• 한국초전도ㆍ저온공학회논문지
• /
• 제21권2호
• /
• pp.40-44
• /
• 2019

In this study, the effects of the compaction method for (Mg+2B) powders on the apparent density and superconducting properties of $MgB_2$ bulk superconductor were investigated. The raw powders used in this study were nano-sized boron (B) and spherical magnesium (Mg). A batch of a powder mixture of (Mg+2B) was put in a steel mold and uniaxially pressed at 1 ton or 3 tons into pellets. Another batch of the powder mixture was uniaxially pressed at 1 ton and then pressed isostatically at $1800kg/cm^2$ in the water chamber. All pellets were heat-treated at $650^{\circ}C$ for 1 h in flowing argon gas for the formation of $MgB_2$. The apparent density of powder compacts pressed at 3 ton was higher than that at 1 ton. The cold isostatic pressing (CIP) in a water chamber allowed further increase of the apparent density of powder compacts, which influenced the pellet density of the final products ($MgB_2$). The compaction methods (uniaxial pressing and CIP) did not affect the formation of $MgB_2$ and superconducting critical temperature ($T_c$) of $MgB_2$, but affected the critical current density ($J_c$) of $MgB_2$ significantly. The sample with the high apparent density showed high $J_c$ at 5 K and 20 K at applied magnetic fields (0-5 T).

• 한국약용작물학회지
• /
• 제5권1호
• /
• pp.49-55
• /
• 1997

가시오갈피의 조직배양을 통한 대량증식방법체계 확립의 방법으로 기내배양에서의 캘러스형성 및 식물체 분화에 영향을 미치는 배지와 식물생장 조절물질 및 농도의 최적조건을 구명코자 실시한 실험 결과는 다음과 같다. 1. MS배지를 기본으로하여 여러 가지 식물생장 조절물질(2, 4-D, TDZ, IAA, NAA, BAP) 을 단독 처리할 때 2, 4-D 2mg/l 에서 callus 형성율이 45.5%로 가장 양호하였으며 shoot의 분화는 TDZ 처리시 양호하였으며 간헐적으로 multiple shoot와 root분화가 생겼다. 2. MS배지를 기본으로하여 식물생장조절물질을 2, 4-D와 TDZ의 조합처리시 callus 형성율은 2, 4-D 2mg/ l +TDZ 0.7mg/ l 일때 가장 양호하였으며 shoot의 분화는 2, 4-D의 농도가 낮고 TDZ의 농도가 높은 2, 4-D 0.1mg/ l +TDZ 0.7mg/ l 에서 양호하였다. 3. 배지조성에 따른 callus 형성은 $B_5,\;MSB_5$ 배지 모두 MS배지를 기본으로하여 실시한 실험과 마찬가지로 2, 4-D 2mg/ l +TDZ 0.7mg/ l 에서 양호하였으며, $B_5$배지에서 2, 4-D 2mg/ l +TDZ 0.7mg/ l 처리시 100%의 callus형성율을 나타냈다. Shoot의 분화는 auxin류인 2, 4-D보다 cytokinin류인 TDZ처리시 양호하였고 조합처리 또한 2, 4-D의 농도가 낮은 2, 4-D 0,1mg/ l 일때 shoot분화가 형성되었으며 $MSB_5$ 배지에서 양호한 shoot의 분화가 형성되었다.

• 한국세라믹학회지
• /
• 제30권9호
• /
• pp.723-730
• /
• 1993

The mechanism of formation of perovskite phase and the dielectric properties of PZMN[Pb(Zn, Mg)1/3Nb2/3O3] ceramics were examined using two different types of the columbite precursors, (Mg, Zn)Nb2O6 (MZN) and MgNb2O6＋ZnNb2O6 (MN＋ZN). The formatin of perovskite phase in PbO＋MN＋ZN system is characterized by an initial rapid formation of Mg-rich perovskite phase, followed by a sluggish formation of Zn-rich perovskite phase. On the other hand, thepyrochlore/perovskite transformation in the PbO＋MZN system proceeded uniformly with a spatial homogeneity. The degree of diffuseness of the rhombohedral/cubic phase transitionis higher in the PbO＋MN＋ZN system than in the PbO＋MZN specimen, indicating a broadened compositional distributjion of the B-site catons (Nb+5, Zn+2, Mg+2) in the PbO＋MN＋ZN system.

