• 소성∙가공
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• 제16권4호
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• pp.266-270
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• 2007

Inertia welding is a solid-state welding process in which butt welds in materials are made in bar and in ring form at the joint face, and energy required for welding is obtained from a rotating flywheel. The stored energy is converted to frictional heat at the interface under axial load. The quality of the welded joint depends on many parameters, including axial force, initial revolution speed and energy, amount of upset, working time, and residual stresses in the joint. Inertia welding was conducted to make the large rotor shaft for low speed marine diesel engine, alloy steel for shaft of 140mm. Due to material characteristics, such as, thermal conductivity and high temperature flow stress, on the two sides of the weld interface, modeling is crucial in determining the optimal weld parameters. FE simulation is performed by the commercial code DEFORM-2D. A good agreement between the predicted and actual welded shape is observed. It is expected that modeling will significantly reduce the number of experimental trials needed to determine the weld parameters.

• 한국분말재료학회지
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• 제19권4호
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• pp.278-284
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• 2012

$Al_2O_3$ foam is an important engineering material because of its exceptional high-temperature stability, low thermal conductivity, good wear resistance, and stability in hostile chemical environment. In this work, $Al_2O_3$ foams were designed to control the microstructure, porosity, and cell size by varying different parameters such as the amount of amphiphile, solid loading, and stirring speed. Particle stabilized direct foaming technique was used and the $Al_2O_3$ particles were partially hydrophobized upon the adsorption of valeric acid on particles surface. The foam stability was drastically improved when these particles were irreversibly adsorbed at the air/water interface. However, there is still considerable ambiguity with regard to the effect of process parameters on the microstructure of particle-stabilized foam. In this study, the $Al_2O_3$ foam with open and closed-cell structure, cell size ranging from $20{\mu}m$ to $300{\mu}m$ having single strut wall and porosity from 75% to 93% were successfully fabricated by sintering at $1600^{\circ}C$ for 2 h in air.

• Current Applied Physics
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• 제18권12호
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• pp.1540-1545
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• 2018

SiGe alloy is widely used thermoelectric materials for high temperature thermoelectric generator applications. However, its high thermoelectric performance has been thus far realized only in alloys synthesized employing mechanical alloying techniques, which are time-consuming and employ several materials processing steps. In the current study, for the first time, we report an enhanced thermoelectric figure-of-merit (ZT) ~ 1.1 at $900^{\circ}C$ in ntype $Si_{80}Ge_{20}$ nano-alloys, synthesized using a facile and up-scalable methodology consisting of rapid solidification at high optimized cooling rate ${\sim}3.4{\times}10^7K/s$, employing melt spinning followed by spark plasma sintering of the resulting nano-crystalline melt-spun ribbons. This enhancement in ZT > 20% over its bulk counterpart, owes its origin to the nano-crystalline microstructure formed at high cooling rates, which results in crystallite size ~7 nm leading to high density of grain boundaries, which scatter heat-carrying phonons. This abundant scattering resulted in a very low thermal conductivity ${\sim}2.1Wm^{-1}K^{-1}$, which corresponds to ~50% reduction over its bulk counterpart and is amongst the lowest reported thus far in n-type SiGe alloys. The synthesized samples were characterized using X-ray diffraction, scanning electron microscopy and transmission electron microscopy, based on which the enhancement in their thermoelectric performance has been discussed.

• 한국결정성장학회지
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• 제23권5호
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• pp.213-217
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• 2013

GaN는 대표적인 III-V족 질화물반도체로 주로 값싸고 다루기 쉬운 사파이어 기판 위에 성장된다. 하지만 사파이어 기판은 부도체이며, GaN과의 격자부정합을 일으키고 열전도도 또한 낮은 기판으로 알려져 있다. 본 논문에서는 방열기능과 열 전기전도도가 뛰어난 금속 화합물 탄소체 기판 위에 poly GaN epilayer를 HVPE법으로 성장시켜보았다. 비정질의 금속 화합물 탄소체 기판위에 성장되는 GaN epilayer의 성장메카니즘을 관찰하였다. GaN epilayer의 성장을 위해 HCl과 $NH_3$를 흘려주었다. 성장하기 위해 source zone과 growth zone의 온도는 각각 $850^{\circ}C$와 $1090^{\circ}C$로 설정했다. 성장이 끝난 샘플은 SEM, EDS, XRD측정을 통해 분석하였다.

