• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2004년도 하계학술대회 논문집 Vol.5 No.1
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• pp.433-436
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• 2004

In this paper, we studied on the electrical safety evaluations of transformer insulation cover. In order to take preventive measures against an electric shock disaster in 22.9kV transformer installation, we put the insulation cover on a transformer charging parts. It needs to be designed so that the insulation covers have superior properties such as, arc-resistance, weather-resistance and heat-resistance, because they are used until the damage and destruction occur. To establish the protection cover to reduce the electrical shock, we analyzed damage mechanism and risk factors which happened by structural fault of an insulation cover in this paper. Also, based on the experimental results, we are planing to suggest new improved insulation cover models.

• 한국재료학회지
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• 제29권1호
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• pp.7-10
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• 2019

Cr-Al alloys are attracting attention as oxidation resistant coating materials for high temperature metallic materials due to their excellent high temperature stability. However, the mechanical properties and oxidation resistance of Cr-Al alloys can be further enhanced, and such attempts are made in this study. To improve the properties of Cr-Al alloys, Si is added up to 5 wt%. Casting specimens with different amounts of Si content are prepared by a vacuum arc remelting method and isothermally heated under steam conditions at $1,100^{\circ}C$ for 1 hour. The as-cast microstructure of low Si alloys is mainly composed of only a Cr phase, while $Al_8Cr_5$ and $Cr_3Si$ phases are also observed in the 5 % Si alloy. In the high Si alloy, only Cr and $Cr_3Si$ phases remain after the isothermal heating at $1,100^{\circ}C$. It is found that Si additions slightly decrease the oxidation resistance of the Cr-Al alloy. However, the microhardness of the Cr-Al alloy is observed to increase with an increasing Si content.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2003년도 추계학술발표회초록집
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• pp.134-135
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• 2003

The dental implant materials required good mechanical properties, such as fatigue strength, combined with a high resistance to corrosion. For increasing fatigue resistance and delaying onset of stress corrosion cracking, shot peening has been used for > 50 years to extend service life of metal components. However, there is no information on the electrochemical behavior of shot peened and hydroxyapatite(HA) coated Ti-6Al-4V alloys. To increase fatigue strength, good corrosion resistance, and biocompatibility, the electrochemical characteristics of Ti/TiN/HA coated and shot peened Ti-6Al-4V alloys by electron beam physical vapor deposition(EB-PVD) have been researched by various electrochemical method in 0.9%NaCl. Ti-6Al-4V alloys were prepared under the condition of hydrogen and vacuum arc furnace. The produced materials were quenched at 1000$^{\circ}C$ under high purity dried Ar atmosphere and were hold at 500$^{\circ}C$ for 2 hrs to achieve the fatigue strength(1140㎫) of materials. Ti-6Al-4V alloys were prepared under the condition of hydrogen and vacuum arc furnace. Shot peening(SP) and sand blasting treatment was carried out for 1, 5, and 10min. On the surface of Ti-6Al-4V alloys using the steel balls of 0.5mm and alumina sand of 40$\mu\textrm{m}$ size. Ti/TiN/HA multilayer coatings were carried out by using electron-beam deposition method(EB-PVD) as shown Fig. 1. Bulk Ti, powder TiN and hydroxyapatite were used as the source of the deposition materials. Electrons were accelerated by high voltage of 4.2kV with 80 - 120mA on the deposition materials at 350$^{\circ}C$ in 2.0 X 10-6 torr vacuum. Ti/TiN/HA multilayer coated surfaces and layers were investigated by SEM and XRD. A saturated calomel electrode as a reference electrode, and high density carbon electrode as a counter electrode, were set according to ASTM GS-87. The potentials were controlled at a scan rate of 100 mV/min. by a potentiostat (EG&G Co.273A) connected to a computer system. Electrochemical tests were used to investigate the electrochemical characteristics of Ti/TiN/HA coated and shot peened materials in 0.9% NaCl solution at 36.5$^{\circ}C$. After each electrochemical measurement, the corrosion surface of each sample was investigated by SEM.

• 마이크로전자및패키징학회지
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• 제27권4호
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• pp.55-60
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• 2020

태양광 발전소에 설치된PERC 태양광 모듈 스트링-어레이는 고전압의 전위차로 인해 여전히 potential-induced degradation(PID) 열화 현상이 여전히 보고되고 있다. 이는 태양전지 모듈 커버글라스의 Na+ 이온이 태양전지 봉지재(EVA)를 투과하여 셀 표면으로 전이되고 결함이 많이 분포되어 있는 ARC(SiOx/SiNx) 계면에 양전하가 축적됨으로써 shunt-Resistance(Rsh)가 감소되고 누설전류량이 증가되어 태양전지 출력이 저하되는 현상이다. 본 연구에서는 이를 방지하기 위해 나노임프린트 리소그래피(nano-imprint lithography, NIL) 방식을 이용하여 모스아이(Moth-eye) 나노 구조를 광학 필름 후면에 증착 하였고, 이를 커버글라스와 EVA 사이에 삽입하여 태양광 미니 모듈을 구성하였다. PID 열화 현상을 확인하기 위해 IEC 62804-1 규격에 기반한 셀 단위 PID 열화가속시험을 진행하였고, Light I-V, Dark I-V 분석을 통해 출력(Pmax), 효율(Efficiency), 병렬 저항(shunt resistance)을 확인하였다. 그 결과 기존의 태양전지는 초기 효율 19.76%에서 6.3% 감소하였으나 모스아이 나노 구조 광학 필름(Moth-eye film)이 적용된 태양전지는 0.6% 만 감소하여 PID 열화 현상이 방지되는 것을 확인하였고, 모스아이 나노구조를 통해 투과도가 4% 향상되어 미니 모듈 출력이 2.5% 향상되었다.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2004년도 학술대회지
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• pp.365-369
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• 2004

