• 한국수소및신에너지학회논문집
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• 제1권1호
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• pp.1-8
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• 1989

The hydriding kinetic mechanism and the change of the hydriding reaction rate of $MmNi_{4.5}Al_{0.5}$ during the thermally induced hydrogen absorption-desorption cycling are investigated. Comparison of the reaction rate data which are obtained by the pressure sweep method with the theoretical rate equations suggests that the hydriding rate controlling step has changed from the dissociative chemisorption of hydrogen molecules at the surface to the hydrogen diffusion through the hydride phase with the increase of the hydriding fraction. These hydriding kinetic mechanism is not changed during the cycling. However, the intrinsic hydriding reaction rate of $MmNi_{4.5}Al_{0.5}$ after 5500 cycles increases significantly comparing with the activated one. It is suggested that the change of the hydriding kinetic behavior due to intrinsic degradation of $MmNi_{4.5}Al_{0.5}$ can be interpreted as follows ; the formation of nickel cluster at the surface of the sample and the host metal atom exchange in bulk by thermal cycling.

• Nuclear Engineering and Technology
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• 제35권5호
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• pp.378-386
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• 2003

Recently failures of nuclear fuel rods in Korean nuclear power plants were reported and their failure causes have been investigated by using PIE techniques. Destructive and physico-chemical examinations reveal that the clad hydriding phenomena had caused the rod failures primarily and secondarily in each case. In this study, the basic mechanisms of the primary and the secondary hydriding failures are reviewed, PIE data such as cladding inner and outer surface oxide thickness and the restructuring of the fuel pellets are analyzed, and they are compared with the predicted behaviors by a fuel performance code. In addition, post-defected fuel behaviors are reviewed and qualitatively analyzed. The results strongly support that the hydriding processes, primary and secondary, played critical roles in the respective fuel rods failures and the secondary hydriding failure can take place even in the fuel rod with low linear heat generation rate.

• 대한금속재료학회지
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• 제50권6호
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• pp.463-468
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• 2012

A 71.5 wt%Mg-23.5 wt%Ni-5 wt%$Fe_2O_3$ (Mg-23.5Ni-$5Fe_2O_3$) sample was prepared by a quite simple process, reactive mechanical grinding, and its hydriding and dehydriding properties were then investigated. The reactive mechanical grinding of Mg with Ni and $Fe_2O_3$ is considered to facilitate nucleation and shorten the diffusion distances of the hydrogen atoms. After the hydriding-dehydriding cycling, the Mg-23.5Ni-$5Fe_2O_3$ sample contained $Mg_2Ni$ phase. Expansion and contraction of the hydride-forming materials (Mg and $Mg_2Ni$) with the hydriding and dehydriding reactions are also considered to increase the hydriding and dehydriding rates of the mixture by forming defects and cracks leading to the fragmentation of the particles. The temperature dependence of the hydriding rate of the sample is discussed.

• 한국수소및신에너지학회논문집
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• 제9권4호
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• pp.143-150
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• 1998

순수한 Mg의 수소와의 반응속도를 증가시키기 위하여 기계적으로 합금처리한 Mg-10wt.%Ni 혼합물의 수소화물 형성 분해 성질을 조사하였다. 수소화물 형성 분해 cycling을 시킴에 따라 $Mg_2Ni$상이 형성되고 그 양이 증가한다. 기계적인 합금 처리와 수소화물 형성 분해 cycling의 주요 효과는 결함의 수를 증가시키고, 비표면적을 크게하는 것으로 생각된다. 기계적으로 합금처리한 Mg-10wt.%Ni 혼합물은 활성화가 용이하게 이루어지고, 순수한 Mg, Mg-10wt.%Ni합금, Mg-25wt.%Ni합금, 그리고 $Mg_2Ni$합금과 비교하여, 수소화물 형성 속도와 수소 저장 용량이 아주 크고, 수소화물 분해 속도가 비교적 높다.

• 한국수소및신에너지학회논문집
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• 제10권1호
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• pp.9-17
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• 1999

기계적인 합금처리된 여러 Mg-Ni 혼합물 중에서 가장 우수한 수소저장 성질을 가지고 있는 Mg-25wt.%Ni 혼합물의 수소화물 형성 및 분해 반응에 대한 반응속도론적 연구를 하였다. 수소화물 형성 및 분해 속도를 측정하여 이론적인 반응 속도식과 비교함으로써 율속 단계를 결정하였다. Mg-25wt.%Ni의 수소화물 형성의 율속단계는 $H_a$ = 4.0 미만의 여러 $H_a$ 범위에서는 입자간 통로 (interparticle channel), 입자의 갈라진 틈(crack) 등을 통한 수소 분자의 이동 단계인 Knudsen 유동과 보통의 기체 확산이고, 4.0 < $H_a{\leq}4.25$ 범위에서는 성장하는 수소화물 층을 통한 수소 원자의 확산으로 생각된다. Mg-25wt.%Ni의 수소화물 분해의 율속 단계는 전 $H_d$ 범위에 걸쳐 수소 분자의 이동 단계인 Knusden 유동과 보통의 기체 확산이다.

