• Journal of the Korean Electrochemical Society
• /
• v.9 no.3
• /
• pp.118-123
• /
• 2006

Degradation of polymer electrolyte membrane fuel cell (PEMFC) that is facilitated by on/off cycles is one of the most important issues for commercialization of fuel cell vehicles. When a PEMFC stack is shut down, residual hydrogen and induce high voltage equivalent to open circuit voltage to the cathode side that might cause sintering of Pt catalyst and facilitate formation of hydrogen peroxide at the anode side that might decompose $Nafionc\'{A}$ membrane. In this study, degradation of PEMFC exposed to repetitive on/off cycles was investigated by measuring i-V characteristics, ac impedance, cyclic voltammograms, gas leak, cross-sectional SEM images, and TEM images. To prevent degradation of PEMFC caused by the residual gases, hydrogen was removed from anode gas channel by gas-purging and by using a dummy resistance, that were found to be a very effective method.

• 한국신재생에너지학회:학술대회논문집
• /
• 2006.11a
• /
• pp.494-497
• /
• 2006

For commercialization of polymer electrolytemembrane fuel cell (PEMFC), durability of membrane electrode assemblies (MEAs) has to be improved. Especially, long-term stability of MEA is one of the most important issues for frequent shut-down and start-up processes of PEMFC. The degradation of MEA could be attributed to chemical attack of hydrogen peroxide radicals that are formed at high cell voltages without any special treatment to remove residual hydrogen from anode gas channel after shut-down of the fuel cell. In this study, we investigated the long-term stability of MEA under different on/off operation conditions. Residential hydrogen gas was removed from the anode flow channel by purging air or nitrogen. Also, a dummy resistance was applied to the fuel cell to exhaust residential hydrogen at the anode. In these cases, MEA showed much more stable durability. Electrochemical characteristics of the fuel cell were measured byrepeating the on/off cycles with the hydrogen removal processes. Also, degradation of MEA components was examined by SEM, TEM and XRD analyses.

• Journal of the Korean Society of Industry Convergence
• /
• v.25 no.6_2
• /
• pp.961-968
• /
• 2022

Hydrogen embrittlement leads to the damages in bolts, nut, especially, high pressure valves, in the semiconductor facilities, hydrogen vehicles, hydrogen stations and so on. Monel material has higher strength than SUS material. Therefore, even though Monel material with special alloy is usually used to prevent the hydrogen embrittlement, it needs powerful drawing system to manufacture the rectangular or hexagonal bar using circular bar. The purpose of this study is to investigate the characteristics of plastic deformation of Monel material and 2 rollers of rolling unit in plastic limit through numerical analysis. As the results, it was predicted that, based on mean stress, as the rolling step was increased, the rolling force of rolling unit was decreased. In addition, the heat treatment for Monel material was needed because of residual stress due to plastic deformation. As for rollers, the roller was safe about 1.86 times compared with that of ultimate strength. In this study, as the roller 2 showed larger stress than roller 1, thus, roller 2 should be designed carefully to guarantee the safety. Further it was confirmed that the reaction force of roller could be helpful in bearing design.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.31 no.10
• /
• pp.855-859
• /
• 2007

Hydrogen as an energy carrier in fuel cell offers perhaps the largest potential benefits of reduced emissions of pollutants and greenhouse gases. The generation of high-purity hydrogen from hydrocarbon fuels is essential for efficient operation of fuel cell. Reduction of carbon monoxide to an acceptable level of 10ppm involves high temperature and low temperature water gas shift (WGS), followed by selective oxidation of residual carbon monoxide. The WGS reactor was designed and tested in this study to produce hydrogen-rich gas with CO to less than 5000 ppm. In the water gas shift operation, gas emerges from the reformer is taken through a high temperature shift (HTS) catalyst to reduce the CO concentration to about $2{\sim}4%$ followed to about 5000 ppm via a low temperature shift (LTS) catalyst.

