• Korean Journal of Materials Research
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• v.8 no.11
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• pp.1067-1073
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• 1998

High quality diamond films of the silicon on diamond (SOD) structure are deposited using CO and $H_2$ gas mixture in microwave plasma chemical vapor deposition (CVD), a SOD structure is fabricated using low pressure CVD polysilicon on diamond/ Si(100) substrate. The crystalline structure of the diamond films which composed of { 111} and {100} planes. were changed from octahedral one to cubo-octahedron one as the CO/$H_2$ ratios are increased. The high quality diamond films without amorphous carbon and non-diamond elements were deposited at the CO/$H_2$ flow rate of 0.18. and the main phase of the diamond films shows (111) plane. The diamond/Si(lOO) structure shows that the interface is flat without voids. The measured dielectric constant. leakage current and breakdown field were $5.31\times10^{-9}A/cm^2$ and $9\times{10^7}{\Omega}cm$ respectively.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.4
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• pp.70-75
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• 2006

The performance of a turbopump system composed of an inducer, an impeller, a volute and seals has been computationally analyzed. To save the computational time, only one flow passage of the inducer and impeller is considered for the computations. A steady mixing-plane method is used on the impeller/volute interface for simulating the unsteady interaction phenomena. The axial thrust is predicted from the turbopump calculation in its entirety, which is necessary for such estimation. Moreover, the effects of each component on the pump performance are investigated at a design condition through the analysis of flow structures. The predicted performance is in good agreement with experimental data in terms of head rise, efficiency and volute wall pressure distributions despite of highly complex flow structures being present. The computational results also show that the axial and radial thrusts are within the design limit although corresponding experimental measurements were not taken.

• Journal of the Korean Vacuum Society
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• v.16 no.5
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• pp.348-352
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• 2007

In submicron processes, the feature size of ULSI devices is critical, and it is necessary both to reduce the RC time delay for device speed performance and to enable higher current densities without electromigration. In case of contacts between semiconductor and metal in semiconductor devices, it may be very unstable during the thermal annealing process. To prevent these problems, we deposited tungsten carbon nitride (W-C-N) ternary compound thin film as a diffusion barrier for preventing the interdiffusion between metal and semiconductor. The thickness of W-C-N thin film is $1,000{\AA}$ and the process pressure is 7mTorr during the deposition of thin film. In this work we studied the interface effects W-C-N diffusion barrier using the XRD and 4-point probe.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.10
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• pp.1229-1235
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• 2011

Fatigue tests were conducted on the aluminum alloy, A7075-T6 to determine the most reliable fretting fatigue damage parameter. Specimens with grooves were used, so that either fretting fatigue crack at the pad/specimen interface or plain fatigue crack at the groove could be nucleated, depending on the pad pressure. Both the crack nucleation location and initial crack orientation were examined using optical microscopy, and the results were used to assess the reliability of the various fretting fatigue damage parameters that have been most commonly used in the literature. Finite element analysis was employed to obtain the stress and strain data of the specimen, which were needed to estimate the parameter values and the orientation of the critical plane. It was revealed that both the Fatemi.Socie and McDiarmid parameters, which assume shear-mode fatigue cracking, are the most reliable.

• Journal of Sensor Science and Technology
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• v.5 no.1
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• pp.43-50
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• 1996

This paper presents a manufacture of the multiple subjects biotelemetry system using custom CMOS IC fabricated $1.5{\mu}m$ n-well process technology. The implantable circuits of the system except sensor interface circuits including FM transmitter are fabricated on a single chip with the sire of $4{\times}4mm^{2}$. It is possible to assemble the implantable system in a hybrid package as small as $3{\times}3{\times}2.5cm$ by using this chip, It's main function is to enable continuous measurement simultaneously up to 7-channel physiological signals from the selected one among 8 subjects. Another features of this system are to enable continuous measurement of physiological signals, and to accomplish ON/OFF switching of an implanted battery by subject selection signal with command signal from the external circuit. If this system is coupled with another appropriate sensors in medical field, various physiological parameters such as pressure, pH and temperature are to be measured effectively in the near future.

• Journal of the Korean institute of surface engineering
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• v.48 no.4
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• pp.158-162
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• 2015

