• 한국재료학회지
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• 제28권3호
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• pp.166-173
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• 2018

Molybdenum (Mo) is one of the representative refractory metals for its high melting point, superior thermal conductivity, low density and low thermal expansion coefficient. However, due to its high melting point, it is necessary for Mo products to be fabricated at a high sintering temperature of over $1800-2000^{\circ}C$. Because this process is expensive and inefficient, studies to improve sintering property of Mo have been researched actively. In this study, we fabricated Mo nanopowders to lower the sintering temperature of Mo and tried to consolidate the Mo nanopowders through ultra high pressure compaction. We first fabricated Mo nanopowders by a mechano-chemical process to increase the specific surface area of the Mo powders. This process includes a high-energy ball milling step and a reduction step in a hydrogen atmosphere. We compacted the Mo nanopowders with ultra high pressure by magnetic pulsed compaction (MPC) before pressureless sintering. Through this process, we were able to improve the green density of the Mo compacts by more than 20 % and fabricate a high density Mo sintered body with more than a 95 % sintered density at relatively low temperature.

• Journal of Magnetics
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• 제17권2호
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• pp.86-95
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• 2012

This study investigated the effects of adding a third alloying element, Ni, to create $Fe_{70-x}Pd_{30}Ni_x$ (x = 2, 4, 6, 8 at.% Ni) ferromagnetic shape memory alloys (FSMAs). The Ni replaced a portion of the Fe. The $Fe_{70-x}Pd_{30}Ni_x$ alloys were homogenized through hot and cold forging to gain a ~38% reduction in thickness, next they were solution-treated (ST) with annealing recrystallization at $1100^{\circ}C$ for 8 h and quenched in ice brine, and then aged at $500^{\circ}C$ for 100 h. Investigation of the microstructures and magnetostriction indicated that the greater Ni amount in the $Fe_{70-x}Pd_{30}Ni_x$ alloys reduced saturation magnetostriction at room temperature (RT). It was also observed that it was more difficult to generate annealed recrystallization. However, with greater Ni addition into the $Fe_{70-x}Pd_{30}Ni_x$ (x = 6, 8 at.% Ni) alloys, the $L1_0+L1_m$ twin phase decomposition into stoichiometric $L1_0+L1_m+{\alpha}_{bct}$ structures was suppressed after the $500^{\circ}C$/100 h aging treatment. The result was that the $Fe_{70-x}Pd_{30}Ni_x$ (x = 6, 8 at.% Ni) alloys maintained a high magnetostriction and magnetostrictive susceptibility (${\Delta}{\lambda}{_\parallel}{^s}/{\Delta}H$) after the alloys were aged at $500^{\circ}C$ for 100 h. This magnetic property of the $Fe_{70-x}Pd_{30}Ni_x$ (x = 6, 8 at.% Ni) alloys make it suitable for application in a high temperature (T > $500^{\circ}C$) and high frequency environments.

• 한국진공학회:학술대회논문집
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• 한국진공학회 1999년도 제17회 학술발표회 논문개요집
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• pp.122-122
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• 1999

Graphite with its advantages of high thermal conductivity, low thermal expansion coefficient, and low elasticity, has been widely used as a structural material for high temperature. However, graphite can easily react with oxygen at even low temperature as 40$0^{\circ}C$, resulting in CO2 formation. In order to apply the graphite to high temperature structural material, therefore, it is necessary to improve its oxidation resistive property. Silicon Carbide (SiC) is a semiconductor material for high-temperature, radiation-resistant, and high power/high frequency electronic devices due to its excellent properties. Conventional chemical vapor deposited SiC films has also been widely used as a coating materials for structural applications because of its outstanding properties such as high thermal conductivity, high microhardness, good chemical resistant for oxidation. Therefore, SiC with similar thermal expansion coefficient as graphite is recently considered to be a g행 candidate material for protective coating operating at high temperature, corrosive, and high-wear environments. Due to large lattice mismatch (~50%), however, it was very difficult to grow thick SiC layer on graphite surface. In theis study, we have deposited thick SiC thin films on graphite substrates at temperature range of 700-85$0^{\circ}C$ using single molecular precursors by both thermal MOCVD and PEMOCVD methods for oxidation protection wear and tribological coating . Two organosilicon compounds such as diethylmethylsilane (EDMS), (Et)2SiH(CH3), and hexamethyldisilane (HMDS),(CH3)Si-Si(CH3)3, were utilized as single source precursors, and hydrogen and Ar were used as a bubbler and carrier gas. Polycrystalline cubic SiC protective layers in [110] direction were successfully grown on graphite substrates at temperature as low as 80$0^{\circ}C$ from HMDS by PEMOCVD. In the case of thermal MOCVD, on the other hand, only amorphous SiC layers were obtained with either HMDS or DMS at 85$0^{\circ}C$. We compared the difference of crystal quality and physical properties of the PEMOCVD was highly effective process in improving the characteristics of the a SiC protective layers grown by thermal MOCVD and PEMOCVD method and confirmed that PEMOCVD was highly effective process in improving the characteristics of the SiC layer properties compared to those grown by thermal MOCVD. The as-grown samples were characterized in situ with OES and RGA and ex situ with XRD, XPS, and SEM. The mechanical and oxidation-resistant properties have been checked. The optimum SiC film was obtained at 85$0^{\circ}C$ and RF power of 200W. The maximum deposition rate and microhardness are 2$mu extrm{m}$/h and 4,336kg/mm2 Hv, respectively. The hardness was strongly influenced with the stoichiometry of SiC protective layers.

