• Proceedings of the Materials Research Society of Korea Conference
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• 2011.05a
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• pp.48.2-48.2
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• 2011

열전재료는 열과 전기에너지의 상호 변환이 가능한 재료로 이를 이용한 응용제품의 개발이 크게 주목을 받고 있으며, 특히 $Bi_2Te_3$계 합금의 경우 상온에서 가장 우수한 성능지수를 가지는 재료로 많은 연구가 진행되고 있다. 그러나 기존의 $Bi_2Te_3$계 합금은 일방향응고법으로 제조되어 많은 시간과 비용을 필요로 하고, 특히 C축의 Van der Waals 결합으로 인해 기계적 강도가 약하다는 단점이 있었다. 최근 분말야금법을 이용하여 기계적강도를 높이고, 격자산란에 의한 열전도도의 감소로 성능지수를 높일수 있는 방법들이 제시되고 있다. 본 연구에서는 급속응고공정인 가스분무법을 이용하여 n-type의 $95%Bi_2Te_3-5%Bi_2Se_3$분말을 제조하였고, 이 재료의 경우 성형조건에 따라 조직이 쉽게 변하기 때문에 이를 제어하기 위해 단시간동안 고압으로 성형가능한 자기펄스압축성형법(Magnetic Pulsed Compaction)을 이용하여 성형체를 제조하였다. 제조된 성형체는 밀도를 증가시키고 결정립성장을 억제시킬수 있는 방전플라즈마소결법(Spark Plasma Sintering)을 이용하여 소결체로 제조되었으며, 각각의 공정이 열전성능에 미치는 영향을 고찰하였다. OM (Optical Microscope) 및 SEM (Scaning Electric Microscope)을 이용하여 미세구조를 관찰하였고 XRD (X-Ray Diffraction)를 이용하여 상의 변화를 분석하였으며, 상온에서 경도를 측정함으로서 공정조건에 따른 기계적강도를 비교하였다. Seebeck계수는 시편의 양단에 온도차를 주어 발생하는 기전압을 측정하여 계산하였고, 전기비저항은 4point probe방법으로 측정하였다. 전하이동도 및 전하농도는 Hall측정으로부터 구하였고 열전도도를 측정하여 종합적인 열전성능을 평가하였다.

• The Korean Journal of Pain
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• v.7 no.2
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• pp.287-291
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• 1994

A 49 years old male patient was admitted to our neuro-pain clinic with symptoms of left 11th intercostal neuralgic pain and low back pain that developed 2 months prior to admission. Upon initial physical examination, motor weakness or sensory deficit were absent. Intercostal neuralgic pain improved significantly after we performed thoracic root thermocoagulation. However on the afternoon of the procedure the patient started to experience voiding difficulty, saddle anesthesia and rapidly progressing motor weakness and hypoesthesia that involved the lower back area and the lower extremities for three days. Based on these symptoms spinal cord compression was suspected and subsequently plain T-L spine X-rays and T-L spine MRI were performed. A spinal tumor that appeared metastatic in origin was seen at the T11 and T12 level. Liver ultrasonography demonstrated the presence of a $4{\times}4cm$ sized ill defined mass in the posterior segment of the right lobe. The patient was diagnosed to have hepatocellular carcinoma after needle aspiration biopsy and cytologic studies. Further orthopedic surgery was recommended but as the patient rejected any further treatment and examination, it was not possible to confirm the primary focus of the tumor. However as metastasis of a primary liver tumor to the spine is a rare occurrence, some other primary focus of metastasis or even a malignant primary tumor of the spine is more likely to explain this patient's condition.

• Journal of the Korean Magnetics Society
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• v.5 no.1
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• pp.38-41
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• 1995

The effects of Nb and Cu additives as will as substitutional Co into $Nd_{4}Fe_{85.5}B_{10.5}$ melt-spun alloy were studied aiming for finding a $\alpha$-Fe based Nd-Fe-B composite alloys with high energy product. The addition of Nb and Cu to $Nd_{4}Fe_{85.5}B_{10.5}$ decreased the average grain size and increased the coercivity up to 207kA/m(2.6kOe), Further-more, the substitution of Co for Fe in $Nd_{4}Fe_{82}B_{10}Nb_{3}Cu_{1}$ alloy resulted in the decrease of the average grain size (<20nm) and improved the hard magnetic properties. The remanence, coercivity and energy product of optimally annealed $Nd_{4}Fe_{74}Co_{8}B_{10}Nb_{3}Cu_{1}$ alloy were 1.345, 219kA/m(2.75kOe) and $95.5kJ/m^{3}$(12MGOe), respectively.

