• Applied Microscopy
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• 제36권spc1호
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• pp.57-61
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• 2006

High-resolution microscopy was applied for surveying hydride stability in Vanadium alloys, which are candidate for hydrogen storage materials of advanced hydrogen energy systems. $V_2H$ hydride in V alloys was stable at room temperature under the vacuum condition, but it was decomposed during heating up to $100^{\circ}C$. It was confirmed from HRTEM image and FFT that $V_2H$ has a BCT structure, where hydrogen atoms locate at octahedral sites. Crystal orientation was <110> beta// <110> mat., and lattice strain is about 10%. After the decomposition of the hydride, relatively large lattice expansion was observed in the matrix, which suggests that hydrogen atoms should be trapped by lattice defects and included in the matrix. Intensive electron beam also enhanced the decomposition.

• 전기화학회지
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• 제2권2호
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• pp.106-111
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• 1999

[ $CaNi_5$ ] 수소저장합금의 전기화학적 충$\cdot$방전 특성에 미치는 MG(mechanical grinding) 영향이 Ar및 $H_2$ 가스분위기에서 조사되었다 MG공정중 $CaNi_5$ 합금은 표면 산화층의 파괴와 재생성 및 산화층 근방의 불균질화로 인하여 MG 15시간 이후부터 CaO와 Ni로 뚜렷한 상분리가 일어났다. $MG-CaNi_5$는 MG시간이 길어질수록 초기의 전기화학적 방전용량은 현저히 감소하였지만 충$\cdot$방전 싸이클의 증가에 따른 용량저하 속도는 $CaNi_5$합금에 비하여 낮았다. MG처리된 $CaNi_5$합금의 퇴화는 MG공정중의 상분리 및 불규칙화에 의한 수소의 가역반응 site의 감소 및 분극저항의 증가, KOH 전해질 내에서 합금 표면의 산화반응에 의한 부동태 피막형성에 기인하는 것으로 판단되었다.

• 한국수소및신에너지학회논문집
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• 제35권2호
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• pp.146-151
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• 2024

The demand for research on materials with excellent cryogenic strength and ductility has been increasing, particularly for applications such as liquid hydrogen (20 K) storage tanks. To effectively utilize liquid hydrogen, a system capable of maintaining and operating at 20 K is essential. Therefore, preliminary research and verification of the cooling system are crucial. In this study, a heat transfer analysis was conducted on a cooling system to meet the cryogenic environment requirements for cryogenic hydrogen chamber, which are conducted at liquid helium temperatures (4 K). The cooling mechanism in a helium cooling system was examined using numerical analysis. The numerical cooling trends were compared with experimentally obtained cooling results. The good agreement between numerical and experimental results suggests that the numerical approach developed in this study is applicable over a wide range of cryogenic systems.

• 조명전기설비학회논문지
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• 제20권6호
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• pp.69-74
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• 2006

[ $Mg_2Ni$ ] 합금 및 $Mg_2Ni$와 카본 혼합물 입자의 수소저장 특성에 대한 기계적 분쇄(MG, Mechanical Grinding) 처리 효과를 고온 가스상의 PCT 측정 및 전기화학적인 마이크로 전극 측정법 등에 의해 검토되었다. PCT 측정은 약 $300[^{\circ}C]$의 고온에서 실시되었으며 전기화학적인 실험은 카본-섬유로 구성된 마이크로 전극을 1M KOH 수용액 속에서 조정자를 사용하여 MG 처리한 합금 단일입자에 접촉시켰다. 그 결과 $Mg_2Ni$ 합금과 카본 혼합물 입자의 경우 가스상에서 수소 해리압이 감소하고 상온에서 전기화학적인 수소화 특성이 크게 개선되었다. 이것은 기계적 분쇄(MG) 작용에 의한 합금의 미세화 및 나노화에 기인한다고 판단된다. 즉 고온 가스상의 PCT 측정 결과 수소 해리압이 MG 처리에 의해 0.55[MPa]에서 0.42[MPa]로 감소하였으며 동일 샘플 입자에 대해 마이크로 전극에 의한 평가에서도 수소화 피크가 보다 분명하게 관찰되었다.

• 한국수소및신에너지학회논문집
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• 제6권1호
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• pp.35-41
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• 1995

The MmNi-based alloy electrode was studied for use as a negative electrode in Ni-MH battery. Alloys with $MmNi_5-_xM_x$(M=Co,Al,Mn) composition were synthesized, and their electrode charateristics of activation rate, temperature dependence, electrode capacity and cycle life were investigated. With increasing Al content and decreasing Mn content in the alloys, the discharge capacity increased while the cycle life decreased. As x in $MmNi_5-_xM_x$ increased from 1.5 to 2.0, decreasing the Ni content, the discharge capacity, the low temperature property and the rate capability decreased. However its cycle life was improved. Increasing Co content resulted in a prolonged cycle life and decrease of high rate discharge capacity. It can be concluded that the most promising alloy in view of discharge capacity and cycle life is $MmNi_{3.5}Co_{0.7}Al_{0.5}Mn_{0.3}$.

