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Song, K.J.,Ko, R.K.,Kim, H.S.,Ha, H.S.,Ha, D.W.,Oh, S.S.,Park, C.,Yoo, S.-I.,Kim, M.W.,Kim, C.J.,Joo, J.H. Institute of Electrical and Electronics Engineers 2007 IEEE transactions on applied superconductivity Vol.17 No.2
<P>The degree of ferromagnetism of Ni-W<SUB>y</SUB> alloys decreases as W-content y increases. Both the saturation magnetization <I>M</I> <SUB>sat</SUB> and Curie temperature <I>T</I> <SUB>c</SUB> decrease linearly with W-content y, and both <I>M</I> <SUB>sat</SUB> and <I>T</I> <SUB>c</SUB> go to zero at critical concentration of y<SUB>c</SUB> ~9.50 at.% W. To compare with Ni-W alloys, the magnetic properties of a series of both as-rolled (non-textured) and annealed (biaxially textured) [Ni<SUB>97at.%</SUB>-W<SUB>3at.%</SUB>]<SUB>100-x</SUB>-Cu<SUB>x</SUB> alloy tapes with compositions x = 0, 1, 3, 5, and 7 at.%, were studied. Characterization methods included XRD analyses to investigate the biaxial texturing of the annealed [Ni-W]-Cu alloy tapes and studies of the magnetization for both as-rolled and annealed [Ni-W]-Cu alloy tapes. Both the isothermal mass magnetizations <I>M</I>(<I>H</I>) of a series of samples at different fixed temperatures and <I>M</I>(<I>T</I>) in fixed field, were measured. The effect of Cu addition on both the saturation magnetization and Curie temperature T<SUB>c</SUB> of the Ni<SUB>97at.%</SUB>-W<SUB>3at.%</SUB> alloy was investigated.</P>
Improvement of high-field J<sub>c</sub> of MgB<sub>2</sub> wires by polymethyl-methacrylate doping
Park, G.C.,Hwang, S.M.,Lee, C.M.,Choi, J.H.,Joo, J.,Lim, J.H.,Kang, W.N.,Kim, C.J. North-Holland 2010 Physica. C, Superconductivity Vol.470 No.suppl1
We applied polymethyl-methacrylate (PMMA) as a new doping material for MgB<SUB>2</SUB> and fabricated C-doped MgB<SUB>2</SUB> wires by in situ powder-in-tube (PIT) process. With increasing PMMA doping level, the transition temperature (T<SUB>c</SUB>) decreased and the MgO content increased, whereas the magnetic field dependence of the critical current density (J<SUB>c</SUB>) weakened. The MgB<SUB>2</SUB> wires doped with 3-10wt.% PMMA showed significantly higher J<SUB>c</SUB> by more than one order of magnitude than that of the undoped wire at 5K and 6.6T. These results confirmed the potential of PMMA as a promising material for the effective substitution of B by C in MgB<SUB>2</SUB>.
Hwang, S.M.,Sung, K.,Choi, J.H.,Kim, W.,Joo, J.,Lim, J.H.,Kim, C.J.,Park, Y.S.,Kim, D.H. North-Holland 2010 Physica. C, Superconductivity Vol.470 No.20
We selected polyacrylonitrile (PAN, -[C<SUB>3</SUB>H<SUB>3</SUB>N]-) as an O-free organic dopant and fabricated C-doped MgB<SUB>2</SUB> wires by in situ and powder-in-tube techniques. 0-5 wt.% PAN powders were uniformly mixed with B powder using a liquid mixing method. The precursor powders were mixed with Mg powder, filled into Fe tubes, and then drawn into wires. Sintering was performed at 900<SUP>o</SUP>C for 1h in a flowing Ar gas. The PAN doping decreased the critical temperature (T<SUB>c</SUB>) and a-axis lattice parameter, but significantly improved the critical current density (J<SUB>c</SUB>) in high fields, upper critical field (H<SUB>c2</SUB>), and irreversibility field (H<SUB>irr</SUB>) performances. These results are attributed to the replacement of B sites with C by the PAN doping. Furthermore, as expected, the MgO amount did not increase as the doping content increased. The J<SUB>c</SUB> of the PAN-doped MgB<SUB>2</SUB> wires was more than one order of magnitude higher than that of the undoped MgB<SUB>2</SUB> wire at 5K and 6.6T (1.46-3.82kA/cm<SUP>2</SUP> vs. 0.11kA/cm<SUP>2</SUP>).
Magnetism in Ni-W textured substrates for coated conductors
Song K. J.,Park Y. M.,Yang J. S.,Kim S. W.,Ko R. K.,Kim H. S.,Ha H. S,Oh S. S.,Park C.,Joo J. H.,Kim C. J. The Korea Institute of Applied Superconductivity a 2005 한국초전도저온공학회논문지 Vol.7 No.2
The magnetic properties of a series of both annealed (biaxially textured) and as-rolled (non-textured) Ni-xW alloy tapes with compositions x = 0,1,3, and 5 at.$\%$, were studied. Characterization methods included XRD analyses to investigate the biaxial cube texturing of the annealed Ni-W alloy tapes and studies of the magnetization M for both annealed and as-rolled Ni-W alloy tapes. Both the isothermal mass magnetizations M(H) of a series of samples at different fixed temperatures and M(T) in fixed field, employing a PPMS-9 (Quantum Design), were measured. The Ni-W alloys have shown much reduced ferromagnetism as W-content x increases. Both the saturation magnetization Msat and Curie temperature Tc decrease linearly with W-content x, and both Msat and Tc go to zero at critical concentration of Xc - 9.50 at. $\%$ W.
