• 한국전기전자재료학회논문지
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• 제26권5호
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• pp.401-409
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• 2013

Numerical analysis on RF (Radio-Frequency) thermal plasma treatment of micro-sized Ni metal was carried out to understand the synthesis mechanism of nano-sized Ni powder by RF thermal plasma. For this purpose, the behaviors of Ni metal particles injected into RF plasma torch were investigated according to their diameters ($1{\sim}100{\mu}m$), RF input power (6 ~ 12 kW) and the flow rates of carrier gases (2 and 5 slpm). From the numerical results, it is predicted firstly that the velocities of carrier gases need to be minimized because the strong injection of carrier gas can cool down the central column of RF thermal plasma significantly, which is used as a main path for RF thermal plasma treatment of micro-sized Ni metal. In addition, the residence time of the injected particles in the high temperature region of RF thermal plasma is found to be also reduced in proportion to the flow rate of the carrier gas In spite of these effects of carrier gas velocities, however, calculation results show that a Ni metal particle even with the diameter of $100{\mu}m$ can be completely evaporated at relatively low power level of 10 kW during its flight of RF thermal plasma torch (< 10 ms) due to the relatively low melting point and high thermal conductivity. Based on these observations, nano-sized Ni metal powders are expected to be produced efficiently by a simple treatment of micro-sized Ni metal using RF thermal plasmas.

• Nuclear Engineering and Technology
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• 제55권5호
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• pp.1734-1741
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• 2023

This work presents the synthesis and preparation of a new glass system described by the equation of (70-x) B₂O₃-5TeO₂ -20SrCO₃-5ZnO -xBi₂O₃, x = 0, 1, 5, 10, and 15 mol. %, using the melt quenching technique at a melting temperature of 1100 ℃. The photon-shielding characteristics mainly the linear attenuation coefficient (LAC) of the prepared glass samples were evaluated using Monte Carlo (MC) simulation N-particle transport code (MCNP-5) at gamma-ray energy extended from 59 keV to 1408 keV emitted by the radioisotopes Am-241, Ba-133, Cs-137, Co-60, Na-22, and Eu-152. Furthermore, we observed that the Bi₂O₃ content of the glasses had a significantly stronger impact on the LAC at 59 and 356 keV. The study of the lead equivalent thickness shows that the performance of fabricated glass sample with 15 mol.% of Bi₂O₃ is four times less than the performance of pure lead at low gamma photon energy while it is enhanced and became two times lower the perforce of pure lead at high energy. Therefore, the fabricated glasses special sample with 15 mol.% of Bi₂O₃ has good shielding properties in low, intermediate, and high energy intervals.

• 자원리싸이클링
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• 제12권6호
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• pp.13-18
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• 2003

Fe($NO_3$)$_3$ㆍ$9H_2$O, Zn($NO_3$)$_2$ㆍ$6H_2$O, Ni($NO_3$3)$_2$ㆍ $6H_2$O, Cu($NO_3$)$_2$ㆍ $3H_2$O와 같은 질산 금속염들을 $150^{\circ}C$로 24시간 동안 열분해하여 최초 NiCuZn ferrite 분체를 얻었으며, 이 분체 시료를 $500^{\circ}C$로 가소한 후 각각 볼밀 분쇄를 행하고 $700∼1000^{\circ}C$까지 각각 1시간씩 소결을 행하여 이에 대한 자기적 특성을 조사하였다. 일반 세라믹스 공정 보다 질산금속염들의 $ 200^{\circ}C$이하의 저 융점인 것을 이용하여 이들 출발 시료를 $150^{\circ}C$의 저온에서 액상의 화학결합이 가능하게 입자간의 거리를 분자적 거리로 좁힐 수 있었으며, 이로 인해 소결반응 점을 최소한 200∼ $300^{\circ}C$ 이상 낮출 수 있었다. 또한 이들의 초투자율은 50∼490, 포화자속밀도 및 보자력은 각각 2,400G와 0.3∼1.2 Oe정도로 보통의 ferrite 소결체의 특성과 유사하게 나타났다.

