• Journal of Magnetics
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• 제15권4호
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• pp.155-158
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• 2010

The HDDR (hydrogenation, disproportionation, desorption, and recombination) process can be used as an effective way of converting a no coercivity Nd-Fe-B ingot material, with a coarse $Nd_2Fe_{14}B$ grain structure, to a highly coercive one with a fine grain structure. Careful control of the HDDR process can lead to an anisotropic powder with good $Nd_2Fe_{14}B$ grain texture; the most critical step for inducing texture is disproportionation. The critical conditions (hydrogen pressure and temperature) for the disproportionation reaction of fully hydrogenated $Nd_{12.5}Fe_{81.1-(x+y)}B_{6.4}Ga_xNb_y$ (x = 0 or 0.3, y = 0 or 0.2) alloys, in different atmospheres of pure hydrogen and a mixed gas of hydrogen and argon, was investigated with TPA (thermopiezic analyser). From this, the hydrogen pressure-temperature diagram showing the critical conditions was established. The critical disproportionation temperature of the fully hydrogenated $Nd_{12.5}Fe_{81.1-(x+y)}B_{6.4}Ga_xNb_y$ alloys was slightly increased as the hydrogen pressure decreased in both pure hydrogen and mixed gas. The critical disproportionation temperature of the hydrogenated alloys was higher in the mixed gas than in pure hydrogen. Addition of Ga and Nb increased the critical disproportionation temperature of the fully hydrogenated Nd-Fe-B alloys.

• Journal of Magnetics
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• 제22권2호
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• pp.244-249
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• 2017

To get deeper insight into the effect of intergranular additives in sintered Nd-Fe-B magnet and consequently improve the properties better, the interaction between additives (oxide, nitride, and carbide) and Nd-rich phase in the temperature range of 298.15-1400 K was analyzed thermodynamically. It can be found that the oxide additives became less stable than nitrides and carbides. Except for calcium oxide, almost all oxides could react with Nd from Nd-rich phase. To be different from oxide additives, the mechanism of nitrides and carbides was defined with various elements, either reaction with Nd from Nd-rich phase or not. The two different mechanisms would show different effects on the microstructure and hence properties of magnet. The thermodynamic analysis had a better agreement with the experimental information.

• Journal of Magnetics
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• 제7권4호
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• pp.127-131
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• 2002

HDDR characteristics and magnetic properties of $Nd_{15}{(Fe_{1-x}Co_{x})}_{77}B_{8}$(x=0-0.6) alloys were investigated. The effect of applying magnetic field during the recombination step on the anisotropic nature of the HDDR-treated material was also examined. The $Nd_{15}{(Fe_{1-x}Co_{x})}_{77}B_{8}$ phase in the Nd-Fe-B alloys with high Co-substitution alloy had remarkably enhanced phase stability. The $Nd_{15}{(Fe_{1-x}Co_{x})}_{77}B_{8}$(x=0-0.6) alloys with high Co-substitution could be HDDR-treated successfully by only using high pressure hydrogen. However, these alloys had no appreciable coercivity. The poor coercivity of the HDDR-treated $Nd_{15}{(Fe_{1-x}Co_{x})}_{77}B_{8}$(x=0-0.6) alloys with high Co-substitution was attributed to the $Nd{(Fe,Co)}_2$ phase in the alloys. The magnetic filed applied during the recombination step had little effect on the anisotropic nature of the HDDR-treated powder.

• 한국분말재료학회지
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• 제30권2호
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• pp.116-122
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• 2023

Because magnets fabricated using Nd-Fe-B exhibit excellent magnetic properties, this novel material is used in various high-tech industries. However, because of the brittleness and low formability of Nd-Fe-B magnets, the design freedom of shapes for improving the performance is limited based on conventional tooling and postprocessing. Laser-powder bed fusion (L-PBF), the most famous additive manufacturing (AM) technique, has recently emerged as a novel process for producing geometrically complex shapes of Nd-Fe-B parts owing to its high precision and good spatial resolution. However, because of the repeated thermal shock applied to the materials during L-PBF, it is difficult to fabricate a dense Nd-Fe-B magnet. In this study, a high-density (>96%) Nd-Fe-B magnet is successfully fabricated by minimizing the thermal residual stress caused by substrate heating during L-PBF.

