• Bulletin of the Korean Chemical Society
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• 제19권12호
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• pp.1310-1314
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• 1998

The oligo(methylsilene) (1) was treated with the group 4 metallocene Cp2MCl2/Red-Al (M = Ti, Zr, Hf) combination catalysts and with the group 6 metal carbonyl M(CO)6 (M = Cr, W) catalysts, producing the modified, cross-linked polymers. The average molecular weights and percent ceramic residue yields of modified polymers increase as the catalyst goes down from Ti to Hf and similarly as the catalyst goes down from Cr to W. An interrelationship between average molecular weights and percent ceramic residue yield is found within the respective group of catalysts, but is not observed as the catalyst goes down from Ti to W. The polymers modified with the group 4 metallocene combination catalysts have higher molecular weights and similar percent ceramic residue yields as compared to the polymers modified with the group 6 metal carbonyl catalysts. The catalytic activities of group 4 metallocene combinations appear to be higher -100 ℃, but to be lower at very high temperature than those of group 6 metal carbonyls.

• Coupled systems mechanics
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• 제3권1호
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• pp.111-145
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• 2014

In this paper we present a new model for computing the nonlinear response of reinforced concrete frame systems subjected to extreme thermomechanical loads. The first main feature of the model is its ability to account for both bending and shear failure of the reinforced concrete composites within frame-like model. The second prominent feature concerns the model capability to represent the total degradation of the material properties due to high temperature and the thermal deformations. Several numerical simulations are given to confirm these capabilities and illustrate a very satisfying model performance.

• 열처리공학회지
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• 제35권5호
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• pp.239-245
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• 2022

The purpose of this study is to evaluate the degree of microstructural change of materials using ultrasonic nonlinear parameters. For microstructure change, isothermal heat-treated ferritic 2.25Cr steel and low-cycle fatigue-damage copper alloy were prepared. The variation in ultrasonic nonlinearity was analyzed and evaluated through changes in hardness, ductile-brittle transition temperature, electron microscopy, and X-ray diffraction tests. Ultrasonic nonlinearity of 2.25Cr steel increased rapidly during the first 1,000 hours of deterioration and then gradually increased thereafter. The variation in non-linear parameters was shown to be coarsening of carbides and an increase in the volume fraction of stable M6C carbides during heat treatment. Due to the low-cycle fatigue deformation of oxygen-free copper, the dislocation that causes lattice deformation developed in the material, distorting the propagating ultrasonic waves, and causing an increase in the ultrasonic nonlinear parameters.

• 생명과학회지
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• 제18권10호
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• pp.1447-1454
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• 2008

열처리 조건 및 농도의 차이에 따른 칡 이소플라본인 daidzin과 genistin의 열 안정성에 대하여 조사하였다. Daidzin과 genistin 두 종류의 이소플라본은 처리방법에 상관없이 $140^{\circ}C$이상의 열처리 조건에서 초기 30분 동안 급격히 열 안정성이 떨어지고 그 이후 변화가 적게 나타나 처리 온도가 높을수록 열 안정성의 변화가 큰 것으로 나타났으며, genistin은 daidzin에 비해 농도차이 에 따른 변화의 차이가 크지 않은 것을 알 수 있었다. 또한 열처리 조건에 따른 반응속도는 모두 두 단계로 나타났는데, daidzin과 genistin 모두 2단계보다 1단계에서 빠른 반응속도를 보여 주었고, daidzin은 고농도 일 수록 더 빠른 반응속도를 나타내는 것을 알 수 있었으나, genistin은 농도에 따른 유의차가 적은 것을 알 수 있었다. Daidzin은 1단계의 고농도에서 온도 의존성이 높게 나타났으며 2단계는 농도에 따른 온도 의존성에 유의차가 없었다. Genistin의 경우 1단계에서는 농도에 의한 온도 의존성이 작게 나타났지만 2단계의 저농도에서 온도 의존성이 높은 것을 알 수 있었다. 농도에 따른 변화를 보면 genistin은 고농도와 저농도 모두 1단계에서 온도 의존성이 큰 것으로 나타났으며 반면 daidzin은 고농도, 저농도 모두 2단계에서 온도 의존성이 높은 것을 알 수 있었다. 또한 daidzin과 genistin 모두 $140^{\circ}C$ 이상의 열처리에 의해 이소플라본 glucosidic group이 열에 의해 가수분해되어 daidzein, genistein, glycitein, malonyl-glycitin, acetyl-genistin 등의 중간 유도체 및 aglycone이 생성되며 $140^{\circ}C$, 15 min의 처리 조건에서 대부분 가장 많은 양이 생성되는 것을 알 수 있었고, 농도 변화에 따른 함량의 증가는 유의차가 적은 것을 알 수 있었으나 그 중 malonyl daidzin의 경우 열처리 조건에 의해 따른 생성량의 차이가 큰 것을 알 수 있었다. 열처리 후 농축조건이 농축 후 열처리보다 더 많은 daidzin, genistin 유도체들을 생성시킨 것으로 보아 칡 이소플라본의 각 열처리 조건에 따른 열 안정성은 농축 후 열처리보다 열처리 후 농축이 훨씬 더 열에 안정하다는 것을 알 수 있었다. 따라서 칡 이소플라본의 열안정성은 콩 이소플라본과 유사하게 $140^{\circ}C$ 이상 열처리에 의해 가수분해반응을 보였고, 이소플라본의 중간 유도체들과 aglycone이 $140^{\circ}C$ 이상의 열처리 시 생성되었다. 따라서 칡 이소플라본의 열 안정성은 가열온도와 농도에 의해 큰 영향을 받으며, 콩 이소플라본의 열 안정성과 매우 유사한 특성을 나타내었다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2011년도 제40회 동계학술대회 초록집
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• pp.288-289
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• 2011

