• Journal of the Korean Electrochemical Society
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• v.7 no.1
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• pp.21-25
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• 2004

The electrochemical behaviors of dissolved hydrogen and hydrogen peroxide at a platinum disk electrode were investigated in boric acid solution by potentiostatic polarization method at the temperature of 25 and $200^{\circ}C$. The oxidation of dissolved hydrogen at $25^{\circ}C$ was kinetically controlled reaction, the rate of which depends upon the electron transfer on the electrode surface. As temperature was raised, however, the electrochemical characteristics of dissolved hydrogen were changed from a kinetically controlled reaction to a diffusion controlled one. One notable feature, with dissolved hydrogen at high temperature, is that an abnormal potential range was observed, where the oxidation rate of dissolved hydrogen rapidly decreased just before starting potential of water oxidation. We think it is caused by the deactivation of the electrode that results from the adsorption of hydroxyl ion on the surface of the platinum disk. On the contrary, a definite change with temperature was not identified in the case of the hydrogen peroxide except for the increase in current density that was due to the increasing diffusion coefcient with an increase of temperature.

• Transactions of the KSME C: Technology and Education
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• v.5 no.2
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• pp.135-143
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• 2017

The domestic unique research reactor, HANARO (Hi-flux Advanced Neutron Application ReactOr), has been constructed with the open-pool, the core is submerged in, for the multi-purpose neutron application. The reactor has a primary cooling system to remove the fission heat from the core and its connected fluidic systems. Since the works are required at the reactor pool top as a characteristic of the research reactor, the radiation shall be minimized with the operation of the hot water layer system to avoid unnecessary radiation exposure on the workers during work at the pool top. Moreover, the pool water management system is connected to the reactor pool to maintain the pool temperature below $50^{\circ}C$ to minimize the uprising radioactive gas or impurity from the colder pool bottom. For the efficient flow rate of the PWMS, the thermal capacity of heat exchanger is selected with 260 kW in the normal operation condition. In this paper, the modeling is formulated to figure out whether or not each pool temperature maintains below the temperature limit and the calculation results show that the designed PWMS heat exchanger has enough capacity with the design margin regardless of the reactor operation mode.

• Journal of the Korean Society of Marine Environment & Safety
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• v.27 no.7
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• pp.1074-1081
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• 2021

Nitrous oxide (N₂O) is one of the six major greenhouse gases and is known to produce a greenhouse ef ect by absorbing infrared radiation in the atmosphere. In particular, its global warming potential (GWP) is 310 times higher than that of CO₂, making N₂O a global concern. Accordingly, strong environmental regulations are being proposed. N₂O reduction technology can be classified into concentration recovery, catalytic decomposition, and pyrolysis according to physical methods. This study intends to provide information on temperature conditions and reaction time required to reduce nitrogen oxides with cost. The high-temperature ranges selected for pyrolysis conditions were calculated at intervals of 100 K from 1073 K to 1373 K. Under temperatures of 1073 K and 1173 K, the N₂O reduction rate and nitrogen monoxide concentration were observed to be proportional to the residence time, and for 1273 K, the N₂O reduction rate decreased due to generation of the reverse reaction as the residence time increased. Particularly for 1373 K, the positive and reverse reactions for all residence times reached chemical equilibrium, resulting in a rather reduced reaction progression to N₂O reduction.

• Clean Technology
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• v.28 no.2
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• pp.117-122
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• 2022

This study developed and tested an ultra-low NO_x burner in an 80 kW combustion furnace. The experiment was conducted in an 80 kW single burner combustion furnace with changing the swirl numbers, total equivalence ratios, and primary/secondary oxidizer ratios. In this study, liquefied natural gas (LNG) was used as an auxiliary fuel to significantly reduce NO_x production. In a thermal power plant, the amount of NO_x generated during coal combustion is about 300 ppm. However, using the burner tested in this study, it was possible to reduce the amount of NO_x generated via LNG co-firing to 40 ppm. If the input amount of the primary oxidizer is enough for the gas to be completely combusted and the gas and coal are added simultaneously, the combusted gas forms a high-temperature region at the burner outlet and volatilizes the coal. As a result, the N contained in the devolatilized coal is discharged. Therefore, when the coal is subsequently burned, the amount of NO_x produced decreases because there is almost no N remaining in the coal. If a thermal power plant burner is developed based on the results of this study, it is expected that the NO_x generation will be significantly lower in the early stage of combustion.

