• The Journal of the Acoustical Society of Korea
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• v.20 no.6
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• pp.66-74
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• 2001

The temperature measurement of yen high temperature core melt is of importance in LAVA (Lower-plenum Arrested Vessel Attack) experiment in which gap formation between core melt and the reactor lower head, and the effect of the gap on thermal behavior are to be measured. The delay time of ultrasonic wavelets due to high temperature is suggested. As a first stage, a molten material temperature was measured up to 2300℃. Also, the optimization design of the ultrasonic temperature sensor with persistence at the high temperature was suggested in this paper. And the utilization of the theory suggested in the reference〔1〕and the efficiency of the developed system are certified by performing experiments. This sensor welded magnetostrictive element and tungsten element will be able to measure a temperature range of 3000℃ hereafter.

• Transactions of Materials Processing
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• v.9 no.4
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• pp.395-403
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• 2000

Formation of Shear Band under the adiabatic condition is widely observed In the engineering materials during rapidly forming process lot a thermally rate-dependent material. The shear band stems from evolution of a narrow region in which an intensive plastic flow occurs. The shear band often plays a role of a precursor of the ductile fracture during a forming process. The objective of this study is to investigate the localization behavior using numerical method. In this work, the implicit finite difference scheme is employed due to the ease of convergence and the numerical stability It is noted that physical and mechanical properties of materials determine how the shear band is formed and then localized. Material properties can be characterized with inertia number dissipation number and diffusion number. It is observed that the dimensionless numbers effect on localization. Using a parametric study, comparison was made between CRS-1018 steel with WHA (tungsten heavy alloy). The deformation behavior of material in this study include an isotropic hardening as well as thermal softening. Moreover, this study suggests that a kinematic hardening constitutive relation be required to predict a more accurate strain level at a shear band.

• Journal of Welding and Joining
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• v.33 no.1
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• pp.41-48
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• 2015

In this study, the effect of heat input on weld metal microstructure and the effects of dissimilar weld heat affected zone in quenched and tempered ASTM A517 on the stainless steel AISI 316L is investigated through the optimization of welding parameters. For this purpose, two welding techniques are used, tungsten-conventional gas and pulsed gas with weld wire ER 309MoL with Diameter 2.4 mm. Research showed that the grain size of the heat affected zone in pulsed welding is less compared with conventional welding; weld metal structure is fully austenitic, it has a finer structure in the pulsed method. Additionally, the growth of weld metal adjacent steel A517 is different from steel 316L. Further, investigation showed that the rate of dilution is less in the pulsed method and the impact energy is increased in each three regions of the weld metal and heat affected zones in the pulsed method; the fracture in the weld metal and heat affected zone of steel 316L is quite soft and it is semi-crispy in the heat affected zone of steel A517.

• Journal of Welding and Joining
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• v.33 no.1
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• pp.49-53
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• 2015

An experimental study was conducted to investigate the effect of carbon nanotubes on the zinc corrosion resistance of sealing layer formed on the Tungsten Carbide spray coating. Using the nanotubes, a sealing agent in the form of solid-liquid suspensions was made and applied to the surface of spray coating. A series of experiments, consisted of three stages such as preparation of test piece, molten-pot immersion test, and evaluation of micro structure, were undertaken to demonstrate complicated interaction existing between zinc ions and sealing layer containing the nanotubes. Experimental results showed newly developed sealing layer were less susceptible to corrosion and thus coated layer was well protected even in the case of 10 days exposure. Comparison of the micro structure after molten pot test also indicated that carbon nanotubes still remained in the matrix and organized more reliable frame work constituted with boron nitride and chromium compound. It was revealed that carbon nanotubes in the sealing layer played positive role to enhance zinc corrosion resistance in the perspective of both fibrous structure and inherent chemical stability.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2018.06a
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• pp.49.2-49.2
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• 2018

스퍼터링에 의해 증착된 박막 내 기계적 응력 발생 현상을 규명하기 위하여 활발한 이론적, 실험적 접근이 있었으나, 복잡한 플라즈마 증착환경 내에서 다양한 증착 파라미터로 인해 정확한 응력 발생 메커니즘에 대해 아직도 완벽한 규명이 되지 않은 상황이다. 본 연구에서는 몰리브데늄 (Mo)과 텅스텐 (W) 박막을 마그네트론 스퍼터링법을 이용하여 증착 시 발생하는 잔류응력 발생 현상에 대해 논의하겠다. Mo 박막의 경우 증착압력을 2.5 mTorr와 4.1 mTorr로 고정시킨 채 기판 바이어스를 0-250 V 간격으로 변화시킨 결과, 2.5 mTorr에서는 기판바이어스가 증가할수록 압축응력이 증가하는 반면 4.1 mTorr에서는 기판바이어스가 증가할수록 인장응력이 증가하는 것이 확인되었다. 이러한 반대 경향의 잔류응력을 발생시키는 기판 바이어스 효과를 확인하기 위하여 증착 파라미터 변경에 따른 박막 성장 거동 모델을 제시한다. W 박막은 준안정상인 ${\beta}$-상이 증착 초기(2.5 nm)에 형성이 되고, 증착 과정에서 열역학적 안정상인 ${\alpha}$-상으로 상변태 하였다. 상변태에 의한 부피 변화에 따른 잔류응력 발생의 분석을 위하여 X-ray 회절피크의 비대칭성을 분석한 결과 압축응력과 인장응력이 공존하고 있는 것으로 확인되었다. 본 연구결과는 스퍼터링 공정 시 높은 에너지를 가지는 중성화된 Ar과 스퍼터된 원자가 기판과 충돌 시 atomic peening effect에 의해 압축응력이 발생한다는 일반적인 이론과 상충되는 결과로서, Mo 및 W 박막 내 잔류응력 제어를 위한 방안을 제시한다.