Indium Tin Oxide (ITO) is a typical highly Transparent Conductive Oxide (TCO) currently used as a transparent electrode material. Most widely used deposition method is the sputtering process for ITO film deposition because it has a high deposition rate, allows accurate control of the film thickness and easy deposition process and high electrical/optical properties. However, to apply high quality ITO thin film in a flexible microelectronic device using a plastic substrate, conventional DC magnetron sputtering (DMS) processed ITO thin film is not suitable because it needs a high temperature thermal annealing process to obtain high optical transmittance and low resistivity, while the generally plastic substrates has low glass transition temperatures. In the room temperature sputtering process, the electrical property degradation of ITO thin film is caused by negative oxygen ions effect. This high energy negative oxygen ions(about over 100eV) can be critical physical bombardment damages against the formation of the ITO thin film, and this damage does not recover in the room temperature process that does not offer thermal annealing. Hence new ITO deposition process that can provide the high electrical/optical properties of the ITO film at room temperature is needed. To solve these limitations we develop the Magnetic Field Shielded Sputtering (MFSS) system. The MFSS is based on DMS and it has the plasma limiter, which compose the permanent magnet array (Fig.1). During the ITO thin film deposition in the MFSS process, the electrons in the plasma are trapped by the magnetic field at the plasma limiters. The plasma limiter, which has a negative potential in the MFSS process, prevents to the damage by negative oxygen ions bombardment, and increases the heat(-) up effect by the Ar ions in the bulk plasma. Fig. 2. shows the electrical properties of the MFSS ITO thin film and DMS ITO thin film at room temperature. With the increase of the sputtering pressure, the resistivity of DMS ITO increases. On the other hand, the resistivity of the MFSS ITO slightly increases and becomes lower than that of the DMS ITO at all sputtering pressures. The lowest resistivity of the DMS ITO is $1.0{\times}10-3{\Omega}{\cdot}cm$ and that of the MFSS ITO is $4.5{\times}10-4{\Omega}{\cdot}cm$. This resistivity difference is caused by the carrier mobility. The carrier mobility of the MFSS ITO is 40 $cm^2/V{\cdot}s$, which is significantly higher than that of the DMS ITO (10 $cm^2/V{\cdot}s$). The low resistivity and high carrier mobility of the MFSS ITO are due to the magnetic field shielded effect. In addition, although not shown in this paper, the roughness of the MFSS ITO thin film is lower than that of the DMS ITO thin film, and TEM, XRD and XPS analysis of the MFSS ITO show the nano-crystalline structure. As a result, the MFSS process can effectively prevent to the high energy negative oxygen ions bombardment and supply activation energies by accelerating Ar ions in the plasma; therefore, high quality ITO can be deposited at room temperature.

• 한국전기전자재료학회논문지
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• 제37권5호
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• pp.500-506
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• 2024

The transparent electrode characteristics of the SnO₂/AgNi/SnO₂ (OMO) multilayer structures prepared by sputtering were investigated according to the annealing temperature. Ni-doped Ag of various compositions was selected as the metal layer and heat treatment was performed at 100~300℃ to evaluate the thermal stability of the metals. The manufactured OMO multilayer structures were heat treated for 6 hours at 400~600℃ in an N₂ atmosphere. The structural, electrical, and optical properties of the OMO structures before and after annealing were evaluated and analyzed using a UV-VIS spectrophotometer, 4-point probe, XPS, FE-SEM, etc. OMO with Ni-doped Ag shows improved performance due to the reduction of structural defects of Ag during annealing, but OMO structure with pure Ag shows degradation characteristics due to Ag diffusion into the oxide layer during high-temperature annealing. The figure of merit (FOM) of SnO₂/Ag/SnO₂ was highest at room temperature and gradually decreased as the heat treatment temperature increased. On the other hand, the FOM value of SnO₂/AgNi/SnO₂ mostly showed its maximum value at high temperature(~550℃). In particular, the FOM value of SnO₂/Ag-Ni (3.2 at%)/SnO₂ was estimated to be approximately 2.38×10^-2 Ω^-1. Compared to transparent electrodes made of other similar materials, the FOM value of the SnO₂/Ag-Ni (3.2 at%)/SnO₂ multilayer structure is competitive and is expected to be used as an alternative transparent conductive electrode in various devices.

