• Transactions of Materials Processing
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• v.33 no.3
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• pp.185-192
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• 2024

This study examined how varying tempering temperatures affect the susceptibility of Cr-Mo low alloy steels to hydrogen embrittlement. A slow strain-rate test (SSRT) was carried out on the steels electrochemically pre-charged with hydrogen in order to examine the hydrogen embrittlement behavior. The results showed that the hydrogen embrittlement resistance of the Cr-Mo low alloy steels improved with increasing tempering temperature. Thermal desorption analysis (TDA) revealed that diffusible hydrogen content decreased with increasing tempering temperature, accompanied by a slight increase in the peak temperature. This decrease in hydrogen content was likely due to a reduction in dislocation density which served as reversible hydrogen trap sites. These findings underline the significant role of tempering temperature in enhancing the hydrogen embrittlement resistance of Cr-Mo low alloy steels.

• Journal of the Korean Society of Propulsion Engineers
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• v.23 no.3
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• pp.88-95
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• 2019

The hydrogen torch ignition system has been widely used to ignite a pure aluminum for aluminum powder combustion system because of its simple ignition method. However, the conventional hydrogen torch ignition system has a disadvantage that requires a high-pressure tank to supply hydrogen, which leads to the increase of the weight. In order to solve this problem, a hydrogen ignition system using $NaBH_4$, a solid chemical hydride, was designed in this study. The thermal decomposition of $NaBH_4$ was initiated approximately at $500^{\circ}C$ and hydrogen was generated. The parameters affecting the thermal decomposition characteristics of $NaBH_4$ were analyzed and the aluminum combustion test was carried out using $NaBH_4$-based hydrogen ignition system to study the applicability to a practical aluminum-combustion propulsion system.

• Journal of the Korean Institute of Gas
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• v.15 no.3
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• pp.67-73
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• 2011

One of the important topics to prepare the up-coming era of so-called ‘hydrogen economy’ is hydrogen transmission. Pipeline is conceivably the most economic way to consistently and safely transport a large amount of hydrogen over a long distance, which may be strongly requested in hydrogen economy era. As a good starting point for the purpose, one might wonder whether conventional API pipeline steels as designed for natural gas transmission can be used as the hydrogen pipeline materials or not. To answer the question, here we performed a series of micro-/nano-indentations together with tensile tests on the hydrogen-charged API X65, X70 and X100 steels having different strength level. In this paper, from the results of tensile tests, the hydrogen effects on the mechanical behavior in the API steels are systematically evaluated.

• Journal of the Korean Chemical Society
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• v.36 no.5
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• pp.627-631
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• 1992

A simple one dimensional model was proposed to describe a hydrogen bonding in crystals, which was based on the Lippincott's empirical potential. The model was used to calculate internal stretching vibrational frequencies of $NH_4I$ crystal at high pressures. The calculated results were in agreement with Raman experimental results qualitatively. At relatively lower high pressures, as pressure increases internal stretching vibrational frequencies shift lower due to increase of the hydrogen bonding effect. At higher pressures, the frequencies shift higher due to the repulsive contribution of interatomic potential induced by the reduction of interatomic distance as pressure increases.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2016.11a
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• pp.190.2-190.2
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• 2016

청정에너지 개발은 화석연료를 대체하기 위하여 꾸준한 관심을 받고 있다. 많은 대체에너지중 수소는 그 반응물이 순수한 물로써 환경오염이 없다. 기존의 수소를 얻어내는 방법은 메탄을 고온 고압에서 수증기와 반응시켜 얻는데 이 때 이산화탄소가 생성이 된다. 전기화학적 물분해 방법은 물을 수소와 산소로 선택적으로 분해시킬 수 있는 방법이다. $TiO_2$는 전기적으로 합성할 때 표면의 구조제어가 쉽고 열역학적, 화학적 안정성이 높아 자체의 높은 밴드갭(3.0~3.2 eV)에도 불구하고 산업적으로 염소분해 전극으로써 사용되고 있으며 최근에는 물분해 전극으로도 적용하는 연구가 진행되고 있다. 전기화학적 물분해 반응을 위해서는 높은 과전압이 요구되므로 산업적으로 이용하기 위해 전도성을 향상시키기 위한 연구가 필요하다. 낮은 전압에서도 물을 분해할 수 있는 촉매제의 도핑이 연구되고 있으나 대부분 촉매로 사용되는 금속은 루테늄과 이리듐 등의 귀금속이다. 본 연구에서는 저가촉매로써 몰리브덴을 도핑한 후 농도별 성능을 비교하였다. 전극의 성능비교를 위해 각 촉매의 농도별로 다른 전해질 농도조건에서 성능비교실험을 진행하였다.