• Journal of the Korea Safety Management & Science
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• v.1 no.1
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• pp.241-258
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• 1999

For hazardous air pollutants(HAP) such as NO and $NO_{2}$ decomposition efficiency, power consumption, and applied voltage were investigated by SPCP(surface induced discharge plasma chemical processing) reactor to obtain optimum process variables and maximum decomposition efficiencies. Decomposition efficiency of HAP with various electric frequencies(5~50 kHz), flow rates(100~1,000 mL/min), initial concentrations(100~1,000 ppm), electrode materials(W, Cu, Al), electrode thickness(1, 2, 3 mm) and number of electrode windings(7, 9, 11) were measured. Experimental results showed that for the frequency of 10 kHz, the highest decomposition efficiency of 94.3 % for NO and 84.7 % for $NO_{2}$ were observed at the power consumptions of 19.8 and 20W respectively and that decomposition efficiency decreased with increasing frequency above 20 kHz. Decomposition efficiency was increased with increasing residence times and with decreasing initial concentration of pollutants. Decomposition efficiency was increased with increasing thickness of discharge electrode and the highest decomposition efficiency was obtained for the electrode diameter of 3 mm in this experiment. As the electrode material, decomposition efficiency was in order : tungsten(W), copper(Cu), aluminum(Al).

• Journal of Welding and Joining
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• v.25 no.5
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• pp.64-71
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• 2007

The aim of this paper is to investigate the effects of welding parameters on the weld shape in seal-welding of STS304L capsule for manufacturing a radioisotope source which is widely used in nondestructive testing of metal structures using gamma ray. Pulsed gas tungsten arc (Pulsed GTA) welding is performed for thin cross sectional area of the capsule. Seven welding parameters including current waveform parameters and arc length etc. are selected as main process parameters using design of experiment. The weld shape such as bead width, penetration depth, weld area, aspect ratio and area rate is investigated to assess the effects of welding parameters. As results, the combination of pulse duty/welding speed largely affects on bead width, penetration depth, area and aspect ratio. Finally, it is concluded that the key parameters are the combination of pulse duty/welding speed, base current and arc length, and their optimal conditions are 50%/1.77mm/s, 6.4A and 1 mm.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.30 no.9 s.252
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• pp.1148-1153
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• 2006

This paper deals with the effect of the direct heating method(DHM) for straightening the micro wire. Straightened micro wires have been widely used in the fields of the medicine and the semi-conductor. We have developed a micro wire straightening system by using the direct wire heating method. To controling the tension of the micro wire during the heating and straightening process, a precision tension sensor was set up. In order to avoid the surface oxidation during the heating process, the argon inert gas was supplied to the vicinity of the wire. And, this paper shows the correlation between the tension and the current when arson gas supplied to the tungsten wire. Through several experiments, the optimal tension and current were found. Also, higher straightness $({\approx}1{\mu}m/1000{\mu}m)$ and roundness$(<{\Phi}{\pm}2{\mu}m/100{\mu}m)$ founded when $500{\mu}600gf$ tension and 1.5 ampere.

• Electrical & Electronic Materials
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• v.8 no.6
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• pp.737-743
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• 1995

Two step RTD(Rapid Thermal Diffussion) of P into silicon wafer using tungsten halogen lamp was used to fabricated very shallow n$^{+}$p junction. 1st RTD was performed in the temperature range of 800.deg. C for 60 see and the heating rate was in the 50.deg. C/sec. Phosphrous solid source was transfered on the silicon surface. 2nd RTD process was performed in the temperature range 1050.deg. C, 10sec. Using 2 step RTD we can obtain a shallow junction 0.13.mu.m in depth. After RTD, the Ti-silicide process was performed by the two step RTA(Rapid Thermal Annealing) to reduced the electric resistance and to improve the n$^{+}$p junction diode. The titanium thickness was 300.angs.. The condition of lst RTA process was 600.deg. C of 30sec and that of 2nd RTA process was varied in the range 700.deg. C, 750.deg. C, 800.deg. C for 10sec-60sec. After 2 step RTA, sheet resistance was 46.ohm../[]. Ti-silicide n+p junction diode was fabricated and I-V characteristics were measured.red.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.29 no.1
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• pp.50-57
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• 2016

Transmission equipment is mainly used for the XLPE (cross-linked polyethylene) insulation cable for ultra high voltage power to minimize power loss. The experiment examined the partial discharge characteristics according to the insertion of the bar electrode and needle electrode into the XLPE specimen and the air voids. XLPE insulation cable manufactured by T. company and tungsten electrode material by K. company were used for specimens, by adhering conductive tape on the semi-conductive material of the lower electrode of XLPE specimen with the dimension of $16{\times}40{\times}30$ [mm] was used as negative electrode. In order to investigate the PD with ${\phi}$-q-n of XLPE specimen according to the electrode shape and the size of air voids. we examined the PD by varying the voltage after applying voltage of 3~20 kV on the electrode. Therefore, it was confirmed from the result of PD characteristics of specimen that the larger the air void than the gap between electrode (+) and electrode(-), the larger effect on the discharge when the bar electrode and needle electrode inserted into XLPE, and the closer the distance between the insulation and the needle electrode, the faster insulation breakdown.