• Journal of the Korean Magnetics Society
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• v.7 no.1
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• pp.44-48
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• 1997

The nanocrystalline Nd-Fe-B alloys with low Nd content were prepared by rapid solidification technique. The alloys consist of both$\alpha$-Fe as the main phase and $Nd_2Fe_{14}B_1$ as a secondary phase and have an ultrafine grain structure of about 30 nm. The addition of Ga in $Nd_4Fe_{82}B_{10}Mo_3Cu_1$ alloy increases remanence up to 1.29 T and improves squareness. The nanocrystalline $Nd_5Fe_{81}B_9Mo_3Cu_1Ga_1$ alloy has a volume fraction of $Nd_2Fe_{14}B_1$ phase of around 35% due to the increase of Nd content and shows an improved coercivity. The remanence, coercivity and energy product of optimally annealed nanocrystalline $Nd_5Fe_{81}B_9Mo_3Cu_1Ga_1$ alloy are 1.24 T, 257.4 kA/m (3.23 kOe), and 100.3 kJ/ ㎥ (12.6 MGOe), respectively.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.7 no.5
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• pp.811-816
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• 2006

The single layered magnetic thin films with anisotropic magnetoresistance behavior have advantage on micro integration due to their low cost in manufacturing. Although the conventional MCo (M=Cu, Ag) amorphous ribbons using a rapid solidification process have showed appropriate for magnetic property for bulk devices, they are not appropriate for micro-scale devices due to their brittleness. We prepared the thermal evaporated 100 nm-thick $Cu_{1-x}Co_x\;and\;Ag_{1-x}Co_x(x=0.1{\sim}0.7)$ films on silicon wafers and investigated the magnetic property of the as-depo films such as magnetization and magnetoresistance ratio. We confirmed that the maximum MR ratio of 1.4 and 2.6% at the external field of 0.5 Tesla in $CuCo_{30},\;AgCo_{40}$ films, respectively. Our result implies that AMR may be slightly less than those of the conventional CuCo and AgCo ribbons due to surface scattering, but their AMR ratio be enough for micro-scale application with easy integration compatibility for the process without surface oxidation.

• Journal of the Korean Magnetics Society
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• v.3 no.4
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• pp.284-288
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• 1993

Low temperature magnetic properties and crystal structures of melt-spun $Sm_{2}Co_{7}B_{3}$ compound were characterized. The magnetic measurements in the temperature range 77 K~450 K indicated that a spin-reorientation took place at about 150~160 K. A large anisotropy was observed(Ha=135 kOe at 300 K, 725 kOe at 77 K) for $Sm_{2}Co_{7}B_{3}$ although the magnetic moment is rather low. The crystal structure of the $Sm_{2}Co_{7}B_{3}$ compound was analyzed in detail by Rietveld analysis of powder diffraction pattern, and it was revealed that B(4h) atoms are not placed in the Sm(2e) layer but in between the Sm(2e) and Co($6i_{1}$) layers.

• Journal of the Korean Magnetics Society
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• v.2 no.3
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• pp.233-238
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• 1992

Melt-spun $Nd_{14}Fe_{76}Co_4B_6$ and $Nd_{10.5}Fe_{79}Co_2Zr_{1.5}B_7$ ribbons were prepared under an externally applied magnetic field. Magnetic properties in terms of anisotropy were evaluated by discussing the effect of textured structure of the ribbon samples as well as its powders. About 32 % increase in $(B{\cdot}H)_{max}$ and 18.8 % increase in $B_r$ were observed along the perpendicular direction of the ribbon plane which is more prominent for the Nd-Fe-Co-Zr-B than for the Nd-Fe-Co-B alloy. The enhancement of magnetic anisotropy was monitored by measuring the anisotropy constant of each alloy as a function of quenching rate of the ribbon. It was found that for the melt-spun ribbon quenched at slow rate(less than 7 m/s) the magnetic field effect was overwhelmed by the heat gradient effect through the ribbon thickness while the field effect was prominent at intermediate quenching rate (more than 7~11 m/s). The reproducible maximum energy product, $(B{\cdot}H)_{max}$=16.4 MGOe can be obtained from the Nd-Fe-Co-Zr-B alloy.

