• Corrosion Science and Technology
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• v.22 no.5
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• pp.341-350
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• 2023

In the present study, effects of a thin Zn-flash coating on hydrogen evolution, infusion, and embrittlement of advanced high strength steel during electro-galvanizing were examined. The electrochemical permeation technique in conjunction with impedance spectroscopy was employed under applied cathodic polarization. Moreover, a slow-strain rate test was conducted to evaluate loss of elongation (i.e., indicative of hydrogen embrittlement (HE)) and examine fracture surfaces. Results showed that the presence of a thin Zn-flash coating, even when it was not distributed uniformly, reduced hydrogen evolution rate and substantially impeded infusion of hydrogen into the steel substrate. This was primarily due to a hydrogen overvoltage on Zn coating and trapping of hydrogen at the interface of Zn coating/flash coating/steel substrate. Consequently, the sample with flash coating had a smaller HE index than the sample without flash coating. These results suggest that a thin Zn-flash coating could be an effective technical strategy for mitigating HE in advanced high-strength steels.

• Corrosion Science and Technology
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• v.17 no.5
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• pp.242-248
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• 2018

Martensitic high-strength steels revealed superior mechanical properties of high tensile strength exceeding 1000 Mpa, and have been applied in a variety of industries. When the steels are exposed to corrosive environments, however, they are susceptible to hydrogen embrittlement (HE), resulting in catastrophic cracking failure. To improve resistance to HE, it is crucial to obtain significant insight into the exact physical nature associated with hydrogen diffusion behavior in the steel. For martensitic steels, tempering condition should be adjusted carefully to improve toughness. The tempering process involves microstructural modifications, that provide changes in hydrogen diffusion/trapping behavior in the steels. From this perspective, this study examined the relationship between tempering condition and hydrogen diffusion behavior in the steels. Results based on glycerin measurements and hydrogen permeation evaluations indicated that hydrogen diffusion/trapping behavior was strongly affected by the characteristics of precipitates, as well as by metallurgical defects such as dislocation. Tempering condition should be adjusted properly by considering required mechanical properties and resistance to HE.

• Proceedings of the Korea Society for Energy Engineering kosee Conference
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• 2010.04a
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• pp.172-172
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• 2010

• Korean Chemical Engineering Research
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• v.43 no.1
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• pp.66-70
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• 2005

For the application in HI decomposition reaction of thermochemical water-splitting IS process, the carbonized membranes using the polymer material (polyimide) were prepared, and SiC membrane was also prepared by SiO treatment on those carbonized membranes. The weight change by the carbonation of polyimide was about 50%, and the weight decreased with an increase of carbonation temperature. The gas permeance ($H_2$ or $N_2$) of carbonized membrane decreased with an increase of carbonation temperature led to the pore closing. The gas permeance ($H_2$ or $N_2$) of SiC membrane increased with an increase of SiO treatment concentration, and the gas permeation mechanism was changed from the activiation energy flow to Knudsen flow.

• Corrosion Science and Technology
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• v.18 no.3
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• pp.102-109
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• 2019

The hydrogen diffusion and trapping model with a numerical finite difference method (FDM) was modified and extended to accommodate $H_2S$ corrosion and scale forming processes of high-strength steel under tensile stress condition. The newly proposed diffusion model makes it possible to clearly understand combined effect of tensile stress and $H_2S$ corrosion process on hydrogen diffusion behaviors. The core concept of this theoretical approach is that overall diffusion behavior is separated into diffusion process through two respective layers: an outer sulfide scale and an inner steel matrix. Diffusion coefficient values determined by curve-fitting permeation data reported previously with the newly proposed diffusion model indicate that the application of tensile stress can contribute to continual increase in the diffusivity in the sulfide scale with a high density of defect. This suggests that the scale with a lower stability under the stress condition can be a key parameter to enhance hydrogen influx in the steel matrix. Consequently, resistance to hydrogen assisted cracking of the steel under tensile stress can be decreased significantly.

• Membrane Journal
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• v.34 no.2
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• pp.146-153
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• 2024

In this experiment, a Ti-based flat hydrogen separation membrane was designed and manufactured. In order to find a Ti-based hydrogen separation membrane of a new composition, the correlation between the physical-chemical properties and hydrogen permeability of various alloys was investigated. Based on this, two types of new alloy films (Ti_14.2Zr_66.4Ni_12.6Cu_6.8 (70 ㎛), Ti_17.3Zr_62.7Ni₂₀ (80 ㎛)) was designed and manufactured. The manufactured flat hydrogen separation membrane was tested for hydrogen permeation using mixed gas (H₂, N₂) and sweep gas (Ar) at 300~500℃ and 1~4 bar. The Ti_14.2Zr_66.4Ni_12.6Cu_6.8 alloy film has a maximum flux of 16.35 mL/cm² min at 500℃ and 4 bar, and the Ti_17.3Zr_62.7Ni₂₀ alloy film has a maximum flux of 10.28 mL/cm² min at 450℃ and 4 bar.