• 한국정밀공학회지
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• 제20권5호
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• pp.218-224
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• 2003

This paper describes a novel MEMS integration technique on a CMOS chip. MEMS integration on CMOS circuit has many advantages in view of manufacturing cost and reliability. The surface topography of a CMOS chip from a commercial foundry has 0.9 ${\mu}{\textrm}{m}$ bumps due to the conformal coating on aluminum interconnect patterns, which are used for addressing each MEMS element individually. Therefore, it is necessary to achieve a flat mirror-like CMOS chip fer the microelectromechanical system (MEMS) such as micro mirror array. Such CMOS chip needs an additional thickness of the dielectric passivation layer to ease the subsequent planarization process. To overcome a temperature limit from the aluminum thermal degradation, this study uses RF sputtering of silicon nitride at low temperature and then polishes the CMOS chip together with the surrounding dummy pieces to define a polishing plane. Planarization reduces 0.9 ${\mu}{\textrm}{m}$ of the bumps to less than 25 nm.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 1999년도 추계학술발표대회 논문집
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• pp.160-163
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• 1999

The mechanical properties and failure behaviour of carbon/phenolic composites were inverstigated by tension and compression. Carbon/phenolic composites were fabricated by infiltration of matrix into 8 harness satin woven fabric of PAN-based carbon fibers. The tensile and compressive tests were performed at 25℃ under air atmosphere and, at 400℃ and 700℃ under N₂ atmosphere. The tensile strengths of carbon/phenolic composites in with-laminar/0° warp direction were about 10 times higher than those in with-laminar/45° warp direction, which was analyzed due to a change of fracture mode from fiber pull-out by shear to tensile fracture of fibers. The fracture of carbon/phenolic composites in with-laminar/45° direction was analyzed due to delamination by buckling. Tensile and compressive strength of carbon/phenolic composites decreased to about 50% at 400℃, and to about 10% at 700℃ compared to that at room temperature. The main reason for the decrease of tensile or compressive strength with increasing temperature was analyzed due to a reduction of bond strength between fibers and matrix resulting from thermal degradation of phenolic resin.

• 환경위생공학
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• 제15권4호
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• pp.123-133
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• 2000

The kinetic analysis was carried out for commercial rubbers such as NR, IR, BR, SBR 1500, and SBR 1700. Kinetic analysis for the commercial rubbers was performed using the thermogravimetric method, with which the activation energies of NR obtained by Kissinger, Friedman, and Ozawa's method were 195.0, 198.3 and 186.3kJ/mol, whereas that of SBR 1500 were 246.4, 247.5 and 254.8kJ/mol, respectively. It was shown that the yield of pyrolytic oil was generally increased with final temperature increasing, yet slightly decreased or increased over $700^{\circ}C$. Considering the effect of heating rate, it was found that the yield of pyrolytic oil was not consistent for each sample. The number average molecular weight of SBR 1500 was in the range of 740~2486. The calorific value of SBR 1500 was 39~40kJ/g, which were made comparative study of the conventional fuel such as kerosene, diesel, light fuel, and heavy fuel. Therefore it was essential that the selection of the suitable kinetic model and the mathematical solution because of the difference in parameters obtained from each method. It was proposed that the range of $600~700^{\circ}C$ in final temperature and high heating rate due to short run time. It was suggested that the pyrolytic oil be available to use to the fuel.

• 한국수소및신에너지학회논문집
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• 제1권1호
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• pp.1-8
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• 1989

The hydriding kinetic mechanism and the change of the hydriding reaction rate of $MmNi_{4.5}Al_{0.5}$ during the thermally induced hydrogen absorption-desorption cycling are investigated. Comparison of the reaction rate data which are obtained by the pressure sweep method with the theoretical rate equations suggests that the hydriding rate controlling step has changed from the dissociative chemisorption of hydrogen molecules at the surface to the hydrogen diffusion through the hydride phase with the increase of the hydriding fraction. These hydriding kinetic mechanism is not changed during the cycling. However, the intrinsic hydriding reaction rate of $MmNi_{4.5}Al_{0.5}$ after 5500 cycles increases significantly comparing with the activated one. It is suggested that the change of the hydriding kinetic behavior due to intrinsic degradation of $MmNi_{4.5}Al_{0.5}$ can be interpreted as follows ; the formation of nickel cluster at the surface of the sample and the host metal atom exchange in bulk by thermal cycling.