• 대한금속재료학회지
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• 제46권5호
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• pp.296-303
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• 2008

Hydrogen permeation through dense palladium-based membranes has attracted the attention of many scientists largely due to their unmatched potential as hydrogen-selective membranes for membrane reactor applications. Although it is well known that the permeation mechanism of hydrogen through Pd involves various processes such as dissociative adsorption, transitions to and from the bulk Pd, diffusion within Pd, and recombinative desorption, it is still unclear which process mainly limits hydrogen permeation at a given temperature and hydrogen partial pressure. In this study, we report an all-electron density-functional theory study of hydrogen permeation through Pd membrane (using VASP code). Especially, we focus on the variation of the energy barrier of the penetration process from the surface to the bulk with hydrogen coverage, which means the large reduction of the fracture stress in the brittle crack propagation considering Griffith's criterion. It is also found that the penetration energy barrier from the surface to the bulk largely decreases so that it almost vanishes at the coverage 1.25, which means that the penetration process cannot be the rate determining process.

• Corrosion Science and Technology
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• 제16권4호
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• pp.209-225
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• 2017

Development of high strength steel requires proper understanding of hydrogen behavior since the higher the steel strength the greater the susceptibility of hydrogen assisted cracking. This paper provides a brief but broad overview on hydrogen entry and transport behavior of high-strength ferritic steels. First of all, hydrogen absorption, diffusion and trapping mechanism of the steels are briefly introduced. Secondly, several experimental methods for analyzing the physical/chemical nature of hydrogen uptake and transport in the steels are reviewed. Among the methods, electrochemical permeation technique utilized widely for evaluating the hydrogen diffusion and trapping behavior in metals and alloys is mainly discussed. Moreover, a modified permeation technique accommodating the externally applied load and its application to a variety of steels are intensively explored. Indeed, successful utilization of the modified permeation technique equipped with a constant load testing device leads to significant academic progress on the hydrogen assisted cracking (HAC) phenomenon of the steels. In order to show how the external and/or residual stress affects mechanical instability of steel due to hydrogen ingress, the relationship among the microstructure, hydrogen permeation, and HAC susceptibility is briefly introduced.

• Corrosion Science and Technology
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• 제22권4호
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• pp.297-303
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• 2023

This study aimed to evaluate hydrogen permeation behaviors of pre-strained twinning-induced plasticity steel with or without Zn coating using electrochemical permeation technique. In contrast to un-strained and 30% strained samples, permeation current density was measured in the 60% strained sample. Tensile pre-straining at 60% involved microstructural modifications, including a high level of dislocation density and stacking fault with a semi-coherent twin boundary, which might provide a high diffusion path for hydrogen atoms. However, reproducibility of measurements of hydrogen permeation current was low due to non-uniform deformation and localized stress concentration. On the other hand, the permeation current was not measured in pre-strained TWIP steel with Zn coating. Instead, numerous blisters with some cracks were observed on the surface of the coating layer. In locally damaged Zn coating under tensile straining, hydrogen atoms could relatively easily permeate through the coating layer. However, they were trapped at the interface between the coating layer and the substrate, which might delay hydrogen penetration into the steel substrate.

• 한국재료학회지
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• 제28권7호
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• pp.428-434
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• 2018

Hydrogen evolution on a steel surface and subsequent hydrogen diffusion into the steel matrix are evaluated using an electrochemical permeation test with no applied cathodic current on the hydrogen charging side. In particular, cyclic operation in the permeation test is also conducted to clarify the corrosion-induced hydrogen evolution behavior. In contrast to the conventional perception that the cathodic reduction reaction on the steel in neutral aqueous environments is an oxygen reduction reaction, this study demonstrates that atomic hydrogen may be generated on the steel surface by the corrosion reaction, even in a neutral environment. Although a much lower permeation current density and significant slower diffusion kinetics of hydrogen are observed compared to the results measured in acidic environments, they contribute to the increase in the embrittlement index. This study suggests that the research on hydrogen embrittlement in ultra-strong steels should be approached from the viewpoint of corrosion reactions on the steel surface and subsequent hydrogen evolution/diffusion behavior.

• 한국세라믹학회지
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• 제52권4호
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• pp.234-236
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• 2015

$Y_2O_3$-SiC composite membrane was dip-coated using $Y_2O_3$ sol solution; this membrane was compared with a non- coated one. Each membrane was characterized by XRD, FE-SEM and BET techniques. Hydrogen and CO permeation were tested with self-manufactured Sievert's type equipment. $Y_2O_3$ coating was enhanced for the selectivity of the membrane ($H_2$ versus CO). The hydrogen permeation was measured at 1 bar with increasing temperatures. In case of the coated membrane, hydrogen permeation was found to be $1.24{\times}10^{-7}mol/m^2sPa$ with perm-selectivity of 4.26 at 323 K.

