• Title/Summary/Keyword: Mg hydride

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Influences of the Addition of Hydride-Forming Elements and Oxide and Hydriding-Dehydriding Cycling on the Hydriding and Dehydriding Characteristics of Mg

  • Song, Myoung Youp;Kwak, Young Jun;Park, Hye Ryoung
    • Korean Journal of Metals and Materials
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    • v.50 no.5
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    • pp.375-381
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    • 2012
  • Magnesium prepared by mechanical grinding under $H_2$ (reactive mechanical grinding) with transition elements or oxides showed relatively high hydriding and dehydriding rates when the content of additives was about 20 wt%. Ni was chosen as a transition element to be added. $Fe_2O_3$ was selected as an oxide to be added. Ti was also selected since it was considered to increase the hydriding and dehydriding rates by forming Ti hydride. A sample $Mg-14Ni-3Fe_2O_3-3Ti$ was prepared by reactive mechanical grinding, and its hydrogen storage properties were examined. This sample absorbs 4.02 wt% H for 5 min, and 4.15 wt% H for 10 min, and 4.42 wt% H for 60 min at n = 2. It desorbs 2.46 wt% H for 10 min, 3.98 wt% H for 30 min, and 4.20 wt% H for 60 min at n = 2. The effects of the Ni, $3Fe_2O_3$, and Ti addition, and hydriding-dehydriding cycling were discussed.

Evaluation of Hydrogenation Properties of Thixotropic Mg-3, 6wt%Ni Hydrogen Absorbing Alloys (이상점성 처리된 Mg-3, 6wt%Ni합긍의 수소화 특성평가)

  • Lee, Sung-Gon;Ha, Won;Hong, Tae-Whan;Kim, Young-Jig
    • Korean Journal of Materials Research
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    • v.12 no.12
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    • pp.935-940
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    • 2002
  • Magnesium-3, 6wt% Nickel alloys were fabricated by Rotation-Cylinder Method(RCM) in ambient atmosphere. The alloys were divided into two different heat-treating conditions, as-cast and thixotropic treated. Thixotropic heat treatment enhances the separation of primary hydride former of Mg and the catalytic phase of $Mg_2$Ni. Hydrogenation properties of the each alloy were evaluated and compared by PCI(Pressure-Composition Isotherm) measurement. The maximum hydrogen capacity and the reversible capacity of as -cast Mg-6wt% Ni alloy were 5.2wt% and 3.8wt% at 623k, respectively.

Hydrogen Generation through the Reaction with Water of MgO, MgCl2 or Ni+Nb2O5 - Added Magnesium Hydrides

  • Hong, Seong-Hyeon;Kim, Hyun-Jin;Song, Myoung Youp
    • Korean Journal of Metals and Materials
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    • v.50 no.2
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    • pp.183-190
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    • 2012
  • Hydrogen was generated by the reaction of metal hydride with water. The variation of hydrogen generation with the kind of powders (milled $MgH_2$, and $MgH_2$ milled with various contents of MgO, $MgCl_2$ or $Ni+Nb_2O_5$) was investigated. $MgH_2$ powder with a hydrogen content of 6.05 wt% from Aldrich Company was used. Hydrogen is generated by the reaction of Mg as well as $MgH_2$ with water, resulting in the formation of byproduct $Mg(OH)_2$. For about 5 min of reaction time, milled $95%MgH_2+5%MgO$ has the highest hydrogen generation rate among milled $MgH_2+x%MgO$ (x=0, 5, 10, 15 and 20) samples. Milled $90%MgH_2+10%MgCl_2$ has the highest hydrogen generation rate among all the samples.

Mass Production of Mg based Hydrogen Absorbing Alloys and Evalution of Hydrogenation and Degradation Properties by Hydriding/Dehydriding Cyclic Test (교반관법에 의한 Mg 기지 수소저항합금의 대량제조와 반복적 수소화 반응에 따른 수소화 특성 및 열화특성 평가)

  • Ha, Won;Lee, Sung-Gon;Hong, Tae-Whan;Kim, Young-Jig
    • Journal of Hydrogen and New Energy
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    • v.13 no.1
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    • pp.13-23
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    • 2002
  • Hydrogenation properties of Mg-Ni and Mg-Ti-Ni alloys were investigated by Pressure-Composition Isotherm (PCI) test. Those alloys were fabricated by a new alloying method, Rotation-Cylinder Method (RCM). The as-cast microstructure of Mg-10 mass% Ni alloy consists of an island-like hydride forming $\alpha$-Mg phase and the eutectic structure. After 350 cyclic tests, Mg-lO mass % Ni alloy was pulverized into fine particles of 100 nm. The fine particles, which have a large specific surface area, are highly reactive with hydrogen. However, extreme pulvehzation can separate Mg from $Mg_2Ni$ in the eutectic structure, so $Mg_2Ni$ of the eutectic structure cannot behave as a dissociated hydrogen supplier.

