• Title/Summary/Keyword: Hydrogenation Properties

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The Evaluation of Hydrogenation Properties on $MgH_x-Fe_2O_3$ Composite by Mechanical Alloying (기계적 합금화법으로 제조된 $MgH_x-Fe_2O_3$ 복합재료의 수소화 특성 평가)

  • Seok, Song;Cho, Kyoung-Won;Hong, Hae-Whan
    • Transactions of the Korean hydrogen and new energy society
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    • v.18 no.1
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    • pp.26-31
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    • 2007
  • Hydrogen has a high potential to be a renewable substitute for fossil fuels, because of its high gravimetric energy density and environment friendliness. In particular, Magnesium have attracted much interest since their hydrogen capacity exceeds that of known metal hydrides. One of the approaches to improve the kinetic is addition of metal oxide. In this paper, the effect of $Fe_2O_3$ concentration on the kinetics of Mg hydrogen absorption reaction was investigated. $MgH_x-Fe_2O_3$ composites have been synthesized by hydrogen induced mechanical alloying. The powder synthesized was characterized by XRD, SEM and simultaneous TG, DSC analysis. The hydrogenation behaviors were evaluated by using a sievert's type automatic PCT apparatus. Absorption and desorption kinetics of Mg catalyzed with 5,10 mass% $Fe_2O_3$ are determined at 423, 473, 523, 573, 623K.

Structural transition of Ti-Cr-V alloys with hydrogenation and dehydrogenation and the improvement of their hydrogen storage properties by heat treatment (Ti-Cr-V 합금의 수소화-탈수소화에 따른 상천이 및 열처리에 의한 수소저장특성의 향상)

  • You, Jeong-Hyun;Cho, Sung-Wook;Shim, Gun-Choo;Choi, Good-Sun;Park, Choong-Nyeon;Choi, Jeon
    • Transactions of the Korean hydrogen and new energy society
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    • v.17 no.2
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    • pp.125-132
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    • 2006
  • The alloys which compositions were represented by the formula, $Ti_{(0.22+X)}Cr_{(0.28+1.5X)}V_{(0.5-2.5X)}$ ($0{\leq}X{\leq}0.12$), had the total hydrogen storage capacity higher than 3 wt% and the effective hydrogen storage capacity higher than 1.4 wt%. Particularly, among all the tested alloys, the $Ti_{0.32}Cr_{0.43}V_{0.25}$ alloy exhibited the best effective hydrogen storage capacity of 1.65 wt%. Furthermore, the reversible bcc${\leftrightarrow}$fcc structural transition was observed with hydrogenation and dehydrogenation, which predicted the possibility of pressure cycling. EDS analysis revealed micro-segregation, which suggested the necessity of microstructure homogenization by heat treatment. The $Ti_{0.32}Cr_{0.43}V_{0.25}$ alloy was selected for heat treatment and for other related studies. The results showed that the total and the effective hydrogen storage capacity increased to 3.7 wt% and 2.3 wt%, respectively. The flatness of the plateau region was also greatly improved and heat of hydride formation was determined to be approximately -36 kJ/mol $H_2$.

Evaluation of Hydrogenation Properties on Ti-Nb-Cr Alloys by Single-Roll Melt Spinning (단롤주조법에 의한 Ti-Nb-Cr 합금의 제조와 수소화 특성 평가)