• 한국수소및신에너지학회논문집
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• 제21권4호
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• pp.264-270
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• 2010

Recently, the most promising methods for high purity hydrogen production are membranes separation such as polymer, metal, ceramic and composites. It is well known that Pd and Pd-alloys membranes have excellent properties for hydrogen separation. However, it has hydrogen embrittlement and high cost for practical applications. Therefore, most scientists have studied new materials instead of Pd and Pd-alloys. On the other hand, TiN powders are great in resistance to acids and chemically stable under high operating temperature. In order to get specimens for hydrogen permeation, the TiN powders synthesized were consolidated together with Co, Ni powders by hot press sintering (HPS). During the consolidation of powders at HPS, heating rate was 10 K/min and the pressure was 10 MPa. It was characterized by XRD, SEM. Also, we estimated the hydrogen permeability by Sievert's type hydrogen permeation membrane equipment.

• 한국수소및신에너지학회논문집
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• 제14권1호
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• pp.17-23
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• 2003

$H_2$ permeation flux though a $100{\mu}m-thick$ Pd-Ru (6wt%) membrane was measured at various temperatures and pressures. The permeation flux followed the Sievert's law and thus the rate-limiting step of the hydrogen permeation was the bulk atomic diffusion step. The activation energy of the permeation flux was obtained at 17.9 kJ/mol and this value is consistent with those published previously. While no degradation of the permeation flux wasfound in the membrane exposed to the $O_2$ and $CO_2$ environments for 100 hours, the membrane exposed to $N_2$ environment for 100 hours showed the degradation in the $H_2$ permeation flux. The $H_2$ permeation was decreased as the exposure temperature to $N_2$, environment was increased. The $H_2$ permeation flux was fully recovered after the membrane was kept in the $H_2$ environment for certain time. The permeation flux degradation might be caused by the formation of metal nitride on the membrane surface.

• 멤브레인
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• 제21권3호
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• pp.290-298
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• 2011

팔라듐이 코팅된 $V_{53}Ti_{26}Ni_{21}$ 합금 분리막을 통해 수소 투과시 혼합가스의 영향에 대해 알아보았다. 순수 수소, 수소, 이산화탄소 및 일산화탄소의 혼합가스를 공급가스로 주입할 때, $450^{\circ}C$, 1-3 bar의 압력에서 팔라듐이 코팅된 $V_{53}Ti_{26}Ni_{21}$ 합금 분리막의 수소 투과 실험을 수행하였다. 수소만을 공급한 투과 실험에서 팔라듐 코팅된 $V_{53}Ti_{26}Ni_{21}$ 합금 분리막(두께: 0.5 mm)의 수소 투과량은 3 bar, $450^{\circ}C$ 조건에서 $5.36mL/min/cm^2$였다. 또한 수소/이산화탄소, 수소/일산화탄소 및 수소/이산화탄소/일산화탄소를 공급한 투과실험에서 $V_{53}Ti_{26}Ni_{21}$ 합금 분리막의 수소 투과량은 각각 4.46, 5.20, $3.91mL/min/cm^2$였다. 따라서, 수소/이산화탄소, 수소/일산화탄소 및 수소/이산화탄소/일산화탄소 혼합가스를 각각 공급할 때 투과량은 온도와 압력에 상관없이 수소 분압 감소만큼 감소하였고 모든 경우 Sievert 법칙을 잘 만족시켰다. 투과 후 분리막의 XRD 결과로부터 $V_{53}Ti_{26}Ni_{21}$ 합금 분리막은 여러 혼합가스에 대해 안정성과 내구성이 우수하다는 것을 알 수 있었다.

• Corrosion Science and Technology
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• 제5권4호
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• pp.117-122
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• 2006

Hydrogen permeation measurements have been carried out on API X65 grade linepipe steel. In order to study the effect of steel microstructure on hydrogen diffusion behavior in linepipe steel, the accelerated cooling condition was applied and then three different kinds of microstructures were obtained. Hydrogen permeation measurement has been performed in reference to modified ISO17081 (2004) and ZIS Z3113 method. Hydrogen trapping parameters in these steels were evaluated in terms of the effective diffusivity ($D_{eff}$), permeability ($J_{ss}L$) and the amount of diffusible hydrogen. In this study, microstructures which affect both hydrogen trapping and diffusion were degenerated pearlite (DP), acicular ferrite (AF), bainite and martensite/austenite constituents (MA). The low $D_{eff}$ and $J_{ss}L$ mean that more hydrogen can be trapped reversibly or irreversibly and the corresponding steel microstructure is dominant hydrogen trapping site. The large amount of diffusible hydrogen means that corresponding steel microstructure is predominantly reversible. The results of this study suggest that the hydrogen trapping efficiency increases in the order of DP, bainite and AF, while AF is the most efficient reversible trap.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2008년도 춘계학술발표대회 및 제14회 신소재 심포지엄
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• pp.11.1-11.1
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• 2008