• 한국세라믹학회지
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• 제40권6호
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• pp.560-565
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• 2003

방전 플라즈마 소결법(SPS: Spark Plasma Sintering)을 이용하여 800~100$0^{\circ}C$의 낮은 소결 온도에서 완전 치밀화를 이루는 M-doped ZnO를 (M=Al, Ni) 제조하여 그 소결 특성과 미세구조를 분석하였다. 전자현미경 분석 결과, NiO의 첨가는 ZnO 결정격자와의 고용체 형성을 촉진시키고 결정립 성장을 유발하였고, A1$_2$O$_3$는 순수한 ZnO 소결 시 나타나는 입계에서의 증발현상을 제어하고, 이차상 형성을 통하여 결정립 성장을 억제함을 확인할 수 있었다 NiO와 $Al_2$O$_3$를 동시에 첨가한 시편이 가장 우수한 미세구조가 형성됨을 확인하였고, SEM-EBSP (Electron Back-scattered Diffraction Pattern) 분석 결과 또한 우수한 결정립계 분포를 가지고 있음을 확인하였다. 이러한, 소결체의 우수한 미세구조적 특징은 carrier 농도 증가에 따른 전기 전도도와 증가 및 phonon scattering 효과에 의한 열전도도의 감소 효과를 유발하여 ZnO의 열전 특성을 향상시키리라 사료된다.

• Advances in materials Research
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• 제1권4호
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• pp.299-310
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• 2012

This article describes the synthesis of a novel N-substituted pyrrole monomer containing an azobenzene group. The 2-[N-ethyl-N-[4-[(4-nitrophenyl) azo]-phenyl] amino] ethyl-3-chloropropionate (RedII) compound was synthesized via reaction of 4-nitro-4'-[N-ethyl-N-(2-hydroxyethyl)-amino] azobenzene (RedI) and 3-chloropropionic acid. RedII was reacted with the potassium salt of pyrrole then 2-[N-ethyl-N-[4-[(nitro phenyl) azo] phenyl] amino] ethyl-N-pyrrolyl propionate (Py-RedII) was prepared. Chemical polymerization of Py-RedII and copolymerization of Py-RedII with pyrrole carried out using $FeCl_3$. Poly (2-[N-ethyl-N-[4-[(nitro phenyl) azo] phenyl] amino] ethyl-N-pyrrolyl propionate) (PPy-RedII) was characterized by UV, IR, $^1HNMR$, $^{13}CNMR$ spectroscopies. Electropolymerization of Py-RedII and electroco-polymerization of Py-RedII and pyrrole were studied using conventional three electrodes system, Ag/AgCl reference electrode, platinum counter electrode and GC disk working electrode. Scanning electron microscopy (SEM), thermogravimetry analysis (TGA) and differential scanning calorimetry (DSC) were used for thermal and rheological studies. The TGA curve of PPy-RedII demonstrated a high thermal stability up to 200°C and its DSC thermogram showed two endothermic peaks at 88 and $122^{\circ}C$. The glass transition temperature of the polymer was found to be above the room temperature. Electrical conductivities of PPy-RedII and it's copolymer with pyrrole (PPy-RedII-co-Py) were studied by the four-probe method and produced conductivities of $7.5{\times}10^{-4}$ and $6.5{\times}10^{-3}Scm^{-1}$, respectively.

• 전기화학회지
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• 제14권3호
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• pp.152-156
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• 2011

A room temperature ionic liquid (RTIL) based on trihexyl (tetradecyl)phosphonium bis(trifluoromethanesulfonyl) imide ([$(C_6H_{13})_3P(C_{14}H_{29)}$] [TFSI];P66614TFSI) was synthesized and analyzed to determine their characteristics and properties. The bis(trifluoromethanesulfonyl)imide (TFSI) anion is widely studied as an ionic liquid (IL) forming anion which imparts many useful properties, notably electrochemical stability. Especially its electrochemical and physical characteristics for solvent of lithium ion battery were investigated in detail. $P_{66614}$ TFSI exhibits fairly low conductivity (0.89 mS $cm^{-1}$) and higher viscosity (298 K: 277 cP; 343 K: 39 cP) than other ionic liquids, but it exhibits a high thermal stability (over $400^{\circ}C$). Especially corrosion behavior on Al current collector was tested at room temperature and further it was confirmed that thermal resistivity for Al corrosion was highly increased in 1.0M LiTFSI/$P_{66614}$-TFSI electrolyte comparing with other RTILs by linear sweep thermometry.

