• Corrosion Science and Technology
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• 제19권1호
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• pp.8-15
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• 2020

In this paper, the efficiency and the inhibition mechanisms of cobalt salts (cobalt nitrate and cobalt-exchange silica Co/Si) for the corrosion protection of AA2024 were investigated in a neutral aqueous solution by using the electrochemical impedance spectroscopy (EIS) and polarization curves. The experimental measurements suggest that cobalt cation plays a role as a cathodic inhibitor. The efficiency of cobalt cation was important at the concentration range from 0.001 to 0.01 M. The formation of precipitates of oxides/hydroxides of cobalt on the surface at low inhibitor concentration was confirmed by the Scanning Electron Microscopy/Energy Dispersive X-Ray Spectroscopy (SEM/EDS) analysis. EIS measurements were also conducted for the AA2024 surface covered by water-based epoxy coating comprising Co/Si salt. The results obtained from exposure in the electrolyte demonstrated the improvement of the barrier and inhibition properties of the coating exposed in the electrolyte solution for a lengthy time. The SEM/EDS analysis in artificial scribes of the coating after salt spray testing revealed the release of cobalt cations in the coating defect to induce the barrier layer on the exposed AA2024 substrate.

• 전기학회논문지
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• 제63권1호
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• pp.80-84
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• 2014

The discharge characteristics of Surface Dielectric Barrier Discharge (SDBD) reactor are investigated to find optimal driving condition with adjusting various parameter. When the high voltage with sine wave form is applied to SDBD source, successive pulsed current waveforms are observed owing to multiple ignitions through the long discharge channel and wall charge accumulation on the dielectric surface. The discharge voltage, total charge between dielectrics, mean energy and power are calculated from measured current and voltage according to electrode gap and dielectric thickness. Discharge mode transition from filamentary to diffusive glow is observed for narrow gap and high applied voltage case. However, when the diffusive discharge is occurred with high applied voltage, the actual firing voltage is always lower than that with low driving voltage. The $Si_3N_4$, $MgF_2$, $Al_2O_3$ and $TiO_2$ are considered for dielectric protection and high secondary electron emission coefficient. SDBD with $MgF_2$ shows the lowest breakdown voltage. $MgF_2$ thin film is proposed as a protection layer for low voltage atmospheric dielectric barrier discharge devices.

• Journal of Radiation Protection and Research
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• 제47권1호
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• pp.39-49
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• 2022

Background: For proper monitoring of the eye lens dose, an appropriate calibration factor of a dosimeter and information about the mean energies of X-rays are indispensable. The scattered X-ray energy spectra should be well characterized in medical practices where eye lenses of medical staffs might be high. Materials and Methods: Scattered X-ray energy spectra were experimentally derived for three different types of X-ray diagnostic and therapeutic equipment, i.e., the computed tomography (CT) scan, the angiography and the fluoroscopy. A commercially available CdZnTe (CZT) spectrometer with a lead collimator was employed for the measurement of scattered X-rays, which was performed in the usual manner. Results and Discussion: From the obtained energy spectra, the mean energies of the scattered X-rays lied between 40 and 60 keV. This also agreed with that obtained by the conventional half value layer method. Conclusion: The scattered X-rays to which medical workers may be exposed in the region around the eyes were characterized by means of spectrometry. The obtained mean energies of the scattered X-rays were found to match the flat region of the dosimeter response.

• 한국재난정보학회:학술대회논문집
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• 한국재난정보학회 2023년 정기학술대회 논문집
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• pp.221-221
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• 2023

1969년에 발간된 API521 1st edition에서는 Flare Load 저감용으로 적용되는 HIPS (High Integrity Protection System)는 모두 Pressure Safety Valve의 고장확률보다 낮은 SIL 3 (Safety Integrity Level)등급을 적용할 것을 요구하고 있다. Flare Stack 저감용 HIPS는 주로 압축기 출력압력상승, Reboiler Steam 과다주입, 전력공급중단냉각펌프고장 등에 의한 Flare 발생을 예방하기 위한 기능을 가진 SIF (Safety Instrumented Function)로 구성된다. 하지만 2007년도 발간된 API521 5th edition에서는 LOPA (Layer Of Protection Analysis) 분석을 통해 Target SIL을 도출하는 것으로 요구사항을 변경했다. 이에 따라 이번 연구에서는 Flare Load에 가장 큰 영향을 미치는 시나리오 중 대표적인 시나리오를 대상으로 HAZOP(Hazard and Operability Study)과 LOPA분석을 실시해서 Target SIL이 어떻게 도출되는지를 연구했다. Flare Stack에서 Flare를 발생시키는 대표적인 시나리오들에 대해 LOPA분석을 실시한 결과 압축기 출력압력상승은 SIL 2, Reboiler Steam 과다주입은 SIL 3, 전력공급중단은 SIL 0, 냉각펌프고장은 SIL 0로 모두가 SIL 3 가 나오지는 않았다. SIF 설계 시 Target SIL을 만족시키는 것도 중요하지만 운전 시 SIL 등급이 계속 유지되게 하지 위해 인적오류, 시스템적 고장, 하드웨어고장 등에 의해 SIF 기능불능화가 되는 것을 예방하기 위한 기능안전관리시스템 (FSMS)를 적용하는 것도 중요하다.