• Journal of Welding and Joining
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• 제33권5호
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• pp.31-34
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• 2015

Microstructure and tensile property in the weld heat-affected zone (HAZ) of austenitic Fe-Mn-Al-C low density steels were investigated through transmission electron microscopy analysis and tensile tests. The HAZ samples were prepared using Gleeble simulation with high heat input welding condition of 300 kJ/cm, and the HAZ peak temperature of $1200^{\circ}C$ was determined from differential scanning calorimetry (DSC) test. The strain- stress responses of base steels showed that the addition of V improved the tensile and yield strength by grain refinement and precipitation strengthening. Tensile strength and elongation decreased in the weld HAZ as compared to the base steel, due to grain growth, while V-added steel had a higher HAZ strength as compared than V-free steel.

• 한국고분자학회:학술대회논문집
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• 한국고분자학회 2006년도 IUPAC International Symposium on Advanced Polymers for Emerging Technologies
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• pp.349-349
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• 2006

Vinyl-polynorbornene has good thermal stability, high transparency and low dielectric constant. However, it has low solubility, poor mechanical and adhesive properties. In this work, polynorbornene derivatives were prepared by Pd(II) late transition metal catalyst. The polymers have good solubility, and are thermally stable up to$300^{\circ}C$ The glass transition temperature is decreased as the side-chain becomes bulkier. Structure-property relationship of polynorbornene derivatives measured by X-ray scattering, mechanical and electrical properties will be discussed.

• 한국주조공학회지
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• 제27권3호
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• pp.131-134
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• 2007

[ $SF_6$ ] gas that is used as a protective cover gas for Mg and Mg alloys during melting and casting has extremely high greenhouse effect. CaO added Mg alloys could maintain their original mechanical properties and original abilities such as fluidity and hot tearing susceptibility. The ignition temperature increased with increasing CaO addition under ambient atmosphere and nitrogen atmosphere. The minimum amount of $SF_6$ gas decreased by 0.13 wt%CaO added AZ91D Mg alloy in the sealed condition.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2000년도 추계학술대회 논문집
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• pp.547-550
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• 2000

The steel pipe for fluid catalytic cracking(FCC) unit. petroleum refinery, is lined with refractory to protect the system from high-temperature of the internal flow. The property of the refractory has an effect upon the stress analysis of FCC unit. Because 1-D pipe element or 3-D shell element are usually used in commercial codes of stress analysis to evaluate the structural soundness, the equivalent elastic modulus considering steel and refractory should be applied. In the research, the theoretical method to obtain the value of the equivalent property is introduced and then the stress analysis is carried out with the part of FCC unit.

• Transactions on Electrical and Electronic Materials
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• 제18권1호
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• pp.13-15
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• 2017

Low emissivity glass for high transparency in the visible range and low emissivity in the IR (infrared) range was fabricated and investigated. The multilayers were have been fabricated, and consisted of two outer oxide layers and a middle layer of Ag as a metal layer. Oxide layers were formed by rf sputtering and metal layers were formed using by an evaporator at room temperature. SiInZnO (SIZO) film was used as an oxide layer. The OMO (oxide-metaloxide) structures of SIZO/Ag/SIZO were analyzed by using transmittance, AFM (atomic force microscopye), and XRD (X-ray diffraction). The OMO multilayer structure was designed to investigate the effect of Ag layer thickness on the optical property of the OMO structure.

• 한국정밀공학회지
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• 제27권7호
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• pp.49-54
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• 2010

The cryogenic ball milling was performed on carbon nanotubes (CNTs) at an extremely low temperature to increase the dispersion of CNTs. The effects of milling speed and time on the deagglomeration and structural changes of CNTs were studied. FESEM was used to analyze the dispersion and the change of particle size before and after milling process. Transmission electron microscopic (TEM) analysis was also investigated the effect of cryogenic ball milling on the morphological characteristics of CNTs. The structural changes by the cryogenic ball milling process were further confirmed by x-ray diffraction (XRD) and Raman spectroscopic analysis. The results showed that the agglomeration of CNTs was significantly reduced and amorphous structure was observed at high milling speed. However, the milling time has no great effect on the dispersion property and structural change of CNTs compared with milling speed.

• 펄프종이기술
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• 제39권2호
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• pp.45-53
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• 2007

When micro flute corrugated paperboards are used for food packaging, they necessarily need to meet the requirements for the distribution, transportation, and storage of food. The requirements could vary ac-cording to the contents in the packaging boxes. Microflute corrugated packaging paperboard for hot foods such as just-made coffee and hamburger requires to have a decent resistance property against high temperature. Along with a recent trend for small-quantity-multi-item upgraded packaging, semiconductor products and consumer-electronic appliances become to be packed using the environmental friendly micro flute corrugated paperboard. In this case, the electric resistance property of the microflute corrugated paperboard becomes important. This study was carried out to investigate on the thermal conductivity and electric resistance properties of micro flute corrugated paperboard.