Fabrication of ex situ processed MgB<sub>2</sub> wires using nano carbon doped powder
Lee, C.M.,Park, J.H.,Hwang, S.M.,Lim, J.H.,Joo, J.,Kang, W.N.,Kim, C.J. North-Holland 2009 Physica. C, Superconductivity Vol.469 No.15
We fabricated ex situ MgB<SUB>2</SUB> wires using C-doped MgB<SUB>2</SUB> powder as a precursor in order to improve the core density of the wires and their C doping content. The C-doped powder was prepared with Mg, B, and nano carbon (NC) powders by the in situ technique and then MgB<SUB>2-x</SUB>C<SUB>x</SUB> (x=0, 0.01, and 0.03) wires were fabricated by the ex situ technique using the powder-in-tube method. The phase formation, lattice change, and microstructure were characterized and correlated with the T<SUB>c</SUB> and J<SUB>c</SUB> variations. We observed that the ex situ wire had a higher core density than the in situ wire, however its morphology consisted of agglomerated particles, indicating that sintering and grain growth did not occur completely, even though the sintering was conducted at high temperature (1000<SUP>o</SUP>C). As the C content increased, T<SUB>c</SUB> decreased, while the decrease of J<SUB>c</SUB> with increasing magnetic field became smaller. The J<SUB>c</SUB> of MgB<SUB>1.97</SUB>C<SUB>0.03</SUB> wire made by the ex situ technique was 3.34kA/cm<SUP>2</SUP> at 6.6T and 5K which is comparable to that of the in situ wire (4.81kA/cm<SUP>2</SUP> at 6.6T and 5K).
다구찌 방법을 이용한 유분리기의 브레이징 최적 공정 해석
주원경(W. K. Joo),왕일기(Y. Q. Wang),양현태(H. T. Yang),심창영(C. Y. Sim),송정일(J. I. Song) 대한기계학회 2007 대한기계학회 춘추학술대회 Vol.2007 No.11
The purpose of this study is to find the optimization processing on Oil-separator brazing using Taguchi method which was generally used to analyze the effects of various control factors. Mini-Tab is a good for program that is making a selection using Taguchi method. The microstructures and mechanical properties of OFHC copper/STKM 11 A for Oil-separator joints brazed using BAg and BCuP filler metal in NH₃ atmospheres were performed. Interfacial microstructures were observed in reaction layer. First, We selected proper filler metal for Oil-separator brazing through the observation of SEM micrographs and tensile test. A brazing strength causes of decline with defects of pin hole and base metal by lack of penetration. In tensile test, the properties of BCuP are better than other filler metal that has yield strength of elasticity area But it have so many defects. Second, using seleted filler metal, We applied Diffused Taguchi method by Mini-Tab. Finally, selected conditions improved more 12% for brazing strength than current processing on Oil-separator.
주윤하(Y. H. Joo),전철웅(C. W. Jun),이다혜(D. H. Lee),한효주(H. J. Han),안진효(J. H. An),이종민(J. M. Lee),박철우(C. W. Park) 대한기계학회 2011 대한기계학회 춘추학술대회 Vol.2011 No.10
In the present study, we performed design processes of reciprocating pump to make pulsatile flow for simulation of aortic blood flow in arteries. To design a pulsatile pump, we firstly calculated the pressure for working fluid in a cylinder accurately based on fundamentals of fluid mechanics. According to the pressure expectation, every compartments, such as piston, crank shaft and gear, were designed to overcome plastic deformation. As a result, we evaluated the power requirement effectively for a reciprocating pump motor selection.
주윤하(Y. H. Joo),박현우(H. W. Park),안진효(J. H. An),이춘영(C. Y. Lee),박철우(C. W. Park) 대한기계학회 2010 대한기계학회 춘추학술대회 Vol.2010 No.11
Recently, the precise cell separation method has great attentions in the bio-engineering research field with advancement of bio technology. The separation technique is applied to recognize particular cell from the suspension solution by specifying fluorescence light on a target material. In the present study, we separated the marker particles from the suspending particle mixture solution using isotachophoresis technique in the micro-channel. As a result, isotachophoresis zones were clearly visualized as going downstream in the electric field. The particle migration velocity has proportional to the applied voltage.
주원경(W. K. Joo),왕일기(Y. Q. Wang),양현태(H. T. Yang),심창영(C. Y. Sim),송정일(J. I. Song) 대한기계학회 2007 대한기계학회 춘추학술대회 Vol.2007 No.10
The microstructures and mechanical properties of OFHC copper/STKM 11A for D-tube joints brazed using BAg filler metal at 870℃ for 20 minutes in NH₃ atmospheres were performed. Interfacial microstructures were observed in reaction layer. A brazing strength causes of decline with defects of pin hole and base metal by lack of penetration. In tensile test, the properties of joints clearance of 0.01㎜ are better than other joints clearance that has yield strength of elasticity area with the brazing length of 2.5㎜, and also suitable for the case of brazing length of 5.0mm. According to the results of FEA (finite element analysis) on the tensile test, the maximum stress and strain were generated apart from the interface in large deformation. Diffused layer was formed by counter diffusion action of base metal and filler metal layer, and crack between two base metals was not discovered. This is the main reason that fracture of test piece does not appear in copper base metal, and brazing department forms good junctures.