• 한국초전도ㆍ저온공학회논문지
• /
• 제14권4호
• /
• pp.12-15
• /
• 2012

$MgB_2$ superconductor is highly sensitive to the Mg content. Even if the samples are synthesized with the appropriate looking stoichiometric ratio, the heat treatment leads to the loss of Mg either to ambiance or to MgO. To avoid it, either excess Mg is added in the starting powder or sealed ampoule annealing is employed. In this paper the effect of open Mg sintering ambiance on the ex-situ $MgB_2$ was studied to enhance its superconducting properties. The open Mg ambiance was created to avoid any overpressure of Mg by providing a hole in Fe tube used as sample holder. The decrease in resistivity of the synthesized sample was observed through the increased temperature dependence of electron-phonon interactions. A clear enhancement in the superconducting cross-sectional area and hence the in-field critical current density is obtained.

• 한국초전도ㆍ저온공학회논문지
• /
• 제9권2호
• /
• pp.15-18
• /
• 2007

The sub micron sized spherical $MgB_2$ powders were synthesized by spray reaction method. $MgB_2$ tapes with Al addition were fabricated by Powder in Tube (PIT) method. The superconducting property and microstructure of Al doped $MgB_2$ tapes were characterized by X-ray diffraction, optical microscopy and transport measurement under magnetic field. The $J_c$ value of $MgB_2$ tapes was increased with 10 vol. % Al addition. The $J_c$ value of 5,500 A/$cm^2$ and 11,000 A/$cm^2$ at 4.2 K and 5 T were obtained for the $MgB_2$ tape and 10 vol. % of Al added $MgB_2$ tape without heat treatment, respectively. The $J_c$ value of 8,000 A/$cm^2$ and 33,000 A/$cm^2$ at 4.2 K and 5 T were obtained for the $MgB_2$ tape and 10 vol. % of Al added $MgB_2$ tape with heat treatment, respectively. The $J_c$-B curves show enhancement in $J_c$ (B), which suggests that the microstructure and transport properties of $MgB_2$ tapes have been improved with Al addition.

• Progress in Superconductivity
• /
• 제13권3호
• /
• pp.184-188
• /
• 2012

$MgB_2$ superconducting sheets have been fabricated by powder rolling method using mixture of Mg and B powders. Sheet-type $MgB_2$ bulk samples of ~10 mm width and 50-100 mm long were squeezed out after compacted by two rotating rolls of 130 mm diameter with gap distance of 0.5 mm and speed of ~40 cm/min (~1 rpm). The nominal composition of Mg, which is ductile metal, was added up to 30% to facilitate forming the $MgB_2$ sheets. The annealed samples at $900^{\circ}C$ and 3 hrs showed superconducting transition temperature of ~32 K and critical current densities at zero fields were ${\sim}10^5A/cm^2$ at 5 K and ${\sim}5{\times}10^4A/cm^2$ at 20 K.

• 한국수산과학회지
• /
• 제29권6호
• /
• pp.787-796
• /
• 1996

The biodegradation experiment, the TOD analysis and the element analysis for dispersant, Bunker-A oil and Bunker-B oil were conducted to study the biodegradation characteristics of a mixture of Bunker-A oil with dispersant and a mixture of Bunker-B oil with dispersant in the seawater. The results of biodegradation experiment showed 1mg of dispersant to be equivalent to 0.26 mg of $BOD_5$ and to 0.60 mg of $BOD_{20}$ in the natural seawater. The results of TOD analysis showed each 1 mg of dispersant, Bunker-A oil and Bunker-B oil to be equivalent to 2.37 mg, 2.94 mg and 2.74 mg of TOD, respectively. The results of element analysis showed carbon, hydrogen, nitrogen and phosphorus contents of dispersant to be $82.1\%,\;13.8\%,\;1.8\%\;and\;2.2\%$, respectively. Carbon and hydrogen contents of Bunker-A oil were found to be $73.3\%\;and\;13.5\%$, respectively, and carbon, hydrogen and nitrogen contents of Bunker-B oil to be $80.4\%,\;12.3\%\;and\;0.7\%$, respectively. Accordingly, the detection of nitrogen and phosphorus in dispersant shows that dispersants should be used with caution in coastal waters, with relation to eutrophication. The biodegradability of dispersant expressed as the ratio of $BOD_5/TOD$ was found to be $11.0\%$. As the mix ratios of dispersant to Bunker-A oil (3 mg/l) and a mixture of Bunker-B oil (3mg/l) were changed from 1 : 10 to 5 : 10, the biodegradabilities of a mixture of Bunker-A oil with dispersant and Bunker-B oil with dispersant increased from $2.1\%\;to\;7.2\%$ and from $1.0\%\;to\;4.4\%$, respectively. Accordingly, the dispersant belongs to the organic matter group of middle-biodegradability while mixtures in the mix ratio range of $1:10\~5:10$ belong to the organic matter group of low-biodegradability. The deoxygenation rate constant $(K_1)$ and ultimate biochemical oxygen demand $(L_0)$ obtained from the biodegradation experiment and Thomas slope method were found to be 0.125/day and 2.487 mg/l for dispersant (4 mg/l), respectively. $K_1\;and\;L_0$, were found to be $0.079\~0.131/day$ and $0.318\~2.052\;mg/l$ for a mixture of Bunker-A oil with dispersant and to be $0.106\~0.371/day$ and $0.262\~1.106\;mg/l$ for a mixture of Bunker-B oil with dispersant, respectively, having $1:10\~5:10$ mix ratios of dispersant to Bunker-A oil and Bunker-B oil. The ultimate biochemical oxygen demands of the mixtures increased as the mix ratio of dispersant to Bunker-A, B oils changed from 1 : 10 to 5 : 10. This suggests that the more dispersants are applied to the sea for the cleanup of Bunker-A oil or Bunker-B oil, the more decreases the dissolved oxygen level in the seawater.