• Journal of the Korean Electrochemical Society
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• v.18 no.2
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• pp.68-74
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• 2015

To compare the microstructure and electrochemical properties between two binary alloys (Cr-Si, Ni-Si), two composition of binary alloys with the same capacity were selected using phase-diagram and prepared by matrix-stabilization method to suppress the volume expansion of Si by inactive-matrix. Master alloys were made by Arc-melting followed by fine structured ribbon sample preparation by Rapid Solidification Process (RSP, Melt-spinning method) under the same conditions. Also powder samples were produced by wet grinding for X-Ray Diffraction (XRD) and electrochemical measurements. As predicted from the phase diagram, only active-Si and inactive-matrix ($CrSi_2$, $NiSi_2$) were detected. The results of Scanning Electron Microscope (SEM) and Transmission Electron Microscopy - Energy Dispersive X-ray Spectroscopy (TEM-EDS) show that Cr-Si alloy has finer microstructure than Ni-Si alloy, which was also predictable through phase diagram. The electrochemical properties related to microstructure were evaluated by coin type full- and half-cells. Separately, self-designed test-cells were used to measure the volume expansion of Si during reaction. Volume expansion of Cr-Si alloy electrode with finer microstructure was suppressed significantly and improved in cycle capability, in comparison Ni-Si alloy with coarse microstructure. From these, we could infer the correlation of microstructure, volume expansion and electrochemical degradation and these properties might be predicted by phase diagram.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.29 no.5
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• pp.681-688
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• 1996

To investigate the effort of drying methods on the physicochemical properties of agar, gel strength, viscosity, melting and setting point, and phase transition by differential scanning calorimetery (DSC) during its heating were determined. In addition the structural differences of agar powder by scanning electron microscope (SEM) was examined. The most shortest onset temperature of gel strength increase was extruding method among any other methods. Viscosity of agar with hot air method, 400.00 cps at $45^{\circ}C$, was markedly increased, but with spraying and extruding ones were little change. The melting and setting point, and the temperature for maximum endothermic and enthalpy for agar with extruding one, $80.01^{\circ}C,\;36.05^{\circ}C\;and\;61.72^{\circ}C,\;0.73\;cal/g$, respectively, were lowest among the drying ones. But in the case of reheating after gelling, there were little change in all methods. Observing the surface structure of agar with SEM, extruding method showed the most unstable with absorptive property.

• Journal of the Korean Magnetics Society
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• v.5 no.5
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• pp.880-894
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• 1995

Magnetic properties of $Nd_{x}{(Fe_{0.9}Co_{0.1})}_{90-x}B_{6}Nb_{3}Cu_{1}(x=\;3,\;4,\;5)$ rrelt-spun alloys with 6 at% B content were studied aiming for finding out a new $\alpha$-Fe based Nd-Fe-B nanocrystalline alloy with good hard magnetic properties. $Nd_{x}{(Fe_{0.9}Co_{0.1})}_{90-x}B_{6}Nb_{3}Cu_{1}$ melt-spun alloys prepared by RSP crystallized to nanocrystalline phase. An optimally annealed $Nd_{3}{(Fe_{0.9}Co_{0.1})}_{87}B_{6}Nb_{3}Cu_{1}$ melt-spun alloys had larger volume ratio of $\alpha$-Fe(Co) than that of higher Nd content alloy and showed high remanence of about 1.6 T. On the contrary, the increase of Nd content in $Nd_{x}{(Fe_{0.9}Co_{0.1})}_{90-x}B_{6}Nb_{3}Cu_{1}$ alloys gave rise to gradual increase of an amount of $Nd_{2}{(Fe,\;Co)}_{14}B$ phase and improved coercivity. An optimally annealed $Nd_{5}{(Fe_{0.9}Co_{0.1})}_{85}B_{6}Nb_{3}Cu_{1}$ alloy showed the most improved hard mag¬netic properties. The remanence, coercivityand energy product of the alloy were 1.35 T, 219 kA/m (2.75 kOe), and $129\;kJ/m^{3}$ (16.2 MGOe), respectively.