To substitute indium tin oxide (ITO), many substituents have been studied such as metal nanowires, carbon based materials, 2D materials, and conducting polymers. These materials are not good enough to apply to an electrode because theses exhibit relatively high resistance. So metal grids are required as an additionalelectrode to improve the conductivities of substituents. The metal grids were printed by electrohydrodynamic printing system using Ag nanoparticle based ink. The Ag grids showed high uniformity and the line width was about $10{\mu}m$. The Ag nanoparticles are surrounded by dispersants such as unimolecular and polymer to prevent aggregation between Ag nanoparticles. The dispersants lead to low conductivity of Ag grids. Thus, the sintering process of Ag nanoparticles is strongly recommended to remove dispersants and connect each nanoparticles. For sintering process, the interface and microstructure of the Ag grid were controlled in 1.0 torr Ar atmosphere at aound $400^{\circ}C$ of temperature. From the sintering process, the uniformity of the Ag grid was improved and the defects on the Ag grids were reduced. As a result, the resistivity of Ag grid was greatly reduced up to $5.03({\pm}0.10){\times}10^{-6}{\Omega}{\cdot}cm$. The metal grids embedded substrates containing low pressure Ar sintered Ag grids showed 90.4% of transmittance in visible range with $0.43{\Omega}/{\square}$ of sheet resistance.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.43 no.11
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• pp.1008-1015
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• 2015

Thermal vacuum test should be performed prior to launch to verify satellites' functionality in extremely cold/hot temperatures and vacuum conditions. A thermal vacuum chamber used to perform the thermal vacuum tests of a satellite system and its components. A cryogenic blower is a core component of the gaseous nitrogen (GN2) closed loop thermal control system for thermal vacuum chambers. A final goal of this research is development of cryogenic blower. Design requirements of a blower are 150 CFM flow rate, 0.5 bara pressure difference, hot and cold temperatures. This paper describes the performance analysis of impeller by 1D, CFD commercial software, the design of the thermal protection interface between the driving part and the fluid part. The performance of the cryogenic blower is confirmed by test at the standard air condition and is verified by on the thermal vacuum chamber at the real operating condition.

• The KSFM Journal of Fluid Machinery
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• v.18 no.3
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• pp.38-45
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• 2015

In this study, two computational methodologies were compared to consider an effective conjugate heat transfer analysis technique for the cooled vane with thermal barrier coating. The first one is the physical modeling method of the TBC layer on the vane surface, which means solid volume of the TBC on the vane surface. The second one is the numerical modeling method of the TBC layer by putting the heat resistance interface condition on the surface between the fluid and solid domains, which means no physical layer on the vane surface. For those two methodologies, conjugate heat transfer analyses were conducted for the cooled vane with TBC layer having various thickness from 0.1 mm to 0.3 mm. Static pressure distributions for two cases show quite similar patterns in the overall region while the physical modeling shows quite a little difference around the throat area. Thermal analyses indicated that the metal temperature distributions are quite similar for both methods. The results show that the numerical modeling method can reduce the computational resources significantly and is quite suitable method to evaluate the overall performance of TBC even though it does not reflect the exact geometry and flow field characteristics on the vane surface.

• Nuclear Engineering and Technology
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• v.48 no.4
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• pp.1009-1014
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• 2016

SiC-based ceramic composites are currently being considered for use in fuel cladding tubes in light-water reactors. The joining of SiC ceramics in a hermetic seal is required for the development of ceramic-based fuel cladding tubes. In this study, SiC monoliths were diffusion bonded using a Ti foil interlayer and additional Si powder. In the joining process, a very low uniaxial pressure of ~0.1 MPa was applied, so the process is applicable for joining thin-walled long tubes. The joining strength depended strongly on the type of SiC material. Reaction-bonded SiC (RB-SiC) showed a higher joining strength than sintered SiC because the diffusion reaction of Si was promoted in the former. The joining strength of sintered SiC was increased by the addition of Si at the Ti interlayer to play the role of the free Si in RB-SiC. The maximum joint strength obtained under torsional stress was ~100 MPa. The joint interface consisted of $TiSi_2$, $Ti_3SiC_2$, and SiC phases formed by a diffusion reaction of Ti and Si.

• Nuclear Engineering and Technology
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• v.50 no.1
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• pp.116-125
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• 2018

Modified 9Cr-1Mo ferritic steel is a preferred material for steam generators in nuclear power plants for their creep strength and good corrosion resistance. Austenitic stainless steels, such as type 316LN, are used in the high temperature segments such as reactor pressure vessels and primary piping systems. So, the dissimilar joints between these materials are inevitable. In this investigation, dissimilar joints were fabricated by the Shielded Metal Arc Welding (SMAW) process with Inconel 82/182 filler metals. The notch tensile properties and Charpy V-notch impact toughness properties of various regions of dissimilar metal weld joints (DMWJs) were evaluated as per the standards. The microhardness distribution across the DMWJs was recorded. Microstructural features of different regions were characterized by optical and scanning electron microscopy. Inhomogeneous notch tensile properties were observed across the DMWJs. Impact toughness values of various regions of the DMWJs were slightly higher than the prescribed value. Formation of a carbon-enriched hard zone at the interface between the ferritic steel and the buttering material enhanced the notch tensile properties of the heat-affected-zone (HAZ) of P91. The complex microstructure developed at the interfaces of the DMWJs was the reason for inhomogeneous mechanical properties.