  • Kim, Kyeong-Il;Hong, Tae-Whan
    • Korean Journal of Metals and Materials
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    • v.47 no.7
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    • pp.433-439
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    • 2009
  • Ti and Ti based hydrogen storage alloys have been thought to be the third generation of alloys with a high hydrogen capacity, which makes it difficult to handle because of high reactivity. In order to solve the problem, the activation of a wide range of hysteresis of hydriding/dehydriding and without degradation of hydrogen capacity due to the hydriding/dehydriding cycle have to be improved in order to be aplied. Ti-Cr alloys have a high capacity about 0.8 wt.% in an ambient atmosphere. When the Ti-Cr alloys are added to Nb and Ta elements, they formed a laves phase in the alloy system. The Nb element was expected to make easy diffuse hydrogen in the Ti-Cr storage alloy, which was a catalytic element. In this study, the Ti-Nb-Cr ternary alloy was prepared by melt spinning. As-received specimens were characterized using XRD (X-ray Diffraction), SEM (Scanning Electron Microscopy) with EDX (Energy Dispersive X-ray) and TG/DSC (Thermo Gravimetric Analysis/Differential Scanning Calorimetry). In order to examine hydrogenation behavior, the PCI (Pressure-Composition-Isotherm) was performed at 293, 323, 373 and 423 K.

Hydrogenation Properties of Mg-5 wt.% TiCr10Nbx (x=1,3,5) Composites by Mechanical Alloying Process (기계적 합금화법으로 제조된 Mg-5 wt.% TiCr10Nbx (x=1,3,5) 복합재료의 수소화 특성 평가)

  • Kim, Kyeong-Il;Hong, Tae-Whan
    • Korean Journal of Metals and Materials
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    • v.49 no.3
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    • pp.264-269
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    • 2011
  • Hydrogen and hydrogen energy have been recognized as clean energy sources and high energy carrier. Mg and Mg alloys are attractive hydrogen storage materials because of their lightweight and low cost materials with high hydrogen capacity (about 7.6 wt.%). However, the commercial applications of the Mg hydrides are currently hinder by its high absorption/desorption temperature, and very slow reaction kinetics. However, Ti and Ti based hydrogen storage alloys have been thought to be the third generation of alloys with a high hydrogen capacity, which makes it difficult to handle because of high reactivity. One of the most methods to develope kinetics was addition of transition metal. Therefore, Mg-Ti-Cr-Nb alloy was fabricated to add TiCrNb by hydrogen induced mechanical alloying. TiCrNb systems have included transition metals, low operating temperatures and hydrogen storage materials. As-received specimens were characterized using X-ray Diffraction analysis (XRD), Scanning Electron Microscopy (SEM) and Thermo Gravimetric analysis/Differential Scanning Calorimetry (TG/DSC). $Mg-TiCr_{10}Nb$ systems were evaluated for hydrogen kinetics by Sievert's type Pressure-Composition-Isotherm (PCI) equipment. The operating temperature range was 473, 523, 573 and 623 K.

Study on the Characteristics of Hydride Heat Pump Using the Zr-based Laves Phase Alloys (Zr-based 합금을 이용한 hydride heat pump의 작동 특성에 관한 연구)

  • Lee, Soo-Geun;Lee, Jai-Young
    • Transactions of the Korean hydrogen and new energy society
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    • v.2 no.1
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    • pp.39-46
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    • 1990
  • In order to improve the power of hydride heat pump, prototype heat pump was constructed using $Zr_{0.95}Ti_{0.05}Cr_{0.9}Fe_{1.1}$-$Zr_{0.9}Ti_{0.1}Cr_{0.6}Fe_{1.4}$ which had very good hydrogenation properties. The power changed with operating parameter such as cycle time, air flow rate, and temperature of hot air was investigated. The power shows maximum value with cycle time. The power increased with air flow rate and temperature of hot air. The power of the heat pump was $65-72 Kcal/Kg-alloy{\cdot}h$ under optimum operating condition, which was superior to that the system using $LaNi_{0.9}Al_{0.3}-MmNi_{4.15}Al_{0.66}Fe_{0.2}$ alloy pairs.