• 전기화학회지
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• 제3권3호
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• pp.136-140
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• 2000

용융탄산염 연료전지의 분리판 재료로 사용되는 스테인레스 스틸은 고온 용융탄산염 분위기에서 부식이 심각하여 일반적으로 표면에 알루미늄 확산막을 코팅함으로써 내식성을 향상시켜 사용하고 있다. 본 연구에서는 기존 방법에 비해 보다 경제적인 슬러리 페인팅 및 열처리에 의한 알루미늄 확산막 형성 방법을 고안하여, 스테인레스 스틸 시편 표면에 알루미늄 확산막을 코팅하고, 산화 분위기의 용융탄산염에서 부식 실험을 수행하였다. $650\~800^{\circ}C$에서 제작된 알루미늄 확산막의 두께는 $25\~80{\mu}m$였으며, 열처리 온도가 높고 열처리 시간이 증가할 수록 알루미늄 확산막의 두께가 증가하였다. 부식 실험 결과 스테인레스 스틸 316L의 용융탄산염에 대한 내식성은 알루미늄 확산막을 표면에 형성시킴으로써 크게 향상되었음을 확인하였다. 또한 분극 실험 결과 슬러리 페인팅 및 열처리 방법에 의하여 알루미늄 확산막이 형성된 시편은 기존의 IVD 및 열처리 방법에 의해 알루미늄 확산막이 제작된 시편과 유사하게 안정한 부동태 피막을 형성함으로써 스테인레스 스틸 316L의 부식을 효과적으로 억제시킴을 알 수 있었다.

• 대한환경공학회지
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• 제28권4호
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• pp.438-446
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• 2006

팔당호 경안천 하류 정체수역에서 퇴적물 인 용출 저감을 위한 capping 소재를 개발하고자 실험실 규모의 batch test를 수행하였다. 조사지역 퇴적물 평균 입도는 7.7 ${\phi}$로 매우 세립하고, 유기탄소 함량은 2.4%로 매우 높게 나타났다. 최적의 capping 소재 선정을 위한 인 용출 실험을 위해 150 L 반응기 5개에 모래층, powder-gypsum($CaSO_4{\cdot}2H_2O$), granule-gypsum, 복합층(gypsum+sand)로 capping을 한 경우와 control을 45일간 비교 평가하였다. 모래로 capping할 경우, 퇴적물로부터 용출되는 인을 약 50% 차단 가능한 것으로 나타났다. 그러나 모래층 1 cm로는 $CH_4$ gas 발생으로 인한 퇴적물의 재부유와 유기물 분해에 의한 수층 용존산소 감소(3 mg/L 이하)를 초래하는 것으로 나타났다. 따라서 모래로 capping을 할 경우에는 모래층이 더 높아져야 할 것으로 판단된다. powder-Gypsum과 granule-Gypsum은 80% 이상의 인 용출 저감 효과를 보였으나 수층 ${SO_4}^{2-}$ 농도가 증가되어 상수원보호구역에 적용하기 어려운 것으로 나타났다. 따라서 ${SO_4}^{2-}$의 용해도를 감소시키기 위해 Fe-Gypsum, $SiO_2$-gypsum 소재를 개발하였다. powder-Gypsum은 물과 결합시 경화되어 퇴적물 층위에 공극이 전혀 없는 차단막을 만들기 때문에 gypsum 층에 crack이 생길 경우, $CH_4$ gas 발생으로 인한 인 용출이 한꺼번에 일어날 수 있다. 복합층(granule-Gypsum+sand(1 cm))으로 capping을 할 경우, 인 용출 차단 효과가 높을 뿐만 아니라, ${SO_4}^{2-}$ 농도 역시 powder-Gypsum, granule-Gypsum 보다 수층으로 용출이 적어 상수원보호구역에 적합한 것으로 나타났다. Gypsum으로 capping을 할 경우, 빠른 초기속성작용(early diagenesis)과 ${SO_4}^{2-}$ 농도가 퇴적물에 충분히 공급되어 SRB(sulfate reducing bacteria)의 활성이 높아져 methanogensis의 진행을 저하시킬 수 있는 것으로 나타났다.

