• The Korean Journal of Ceramics
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• 제4권1호
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• pp.43-46
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• 1998

We have investigated the formation and thermal stability of cobalt aluminide(CoAl) thin films on GaAs. In order to obtain cobalt-aluminide thin films, we deposited a multilayer of Co/Al on GaAs, and subsequently annealed the samples at 80$0^{\circ}C$ for 30 min. After annealing, single-phase cobalt aluminide was produced showing a flat and uniform interface with GaAs. which indicates that cobalt aluminide (CoAl) is thermally stable with GaAs. In addition, the adherence and mechanical properties of the as-deposited, and annealed Co/Al multilayer structure on GaAs are compatible with those required for device fabrication processes. The electrical property of the CoAl/GaAs contact shows rectifying characteristics, indicating that the diodes were usable as rectifying gate electrodes.

• 한국광학회지
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• 제32권5호
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• pp.230-234
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• 2021

열응력 완화 기술은 고출력 레이저 다이오드의 빔의 품질과 안정성을 향상시키기 위한 주요 요소기술로 큰 주목을 받고 있다. 본 연구에서는 레이저 다이오드 바(LD-bar) chip-on-submount (CoS)에 발생하는 열응력 분포 양상을 SolidWorks 소프트웨어를 사용하여 해석하고, 마이크로-홈 구조 도입에 따라 열응력 완화에 미치는 영향을 체계적으로 분석한다. 마이크로-홈 구조는 누적응력을 차단하는 효과가 있는 반면, 열흐름을 방해하는 역기능도 있으므로, 시스템 구조와 방열금속판 두께에 따라 홈 깊이를 최적화할 필요가 있다. 간단히 도입된 예시구조에 대하여, LD-bar CoS의 칩 홀더 금속판에 도입하는 마이크로-홈 구조 최적화를 통해 칩 전면부 표면 응력을 마이크로-홈 구조가 없는 경우의 약 1/5 정도로 낮추었다. 향후 초고출력 시스템에서 방열을 위한 열저항과 광출력 빔크기를 최소한으로 유지하면서, 열응력을 효과적으로 완화시키는 구조로 활용이 기대된다.

• 한국초전도ㆍ저온공학회논문지
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• 제24권4호
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• pp.78-83
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• 2022

REBCO coated conductors are widely used for HTS power application, high magnetic field magnet application, and etc. A thermal stability of the REBCO conductor is essential for the operation of HTS-based device, and thermal conductivities of the conductor are relevant parameters for modeling cryogenic heat transfer. REBCO conductors consist of a REBCO layer, copper layers for electrical stabilization and a hastelloy substrate. At cryogenic temperature, thermal conductivity of copper and silver strongly depend on the purity of the material and the intensity of the magnetic field. In this study, thermal conductivities of the laminated composite structure of REBCO conductor are evaluated by using the thermal network model and the multidimensional heat conduction analysis. As a result, the thermal network model is applicable to REBCO conductors configured in series or parallel alone and multidimensional heat conduction analysis is necessary for complex cases of series and parallel configuration.

• Journal of Magnetics
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• 제9권1호
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• pp.13-16
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• 2004

Magnetic tunnel junctions (MTJs) comprising amorphous CoNbZr layers have been investigated. $Co_{85.5}Nb_8Zr_{6.5}$(in at. %) layers were employed to substitute the traditionally used Ta layers with an emphasis given on under-standing underlayer effect. The typical junction structure was $SiO_2/CoNbZr$ or Ta 2/CoFe 8/IrMn 7.5/CoFe 3/Al 1.6 + oxidation/CoFe 3/CoNbZr or Ta 2 (nm). For both as-deposited state and after annealing, the CoNbZr-underlayered structure showed superior surface smoothness up to the tunnel barrier than Ta-underlayerd one (rms roughness of 0.16 vs. 0.34 nm). CoNbZr-based MTJs was proven beneficial for increasing thermal stability and increasing $V_h$ (the bias voltage where MR ratio becomes half) characteristics than Ta-based MTJs. This is because the CoNbZr-based junctions offer smoother interface structure than the Ta-based one.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2004년도 추계학술대회 논문집 Vol.17
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• pp.45-48
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• 2004

본 논문은 니켈실리사이드 (Ni-Silicide)의 열안정성을 개선하기 위해서 Ti와 TiN capping 층을 이용한 새로운 구조 Ni/Ti/Ni/Tin 구조를 제안하였다. 계면특성과 열안정성을 향상시키기 위해 타이타늄(Ti)을 니켈(Nickel) 사이에 적용하고, 니켈 실리사이드 형성 시 산소와의 반응을 억제하여 실리사이드의 응집현상을 개선시키고자 TiN capping을 적용 하였다. 니켈 실리사이드의 형성온도에 따른 $NiSi_2$로의 상변이를 억제할 수 있었고, 열안정성 평가를 위한 $700^{\circ}C$, 30분간 고온 열처리에서도 제안한 구조로 니켈실리사이드의 단면특성과 19 % 정도 면저항 특성을 개선하였다.