• Asian-Australasian Journal of Animal Sciences
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• 제31권5호
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• pp.658-671
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• 2018

Objective: Nandrolone decanoate (ND) is an anabolic-androgenic steroid frequently used for clinical treatment. However, the inappropriate use of ND results in the reduction of serum testosterone level and sperm production. The suppressive effect of ND on testosterone production has not been investigated in detail. The present study was designed to examine the effect of ND on the expression of steroidogenic enzymes in the rat testis. Methods: Male Sprague Dawley rats at 50 days of age were subcutaneously administrated with either 2 or 10 mg of ND/kg body weight/week for 2 or 12 weeks. The changes of transcript and protein levels of steroidogenic enzymes in the testis were determined by real-time polymerase chain reaction and western blotting analyses, respectively. Moreover, immunohistochemical analysis was employed to determine the changes of immunostaining intensity of these enzymes. The steroidogenic enzymes investigated were steroidogenic acute regulatory protein, cytochrome P450 side chain cleavage enzyme, $17{\alpha}-hydroxylase$, $3{\beta}-hydroxysteroid$ dehydrogenase, and cytochrome P450 aromatase. Results: The treatment of ND resulted in depletion of Leydig cells and sloughing of germ cells in the testis. The ND treatment caused significant expressional decreases of steroidogenic enzymes at transcript and protein levels, and the destructive effects of ND on the testis were more apparent with a higher dose and a longer period of the treatment. Evident reduction of immunostaining intensity present in Leydig cells was clearly detected by the ND treatment. Conclusion: The exposure to ND in young male results not only in histological changes of the testis but also in aberrant gene expression of testicular steroidogenic enzymes, consequently leading into the reduction of testosterone production in the testis and thus likely disruption of spermatogenesis.

• 한국결정성장학회지
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• 제8권4호
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• pp.655-659
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• 1998

과냉각된 melt-spun $Nd_{14.73}Fe_{78.67}B_{6.60}$리본의 급속응고속도 및 열처리에 따른 보자력의 변화를 조사하였으며, 이 결과를 분석하기 위하여 비정질로 부터의 결정화 거동을 연구하였다. 리본 제조시 급속응고속도가 증가함에 따라 결정화 후의 고유 보자력은 감소하였다. $Nd_{14.73}Fe_{78.67}B_{6.60}$ 비정질은 안정한 $Nd_2Fe_{14}B$ 상으로 결정화하는 과정에서 $\alpha$-Fe와 $Fe_3B$ 상이 생성된다. $Fe_3B$ 상은 $Nd_2Fe_{14}B$ 상이 결정화됨과 동시에 사라지나 $\alpha$-Fe 상은 완전히 결정화된 이후에도 기지상인 $Nd_2Fe_{14}B$ 상과 함께 잔류한다. 열처리된 리본내에 잔류하는 연자성상인 $\alpha$-Fe에 의해 고유 보자력의 특성이 저하하였다.

• 한국분말재료학회지
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• 제20권5호
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• pp.359-365
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• 2013

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.

