• 산업기술연구
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• 제41권1호
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• pp.25-30
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• 2021

Hydride-dehydride process for efficient recycling of tantalum (Ta) is used for manufacturer of Ta powder. In case of metal powder, Impurities as like nitride, oxygen, hydrogen is decreased of physical properties. For manufacture of Ta powder, control of theses impurities is important. In this study, to decreased of impurities on Ta powder using HDH process optimize dehydride condition. Dehydration behavior of Ta is depended on temperature, time, and atmosphere. Phase transition of Ta hydride is analyzed by X-ray diffraction (XRD). Concentration of hydrogen is decreased with temperature increased. At high temperature, concentration of hydrogen in Ta is similar according to time increased. Size and morphology of powder is not observed after dehydride. Ta powder, which is less than 20 um, concentration of hydrogen under 800 ppm is obtain.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2009년도 춘계학술대회 논문집
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• pp.781-781
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• 2009

We demonstrate that trasition metal catalyst nanoparticle (NP) attached to carbon nitride nanotubes (CNNTs) show selective catalytic activities on hydrogen generation from the water solution including chemical hydride negative ions. The natural bonding orbitals (NBO) obtained from the first-principle calculations shows that the catalysts attached on CNNTs are quite differently polarized when they play for hydrogen generation from chemical hydride ions and hydrogen of water. For Co and Ni nanoparticles attached on CNNTs, their charges are more positively polarized when they interact with $BH_4^-Na^+$ and $H_2O$ while Pt atoms are less positively charged. In this matter, the increased positive charges on catlyst nanoparticles are proven to be more efficient in attracting hydride negative ions, thus improving hydrogen generate rates. Consequently, this result implies that these different charge polarization leads to selective catalytic activities of NPs-CNNTs. In the hydrogen generation experiments, Co-CNNTs shows the highest hydrogen generation rate when the similar amounts of catalyst nanoparticles (Co, Ni, and Pt) are dispersed on the sidewalls of CNNTs.

• 전자공학회논문지 IE
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• 제48권2호
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• pp.1-5
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• 2011

HVPE법으로 $3{\mu}m$의 GaN epi를 성장하고 이 위에 DC 마그네트론 Sputter를 이용하여 Ti stripe 패턴 형성하였으며 다시 HVPE를 이용하여 $120{\mu}m$ ~ $300{\mu}m$ 두께의 GaN를 overgrowth하였다. 성장된 GaN는 SEM 측정으로 Ti 패턴한 부분에서 void가 관찰되었고 보다 두꺼운 GaN를 성장시에는 크랙이 void를 따라 발생할 수 있음을 확인하였으며 XRD측정으로 FWHM은 188 arcsec로 측정되었다. 성장전의 GaN epi와의 반치폭을 비교하였을 때 패턴에 사용된 Ti는 overgrowth시 결정성에는 크게 영향을 주지 않는다는 것을 확인하였다.

• 한국수소및신에너지학회논문집
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• 제21권4호
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• pp.249-257
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• 2010

In this paper, a three-dimensional hydrogen absorption model is developed to precisely study hydrogen absorption reaction and resultant heat and mass transport phenomena in metal hydride hydrogen storage vessels. The 3D model is first experimentally validated against the temperature evolution data available in the literature. In addition to model validation, the detailed simulation results shows that at the initial absorption stage, the vessel temperature and H/M ratio distributions are uniform throughout the entire vessel, indicating that the hydrogen absorption is so efficient during the early hydriding process and thus local cooling effect is not influential. On the other hand, nonuniform distributions are predicted at the latter absorption stage, which is mainly due to different degrees of cooling between the vessel wall and core regions. This numerical study provides the fundamental understanding of detailed heat and mass transfer phenomena during hydrogen absorption process and further indicates that efficient design of storage vessel and cooling system is critical to achieve fast hydrogen charging and high hydrogen storage efficiency.

• 설비공학논문집
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• 제17권9호
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• pp.824-829
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• 2005

MHR(Metal Hydride Refrigerator) powered by MGT exhaust gas is investigated to find out the optimum conditions corresponding to MGT operating powers. There are many factors to affect cooling capacity of MHR. In this study, the effect of switching time, flow rate of brine on cooling temperature and capacity is investigated. The present results show (1) hydrogen reaction is saturated with 25 min switching time at 25 kW MGT power, (2) cooling power shows maximum phenomenon with increasing switching time, (3) optimum switching times are 20 minutes for 15kW MGT power and 15 minutes for 20, 25kW MGT power, (4) according to increasing brine flow rate, cooling capacity shows decrease at 15 kW MGT power and changes little at above 20 kW MGT power.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회B
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• pp.2346-2351
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• 2008