• Journal of Magnetics
• /
• 제11권1호
• /
• pp.25-29
• /
• 2006

Recent experiments have demonstrated high TMR ratios in MTJs with the MgO barrier [1,2]. The CoFeB/MgO/CoFeB junctions showed better properties than the CoFe/MgO/CoFe junctions because the MgO layer had a good crystalline structure with (001) texture and smooth and sharp interface between CoFeB/MgO [3]. The amorphous CoFeB with 20 at%B starts the crystallization at $340^{\circ}C$ [4] and this crystallization of the CoFeB helps obtaining the high TMR ratio. In this work, the compositional changes in the MgO barrier and at the interface of CoFeB/MgO/CoFeB after the CoFeB crystallization were studied in annealed MTJs. XPS depth profiles were utilized. TEM analyses showed that the MgO barrier had (100) texture on CoFeB in the junctions. B in the bottom CoFeB layer diffused into the MgO barrier and B-oxide was formed at the interface of CoFeB/MgO/CoFeB after the CoFeB crystallization.

• 한국식생활문화학회지
• /
• 제10권3호
• /
• pp.133-137
• /
• 1995

우리나라의 남부지방의 대부분 농가에서 대량 생산되고 있으나 농가소득에는 기여하지 못하고 있는 떫은 감의 손쉬운 가공에 의한 대량 소비를 촉진시키기 위하여 감장아찌의 화학적 품질 특성을 규명하고 감장아찌 제조 및 유통과정에서의 품질과 관련된 미생물을 순수분리하여 동정함으로써 감장아찌의 품질관리에 기여코자 하였다. 제조된 감장아찌 완제품의 수분함량은 80.04%, 당질함량은 13.72%로 원료감과 큰 차이가 없었으나 조회분함량은 염액에 침지한 감장아찌의 특성때문에 원료감보다 훨씬 높은 4.26%였다. 수용성 탄닌함량은 81.04mg%로 635.45mg%인 원료감보다 크게 감소되었고 총 비타민 C는 23.76mg%로 약간 감소되었으며 유리당은 포도당, 과당, 자당의 순으로 함유되었다. 유리아미노산은 총 17종이 함유된 것으로 분석되었고 그 함량은 glutamic acid(24.97mg%), aspartic acid(24.02mg%), leucine(22.33mg%)의 순으로 높았으며 methionine이 2.42mg로 가장 낮았다. 감장아찌 제조와 관련된 미생물로는 세균 4균주와 효모 3균주가 각각 동정되었는데 동정된 Bacillus subtilis, B. cereus, B. pumilus, B. thuringiensis였고 효모는 Candida glabrata, C. guilliermondi and Hansenula였으며 진공포장하여 상품화한 감장아찌 완제품의 유통과정에서 포장의 부풀림과 감장아찌 맛의 변화를 일으키는 원인균은 효모인 Candida glabrata인 것으로 확인되었다.

• 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.

• 한국초전도저온공학회:학술대회논문집
• /
• 한국초전도저온공학회 2002년도 학술대회 논문집
• /
• pp.3-4
• /
• 2002

The stainless steel sheathed MgB$_2$ tapes with Cu addition were fabricated by PIT method without heat treatment. The $J_{c}$ value of 5,600 A/ $cm^{2}$and 16,000 A/$cm^{2}$ at 4.2 K and 5 T were obtained for the $MgB_{2}$ tape and 10 vol % of Cu added $MgB_{2}$ tape respectively. The $J_{c}$-B curve shows enhancement in J$_{c}$ under magnetic field, which suggests enhancement in flux pinning property with Cu addition.n.

• 한국초전도ㆍ저온공학회논문지
• /
• 제22권2호
• /
• pp.26-31
• /
• 2020

Since 2014, Sam Dong Co., Ltd. has successfully developed high-performance MgB₂ superconducting wires with a kilometer-scale. Herein, we studied performances of various MgB₂ wires fabricated by the Sam Dong with different Cu fractions and diameters for practical applications. Critical current densities of our commercial wire, 18+'1'Cu multifilamentary MgB₂ wire, are estimated to be 270,000 A/㎠ at 3 T and 4.2 K and 100,000 A/㎠ at 2 T and 20 K, respectively. We further discuss research progress of various MgB₂ superconducting wires at Sam Dong Co., Ltd and make an effort to align with customers' requirements.

• 한국세라믹학회지
• /
• 제45권7호
• /
• pp.418-422
• /
• 2008

The preparation of FeB by SHS in $B_2O_3-Mg-Fe-Fe_3O_4$ system was investigated in this study. In the preparation of FeB, the effects of the initial pressure of inert gas in reactor, the content of Mg and $Fe_3O_4$ in mixture on the reactivity and reaction products was investigated. The minimum initial pressure of inert gas in reactor for SHS reaction in this system was 25 atm, and as the pressure increased, the concentration of unreacted Mg decreased and combustion temperature increased. At the initial inert gas pressure in reactor of 25 atm, the optimum composition for the preparation of pure FeB was $1.5B_2O_3$+3.43Mg+ 1.7Fe+$0.1Fe_3O_4$. The FeB synthesized in this condition had an irregular shape and the particle size of $5\;{\mu}m$.