• 한국광학회지
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• 제14권1호
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• pp.85-91
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• 2003

비평면 고리형 공진기에서의 내부 공진기 주파수 배가를 이용한 단일 모드 Nd:YAG 레이저를 제작하였다. 비평면 고리형 공진기는 두 개의 구면경과 Nd:YAG 결정, KIP 결정으로 구성되어 있다. Nd:YAG 결정의 양단면은 상대적인 비틀림 각을 갖고 있으면서 브루스터 각이 되도록 연마되었으며, 비틀림 각에 의해 형성된 비평면 고리 공진기가 가역적인 편광 회전기 역할을, 자기장이 가해진 Nd:YAC 결정 자체가 비가역적 편광 회전기 역할을, 브루스터 각을 갖고 있는 양단면이 편광자 역할을 각각 담당하여 전체적으로 광 다이오드를 형성하고 있다. 이러한 구조에서 단 방향 발진이 일어날 수 있는 비틀림 각이 이론적으로 추정되었다. 1.2 W, 809 nm 다이오드 레이저로 펌핑하여 532 nm 파장에서 22 ㎽의 단 방향, 단일 모드 출력을 얻었으며, 이것은 약 1.8%의 변환 효율에 해당한다.

• Journal of Periodontal and Implant Science
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• 제26권1호
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• pp.293-308
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• 1996

Recently, dental laser have been applied for removal of soft tissues, hemostasis and blood coagulation, removal of benign and malignant tumor, treatment of leukoplakia, aphthous ulcer and herpetic lesion, implant second surgery, removal of granulation tissue, frenectomy, clinical crown lengthening, gingivectomy, gingivoplasty, and treatment of dentin hypersensitivity. Even though the frequency of laser treatment is increasing, the research on the healing process after gingivectomy using pulsed Nd : YAG laser is very rare. The purpose of this study was to observe and compare the wound healing after gingivectomy using scalpel and pulsed Nd : YAG laser in the rat. Gingivectomy was performed using pulsed Nd : YAG laser(SUNRISE Technologies, U.S.A., 1.5 Watts, 10 pps) on the buccal gingiva of right maxillary first molar and using scalpel(No.12) on the contralateral side. Those sites treated by surgical scalpel were designated as the control, and by pulsed Nd : YAG laser as the experimental group. Animals were sacrificed at 1, 2, 3, 5, 7, 11 and 14 days postoperatively, and specimens were histologically observed under light microscope. The results were as follows : 1. Clinical observation Normal color and shape were observed at the 5th day ill the control group and the 7th day in the experimental group. 2. Histologic findings 1) In the control group, denser inflammatory infiltration was observed. 2) Epithelialization started at the 2nd day in the control group, similar to the experimental group, and completed at the 11th to the 14th day postoperatively. 3) In the experimental group, connective tissue showed the vacuole formation and degenerative change during early healing period. Healing of connective tissue was slower in the experimental group than in the control group by 2 days. 4) In the both groups, wound healing was completed at the 2nd week. From this study, gingivectomy using pulsed Nd : YAG laser seems to result in a little delayed wound healing process, compared to the gingivectomy using scalpel. Considering the clinical advantages of laser surgery, pulsed Nd : YAG laser might be useful device for gingivectomy.

• 한국재료학회지
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• 제8권9호
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• pp.819-824
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• 1998

합금의 주조시 냉각속도가 $\textrm{Nd}_{16}\textrm{Fe}_{72}\textrm{V}_{4}\textrm{B}_{8}$ 소결자석의 결정립 분포와 착자특성에 미치는 영향에 대하여 조사하였다. 냉각속도가 높은 Cu mold를 사용하여 제작한 시료는 좁은 결정립 분포와 착자특성의 향상을 보였다. B화합물을 생성하는 Cr, Mn, Nb 그리고 w과 같은 첨가원소가 Nd-Fe-B계 소결자석의 착자특성에 미치는 영향에 대해서도 조사하였다. Cr이나 W첨가는 보자력의 향상에 효과적이고 $\textrm{Nd}_{16}\textrm{Fe}_{72}\textrm{Cr}_{4}\textrm{B}_{9}$합금은 $\textrm{Nd}_{16}\textrm{Fe}_{72}\textrm{V}_{4}\textrm{B}_{8}$합금과 비슷한 착자특성을 보였다.