Hydrogenation and Electrochemical Characteristics of Amorphous-nanostructured Mg-based Alloys

  • Gebert, A.;Khorkounov, B.;Schultz, L.
    • Journal of Powder Materials
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    • v.13 no.5 s.58
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    • pp.327-335
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    • 2006
  • In the development of new hydrogen absorbing materials for a next generation of metal hydride electrodes for rechargeable batteries, metastable Mg-Ni-based compounds find currently special attention. Amor phous-nanocrystalline $Mg_{63}Ni_{30}Y_7$ and $Mg_{50}Ni_{30}Y_{20}$ alloys were produced by mechanical alloying and melt-spinning and characterized by means of XRD, TEM and DSC. On basis of mechanically alloyed Mg-Ni-Y powders, complex hydride electrodes were fabricated and their electrochemical behaviour in 6M KOH (pH=14,8) was investigated. The electrodes made from $Mg_{63}Ni_{30}Y_7$ powders, which were prepared under use of a SPEX shaker mill, with a major fraction of nanocrystalline phase reveal a higher electrochemical activity far hydrogen reduction and a higher maximum discharge capacity (247 mAh/g) than the electrodes from alloy powder with predominantly amorphous microstructure (216 mAh/g) obtained when using a Retsch planetary ball mill at low temperatures. Those discharge capacities are higher that those fur nanocrystalline $Mg_2Ni$ electrodes. However, the cyclic stability of those alloy powder electrodes was low. Therefore, fundamental stability studies were performed on $Mg_{63}Ni_{30}Y_7$ and $Mg_{50}Ni_{30}Y_{20}$ ribbon samples in the as-quenched state and after cathodic hydrogen charging by means of anodic and cathodic polarisation measurements. Gradual oxidation and dissolution of nickel governs the anodic behaviour before a passive state is attained. A stabilizing effect of higher fractions of yttrium in the alloy on the passivation was detected. During the cathodic hydrogen charging process the alloys exhibit a change in the surface state chemistry, i.e. an enrichment of nickel-species, causing preferential oxidation and dissolution during subsequent anodization. The effect of chemical pre-treatments in 1% HF and in $10\;mg/l\;YCl_3/1%\;H_2O_2$ solution on the surface degradation processes was investigated. A HF treatment can improve their anodic passivation behavior by inhibiting a preferential nickel oxidation-dissolution at low polarisation, whereas a $YCl_3/H_2O_2$ treatment has the opposite effect. Both pre-treatment methods lead to an enhancement of cathodically induced surface degradation processes.

Evaluation of Hydrogen Properties on Mg2NiHx-Graphene Composites by Mechanical Alloying (기계적 합금화법으로 제조한 Mg2NiHx-Graphene 복합재료의 수소화 특성 평가)

  • Lee, Young-Sang;Lee, Soo-Sun;Lee, Byung-Ha;Jung, Seok;Hong, Tae-Whan
    • Journal of Hydrogen and New Energy
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    • v.25 no.1
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    • pp.19-27
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    • 2014
  • Mg hydride has a high hydrogen capacity (7.6%), at high temperature, and is a lightweight and low cost material, thus it a promising hydrogen storage material. However, its high operation temperature and very slow reaction kinetics are obstacles to practical application. In order to overcome these disadvantages of Mg hydride, graphene powder was added to it. The addition of graphene has been shown to reduce the operating temperature of dehydrogenation. Moreover, in this report the environmental aspects of $MgH_x$-Graphene composites are investigated by means of the environmental life cycle assessment (LCA) method. $MgH_x$-Graphene mixture was prepared by hydrogen induced mechanical alloy (HIMA). The synthesized powder was characterized by XRD(X-ray Diffraction). The hydrogenation behaviors were evaluated by using a Sievert's type automatic PCT apparatus. Such evaluation of Materials also conducted in the LCA. From the result of P-C-T(Pressure-Composition-Temperature) curves, the $MgH_x$-3wt.% graphene composite was evaluated as having a 5.86wt.% maximum hydrogen storage capacity, at 523K. From absorption kinetic testing, the $MgH_x$-7wt.% graphene composite was evaluated as having a maximum 6.94wt.%/ms hydrogen absorption rate, at 573K. Environment evaluation results for the $MgH_x$-graphene composites and other materials indicated environmental impact from the electric power used and from the materials themselves.