• 한국신재생에너지학회:학술대회논문집
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• 2009.11a
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• pp.527-527
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• 2009

1세대 바이오디젤인 fatty acid methyl ester(FAME)의 문제점을 극복하기 위하여 많은 연구가 진행 중 이다. 소위 차세대 바이오디젤은 triglyceride의 산소 화합물을 제거하여 정유 공정을 통해 생산된 디젤과 동일한 특성을 지닌 탄화수소로 전환시킨 오일이다. 이를 위하여 수소를 첨가하여 산소를 제거 시키는 Hydrodeoxygenation(HDO) 반응이 필요하다. 고온($300-400^{\circ}C$), 고압(50-100 bar)의 혹독한 조건에서 높은 수율과 안정성을 보이는 촉매 개발이 필요하다. 이를 위하여 반응물중의 산소를 효과적으로 제거하기 위하여 산소 전달능이 뛰어난 $CeO_2$ 담체에 열안정성을 높이는 $ZrO_2$를 조합한 $Ce-ZrO_2$ 담체를 선정하였으며 수소첨가 탈산소 반응에 활성을 나타낼 것으로 예상되는 니켈을 활성성분으로 선정하였다. 본 연구에서는 15%Ni-$Ce_{(1-x)}Zr_{(x)}O_2$ ($0{\leq}x{\leq}1$)촉매를 공침법(co-precipitation)으로 제조하였으며 $500^{\circ}C$에서 소성하였다. 촉매 특성분석은 XRD, BET, H2-TPR을 이용하였다.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2007.04a
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• pp.87-90
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• 2007

Fuel cell power system was developed for high-endurance unmanned aerial vehicle (UAV). Liquid chemical hydride was selected as a fuel due to its high energy density. Liquid storage of the fuel is an ideal alternative solution of the existing compressed hydrogen storage. The fueling system that extracts hydrogen from chemical hydride consists of catalytic reactor, micro-pump, fuel cartridge, separator, and controller. The fuel cell power system including the fueling system and the fuel cell that generates electricity was integrated into a proposed UAV. The performance verification of the fuel cell power system was performed to use as a power plant of the UAV.

• Journal of the Korean Society of Propulsion Engineers
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• v.16 no.1
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• pp.1-8
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• 2012

Acoustic-pressure response of diluted hydrogen-air diffusion flames is investigated numerically by adopting a fully unsteady analysis of flame structures in low and high pressure regimes. As acoustic frequency increases, finite-rate chemistry is enhanced through a nonlinear accumulation of heat release rate for any pressure regime, leading to a high amplification index. Same numerical results are analyzed with application of a pressure-sensitive time lag model, and thereby, interaction index and time lag are calculated for each pressure regime. The interaction index has the largest value in each pressure regime at an acoustic frequency near 1000 Hz. In a high-pressure regime, flames are more unstable than in a low-pressure regime. The interaction index shows a good agreement with the amplification index.

• Journal of the Korean Institute of Gas
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• v.17 no.5
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• pp.15-21
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• 2013

This study evaluated comparison of the risk according to the type of fuel by three-dimensional simulation tool(FLACS). The consequence analysis of fire explosion and jet-fire was carried out in the layout of a typical high-pressure gas filling stations using CNG, hydrogen and 30%HCNG. Under the same conditions, hydrogen had a 30kPa maximum overpressure, CNG had a 0.4kPa and HCNG had a 3.5kPa. HCNG overpressure was 7.75 times higher than the CNG measurement, but HCNG overpressure was only 11.7% compared to hydrogen. In case of flame propagation, hydrogen had a very fast propagation characteristics. On the other hand, CNG and HCNG flame propagation velocity and distance tended to be relatively safe in comparison to hydrogen. The estimated flame boundary distance by jet-fire of hydrogen was a 5.5m, CNG was a 3.4m and HCNG was a 3.9m.

• Journal of the Korean Institute of Gas
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• v.25 no.6
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• pp.92-97
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• 2021

In accordance with the revision of the Enforcement Regulations of the High-Pressure Gas Safety Management Act in February 2021, from August 27, 2021, the operation status of safety devices such as gas leak detection and alarm devices, emergency shut-off devices and flame detectors installed at hydrogen vehicle charging stations can be monitored in real time. It is transmitted and operated by the computer system managed by Korea Gas Safety Corporations. We intend to share the results of statistical analysis of abnormal signals that have occurred along with the results of the monitoring system construction so that they can be used for the safety management of hydrogen refueling stations, and to seek future safety management directions.