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A study on the fabrication process development of FeTi type alloy for Ni/MH battery (니켈-수소 2차전지용 철-티타늄계 전극용 합금제조 공정에 관한 연구)

  • Lee, Moon-Goo;Kim, Eul-Su;Jeong, Sun-Dol;Kim, Ki-Won;Ahn, Hyo-Jun
    • Transactions of the Korean hydrogen and new energy society
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    • v.10 no.1
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    • pp.1-7
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    • 1999
  • In order to study on the effect of fabrication methods on the changes of hydrogenation properties of FeTi alloy, FeTi samples were prepared using three different methods, i.e., arc melting, mechanical alloying and combination of the two methods. The FeTi prepared by mechanical alloying represented amorphous structure. The hydrogen storage capacity of arc melted FeTi alloy is larger than any other samples. However, FeTi electrode fabricated by mechanical alloying after arc melting showed largest discharge capacity among them.

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A Study on the Hydrogenation Properties of Mechanically Alloyed Ti0.7Mg0.3Ni (기계적합금화에 의해 제조된 Ti0.7Mg0.3Ni합금의 수소화학반응특성에 관한 연구)

  • Kim, Eul-Soo;Ahn, Hyo-Jun;Kim, Ki-Won
    • Transactions of the Korean hydrogen and new energy society
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    • v.8 no.4
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    • pp.173-180
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    • 1997
  • The Mechanically Alloyed $Ti_{0.7}Mg_{0.3}Ni$ was investigated as a function of milling time by X-ray diffraction, SEM(scanning electron microscope), EDS(energy dispersive spectrometer), P-C-Isotherm curves. After 10hrs milling, mixed $Ti_{0.7}Mg_{0.3}Ni$ powders were changed to amorphous phase. And amorphous $Ti_{0.7}Mg_{0.3}Ni$ alloys became TiNi phase crystalline after heat treatment at 873K in a vacuum for 1 hour. The hydrogen absorption capacity of the annealed $Ti_{0.7}Mg_{0.3}Ni$ alloy increased as a function of mechanical alloying time.

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Polycrystalline Silicon Thin Film Transistor Fabrication Technology (다결정 실리콘 박막 트랜지스터 제조공정 기술)

  • 이현우;전하응;우상호;김종철;박현섭;오계환
    • Journal of the Korean Vacuum Society
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    • v.1 no.1
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    • pp.212-222
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    • 1992
  • To use polycrystalline Si Thin Film Transistor (poly-Si TFT) in high density SRAM instead of High Load Resistor (HLR), TFT is needed to show good electrical characteristics such as large carrier mobility, low leakage current, high driver current and low subthreshold swing. To satisfy these electrical characteristics, the trap state density must be reduced in the channel poly. Technological issues pertinent to the channel poly fabrication process are investigated and discussed. They are solid phase growth (SPG), Si-ion implantation, laser annealing and hydrogenation. The electrical properties of several CVD oxides used as the gate oxide of TFT are compared. The dependence of the electrical characteristics of TFT on source-drain ion-implantation dose, drain offset length and dopant lateral diffusion are also described.

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Electronic and Bonding Properties of BaGaGeH: Hydrogen-induced Metal-insulator Transition from the AlB2-type BaGaGe Precursor

  • Kang, Dae-Bok
    • Bulletin of the Korean Chemical Society
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    • v.33 no.1
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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.

Characteristics of Hydrogenation and Electronic Properties of Thin Film Y-Hx

  • Cho, Young-Sin;Jee, Chan-Soo;Kim, Sun-Hee;Yoon, Jong-Hwan
    • Transactions of the Korean hydrogen and new energy society
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    • v.3 no.2
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    • pp.35-43
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    • 1992
  • Thin Film yttrium, 500 nm thick, was prepared by electron beam evaportion on sapphire substrate. Film was hydrogenated at room temperature upto 1 bar hydorgen pressure without any activation process. Electrical resistivity was measured by four-point DC method in the temperature range between room temperature and 30 K for various hydorgen concentration x = 0 to 2.924 of $YH_x$ sample. Temperature dependent resistance of $YH_{2\;924}$ shows low temperature minmum at 105K ($36{\mu}{\Omega}cm$ deep), the metal-semiconductor transition at 260K, and a hysteresis, which are similar behavior to bulk $YH_x$(x>2) experimental results.

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