Dehydriding Kinetics of the Mg2NiHx by Isothermal Thermogravimetry Analysis (등온 열중량 분석에 의한 Mg2NiHx 탈수소화 반응속도 연구)

  • Hong, Tae Whan;Kim, Young Jig
    • Journal of Hydrogen and New Energy
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    • v.11 no.1
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    • pp.11-18
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    • 2000
  • In order to investigate the dehydriding properties of the $Mg_2NiH_x$ formed by hydrogen induced mechanical alloying, we performed isothermal thermogravimetry analysis at 453, 463, 473, 483, 493, 503 and 513K for 1 hours. Dehydrogenation kinetics were dependant strongly on the MA conditions which determine the In other words, kinds of synthesized hydrides phases and the crystal microstructures. The MA condition, 66:1 BCR(balls to chips mass ratio), especially 96h milling time, revealed the hydride phases of nano-/ amorphous state and the dehydriding activation energy of $43.4{\pm}3.6kJ/mole$.

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Evaluations of Hydrogen Properties of MgHx-Nb2O5 Oxide Composite by Hydrogen Induced Mechanical Alloying (수소 가압형 기계적 합금화법으로 제조한 MgHx-Nb2O5 산화물 복합 재료의 수소화 특성 평가)

  • Lee, Nari;Lee, Soosun;Hong, Taewhan
    • Journal of Hydrogen and New Energy
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    • v.23 no.5
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    • pp.429-436
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    • 2012
  • Mg and Mg-based alloys are regarded as strong candidate hydrogen storage materials since their hydrogen capacity exceeds that of known metal hydrides. One of the approaches to improve kinetic is addition of metal oxide. In this paper, we tried to improve the hydrogenation properties of Mg-based hydrogen storage composites. The effect of transition metal oxides, such as $Nb_2O_5$ on the kinetics of the Magnesium hydrogen absorption kinetics was investigated. $MgH_x$-5wt.% $Nb_2O_5$ composites have been synthesized by hydrogen induced mechanical alloying. The powder fabricated was characterized by X-ray diffraction (XRD), Field Emission-Scanning Electron Microscopy (Fe-SEM), Energy Dispersive X-ray (EDX), BET and simultaneous Thermo Gravimetric Analysis / Differential Scanning Calorimetry (TG/DSC) analysis. The Absorption / desorption kinetics of $MgH_x$-5wt.% $Nb_2O_5$ (type I and II) are determined at 423, 473, 523, 573 and 623 K.

Reaction Kinetics with Hydrogen and Temperature Dependence of the Hydriding Rate for a Magnesium-Based Nickel Iron Oxide Alloy

  • Song, Myoung Youp;Baek, Sung Hwan;Park, Hye Ryoung
    • Korean Journal of Metals and Materials
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    • v.50 no.6
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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.

Hydrogenation Properties of MgH2-CaO Composites Synthesized by Hydrogen-Induced Mechanical Alloying

  • Kim, Min Gyeom;Han, Jeong-Heum;Lee, Young-Hwan;Son, Jong-Tae;Hong, Tae Whan
    • Korean Journal of Metals and Materials
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    • v.56 no.11
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    • pp.829-834
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    • 2018
  • Although magnesium-based alloys are attractive materials for hydrogen storage applications, their activation properties, hydrogenation/dehydrogenation kinetics, thermodynamic equilibrium parameters, and degradation characteristics must be improved for practical applications. Further, magnesium poses several risks, including explosion hazard, environmental pollution, insufficient formability, and industrial damage. To overcome these problems, CaO-added Mg alloys, also called Eco-Mg (environment-conscious Mg) alloys, have been developed. In this study, $Eco-MgH_x$ composites were fabricated from Mg-CaO chips by hydrogen-induced mechanical alloying in a high-pressure atmosphere. The balls-to-chips mass ratio (BCR) was varied between a low and high value. The particles obtained were characterized by X-ray diffraction (XRD), and the absorbed hydrogen was quantified by thermogravimetric analysis. The XRD results revealed that the $MgH_2$ peaks broadened for the high BCR. Further, PSA results revealed particles size were decreased from $52{\mu}m$ to $15{\mu}m$.