• Korean Chemical Engineering Research
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• v.45 no.2
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• pp.203-207
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• 2007

In this paper efficient method for particle removal from silicon wafers by usage of HF and ozone was studied. It was found that at least 0.3 vol% concentration of HF was required for particle removal and removal efficiency increased with the application of megasonic in ozonated water. Additional cleaning with minute amount of ammonia (0.01 vol%) after HF/Ozone step showed over 99% in removal efficiency. It is proposed that the superior cleaning efficiency of HF-Ozone-ammonia is due to micro-etching of silicon surface and impediment of particle re-adsorption in alkali environment. Compared to SC-1 cleaning method micro roughness has also been slightly improved. Therefore it is expected that HF-ozone-ammonia cleaning method is a viable alternative to the conventional wet cleaning methods.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.7 no.3
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• pp.384-392
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• 1997

Potassium lithium niobate(KLN) single crystal for a nonlinear-optic material, which changes the wavelength of lasers, has a ferroelectric tetragonal tungsten bronze structure at room temperature. It has been very hard to get single crystals of good quality due to the cracks during cooling process. In order to investigate the composition change due to the evaporation of solution during the growth, the thermogravimetric analysis was carried out. In atmospheric condition at $1000^{\circ}C$ which is about $10^{\circ}C$ higher than the crystal growing temperature, the weight change was negligible amount of $1.46{\times}10^{-5}$g/($\textrm{cm}^2$hr). By using both the Pt plate as the nucleation site and the slow cooling method with temperature fluctuation, KLN single crystal of good quality of size 1 cm could be obtained. The phase transition temperature was $490^{\circ}C$, which was higher than that reported by other researchers of the other composition. The optical anisotropy due to the absorption of OH-band exists in the range of IR.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.2
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• pp.203-212
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• 2010

Water spray cooling has been widely used in a variety of industrial applications. The present study concentrated on quantitative measurements of the heat flux and heat transfer coefficient by water spray as it impinges on the rough surface of a hot steel plate at $900^{\circ}C$. A novel experimental technique was developed for a hightemperature heat flux gauge with a test block, cartridge heaters, and thermocouples that was used to measure the surface heat flux information on the hot steel plate for local heat flux measurements. The roles of the surface roughness on heat transfer are presented in this paper for well-characterized four rough surfaces with average rms roughness heights of $40-80{\mu}M$. The results show that the local heat transfer for rough surfaces is higher than that for a smooth surface. Heat transfer can be significantly increased by the presence of surface roughness elements, which can disrupt the thin thermal boundary layer. In addition, the heat transfer enhancement mechanism on a rough surface can be investigated by a different boiling regime.

• Journal of Advanced Marine Engineering and Technology
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• v.40 no.3
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• pp.165-173
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• 2016

On March 11, 2011, a massive earthquake measuring 9.0 on the Richter scale and subsequent 10-.14 m waves struck the Fukushima Daiichi (FD) Nuclear Power Plant. The main and backup electric power was damaged preventing the cooling system from functioning. Fuel rods overheated and led to hydrogen explosions. If heat in the fuel rods is not dissipated, the nuclear fuel coating material (e.g., Zircaloy) reacts with water vapor to generate hydrogen at high temperatures. This hydrogen is released into the containment area. If the released hydrogen burns, the stability of the containment area is significantly impacted. In this study, researchers performed an explosion analysis in a high-risk explosion area, analyzing the hydrogen distribution in a containment building [1] and the effects of a hydrogen explosion on containment safety. Results indicated that a hydrogen explosion was possible throughout the containment building except the middle area. If an explosion occurs at the top of the containment building with more than 40% of the hydrogen collected or in the bottom right or left side of the of containment building, safety of the containment building could be threatened.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.310-310
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• 2012