• 방사성폐기물학회지
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• 제16권2호
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• pp.233-242
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• 2018

본 연구에서는 탄소강 심부시추공 처분용기가 가지는 고온에서의 물성 저하와 내부식성 문제 등을 해결하기 위하여, 열전도도가 우수한 SiC를 이용한 심부시추공 처분용기의 제작 가능성을 살펴보았다. 먼저 사용후핵연료 집합체 1다발을 수용할 수있는 심부시추공 처분용기를 설계하였으며, 설계된 처분용기는 내부 SiC 기밀용기와 취급 편의와 심부정치를 위한 외부 스테인리스 용기로 구성하였다. 그리고 SiC 세라믹 용기의 제작 가능성을 확인하기 위해, 1/3 규모의 소형 SiC 용기를 실제 제작하였다. 제작된 SiC 용기에서 시편을 추출하여 열전도도를 측정하였으며, KURT 지하 $70^{\circ}C$ 고온조건에서 3년간 내구성 시험도 실시하였다. 그 결과 SiC는 $100^{\circ}C$에서도 $70W{\cdot}m^{-1}{\cdot}K^{-1}$ 이상의 열전도도를 보였으며, 내구성 시험 후에도 변화가 전혀 보이지 않았다. 따라서 SiC는 높은 열전도도와 우수한 내부식성을 갖고 있어, 심부시추공 처분용기 재료로 적합하다고 보았다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1993년도 하계학술대회 논문집 B
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• pp.1193-1196
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• 1993

Electrical properties of $C_{22}$-Quinolium(TCNQ) Langmuir-Blodgett(LB) films are reported depending on a type of applied voltage on a type of applied voltage and temperature. A conductivity was identified to be anisotropic with a ratio of ${\sigma}||/{\sigma}{\bot}{\simeq}10^7$ at room temperature. The I-V characteristics along the film surface direction show an ohmic behavior up to a few hundred volts. But the I-V characteristics in the vertical direction display an ohmic behavior for low-electric field, and a nonohmic behavior for high-electric field. This nonohmic behavior has already been interpreted as a conduction mechanism of space-charge limited current and Schottky effect near the electric-field strengh of $10^6$ V/cm. When the electric field exceeds further, there is anormalous phenomia similiar to breakdown. From the study of I-V characteristics with the application of step or pulse voltage, we have found that the breakdown voltage shifts to higher one as the step or pulse interval becomes shorter. These results indicate that the breakdown is due to both electrical and thermal effect. To see the infulence of temperature, current was measured as function of temperature with several bias voltages, which are lower than that of breakdown. It shows that the current increases about 3 orders of magnitude near $60{\sim}70^{circ}C$, and remains constant for a while up to $140^{\circ}C$ and then suddenly drops. Arahidic acid was used to cmpare with $C_{22}$-Quinolium(TCNQ) LB films.

• 한국세라믹학회지
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• 제52권5호
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• pp.344-349
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• 2015

An interconnect is the key component of solid oxide fuel cells that electrically connects unit cells and separates fuel from oxidant in the adjoining cells. To improve their surface stability in high-temperature oxidizing environments, metallic interconnects are usually coated with conductive oxides. In this study, lanthanum nickelates ($LaNiO_3$) with a perovskite structure are synthesized and applied as protective coatings on a metallic interconnect (Crofer 22 APU). The partial substitution of Co, Cu, and Fe for Ni improves electrical conductivity as well as thermal expansion match with the Crofer interconnect. The protective perovskite layers are fabricated on the interconnects by a slurry coating process combined with optimized heat-treatment. The perovskite-coated interconnects show area-specific resistances as low as $16.5-37.5m{\Omega}{\cdot}cm^2$ at $800^{\circ}C$.