• Nuclear Engineering and Technology
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• 제10권3호
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• pp.127-136
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• 1978

온도종속 Thomas-Fermi 이론을 적용하여 금속의 일종인 Na에 대한 상태방정식, chemical potential, % ion 화도, 엔트로피, 원자당운동에너지 및 총에너지 등을 포함한 제열학적동을 산출하였다. $\rho$$_{0}$를 Na의 비등점에서의 정상밀도라 할 때 0.1$\rho$$_{0}$ ~ 10$\rho$$_{0}$ 까지의 밀도영역에서, 또한 Na이 기체 또는 액체상태로 존재할 것으로 기대되는 $textsc{k}$T=60.88Ryd.~0.0216Ryd 까지의 온도영역에 대하여 이들 양을 산출하였다. 본 연구에서는 고온 및 고압상태에서의 물리양 산출하는 것을 주목적으로 하고 있으나 Thomas-Fermi 근사가 기대되는 것처럼 그렇게 조잡하지 않음을 보이기 위하여 극저온 및 극저밀도에서의 물리양들도 산출하였다. 특히 고온에서의 상태방정식, 운동에너지, chemical potential 및 엔트로피를 ideal Fermi gas의 이들 양과 비교하였다. 그 결과, 산출한 chemical potential은 서로 잘 일치하나 엔트로피, 원자당운동에너지 및 상태방정식은 $textsc{k}$T=60.88Ryd.의 고온에서도 상당한 차이가 있음을 발견하였다.

• 한국재료학회지
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• 제29권11호
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• pp.720-726
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• 2019

Recently, research on cost reduction and efficiency improvement of crystalline silicon(c-Si) photovoltaic(PV) module has been conducted. In order to reduce costs, the thickness of solar cell wafers is becoming thinner. If the thickness of the wafer is reduced, cracking of wafer may occur in high temperature processes during the c-Si PV module manufacturing process. To solve this problem, a low temperature process has been proposed. Conductive paste(CP) is used for low temperature processing; it contains Sn57.6Bi0.4Ag component and can be electrically combined with solar cells and ribbons at a melting point of $150^{\circ}C$. Use of CP in the PV module manufacturing process can minimize cracks of solar cells. When CP is applied to solar cells, the output varies with the amount of CP, and so the optimum amount of CP must be found. In this paper, in order to find the optimal CP application amount, we manufactured several c-Si PV modules with different CP amounts. The amount control of CP is fixed at air pressure (500 kPa) and nozzle diameter 22G(outer diameter 0.72Ø, inner 0.42Ø) of dispenser; only speed is controlled. The c-Si PV module output is measured to analyze the difference according to the amount of CP and analyzed by optical microscope and Alpha-step. As the result, the optimum amount of CP is 0.452 ~ 0.544 g on solar cells.

• 한국재료학회지
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• 제28권4호
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• pp.254-259
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• 2018

General D-glass(Dielectric glass) fibers are adaptable to PCBs(Printed circuit boards) because they have a low dielectric constant of about 3.5~4.5. However, very few papers have appeared on the physical characteristics of D-glass fibers. D-glass fibers were fabricated via continuous spinning process using bulk D-glass. In order to fabricate the D-glass, raw materials were put into a Pt crucible, melted at $1650^{\circ}C$ for 2 hrs, and then annealed at $521{\pm}10^{\circ}C$ for 2 hrs. We obtained transparent clear glass. The transmittance and adaptable temperature for spinning of the bulk marble glass were characterized using a UV-visible spectrometer and a viscometer. Continuous spinning was carried out using direct melting spinning equipment as a function of the fiberizing temperature in the range of $1368^{\circ}C$ to $1460^{\circ}C$, while the winder speed was between 100 rpm and 200 rpm. We investigated the physical properties of the D-glass fibers. The average diameters of the glass fibers were measured by optical microscope and FE-SEM. The average diameters of the D-glass fibers were 21.36 um at 100 rpm and 34.06 um at 200 rpm. The mechanical properties of the fibers were confirmed using a UTM(Universal materials testing machine). The average tensile strengths of the D-glass fibers were 467.03 MPa at 100 rpm and 522.60 MPa at 200 rpm.