• Applied Chemistry for Engineering
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• v.33 no.3
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• pp.322-327
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• 2022

Fucoidans were degraded by hydrogen peroxide under the electron beam (2.5 MeV) with various radiation doses (5 kGy, 10 kGy, 15 kGy, and 20 kGy) at room temperature. The degradation property was analyzed with a gel permeation chromatography (GPC-MALLS) method. An average molecular weight of fucoidan decreased from 99,956 at the irradiation dose of 0 kGy to 6,725 at the irradiation dose of 20 kGy. The solution viscosity of fucoidans showed a similar pattern to the molecular weight change. The number of chain breaks per molecule (N) increased with increasing the irradiation dose and concentration of hydrogen peroxide. The radiation yield of scission value markedly increased with increasing the irradiation dose up to 15 kGy. Also a 10% hydrogen peroxide concentration was more efficient than that of 5%. The structures of degraded fucoidan samples were studied with Fourier transform infrared spectroscopy (FT-IR). The results showed that the degradation process did not significantly change the chemical structure or the content of sulfate group. The sulfur content of each sample was determined with an Elemental Analyzer. With increasing the concentration of hydrogen peroxide, the ratios of sulfur/carbon, hydrogen/carbon, and nitrogen/carbon slightly decreased. The antioxidant activities of fucoidans were investigated based on hydroxyl radical scavenging activities. The ability of fucoidan to inhibit the hydroxyl radical scavenging activity was depended on its molecular weight.

• Membrane Journal
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• v.18 no.2
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• pp.176-184
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• 2008

Nano-porous ceramic membranes was synthesized by the sol-gel method. Gas permeation of hydrogen and nitrogen was determined by single composition gas. Pore size $0.1{\mu}m$ and porosity 32% of flat type ${\alpha}-Al_2O_3$ substrate was manufactured. An intermediate ${\gamma}-Al_2O_3$ layer with pore size of 4 nm was formed by dip-coating. Polymeric silica sol was synthesized by acid catalyzed hydrolysis and condensation of tetra-ethyl-ortho-silicate. Supported membranes on alumina were prepared by dipping and calcining. He, $N_2$ permeation experiments with nanoporous sol-gel modified supported ceramic membranes were peformed to determine the gas transport characteristics. $He/N_2$ permselectivity around $100{\sim}160$ and helium permeation in the order of $10^{-7}mol/m^2{\cdot}s{\cdot}Pa$ were measured in the temperature range of $303{\sim}363K$.

• Membrane Journal
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• v.11 no.3
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• pp.124-132
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• 2001

Silica membranes were prepared on a porous ${\alpha}$-alumina tube with pore size of 150nm by sol-gel and chemical vapor deposition(CVD) method for hydrogen separation at high temperatures. Silica and ${\gamma}$-lumina membranes formed by the sol-gel method possessed a large amount of mesopores of a Knudsen diffusion regime. In order to improve the $H_2$ selectivity, silica was deposited in the sol-gel derived silica/${\gamma}$-alumina layer by thermal decomposition of tetraethyl orthosilicate(TEOS) at $600^{\circ}C$. The CVD with forced cross flow through the porous wall of the support was very effective in plugging mesopores that were left unplugged in the membranes. The CVD modified silica/alumina composite membrane completely rejected nitrogen permeation and thus showed a high $H_2$ selectivity by molecular sieve effect. the permeation of hydrogen was explained by activated diffusion and the activation energy was 9.52kJ/mol.

• Journal of the Korea Institute of Military Science and Technology
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• v.20 no.4
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• pp.528-535
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• 2017

Fuel cells have been spotlighted in the world for being highly efficient and environmentally friendly. A hydrogen which is the fuel of fuel cell can be obtained from a number of sources. Hydrogen source for operating the polymer electrolyte membrane fuel cell(PEMFC) in the current underwater environment, such as a submarine and unmanned underwater vehicles are currently from the metal hydride cylinder. However, metal hydride has many limitations for using hydrogen carrier, such as large volume, long charging time, limited storage capacity. To solve these problems, we suggest diesel reformer for hydrogen supply source. Diesel fuel has many advantages, such as high hydrogen storage density, easy to transport and also well-infra structure. However, conventional diesel reforming system for PEMFC requires a large volume and complex CO removal system for lowering the CO level to less than 10 ppm. In addition, because the preferential oxidation(PROX) reaction is the strong exothermic reaction, cooling load is required. By changing this PROX reactor to hydrogen separation membrane, the problem from PROX reactor can be solved. This is because hydrogen separation membranes are small and permeable to pure hydrogen. In this study, we conducted the pressurized diesel reforming and water-gas shift reaction experiment for the hydrogen separation membrane application. Then, the hydrogen permeation experiments were performed using a Pd alloy membrane for the reformate gas.