• Journal of Mechanical Science and Technology
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• 제16권11호
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• pp.1485-1496
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• 2002

In order to investigate the fire-induced smoke movement in a three-dimensional room with an open door, numerical and experimental study was performed. The center, wall, and corner fire plumes for various sized fires were studied experimentally in a rectangular pool fire using methanol as a fuel. The numerical results from a self-developed SMEP (Smoke Movement Estimating Program) field model were compared with experimental results obtained in this and from literature. Comparisons of SMEP and experimental results have shown reasonable agreement. As the fire strength became larger for the center fires, the air mass flow rate in the door, average hot layer temperature, flame angle and mean flame height were observed to increase but the doorway-neutral-planeheight and the steady-state time were observed to decrease. Also as the wall effect became larger in room fires, the hot layer temperature, mean flame height, doorway-neutral-planeheight and steady-state time were observed to increase. In the egress point of view considering the smoke filling time and the early spread of plume in the room space, the results of the center fire appeared to be more dangerous as compared with the wall and the corner fire. Thus it is necessary to consider the wall effect as an important factor in designing efficient fire protection systems.

• 센서학회지
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• 제11권5호
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• pp.294-300
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• 2002

In this study, we fabricated thermopile infrared sensor with floating membrane structure. Floating membrane was formed by SOI(Silicon On Insulator) structure. In SOI structure, silicon dioxide layer between top silicon layer and bottom silicon substrate was etched by HF solution, then membrane was floated over substrate. After membrane was floated, thermopile pattern was formed on membrane. By insertion of SOI technology, we could obtain thermal isolation structure easily and passivation process for sensor pattern protection was not required during fabrication process. Then, the amplifier circuit for thermopile sensor was fabricated by using $1.5{\mu}m$ CMOS process. The voltage gain of fabricated amplifier was about two hundred.

• Applied Microscopy
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• 제48권1호
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• pp.11-16
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• 2018

For Odontamblyopus lacepedii with small and turbid eyes, the gross structure and histology of the olfactory organ, which is important for its survival and protection of the receptor neuron in estuarial environment and its ecological habit, was investigated using a stereo, light and scanning electron microscopes. Externally, the paired olfactory organs with two nostrils are located identically on each side of the snout. These nostrils are positioned at the anterior tip of the upper lip (anterior nostril) and just below eyes covered with the epidermis (posterior nostril). Internally, this is built of an elongated olfactory chamber and two accessory nasal sacs. In histology, the olfactory chamber is elliptical in shape, and lined by the sensory epithelium and the non-sensory epithelium. The sensory epithelium of a pseudostratified layer consists of olfactory receptor neurons, supporting cells, basal cells and lymphatic cells. The non-sensory epithelium of a stratified layer has swollen stratified epithelial cells and mucous cells with acidic and neutral sulfomucin. From these results, we confirmed the olfactory organ of O. lacepedii is adapted to its ecological habit as well as its habitat with burrows at the muddy field with standing and murky waters.

• Advances in aircraft and spacecraft science
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• 제2권1호
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• pp.45-56
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• 2015

The attitude aerodynamic control is an important subject in the design of an aerospace plane. Usually, at high altitudes, this control is fulfilled by thrusters so that the implementation of an aerodynamic control of the vehicle has the advantage of reducing the amount of thrusters fuel to be loaded on board. In the present paper, the efficiency of a wing-flap has been evaluated considering a NACA 0010 airfoil with a trailing edge flap of length equal to 35% of the chord. Computational tests have been carried out in hypersonic, rarefied flow by a direct simulation Monte Carlo code at the altitudes of 65 and 85 km, in the range of angle of attack 0-40 deg. and with flap deflection equal to 0, 15 and 30 deg.. Effects of the flap deflection have been quantified by the variations of the aerodynamic force and of the longitudinal moment. The shock wave-boundary layer interaction and the shock wave-shock wave interaction have been also considered. A possible interaction of the leading edge shock wave and of the shock wave arising from the vertex of the convex corner, produced on the lower surface of the airfoil when the flap is deflected, generates a shock wave whose intensity is stronger than those of the two interacting shock waves. This produces a consistent increment of pressure and heat flux on the lower surface of the flap, where a thermal protection system is required.