• BMB Reports
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• 제33권3호
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• pp.268-275
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• 2000

In contrast to the pyrimidine (6-4)pyrimidone photoproduct [(6-4) adduct], its Dewar valence isomer (Dewar product) is low mutagenic and produces a broad range of mutations with a 42 % replicating error frequency. In order to determine the origin of the mutagenic property of the Dewar product, we used experimental NMR restraints and molecular dynamics to determine the solution structure of a Dewar·lesion DNA decamer duplex, which contains a mismatched base pair between the 3'-T residue and an opposed G residue. The 3'-T of the Dewar lesion forms stable hydrogen bonds with the opposite G residue. The helical bending and unwinding angles of the DW/GA duplex, however, are much higher than those of the DW/AA duplex. The stable hydrogen bonding of the G 15 residue does not increase the thermal stability of the overall helix. It also does not restore the distorted backbone conformation of the DNA helix that is caused by the forming of a Dewar lesion. These structural features implicate that no thermal stability, or conformational benefits of G over A opposite the 3'-T of the Dewar lesion, facilitate the preferential incorporation of an A. This is in accordance with the A rule during translesion replication and leads to the low frequent $3'-T{\rightarrow}C$ mutation at this site.

• 열처리공학회지
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• 제7권1호
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• pp.3-10
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• 1994

The structure and mechanical properties of the extruded specimens were investigated in rapid solidified Al-(1, 3, 5) Cr alloys after mechanical alloying. Finer lamellar microstructure could no longer be resolved in the bars obtained by extrusion of the spherical particles after 200 min. of processing time. The structure of extruded bars are highly depended on the processing time of splats. The isothermal annealing of the extruded bars showed that all the alloys had good thermal stability up to $400^{\circ}C$ and did not show the recrystallization phenomena. Severe working of Al-(1, 3, 5) Cr splats produced a very fine grain size and substructural strengthening (high dislocation density and fine grain size). Effects of mechanical alloying on the thermal stability of the extruded bars Al-(1, 3, 5) Cr alloys decreases, with increasing Cr content. But the ultimate tensile Strength in the extruded bars increases with increasing Cr content.

• Macromolecular Research
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• 제15권2호
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• pp.185-190
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• 2007

Poly(norbornene dimethyl dicarboxylate)s, (PNDMD)s, were prepared by addition polymerization with palladium(II) catalyst from pure exo-monomers, and their structure and properties were compared with those of poly(norbornene dicarboxylic acid dialkyl ester)s, (PNDADA)s. Both polymer series exhibited good solubility in general organic solvents and excellent thermal stability up to $330^{\circ}C$. Wide-angle X-ray scattering (WAXS) study indicated the presence of nano-scale layer-like order in amorphous PNDADAs, while PNDMDs showed random amorphous structure. The glass transition temperatures and dielectric constants of solid polymers were found to decrease as the alkyl side-chain length increases for both polymer series. However, PNDMDs showed lower glass transition temperatures and higher dielectric constants, as compared with those of PNDADAs containing the same alkyl substituents. This difference, caused by the higher side-group mobility of PNDMDs, may be closely related to the nano-scale order in amorphous PNDADAs and its absence in PNDMDs.

• 한국산업융합학회 논문집
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• 제23권6_1호
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• pp.881-888
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• 2020

A butterfly valve is a valve that adjusts flow rate by rotating a disc for about 90° with respect to the axis that is perpendicular to the flow path from the center of its body. This valve can be manufactured for low-temperature, high-temperature and high-pressure conditions because there are few restrictions on the used materials. However, the development of valves that can be used in a 600℃ environment is subject to many constraints. In this study, the butterfly valve's stability was evaluated by a fluid-structured interaction analysis, thermal-structure interaction analysis, and seismic analysis for the development of valves that can be used in high-temperature environments. When the reverse-pressure was applied to the valve in the structural analysis, the stress was low in the body and seat compared to the normal pressure. Compared with the allowable strength of the material for the parts of the valve system, the minimum safety factor was approximately 1.4, so the valve was stable. As a result of applying the design pressures of 0.5 MPa and 600℃ under the load conditions in the thermal-structural analysis, the safety factor in the valve body was about 3.4 when the normal pressure was applied and about 2.7 when the reverse pressure was applied. The stability of the fluid-structure interaction analysis was determined to be stable compared to the 600℃ yield strength of the material, and about 2.2 for the 40° open-angle disc for the valve body. In seismic analysis, the maximum value of the valve's stress value was about 9% to 11% when the seismic load was applied compared to the general structural analysis. Based on the results of this study, the structural stability and design feasibility of high-temperature valves that can be used in cogeneration plants and other power plants are presented.

• 한국세라믹학회지
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• 제53권6호
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• pp.689-699
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• 2016

The effects of composition, structure design, and coating thickness of thermal barrier coating (TBC) on thermal barrier performance were investigated by measuring the temperature differences of TBC samples. TBCs with the thin and thick top coats were used for these studies, including TBCs with rare-earth (Gd, Yb, and La) compositions. The thermal barrier performance was enhanced with increasing the thickness of top coat even for thin TBCs, indicating that the thermal barrier performance was commensurate to the thickness of top coat. On the other hand, the bi-layered TBC, which was prepared with Yb-Gd-YSZ feedstock powder, with the buffer layer of high purity 8YSZ showed a better thermal barrier performance than that of regular purity 8YSZ. The interfaces in the bi-layered TBCs had a decisive effect on the thermal barrier performance, showing the performance enhanced with increasing numbers of interfaces. However, a new structural design and an additional process should be considered to reduce stress concentrations and to ensure interface stability, respectively, for improving thermal durability in the multi-layered TBCs.