• 한국자기공명학회논문지
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• 제12권1호
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• pp.51-59
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• 2008

Convection effect in liquids has been one of the main targets to be overcome in pulsed-field-gradient NMR measurements of self-diffusion coefficients since the temperature gradient along the sample tube generated by the heating and/or cooling process causes the effect, resulting in additional diffusion. It is known that the capillary is the most appropriate tube type for diffusion experiments at variable temperatures since the narrower tube suppresses convection effectively. For evaluating the properties of hydrogen bonding, diffusion coefficients of the $K^+$-complexed and free valinomycin in a micro tube have been determined at various temperatures. From the analysis of the obtained diffusion coefficient values, we could conclude that the intramolecular hydrogen bonding in both of the $K^+$ complexed and free valinomycin in a non-polar solvent is preserved over the observed temperature range, and the temperature dependence of hydrogen bonding is more pronounced in free valinomycin. It is also thought that there is no big change in the radius of the $K^+$-complexed as temperature is varied, and the ratio of overall radius, $r_{complex}/r_{free}$ is slightly decreased as temperature rises.

• 한국수소및신에너지학회논문집
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• 제18권3호
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• pp.265-274
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• 2007

A study has been conducted to clarify NO emission behavior through preferential diffusion effects of $H_2$ and H in methane-hydrogen diffusion flames. A comparison is made by employing three species diffusion models. Special concerns are focused on what is the deterministic role of the preferential diffusion effects in flame structure and NO emission. The behavior of maximum flame temperatures with three species diffusion models is not explained by scalar dissipation rate but the nature of chemical kinetics. The preferential diffusion of H into reaction zone suppresses the populations of the chain carrier radicals and then flame temperature while that of $H_2$ produces the increase of flame temperature. These preferential diffusion effects of $H_2$ and H are also discussed about NO emissions through the three species diffusion models.

• 한국전산구조공학회논문집
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• 제37권4호
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• pp.267-274
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• 2024

수소 취성 파괴는 수소가 풍부한 환경에 노출된 재료의 구조적 무결성을 보장하는 데 있어 다양한 산업 응용 분야에서 큰 도전 과제이다. 본 연구는 연성 파괴 모델인 Gurson-Cohesive 모델과 수소 확산 모델을 통합하는 수치 모델을 제안하고 수소 취화가 파괴 거동에 끼치는 영향을 조사한다. 사용된 연성 파괴 모델은 손상 진화를 모사하는 Gurson 모델과 균열 표면의 불연속성과 응력-균열폭 관계의 연화 거동을 설명하는 표면 요소 기반의 Cohesive zone 모델을 결합한 파괴 모델이며, 균열 시작 기준으로 공극과 삼축성을 고려한다. 또한, 파괴 모델과 통합된 수소 확산 분석은 수소 강화 탈결합(HEDE) 메커니즘과 그에 따른 균열 시작 및 진전에 미치는 영향을 고려하며, 응력-균열폭 관계에 대한 수소의 영향을 고려한다. 수치 예제로 매개변수 연구를 통하여 확산 계수와 수소 취화 파과 특성에 대한 민감도를 조사한다. 수소 확산 모델과 연성 파괴 모델을 통합한 프레임워크를 제시함으로써 본 연구는 수소 취화 파괴에 대한 이해를 제공하여 엔지니어링 응용 분야에서 기여할 수 있을 것이다.

• 한국수소및신에너지학회논문집
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• 제24권3호
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• pp.200-205
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• 2013

The separation of hydrogen depends on porosity, diffusivity and solubility in permeation membrane. Dense membrane is always showing a solution diffusion mechanism but porous membrane is not showing. Therefore, porous membrane has a good hydrogen flux due to pore is carried out transferred media. This mechanism is named as the Knudsen diffusion. Hydrogen molecules or hydrogen atoms are diffused along pore that is a mean free path. In this study, complex layer hydrogen permeation membrane was fabricated by hot press process. And then, it was evaluated and calculated to relationship between hydrogen permeability and membrane porosity.

• 한국재료학회지
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• 제28권5호
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• pp.286-294
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• 2018

Hot-press forming(HPF) steel can be applied successfully to auto parts because of its superior mechanical properties. However, its resistances to aqueous corrosion and the subsequent hydrogen embrittlement(HE) decrease significantly when the steel is exposed to corrosive environments. Considering that the resistances are greatly dependent on the properties of coating materials formed on the steel surface, the characteristics of the corrosion and hydrogen diffusion behaviors regarding the types of coating material should be clearly understood. Electrochemical polarization and impedance measurements reveal a higher corrosion potential and polarization resistance and a lower corrosion current of the Al-coating compared with Zn-coating. Furthermore, it was expected that the diffusion kinetics of the hydrogen atoms would be much slower in the Al-coating, and this would be due mainly to the much lower diffusion coefficient of hydrogen in the Al-coating with a face-centered cubic structure. The superior surface inhibiting effect of the Al-coating, however, is degraded by the formation of local cracks in the coated layer under severe stress conditions, and therefore further study will be necessary to gain a clearer understanding of the effect of cracks formed on the coated layer on the subsequent corrosion and hydrogen diffusion behaviors.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2010년도 춘계학술대회 논문집
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• pp.793-794
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• 2010

