nd-Fe-B powders have been widely used, due to their excellent magnetic properties, especially for sheet motors and sunroof motors of hybrid and electric vehicles. Final microstructure and coercivity of such Nd-Fe-B powders depend on the state of starting mother alloys, so additional homogenization treatment is required for improving magnetic properties of them. In this study, a homogenization treatment was performed at $900\sim1140^{\circ}C$ in order to control the grain size and Nd-rich phase distribution, and at the same time to improve coercivity of the HDDR treated magnetic powders. FE-SEM was used for observing grain size of the HDDR treated powder and EPMA was employed to observe distribution of Nd-rich phase. Magnetic properties were analyzed with a vibrating sample magnetometer.

• 한국분말재료학회지
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• 제9권6호
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• pp.381-393
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• 2002

Recent developments in nanocrystalline and nanocomposite rare earth-transition metal magnets are reviewed and emphasis is placed on research work at IFW Dresden. Principal synthesis methods include high energy ball milling, melt spinning, mold casting and hydrogen assisted methods such as reactive milling and hydrogenation-disproportionation-desorption-recombination. These techniques are applied to NdFeB-, PrFeB- and SmCo-type systems with the aim to produce high remanence magnets with high coercivity. Concepts of maximizing the energy density in nanostructured magnets by either inducing a texture via anisotropic HDDR or hot deformation or enhancing the remanence via magnetic exchange coupling are evaluated. With respect to high temperature applications melt spun $Sm(Co_{0.74}Fe_{0.1}Cu_{0.12}Zr_{0.04})_{7.5}$ ribbons were prepared, which showed coercivities of up to 0.53 T at 50$0^{\circ}C$. Partially amorphous $Nd_{60}Fe_xCo_{30-x}Al_{10}(0{\leq}x{\leq}30)$ alloys were prepared by copper mold casting. The effect of transition metal content on the glass-forming ability and the magnetic properties was investigated. The $Nd_{60}Co_{30}Al_{10}$ alloy exhibits an amorphous structure shown by the corresponding diffraction pattern. A small substitution of Co by 2.5 at.% Fe results In the formation of Fe-rich crystallites embedded in the Nd-rich amorphous matrix. The Fe-rich crystallites show hard magnetic behaviour at room temperature with a coercivity value of about 0.4 T, relatively low saturation magnetization and a Curie temperature of 500 K.

• 한국재료학회지
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• 제18권5호
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• pp.266-271
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• 2008

Magnesium alloys are alloyed with rare earth elements (Re, Ca, Sr) due to the limited use of magnesium in high-temperature conditions. In this study, the influences of Zr and Zn on the aging behavior of a Mg-Nd-Y alloy were investigated. magnesium alloys containing R.E elements require aging treatments Specifically, Nd, Y and Zr are commonly used for high-temperature magnesium alloys. Various aging treatments were conducted at temperatures of 200, 250 and $300^{\circ}C$ for 0.5, 1, 3, 6, and 10 hours in order to examine the microstructural changes and mechanical properties at a high temperature ($150^{\circ}C$). Hardness and high-temperature ($150^{\circ}C$) tensile tests were carried out under various aging conditions in order to investigate the effects of an aging treatment on the mechanical properties of a Mg-3.05Nd-2.06Y-1.13Zr-0.34Zn alloy. The maximum hardness was 67Hv; this was achieved after aging at $250^{\circ}C$ for 3 hours. The maximum tensile, yield strength and elongation at $150^{\circ}C$ were 237MPa, 145MPa and 13.6%, respectively, at $250^{\circ}C$ for 3 hours. The strengths of the Mg-3.05Nd-2.06Y-1.13Zr-0.34Zn alloy increased as the aging time increased to 3 hours at $250^{\circ}C$ This is attributed to the precipitation of a Nd-rich phase, a Zr-rich phase and $Mg_3Y_2Zn_3$.

• 한국자기학회지
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• 제1권2호
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• pp.60-68
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• 1991

급속냉각기술로 제조된 $Nd_{14}Fe_{76}Co_{4}B_{6}$ 및 $Nd_{10.5}Fe_{79}Co_{2}Zr_{15}B_{7}$ 자성분말을 사용하여 성형체와 본드자석을 제조하였다. 자기특성, 최적충진률 등의 분말입도 및 형상비에 따른 거동은 합금조성에 따라 달리 나타난다. Co/Fe 비가 작은 저밀도의 $Nd_{10.5}Fe_{79}Co_{2}Zr_{1.5}B_{7}$ 합금이 같은 성형압력에서 성형체의 성형밀도 및 최적충진률이 높아 자기특성이 우수하였으나 반면에 분말입도에 따라 자기특성이 변화하였다. 성형밀도(p)와 성형압력(P) 사이 에는 ${\phi}(g/cm^{2})=5.2~5.6{\times}P^{0.045~0.065}(ton/cm^{2})$의 관계식이 성립된다. 높은 Nd/Fe 비를 갖는 급속냉각된 $Nd_{14}Fe_{76}Co_{4}B_{6}$ 합금의 초미세립(50~60 nm)으로써 높은 보자력($iH_{c}=14~15kOe$)을 보유하나, Nd/Fe비가 낮은 $Nd_{10.5}Fe_{79}Co_{2}Zr_{1.5}B_{7}$ 합금은 결정립이 조대하고(150~400 nm)Nd-rich한 입경계상의 발달이 부진하여 자벽고착기구가 주 보자력 기구 로 판명된 두 합금에서 고착지점으로서의 역할이 불충분하여 보자력이 낮은 것으로 판명되었다.