• 한국수소및신에너지학회논문집
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• 제16권3호
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• pp.238-243
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• 2005

Mg and Mg-based alloys are most important hydrogen storage materials. It is a lightweight and low-cost materials with high hydrogen storage capacity. However, the formation of hydride at high temperature, the deterioration effect, the hydriding and dehydriding kinetics are bad factor for application. In this study, Mg and Ni have been produced by hydrogen induced mechanical alloying(HIMA) process. The raw materials, Mg(purity 99.9%) chip and Ni(purity 99.95%) chip was prepared by using a planetary ball mill apparatus(FRITSCH pulverisette 5). The balls to chips mass ratio(BCR) are 30:1. The hydrogen pressure induced 2.0MPa and milling times were 12, 24, 48, 72, 96 hours with a rotating speed of 200rpm. X-ray diffraction(XRD) analysis was made to characterize the crystallite size and misfit strain. The crystallite size measured by laser particle size analysis(PSA). Microstructure changes were investigated by scanning electron microscopy(SEM) and the transmission electron microscopy(TEM). The hydrogen storage properties were evaluated by using an Sivert's type automatic pressure-composition-therm(PCT) apparatus.

• Nuclear Engineering and Technology
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• 제52권8호
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• pp.1742-1748
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• 2020

TSSD, TSSP, and TSSP2 of hydrogen for optimized-Zirlo (Zirlo™) alloy were measured by DSC in the range of 53-457 wppm. Solvus curves of the TSSs are derived and proposed in this study. The results show that the temperature gap between TSSD and TSSP solvus lines of Zirlo™ are similar to those of other zirconium alloys, but another gap between the TSSD and TSSP2 line differs significantly. In particular, the TSSP2 solvus line becomes closer to the TSSD solvus line than to TSSP unlike Zircaloy-4, so ΔT_TSSD-TSSP2 of Zirlo™ decreases with decreasing temperature. This implies that hydride reorientation can take place more significantly in Zirlo™ than in Zircaloy-4, and the limited temperature variation of 65 ℃ during the vacuum drying and the cooling-down process may not be sufficient to prevent the triggering of hydride reorientation in Zirlo™ cladding under long-term dry storage.

• 한국산업융합학회 논문집
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• 제26권5호
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• pp.875-884
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• 2023

Hydrogen infiltration into metals has been reported to induce alterations in their mechanical properties under load. In this study, we conducted CTOD (Crack Tip Opening Displacement) tests on steel specimens designed for use in liquid hydrogen storage systems. Electrochemical hydrogen charging was performed using both FCC series austenitic stainless steel and BCC series structural steel specimens, while CTOD testing was carried out using a 500kN-class material testing machine. Results indicate a notable divergence in behavior: SS400 test samples exhibited a higher susceptibility to failure compared to austenitic stainless steel counterparts, whereas SUS 316L test samples displayed minimal changes in displacement and maximum load due to hydrogen charging. However, SEM (Scanning Electron Microscopy) analysis results presented challenges in clearly explaining the mechanical degradation phenomenon in the tested materials. This study's resultant database holds significant promise for enhancing the safety design of liquid hydrogen storage systems, providing invaluable insights into the performance of various steel alloys under the influence of hydrogen embrittlement.

• 한국수소및신에너지학회논문집
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• 제12권1호
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• pp.39-50
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• 2001

Vanadium based solid solution alloys have been studied as a potential negative electrode of Ni/MH battery due to their high hydrogen storage capacity. In order to improve the kinetic property of V-Ti alloy in KOH electrolyte, the ball-milling process with Ni, which has a catalytic effect of hydrogen absorption/desorption, was carried out to modify the surface properties of V-Ti-Cr alloys with high hydrogen storage capacity. Moreover, to overcome the problem of poor cycle life, V-Ti alloy substituted by Cr, V0.68 Ti0.20 Cr0.12, has been developed showing a good cycle performance (keeping about 80 % of initial discharge capacity after 200 cycles). The cycle life of surface-modified V0.68 Ti0.20 Cr0.12 alloy was improved by suppressing the formation of TiO2 layer on the alloy surface while decreasing the amount of dissolved vanadium in the KOH electrolyte. In order to promote the effect of Ni coating on the surface property of V0.68 Ti 0.20 Cr 0.12 alloy by ball-milling, filamentary-typed Ni, which has higher surface coverage area than sphere-typed Ni was used as a surface modifier. Consequently, the surface-modified V0.68 Ti0.20 Cr0.12 alloy electrode showed a improved discharge capacity of 460 mAh/g.

• 한국재료학회지
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• 제20권10호
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• pp.543-549
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• 2010

The hydrogen energy had recognized clean and high efficiency energy source. The research field of hydrogen energy was production, storage, application and transport. The commercial storage method was using high pressure tanks but it was not safety. However metal hydride was very safety due to high chemical stability. Mg and Mg alloys are attractive as hydrogen storage materials because of their lightweight and high absorption capacity (about 7.6 wt%). Their range of applications could be further extended if their hydrogenation properties and degradation behavior could be improved. The main emphasis of this study was to find an economical manufacturing method for Mg-Ti-Ni-H systems, and to investigate their hydrogenation properties. In order to examine their hydrogenation behavior, a Sievert's type automatic pressure-compositionisotherm (PCI) apparatus was used and experiments were performed at 423, 473, 523, 573, 623 and 673 K. The results of the thermogravimetric analysis (TGA) revealed that the absorbed hydrogen contents were around 2.5wt.% for (Mg8Ti2)-10 wt.%Ni. With an increasing Ni content, the absorbed hydrogen content decreased to 1.7 wt%, whereas the dehydriding starting temperatures were lowered by some 70-100 K. The results of PCI on (Mg8Ti2)-20 wt.%Ni showed that its hydrogen capacity was around 5.5 wt% and its reversible capacity and plateau pressure were also excellent at 623 K and 673 K.