• International Journal of Korean Welding Society
• /
• v.2 no.1
• /
• pp.52-56
• /
• 2002

This report was prepared to give informations on a proper way to develop new consumables for the steels with improved weldability. Traditionally, hydrogen control has been pursued mainly for suppressing the HICC in HAZ but it also has contributed to HICC in weld metal. Facing the limitations in reducing the hydrogen content, it is now important to consider the microstructural control approach in order to improve the HICC resistance of weld metal . It has been shown that changes in alloy design, and hence composition and microstructure, was quite effective in producing high strength weld metal with improved resistance to cold cracking. Besides the economic test methods for evaluating susceptibility of multipass weld metal is essential to promote the development of welding consumables.

• Korean Journal of Environmental Agriculture
• /
• v.38 no.1
• /
• pp.54-60
• /
• 2019

BACKGROUND: Hydrogen fluoride is one of the 97 accident preparedness substances regulated by the Ministry of Environment (Republic of Korea) and chemical accidents should be managed centrally due to continual occurrence. Especially, hydrogen fluoride has a characteristic of rapid diffusion and very toxic when leaking into the environment. Therefore, it is important to predict the impact range quickly and to evaluate the residual contamination immediately to minimize the human and environmental damages. METHODS AND RESULTS: In order to estimate the accident impact range, the off-site consequence analysis (OCA) was performed to the worst and alternative scenarios. Also, in order to evaluate the residual contamination of hydrogen fluoride in crop, the samples in accident site were collected from 15-divided regions (East direction from accident sites based on the main wind direction), and the concentration was measured by fluoride ($F^-$) ion-selective electrode potentiometer (ISE). As a result of the OCA, the affected distance by the worst scenario was estimated to be >10 km from the accident site and the range by the alternative scenario was estimated to be about 1.9 km. The residual contamination of hydrogen fluoride was highest in the samples near the site of the accident (E-1, 276.82 mg/kg) and tended to decrease as it moved eastward. Meanwhile, the concentrations from SE and NE (4.96~28.98 mg/kg) tended to be lower than the samples near the accident site. As a result, the concentration of hydrogen fluoride was reduced to a low concentration within 2 km from the accident site (<5 mg/kg), and the actual damage range was estimated to be around 2.2 km. Therefore, it is suggested that the results are similar to those of alternative accident scenarios calculated by OCA (about 1.9 km). CONCLUSION: It is difficult to estimate the chemical accident-affecting range/region by the OCA evaluation, because it is not possible to input all physicochemical parameters. However simultaneous measurement of the residual contamination in the environment will be very helpful in determining the diffusion range of actual chemical accident.

• Journal of Korea Foundry Society
• /
• v.15 no.2
• /
• pp.175-183
• /
• 1995

It is difficult to remove such interstitial impurities as sulfur, oxygen, hydrogen and carbon in Fe-Ni alloys. Thermodynamic and kinetic studies were carried out on the behavior of hydrogen gas, oxygen gas, Si, Al and slag, and the reaction time by the $Ar/Ar-H_2$ plasma and electron beam melting. After the addition of Al, Si, they were melted by Ar plasma with reaction time changed. 80%Ni-Fe alloys showed a better deoxidation than 36%Ni-Fe alloys. At $Ar-H_2$ plasma melting, the deoxidation was significant. In the case of the electron beam melting, the residual oxygen was higher than in Ar plasma melting because electron beam melting temperature was lower than that of Ar plasma. For the decaburization, it was melted by $Ar-O_2$ plasma melting, which could remove effectively carbon by activated oxygen in plasma. We added slag to Fe-Ni alloys for the desulfurization. As the result of this experiments, the amount of residual sulfur was not changed according to the slag ratio and reaction time.