최근 전자산업의 발달에 따른 전자제품의 소형화 및 고기능화 요구에 대응하기 위하여 저항(resistor), 커패시터(capacitor), IC (integrated circuit) 등의 수동소자를 개별 칩(discrete chip) 형태로 형성하여 기판의 표면에 실장하는 기술이 일반화되고 있다. 그러나, 수동 소자의 내장 기술은 기판의 패턴 밀도의 급격한 향상과 더불어 수동소자의 내장 공간도 협소해지는 문제점이 있다. 상기의 문제점을 해결하기 위해 개별 칩 형태의 내장형 저항체를 박막 형태의 내장 저항체를 구현하는 기술의 개발이 최근 주목을 받고 있다. 박막 저항체는 기존의 권선저항 및 후막저항과 비교하여 정밀한 온도저항계수를 가지며 이동통신에 적용시 고주파 영역(GHz)에서의 안정성과 주파수 특성이 좋다는 장점들을 가지고 있다. 박막 저항 물질로는 높은 경도와 우수한 열적 안정성을 가지고 있는 TaN (tantalum nitride)이 주로 사용되고 있다. 일반적으로, TaN 박막은 스퍼터링을 사용하며 제조되며 TaN 박막의 성질은 탄탈륨과 질소의 화학정량비, 박막의 결함 정도, 또는 공정압력 및 증착 온도, 플라즈마 파워 등과 같은 공정조건 등의 변화에 민감하게 변화하므로, TaN 박막의 다양한 연구가 더 필요한 실정이다. 본 연구에서는 반응성 마크네트론 스퍼터링을 사용하여 TaN 박막을 Si 기판 위에 증착하였고 TaN 박막의 원하는 특성을 제어할 수 있도록 질소 분압과 total gas volume을 조절하여 공정을 최적화하는 연구를 진행하였다. 또한 tensile pull-off 방법을 이용하여 TaN 박막의 부착강도를 평가하였고, 온도 사이클 및 고온고습 환경에 노출된 TaN 박막들의 열화 특성들에 대하여 연구하였다.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.161-161
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• 2012

본 연구에서는 InGaAs을 이용한 테라헤르쯔(THz) 발생과 검출 특성을 GaAs에 의한 특성과 비교, 조사하였다. 고온성장(HTG, $530^{\circ}C$) InGaAs를 이용하여 photo-Dember (pD) 효과(표면방출)에 의한 THz 발생 특성을 조사하였으며, THz 검출 특성에는 저온성장(LTG, $530^{\circ}C$) InGaAs: Be을 이용하였다. HTG-InGaAs 기판 위에 패턴한 금속전극 (Ti/Au, ${\sim}500{\times}500{\mu}m$)의 가장자리에 Ti: Sapphire fs 펄스 레이저(30 ps/90 MHz)를 조사하여 LTG-GaAs 수신기(Rx)로 THz를 검출, 전류신호(a)와 Fourier transform (FT) 주파수 스펙트럼(b)을 얻었다. HTG-InGaAs에서 얻은 파형은 SI-GaAs에서와 거의 비슷한 모양이었으나, 주파수 범위(0.5~2 THz)는 SI-GaAs의 1~3 THz 보다 좁고 FT 스펙트럼의 세기는 약 1/8 정도로 낮았다. LTG-InGaAs 수신기 (Rx)의 안테나는 쌍극자 ($5/20{\mu}m$) 형태를 가지고 있으며, SI-GaAs Tx로 발생시킨 광원을 사용하여 THz 영역의 검출 특성을 조사하였다. HTG-InGaAs Tx 및 LTG-InGaAs Rx의 이득은 각각 약 $5{\times}10^{-8}$ A/W과 $2.5{\times}10^{-8}$ A/W인 것으로 분석되었다.