• 원예과학기술지
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• 제18권3호
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• pp.360-367
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• 2000

유명복숭아는 보구력이 매우 강한 독특한 불용질성 품종으로서, 수확기간이 긴 장점이 있으나 너무 늦게 수확하는 경우 수상에서 과실 바람들이 증상이나 내부갈변 현상이 나타나는 경우가 있다. 바람들이 증상은 늦게 수확할수록 큰 과실에서 많이 발생하며 당과 말산 함량은 정상과와 비교하여 차이가 없으나 구연산의 함량이 크게 낮아 산도가 떨어졌다. 바람들이 증상과의 과피에서는 질소, 인산, 칼륨의 함량이 높았으며 과육에서는 질소, 인산, 마그네슘의 함량이 높았으나 칼슘의 경우 과피와 과육 모두에서 낮게 나타났다. 바람들이 발생은 수확전 2개월 간의 강수량이 적고 최고온도가 높은 해에 많이 발생하여 과실비대기의 고온건조가 한 원인이 되는 것으로 생각되었다. 형태학적인 측면에서 바람들이 발생부위의 세포들은 정상부위의 세포들보다 작은 크기의 세포들로 이루어져 있었으며, 내부갈변과에서 액포막이 파괴되고 죽은 세포가 많은 것에 비하여 바람들이과는 액포막의 파괴없이 액포가 수축된 상태로 나타났다. 바람들이 발생조직 주변의 유관속 조직에서 틸로시스가 발견되어 이러한 틸로시스가 일부 과육조직의 발달을 방해하여 바람들이 발생에 관여하는 것으로 추정되었다. 한편, '판타지아'와 '월미' 등의 다른 복숭아에서도 틸로시스가 나타났으며 비정상적으로 작은 세포들의 모임이 과육에서 발견되어 과육 전체 세포들이 균일하게 생장하고 있지 못함을 보여주었다. 이는 복숭아 여러 품종에서 바람들이와 유사한 증상이 나타날 수 있는 가능성을 암시하나 많은 복숭아가 연화기간이 짧아 바람들이 증상이 발견되기 어려운 것으로 추정되었다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2011년도 제41회 하계 정기 학술대회 초록집
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• pp.348-348
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• 2011

Carbon nanotube (CNT) field effect transistors and sensors use CNT as a current channel, of which the resistance varies with the gate voltage or upon molecule adsorption. Since the performance of CNT devices depends very much on the CNT/metal contact resistance, the CNT/electrode contact must be stable and the contact resistance must be small. Depending on the geometry of CNT/electrode contact, it can be categorized into the end-contact, embedded-contact (top-contact), and side-contact (bottom-contact). Because of difficulties in the sample preparation, the end-contact CNT device is seldom practiced. The embedded-contact in which CNT is embedded inside the electrode is desirable due to its rigidness and the low contact resistance. Fabrication of this structure is complicated, however, because each CNT has to be located under a high-resolution microscope and then the electrode is patterned by electron beam lithography. The side-contact is done by depositing CNT electrophoretically or by precipitating on the patterned electrode. Although this contact is fragile and the contact resistance is relatively high, the side-contact by far has been widely practiced because of its simple fabrication process. Here we introduce a simple method to embed CNT inside the electrode while taking advantage of the bottom-contact process. The idea is to utilize a eutectic material as an electrode, which melts at low temperature so that CNT is not damaged while annealing to melt the electrode to embed CNT. The lowering of CNT/Au contact resistance upon annealing at mild temperature has been reported, but the electrode in these studies did not melt and CNT laid on the surface of electrode even after annealing. In our experiment, we used a eutectic Au/Al film that melts at 250$^{\circ}C$. After depositing CNT on the electrode made of an Au/Al thin film, we annealed the sample at 250$^{\circ}C$ in air to induce eutectic melting. As a result, Au-Al alloy grains formed, under which the CNT was embedded to produce a rigid and low resistance contact. The embedded CNT contact was as strong as to tolerate the ultrasonic agitation for 90 s and the current-voltage measurement indicated that the contact resistance was lowered by a factor of 4. By performing standard fabrication process on this CNT-deposited substrate to add another pair of electrodes bridged by CNT in perpendicular direction, we could fabricate a CNT cross junction. Finally, we could conclude that the eutectic alloy electrode is valid for CNT sensors by examine the detection of Au ion which is spontaneously reduced to CNT surface. The device sustatined strong washing process and maintained its detection ability.