• Proceedings of the Korean Institute of Surface Engineering Conference
• /
• 2016.11a
• /
• pp.101-101
• /
• 2016

DLC(Diamond Like Carbon)막은 그 물성의 다양함으로 인하여 산업기계, 금형, 공구, 광학 및 수송기기의 파워셀 부품등 많은 산업분야에 활용되고 있다. 일반적으로 DLC막은 증착에 사용되는 카본의 원료에 따라 크게 두 가지로 나눌 수 있는데, 이는 탄화 수소계 가스(CxHy)를 사용하여 증착된 a-C:H(amorphous Hydro-Carbon)과 고체 카본을 사용하는 a-C(amorphous Carbon)이다. 또한 a-C 중 진공 아크 공법으로 제작된 막(ta-C : tetrahedral amorphous-Carbon)은 다이아몬드 성분인 sp3의 분률이 높아, 그 경도는 40 - 85 GPa 이상이며, 무수소화로 500도 이상의 고온에서도 그 물성의 변화가 적어 그 활용도가 높아지고 있다. 하지만 높은 경도와 더불어 막의 잔류응력이 높아 3 um 이상 후막화하는 것은 어렵다. 이는 높은 잔류응력으로 인한 막의 증착시, 막 자체가 파손되거나, 기판과 막사이의 계면 밀착력이 약하여 박리되거나, 또는 높은 밀착력으로 인하여 모재가 파손되는 등 다양한 문제를 발생한다. 본 연구에서는 이 고경도 무수소 DLC막(ta-C)의 후막화하는 방안으로 주요 코팅 변수와 잔류응력과의 관계를 에너지 관점에서 파악하고 이를 활용 잔류응력을 제어하여 할 수 있는 방법을 제시하고자 한다.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2011.02a
• /
• pp.43-43
• /
• 2011

BN(Boron Nitride)은 온도와 압력 조건에 따라 안정한 상이 sp3 결합인 cubic 구조의 BN(cBN)과 sp2 결합인 hexagonal 구조의 BN(hBN or tBN)으로 나뉘는데, 이 중 cBN은 우수한 기계적, 물리적, 화학적 특성으로 인해 박막 분야에서 매우 높은 응용가능성을 지니고 있다. 하지만 cBN 박막의 합성과정에서의 필수적인 요소인 높은 압축잔류응력은 cBN을 응용분야에 적용하는데 있어 한계점으로 계속 남아 있었다. 그동안 이러한 잔류응력을 감소시키기 위해 열처리, 이온 주입, 제 3의 물질 첨가 등 다양한 관점에서 접근한 연구들이 진행되어 왔다. 본 연구에서는 cBN 합성과정에서 잔류응력을 감소시키기 위한 방법으로 수소를 첨가하였고, 그에 따른 잔류응력의 변화를 분석하고, 그 과정에서 잔류응력의 형성에 수소가 어떤 역할을 하는지 규명하고자 하였다. cBN 박막은 hBN을 target으로한 unbalanced magnetron sputtering를 사용하여, 실리콘 wafer 위에 합성하였다. 증착압력은 1.3mTorr로, 수소의 첨가량을 증가시키며 잔류응력과 cBN fraction을 관찰하였다. cBN fraction은 FTIR로 분석하였고, 잔류응력은 실리콘 strip의 in-situ 곡률측정법으로 계산하였다. cBN 박막의 조성과 구조 분석, 수소의 역할 규명을 위해 RBS 및 HRTEM을 이용하였다.

• Korean Chemical Engineering Research
• /
• v.60 no.2
• /
• pp.237-242
• /
• 2022

In this study, a drying method that can effectively remove residual solvent from (+)-dihydromyricetin was developed. Residual acetone concentration was efficiently removed below ICH-specified value (5,000 ppm) by simple rotary evaporation with ethanol pretreatment. In addition, the residual ethanol met the ICH-specified value (5,000 ppm) by simple rotary evaporation through the addition of water, and the residual moisture also met the specified value (<4%) for active pharmaceutical ingredients. At all the drying temperature (35, 45, and 55 ℃), a large amount of the residual solvent was initially removed during the drying, and the drying efficiency increased when increasing the drying temperature. Removal of residual solvent by ethanol pretreatment was shown to be related to high vapor pressure of acetone-ethanol mixture and hydrogen bonding between acetone and ethanol.