• Progress in Superconductivity
• /
• 제4권2호
• /
• pp.153-156
• /
• 2003

We have studied fabrication of $MgB_2$ thin film on $SrTiO_3$ (001) and r-cut $A1_2$$O_3$ substrates by rf magnetron sputtering method using and $ MgB_2$ single target and two targets of Mg and B, respectively. Based on P -T phase diagram of $MgB_2$ and vapor pressure curves of Mg and B, a three-step process was employed. B layer was deposited at the bottom to enhance the film adhesion to the substrate. Secondly, co-sputtering of Mg and B was done. Finally, Mg was sputtered on top to compensate fur the loss of Mg during annealing. Subsequently, $MgB_2$ films were in-situ annealed in various conditions. The sample fabricated using the three-step process showed $T_{c}$ of 24 K and formation of superconducting $MgB_2$ phase was confirmed by XRD spectra. In case of co-sputtering deposition, $T_{c}$ depended on annealing time and argon pressure. However, those made by single-target sputtering showed non-superconducting behavior or low transition temperature, at best.est.

• 한국초전도학회:학술대회논문집
• /
• 한국초전도학회 2009년도 Korea Superconductivity Society Meeting 2009
• /
• pp.104-104
• /
• 2009

• 한국분말재료학회지
• /
• 제30권2호
• /
• pp.101-106
• /
• 2023

Liquid metal extraction (LME), a pyrometallurgical recycling method, is popular owing to its negligible environmental impact. LME mainly targets rare-earth permanent magnets having several rare-earth elements. Mg is used as a solvent metal for LME because of its selective and eminent reactivity with rare-earth elements in magnets. Several studies concerning the formation of Dy-Fe intermetallic compounds and their effects on LME using Mg exist. However, methods for reducing these compounds are unavailable. Fe reacts more strongly with B than with Dy; B addition can be a reducing method for Dy-Fe intermetallic compounds owing to the formation of Fe₂B, which takes Fe from Dy-Fe intermetallic compounds. The FeB alloy is an adequate additive for the decomposition of Fe₂B. To accomplish the former process, Mg must convey B to a permanent magnet during the decomposition of the FeB alloy. Here, the effect of Mg on the transfer of B from FeB to permanent magnet is observed through microstructural and phase analyses. Through microstructural and phase analysis, it is confirmed that FeB is converted to Fe₂B upon B transfer, owing to Mg. Finally, the transfer effect of Mg is confirmed, and the possibility of reducing Dy-Fe intermetallic compounds during LME is suggested.

• 한국재료학회지
• /
• 제7권1호
• /
• pp.57-61
• /
• 1997

$Y_{0.8}Ta_{0.2}O_{1.7}$-MO(M=Ba, Sr, Ca 및 Mg) 계에서의 형석구조의 생성과 이와 관련된 구조에 관하여 연구하였다. BaO또는 SrO를 4mol% 첨가한 조성에서는 결함형석구조 이외에 입방정 perovskite형 규칙구조인 $Ba_{2}YTaO_{6}$ 및 $Sr_{2}YTaO_{6}$와 입방정 $Y_{2}O_{3}$가 관찰되었다. CaO를 첨가한 경우에는 8mol%이상을 첨가한 조성에서부터 단사정 $Ca_{2}YTaO_{6}$와 $Y_{2}O_{3}$의 2차상이 나타났다. MgO의 경우에는 12mol% MgO를 첨가한 조성까지는 형석구조의 단일상을 나타내어 MgO가 형석구조에 고용되는 것을 알수 있었으며, 16 mol%조성부터는 2차상으로 MgO가 관찰되었다. 그러므로 위의 계에서 형석구조의 생성은 $A_{2}$(B'B")$O_6$의 생성과 첨가된 양이온의 크기에 영향을 받는 것으로 생각된다.생각된다.