• Fibers and Polymers
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• 제6권1호
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• pp.19-27
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• 2005

High-speed melt spinning of syndiotactic polystyrene was carried out using high and low molecular weight poly­mers, HM s-PS and LM s-PS, at the throughput rates of 3 and 6 g/min. The effect of take-up velocity on the structure and properties of as-spun fibers was investigated. Wide angle X-ray diffraction (WAXD) patterns of the as-spun fibers revealed that the orientation-induced crystallization started to occur at the take-up velocities of 2-3 km/min. The crystal modification was a-form. Birefringence of as-spun fibers showed negative value, and the absolute value of birefringence increased with an increase in the take-up velocity. The cold crystallization temperature analyzed through the differential scanning calorimetry (OSC) decreased with an increase in the take-up velocity in the low speed region, whereas as the melting temperature increased after the on-set of orientation-induced crystallization. It was found that the fiber structure development proceeded from lower take-up velocities when the spinning conditions of higher molecular weight and lower throughput rate were adopted. The highest tensile modulus of 6.5 GPa was obtained for the fibers prepared at the spinning conditions of LM s-PS, 6 g/min and 5 km/min, whereas the highest tensile strength of 160 MPa was obtained for the HM s-PS fibers at the take-up velocity of 2 km/min. Elongation at break of as-spun fibers showed an abrupt increase, which was regarded as the brittle-duc­tile transition, in the low speed region, and subsequently decreased with an increase in the take-up velocity. There was a uni­versal relation between the thermal and mechanical properties of as-spun fibers and the birefringence of as-spun fibers when the fibers were still amorphous. The orientation-induced crystallization was found to start when the birefringence reached -0.02. After the starting of the orientation-induced crystallization, thermal and mechanical properties of as-spun fibers with similar level of birefringence varied significantly depending on the processing conditions.

• KSBB Journal
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• 제14권4호
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• pp.511-516
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• 1999

유지의 가수분해시, 반응온도, 금속이온, pH, 교반속도, 물-유지의 무게비 및 효소량 등의 환경 및 조성인자가 효소 Lipase-OF의 역가 및 가수분해특성에 미치는 영향을 규명하였다. 융점이 낮은 유지의 경우 Lipase-OF의 활성이 가장 높은 온도는 37$^{\circ}C$ 근방이었으나 융점이 4$0^{\circ}C$ 이상의 온도 범위에서는 유지의 종류에 관계없이 온도가 상승하면 Lipase-OF의 활성이 급격히 감소하여 $65^{\circ}C$ 이상에서는 효소의 활성이 정지되었다. 교반속도를 150, 250, 350, 450, 550 및 650 rmp으로 변화시켜가면서 유지의 가수분해실험을 수행하여 350 rpm 이하에서는 교반속도가 상승하면 가수분해율도 상승하였으나 교반속도 350 rpm 이상에서는 교반속도 상승에 대한 가수분해율의 변화를 찾아볼 수 없었다. 유지와 물의 무게비를 9 : 1에서 1 : 9까지 변화시켜가면서 가수분해실험을 수행하여 일정한 가수분해 시간에서 가수분해율이 가장 높은 무게비가 1 : 1 근방의 값임을 규명하였다. 금속 이온 중 $Ca^{2+}와\;Mg^{2+}$ 이온이 가수분해율 상승에 기여하였다. 금속이온이 없는 경우에 비하여 $Ca^{2+}$또는 $Mg^{2+}$ 이온 농도가 100 ppm 근방의 값일 때 2 내지 3%의 가수분해율 증가효과를 나타내었다. Lipase-OF에 대한 최적 pH는 7근방이었다. pH가 산성쪽으로 감소하면 가수분해율도 감소하였으며 알칼리쪽으로 증가하여도 가수분해율이 감소하였다. 기질의 0.00075 wt% 와 0.1 wt% 범위내에서 Lipase-OF량이 가수분해율에 미치는 영향을 규명하였다. 효소량 0.013 wt% 이하에서는 효소량이 증가하면 가수분해율도 증가하였으나 0.013 wt% 이상에서는 효소량이 증가하여도 가수분해율은 증가하지 않았다. Lipase-OF의 가수분해율에 미치는 환경 및 조성인자의 영향에 대한 실험을 통하여 최적온도는 37$^{\circ}C$, 최적 pH는 7, $Ca^{2+}\;또는\;Mg^{2+}$의 최적농도는 100 ppm, 최적교반속도는 350 rpm, 유지와 물의 최적무게비는 1 : 1 및 최적 효소량은 유지의 0.013 wt%임을 규명하였다.