• Corrosion Science and Technology
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• 제20권5호
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• pp.295-307
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• 2021

Effects of ε-carbide (Fe_2.4C) on corrosion and hydrogen diffusion behaviors of ultra-strong steel sheets for automotive application were investigated using a number of experimental and analytical methods. Results of this study showed that the type of iron carbide precipitated during tempering treatments conducted at below A₁ temperatures had a significant influence on corrosion kinetics. Compared to a steel sample with cementite (Fe₃C), a steel sample with ε-carbide (Fe_2.4C) showed higher corrosion resistance during a long-term exposure to a neutral aqueous solution. In addition, the diffusion kinetics of hydrogen atoms formed by electrochemical corrosion reactions in the steel matrix with ε-carbide were slower than the steel matrix with cementite because of a comparatively higher binding energy of hydrogen with ε-carbide. These results suggest that designing steels with fine ε-carbide distributed uniformly throughout the matrix can be an effective technical strategy to ensure high resistance to hydrogen embrittlement induced by aqueous corrosion.

• Journal of Welding and Joining
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• 제34권6호
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• pp.42-46
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• 2016

Hydrogen assisted cracking (HAC) is one of the most complicated problem in welding. Huge amount of studies have been done for decades. Based on them, various standards have been established to avoid HAC. But it is still a chronic problem in industrial field. It is well known that the main causes of the hydrogen crack are residual stress, crack susceptible micro structures and a certain critical level of hydrogen concentration. Even though the exact generating mechanism is unclear till today, it has been reported that the hydrogen level in the weld metal should be managed less than a certain amount to prevent it. Matsuda studied that the residual hydrogen level in the weld metal can be varied even if the initial hydrogen content is same. It is also insisted in this report that the residual hydrogen concentration is in stronger correlation with hydrogen crack than the initial hydrogen content. But, in practical point of view, the residual hydrogen is still hard to consider because measuring hydrogen level is time and cost consuming process. In this regard, numerical analysis is the only solution for considering the residual hydrogen content. Meanwhile, Takahashi showed the possibility of predicting the residual hydrogen by a rigorous FE analysis. But, few commercial software suitable for solving the weld metal hydrogen has been reported yet. In this study, two dimensional thermal - hydrogen coupled analysis was developed by using the commercial FE software MARC. Since the governing equation of the hydrogen diffusion is similar to the heat transfer, it is shown that the heat transfer FE analysis in association with hydrogen diffusion property can be used for hydrogen diffusion analysis. A series of simulation was performed to verify the accuracy of the model. For BOP (Bead-On-Plate) and the multi-pass butt welding simulations, remaining hydrogen contents in the weld metal is well matched with measurements which are referred from Kim and Masamitsu.

• 전기화학회지
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• 제4권2호
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• pp.70-76
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• 2001

본 연구는 Pd박막 전극에서 수소 확산시 발생되는 응력해석에 대한 레이저 빔 디플렉션 방법의 응용에 대해 기술하였다. 우선, 탄성에 의한 확산 (고스키 효과) 및 확산에 의한 탄성 현상에 대해 간략히 설명하였고, 주어진 초기 및 경계 조건하에서 Fick 방정식의 해와 Vegard 및 Hooke의 법칙으로부터 확산에 의한 탄성 현상의 모델을 이론적으로 유도하였다. 다음으로 레이저 빔 디플렉션 방법이 수소 확산으로 인해 발생되는 응력해석에 어떻게 사용될 수 있는지 실험 장치 및 시편에 대해 소개하였다 마지막으로, 수학적으로 계산된 디플렉션 시간 추이 곡선과 실험적으로 얻어진 곡선의 비교로부터, 시간에 따른 인장 디플렉션의 변화를 시간에 따른 전극 내부의 수소 농도 구배의 변화 및 수소 확산계수의 차이로 설명하였다.

• 대한기계학회논문집A
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• 제34권6호
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• pp.709-715
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• 2010

수소 확산과 탄-소성 거동이 결합된 모델은 이미 제시되어 있다. 본 논문에서는 수소확산에 미치는 인자들과 그 영향에 대해 연구하였다. 각 인자들의 영향을 비교하기 위해 저탄소강 재료의 균열이 있는 무한 평판 모델에 대해 수소확산과 기계적 하중이 연계된 유한요소 해석을 수행하였다. 유한요소 해석 결과는 Taha와 Sofrinis의 연구(2001) 결과와 비교하여 검증하였다.