• Journal of Welding and Joining
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• 제20권3호
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• pp.109-115
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• 2002

In this study high power Nd:YAG laser welding of structural steel was investigated. For the test steel blocks of $50{\times}50{\times}200mm$ were cut and machined, and bead-on-plate weld was made on the machined surface. Argon, nitrogen, helium, dry air or mixed gases were used to find the effect of shielding conditions on the bead formation. Results demonstrated that there were Fe I rich region and Fe II rich region in the laser induced plasma column based on the spectral analysis with S-2000 field spectrometer The Fe I region was located at the root of the column near keyhole opening. On the other hand, Fe II region was found at the middle of the plasma column. In the Nd:YAG laser welding, Fe I region emitted continuum which had peak value at wave length of around 710nm, and Fe II region had the peak at 580nm. In the welding of steel by $CO_2$ laser, however, no continuum was observed. There showed two groups of strong spikes in the $CO_2$ laser welding; the first group was displayed at the wave band of 450-560nm. This spike group emitted stronger intensity of light and sharper peaks than those group at 680-800nm.

• 한국자기학회:학술대회 개요집
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• 한국자기학회 2006년도 임시총회 및 하계학술연구발표회
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• pp.70-71
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• 2006

• International Journal of Industrial Entomology and Biomaterials
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• 제46권2호
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• pp.41-54
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• 2023

The blue-tailed damselfly, Ischnura elegans Van der Linden, 1820 (Odonata: Coenagrionidae), is a climate-sensitive indicator species in South Korea. In this study, we sequenced the complete mitochondrial genome (mitogenome) of I. elegans collected from South Korea for subsequent population genetic analysis, particularly to trace population movements in response to climate change. The 15,963 base pair (bp)-long complete mitogenome of I. elegans has typical sets of genes including a major non-coding region (the A+T-rich region), and an arrangement identical to that observed in ancestral insect species. The ATP6, ND3 and ND1 genes have the TTG start codon, which, although rare, is the canonical start codon for animal mitochondrial tRNA. The A/T content was 71.4% in protein-coding genes, 72.1% in tRNAs, 72.9% in the whole genome, 74.7% in srRNA, 75.3% in lrRNA, and 83.8% in the A+T-rich region. The A+T-rich region is unusually long (1,196 bp) and contains two subunits (192 bp and 176-165 bp), each of which is tandemly triplicated and surrounded by non-repeat sequences. Comparison of the sequence divergence among available mitogenomes of I. elegans, including the one from the current study, revealed ND2 as the most variable gene, followed by COII and COI, suggesting that ND2 should be targeted first in subsequent population-level studies. Phylogenetic reconstruction based on all available mitogenome sequences of Coenagrionidae showed a strong sister relationship between I. elegans and I. senegalensis.

• 한국자기학회:학술대회 개요집
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• 한국자기학회 2013년도 자성 및 자성재료 국제학술대회
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• pp.110-110
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• 2013

• 한국추진공학회지
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• 제21권4호
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• pp.79-88
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• 2017

램젯 연소실 조건에서 점화보조제가 도포된 Fuel-rich 추진제의 점화 실험을 수행하여 점화 지연과 연소 유지를 확인하였다. 연료 그레인은 HTPB에 AP 파우더 15 wt.%, Al 파우더 5 wt.%가 혼합된 형태로 구성되어 있다. 한편 연료 그레인에 $NC/BKNO_3$와 Composite 추진제로 이루어진 점화보조제를 도포하여 빠른 점화지연이 나타나도록 하였다. 에탄올 블렌딩 과산화수소 가스발생기를 통해 램젯 연소실의 공기와 가깝도록 온도, 압력, 산소 조성을 조절한 산화제 가스를 유속 $200kg/m^2s$으로 공급하였다. 실험 결과, 점화보조제가 잘 작동하여 연료그레인에서 0.6초의 점화 지연시간을 파악하였고 연소 중에는 화염이 유지되는 것을 확인하였다.

• 한국분말재료학회지
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• 제17권2호
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• pp.154-159
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• 2010

In this study, the sintering behavior of (Nd, Dy)-Fe-B powder which fabricated by strip-casting was investigated with various sintering temperatures and holding times. The relative density over 99% could be obtained by both sintering at $1070^{\circ}C$ for 1h and sintering at $970^{\circ}C$ for 20h. The grain growth was observed in sintered specimen at $1050^{\circ}C$ compared to one at $970^{\circ}C$. The isothermal sintering process below $1000^{\circ}C$ led to suppress grain growth showing the improved magnetic properties. The phase transformation of Nd-rich was confirmed by X-ray diffraction pattern.