This study deals with heat pipes inserted into the metal hydride(MH) reactor to increase the effective thermal conductivity of the system and thus to enhance the thermal control characteristics. A numerical analysis was conducted to predict the effect of inserted heat pipes on the heat transfer characteristics of MH, which inherently has extremely low thermal conductivity. The numerical model was a cylindrical container of O.D. 76.3 mm and length 1 m, which is partially filled with about 60% of MH material. The heat pipe was made of copper-water combination, which is suitable for operation temperature range between $10^{\circ}C$ and $80^{\circ}C$. Both inner -and outer- heat pipes were considered in the model. Less than two hours of transient time is of concern when decreasing or increasing the temperature for absorption and discharge of hydrogen gas. FLUENT, a commercial software, was employed to predict the transient as well as steady-state temperature distribution of the MH reactor system. The numerical results were compared and analyzed from the view point of temperature uniformity and transient time up to the specified maximum or minimum temperatures.

• 대한금속재료학회지
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• 제48권12호
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• pp.1123-1129
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• 2010

In order to apply the Sievert's type automatic apparatus to thermal analysis of hydrogen absorbing materials, the dehydrogenation of the Mg-H system was investigated. As the initial wt% of hydrogen was increased to 4.4, the peak temperature of evolution rate shifted to higher temperature. However, with the initial wt% of hydrogen higher than 4.4, peak temperature of evolution rate did not change. The peak temperatures of evolution rate obtained by automatic apparatus were almost the same as those measured by a manual apparatus. As the heating rate was increased, the peak temperatures increased; the peak temperatures for heating rates 1, 2 and 3 K/min were 664, 687 and 702 K, respectively. The activation energy for the decomposition of Mg hydride was 101 kJ/mol. The Sievert's type automatic apparatus can be successively applied to the thermal analysis of metal hydride.

• 한국수소및신에너지학회논문집
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• 제24권1호
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• pp.36-43
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• 2013

In this paper, a three-dimensional hydrogen desorption model is applied to a thin double-layered annulus ZrCo hydride bed and validated against the temperature evolution data measured by Kang et al. The present model reasonably captures the bed temperature evolution behavior and the 90% hydrogen discharging time. In addition, the performance of thin double-layered annulus bed is evaluated by comparing with a simple cylindrical bed using hydrogen desorption model. This study provides multi-dimensional contours such as temperature and H/M atomic ratio in the metal hydride region. This numerical study provides fundamental understanding during hydrogen desorption process and indicates that efficient design of the metal hydride bed is critical to achieve rapid hydrogen discharging performance. The present three-dimensional hydrogen desorption model is a useful tool for the optimization of bed design and operating conditions.

• Bulletin of the Korean Chemical Society
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• 제33권1호
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• pp.153-158
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• 2012

The hydrogenation of $AlB_2$-type BaGaGe exhibits a metal to insulator (MI) transition, inducing a puckering distortion of the original hexagonal [GaGe] layers. We investigate the electronic structure changes associated with the hydrogen-induced MI transition, using extended H$\ddot{u}$ckel tight-binding band calculations. The results indicate that hydrogen incorporation in the precursor BaGaGe is characterized by an antibonding interaction of $\pi$ on GaGe with hydrogen 1s and the second-order mixing of the singly occupied antibonding $\pi^*$ orbital into it, through Ga-H bond formation. As a result, the fully occupied bonding $\pi$ band in BaGaGe changes to a weakly dispersive band with Ge pz (lone pair) character in the hydride, which becomes located just below the Fermi level. The Ga-Ge bonds within a layered polyanion are slightly weakened by hydrogen incorporation. A rationale for this is given.

• Bulletin of the Korean Chemical Society
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• 제11권2호
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• pp.109-114
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• 1990

The anionic transition metal hydrides $(HW(CO)_4P(OMe)_3\;^-,\;HW(CO)_5\;^-,\;HCr(CO)_5\;^-,\;HFe(CO)_4\;^-)$ react with transition metal alkyl $(CpMo(CO)_3(CH_3)$ to yield $CH_4\;and\;CH_3CHO$ in addition to the inorganic products $(CpMo(Co)_3\;^-$, etc.). The reaction of these anionic metal hydrides with CpMo(CO)3{CH2CH(CH2)2} may lead to an elucidation of the reaction mechanisms involved; the organic product distributions are among $CH_4,\;CH_2\;=\;CHCH_2CH_3$, and $CH_3CH(CH_2)_2$, depending upon the anionic metal hydride used. These anionic metal hydrides also are reported to undergo a hydride-halide exchange reaction with organic halides; therefore, these similar reactions have been compared in terms of leaving group ability $(CpMo(CO)_3\;^-\;vs.\;Br^-)$ and the mechanistic pathways.