• Bulletin of the Korean Chemical Society
• /
• 제20권4호
• /
• pp.422-426
• /
• 1999

The Grignard reactions of bis(chloromethyl)dimethylsilane (1) with trimethylchlorosilane (2) in THF give both the intermolecular C-Si coupling and intramolecular C-C coupling products. At beginning stage, 1 reacts with Mg to give the mono-Grignard reagent ClCH2Me2SiCH2MgCl (1) which undergoes the C-Si coupling reaction to give MC2Si(CH2SiMe3)2 3, or C-C coupling to a mixture of formula Me3SiCH2(SiMe2CH2CH2)nR1 (n = 1, 2, 3, ..; 4a, R1I = H: 4b, R1 = SiMe3). In the reaction, two reaction pathways are involved: a) Ⅰ reacts with 2 to give Me3SiCH2SiMe2CH2Cl 6 which further reacts with Mg to afford a Me2SiCH2Mel-SiCH2MgCl (Ⅱ) or b) I cyclizes intramolecularly to a silacyclopropane intermediate A, which undergoes a ring-opening polymerization by the nucleophilic attack of the intermediates I or Ⅱ, followed by the termination reaction with H2O and 2, to give 4a and 4b, respectively. As the mole ratio of 2/1 increased from 2 to 16 folds, the formation of product 3 increased from 16% to 47% while the formation of polymeric products 4 was reduced from 60% to 40%. The intermolecular C-Si coupling reaction of the pathway a becomes more favorable than the intramolecular C-C coupling reaction of the pathways b at the higher mole ratio of 2/1.

• 한국약용작물학회지
• /
• 제4권2호
• /
• pp.132-138
• /
• 1996

패모의 기내 주년 생산 체계를 확립하기 위한 연구의 일환으로 cytokinin이 첨가된 배치에서 배양 방법의 차이가 자구 형성과 비대에 미치는 영향, 배지의 삼투 포텐셜 조절을 위한 mannitol 첨가나 활성 탄소 및 생장 억제제 처리가 기관 형성과 인편 비대에 미치는 영향에 대해서 실험한 결과는 다음과 같다. 1. 0mg/L kinetin과 0. 3mg/L NAA가 혼용 처리된 MS 고체 배지에서 액체 배지나 액체 현탁배지에서보다 효과적인 자구 생장과 증식율을 나타냈으며, 액체 배지나 액체 현탁처리 배지에서는 비슷한 결과를 나타냈다. 활성 탄소의 농도는 $0.01%{\sim}0.1%$ 처리구에서 형성된 자구의 비대가 양호하였고, 0. 5% 이상 농도에서는 오히려 생장이 억제되었다. $1{\sim}2%$ mannitol이 첨가된 배지에서 인편으로부터의 자구 형성수 및 구비대가 양호하였으며, 그 이상의 농도에서는 생장에 저해적으로 작용하였다. 생장 억제제인 B-9과 Chloromequat 처리구에서는 $10{\sim}100mg/L$ 처리구에서 자구 발생 및 비대가 양호하였으나, 발생 인편의 생육 상태가 억제되었으며, ABA 처리구에서는 배양 중 인편이 모두 고사하였다.

• Journal of Korean Biological Nursing Science
• /
• 제12권3호
• /
• pp.127-132
• /
• 2010

Purpose: The aim of this study is to evaluate the effect of Xanthium sibiricum Patr. on carcinogenesis. Method: Water extract from Xanthium sibiricum Patr. (XPW) was prepared and investigated for the potential antitumor activity and inhibition of benzo[a]pyrene-DNA adduct formation and free radical formation. Result: It was shown that the water possess considerable toxicity toward tumor cell lines. Concentration of XPW at 1.0 mg/mL and 2.5 mg/mL resulted in more than 30% inhibition of growth in HeLa cells. Toxicity of XPW to A549 revealed that 54% inhibition of growth at concentration of 2.5 mg/mL. At concentrations of 0.5 mg/mL, 1.0 mg/mL and 2.5 mg/mL of XPW, the binding of [$^3H$]B[a]P metabolites to DNA of human Chang cell was inhibited by 19%, 33%, and 41%, respectively. There 18% and 32% inhibition in the free radical formation with XPW at the concentration of 1.0 mg/mL and 2.5 mg/mL, respectively. Conclusion: Water extract from Xanthium sibiricum Patr. (XPW) has antitumor and cancer chemopreventive activities.