Recently, Inconel 625 is used widely in offshore processing piping in order to extend the maintenance tenn and improve the quality of anti-corrosion. According to the resistance to attack in various corrosive media at temperatures from $200^{\circ}C$ to aver $1090^{\circ}C$, in combination with good low- and high-temperature mechanical strength. In general, High quality weldments for this material are readily produced by commonly used processes. in recent years, the flux cored arc welding(FCAW) process is becoming more popular due to higher deposition rate and a better weld quality as compared to the shielded metal arc welding (SMAW) process, at the same time, exhibiting equally good weld metal toughness similar to the SAW process. In this study, the weldability and weldment characteristics(mechanical properties and corrosive environment) of Inconel 625 are considered in FCAW weld associated with the several weld shielding gases($80\%Ar\;+\;20\%\;CO_2,\;50\%Ar\;+\;50\%\;CO_2,\;100\%\;CO_2$) in viewpoint of welding productivity.

• Bulletin of the Korean Chemical Society
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• 제33권10호
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• pp.3349-3354
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• 2012

Understanding exoelectrogenic reactions of the bioanode is limited due to its complexity and the absence of analytics. Impedance and thermodynamics of bioanode, abiotic anode, and riboflavin-amended anode were evaluated. Activation overpotential of the bioanode was negligible compared with that of the abiotic anode. Impedance spectroscopy shows that the bioanode had much lower charge transfer resistance and higher capacitance than the abiotic anode in low frequency reaction. In high frequency reaction, the impedance parameters, however, were relatively similar between the bioanode and the abiotic anode. At open-circuit impedance spectroscopy, a high frequency arc was not detected in the abiotic anode in Nyquist plot. Addition of riboflavin induced a phase angle shift and created curvature in high-frequency arc of the abiotic anode, and it also drastically changed impedance spectra of the bioanode.

• 동력기계공학회지
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• 제8권3호
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• pp.30-35
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• 2004

In the steel making industries, the continuous casting process has been applied to the number of company because of its economical benefit. Casting rolls are utilized for frictional drive and transport of solidifying slap. Dimensional tolerances, mechanical stability and surface condition of the cast roll can affect both the surface and internal quality of the product being cast. To overcome these problems, the industry is accelerating on the rate of technology improvements. Samples were overlaid on the S45C steel by submerged arc welding process. And the hardness, wear, electrochemical corrosion and oxidation tests were carried out. Test results were that all these materials were satisfying basic requirements of caster rolls. By these results, the addition of 0.1%Nb and 0.15%V increase mechanical properties and tempering resistance by its superior carbide forming characteristics in low carbon $12{\sim}13%Cr$ martensitic stainless steels.

• 한국산학기술학회논문지
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• 제12권5호
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• pp.2019-2024
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• 2011

GMA용접 공정에서 콘택트팁의 마모가 용접비드에 미치는 영향에 대해서 연구하였다. 콘택트팁과 용접비드 사이의 연관성을 조사하기 위하여 초고속 카메라와 파형분석을 이용하여 용적이행을 관찰하였고, 저 배율의 카메라로 비드의 상태를 관찰하였다. 콘택드팁의 마모는 팁과 용접와이어 사이의 접촉 지점을 변화시켜 결과적으로 불규칙비드를 생성하였다. 이것은 마모된 콘택트팁이 용접시 용접저항의 변화를 초래하여 용접아크 불안정의 원인이 되기 때문이다.

• Journal of Welding and Joining
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• 제22권6호
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• pp.57-63
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• 2004

Fracture toughness is an important parameter in designing offshore structures to ensure resistance to fracture at various temperatures. In this study, a series of experiments is carried out to obtain fracture toughness values (CTOD) of API 2W Gr.50B, welded using FCAW(Flux Cored Arc Weld). In particular, a comparison of absorbed impact energy and CTOD values are made with respect to two different welding groove shapes; double-V-groove and double-bevel-groove. Charpy impact tests are performed for specimens sampled near the root gap, and CTOD tests are carried out for three point bending specimens having the notch at weld zone. While Charpy impact test result is determined to be a good qualitative measure of fracture toughness, no quantitative correspondence between impact absorbed energy and CTOD values was found. Based on the experiment, it is observed that double-V-groove welds give lower transition temperature than those of double-bevel-groove.

• Journal of Welding and Joining
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• 제33권3호
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• pp.68-74
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• 2015

Superduplex stainless steels are important materials to the oil and gas industry, especially for off-shore production. TIG welding of super duplex stainless steels to obtain the optimal phase balance between austenite and ferrite is mainly achieved by controlling the cooling rate and the weld chemistry. The latter depends on the filler wire chosen and the shielding gas used. If TIG welding of superduplex stainless steels is performed with argon shielding gas only, then nitrogen gets lost from the weld pool, which can result in a ferrite-rich weld metal, with an inferior corrosion resistance than parent metal. In the present study, nitrogen permeation model from the shield gas which gets into the weld metal in DCEN-TIG welding has suggested. This plasma stream model shows characteristics of permeation of nitrogen ions into the molten metal due to the strong physical effect of plasma stream which formed by the arc pressure rather than the permeation of nitrogen ions caused by electric effect.