• 한국세라믹학회지
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• 제47권2호
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• pp.106-112
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• 2010

This paper presents some experimental results on incubation time for massive hydriding of Zr alloys with oxide thickness. Oxide effects experiments on massive hydriding reaction of commercial Zr alloy claddings and pre-oxidized Zr alloys with hydrogen gas were carried out in the temperature range from 300 to $400^{\circ}C$ with thermo-gravimetric apparatus. Experimental results for oxide effects on massive hydriding kinetics show that incubation time is not proportional to oxide thickness and that the massive hydriding kinetics of pre-filmed Zr alloys follows linear kinetic law and the hydriding rate are similar to that of oxide-free Zr alloys once massive hydriding is initiated. There was a difference in micro-structures between oxide during incubation time and oxide after incubation time. Physical defects such as micro-cracks and pores were observed in only oxide after incubation time. Therefore, the massive hydriding of Zr alloys seems to be ascribed to short circuit path, mechacical or physical defects, such as micro-cracks and pores in the oxide rather than hydrogen diffusion through the oxide resulting from the increase of oxygen vacancies in the hypostoichiometric oxide.

• 한국재료학회지
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• 제10권1호
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• pp.15-20
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• 2000

기계적으로 합금처리한 Mg-18wt.%Ni 혼합물의 수소저장특성이 조사되었다. 1h, 3h, 그리고 6h 동안 기계적으로 합금처리한 혼합물들 중에서 6h동안 기계적으로 합금처리한 혼합물(MA 6h sample)이 가장 좋은 활성화, 수소화물 형성.분해 특성을 보인다. 수소화물 형성.분해 cycling을 시킴에 따라 $Mg_2$Ni상이 형성된다. MA 6h sample은 비교적 쉽게 활성화되며, 순수한 Mg나 Mg-10wt.%Ni 합금보다 수소화물 형성속도가 높으나, $Mg_2$Ni 합금보다는 수소화물 형성속도가 약간 낮다. MA 6h sample은 $Mg_2$Ni 합금에 비해 낮은 수소화물 분해속도를 보이지만, 순수한 Mg나 Mg-25wt.%Ni 합금보다는 높은 수소화물 분해속도를 보인다. MA 6h sample은 순수한 Mg나 다른 합금들보다 큰 수소저장용량을 가지고 있다.

• 한국재료학회지
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• 제24권3호
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• pp.129-134
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• 2014

Pure $MgH_2$ was milled under a hydrogen atmosphere (reactive mechanical grinding, RMG). The hydrogen storage properties of the prepared samples were studied at a relatively low temperature of 423 K and were compared with those of pure Mg. The hydriding rate of the Mg was extremely low (0.0008 wt% H/min at n = 4), and the $MgH_2$ after RMG had higher hydriding rates than that of Mg at 423 K under 12 bar $H_2$. The initial hydriding rate of $MgH_2$ after RMG at 423 K under 12 bar $H_2$ was the highest (0.08 wt% H/min) at n = 2. At n = 2, the $MgH_2$ after RMG absorbed 0.39 wt% H for 5 min, and 1.21 wt% H for 60 min at 423K under 12 bar $H_2$. At 573 K under 12 bar $H_2$, the $MgH_2$ after RMG absorbed 4.86 wt% H for 5 min, and 5.52 wt% H for 60 min at n = 2. At 573 K and 423 K under 1.0 bar $H_2$, the $MgH_2$ after RMG and the Mg did not release hydrogen. The decrease in particle size and creation of defects by reactive mechanical grinding are believed to have led to the increase in the hydriding rate of the $MgH_2$ after RMG at a relatively low temperature of 423 K.

• 한국수소및신에너지학회논문집
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• 제5권1호
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• pp.9-17
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• 1994

Activation behavior, hydriding rate and disintegration were studied for a compact in pellet form and hydrogen storage alloy particles treated with newly developed inorganic solution. Cylindrical disc of 12.95mm diameter and of 7.1mm thickness was prepared by compressing(8ton) a mixture of $MmNi_{4.5}Al_{0.47}$ and PTFE. Chemical treatment of particles with 1mol of solution was performed at room temperature for several hours until the pH of solution did not change. Chemical treatment made much accelerated activation without any incubation period which generally exists in the untreated alloys and the hydriding reaction rate after full activation also was improved.

• 한국수소및신에너지학회논문집
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• 제9권4호
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• pp.151-160
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• 1998

기계적으로 합금처리한 혼합물 속에 포함된 Mg의 수소 저장 성질의, 시료 내의 Ni의 중량 백분율에 따른 변화를 조사하였다. Ni 중량을 기준으로 한, Mg2Ni 상을 형성한 Ni의 중량 백분율은 Mg-10wt.%Ni 시료에서 가장 높다. 첫번째 수소화물 형성 싸이클에서, Mg의 수소화물 형성 속도에 미치는 기계적 합금처리의 효과는 Mg-25wt.%Ni 시료에서 가장 높다. 활성화 후에는, 기계적 합금처리와 수소화물 형성 분해 싸이클링이 Mg의 수소화물 형성 속도에 미치는 효과는 Mg-10wt.%Ni 시료에서 가장 높다. 충분한 수소화물 형성 분해 싸이클링 후에는 Mg의 수소 저장 용량에 미치는 효과는 Mg-10wt.%Ni에서 가장 높다. Mg의 수소화물 형성 속도와 분해 속도에 미치는 효과는 Mg-25wt.%Ni 시료에서 가장 높다. 시료 내에 포함된 Mg의 수소 저장 성질에 가장 좋은 효과를 가지고 있는 최적의 조성은 Mg-25wt.%Ni이고 그 다음이 Mg-10wt.%Ni이다. 기계적 합금 처리와 수소화물 형성 분해 싸이클링은, 활발한 핵 생성 자리 역할을 할 수 있는 많은 결함을 만들고, 비 표면적을 증가시켜 수소의 확산 거리를 짧게한다.