Physico Mechanical Institute of NAS of Ukraine

L'viv, Ukraine

Physico Mechanical Institute of NAS of Ukraine

L'viv, Ukraine
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Denys R.V.,Institute for Energy Technology of Norway | Denys R.V.,Physico Mechanical Institute of NAS of Ukraine | Poletaev A.A.,Institute for Energy Technology of Norway | Poletaev A.A.,Norwegian University of Science and Technology | And 5 more authors.
International Journal of Hydrogen Energy | Year: 2012

Recently, the present authors [17] have reported dramatic improvements in the hydrogenation behaviours of nanostructured LaMg11Ni prepared by Rapid Solidification, caused by modifications of the microstructure and crystal structure. The aim of the present work was to study the mechanism and kinetics of the hydrogen interaction with rapidly solidified LaMg11Ni by employing in situ synchrotron X-Ray diffraction studies of hydrogen absorption-desorption processes in hydrogen gas or in vacuum. These studies uncovered a number of temperature-dependent phase structural transformations contributing to reversible hydrogen absorption and desorption, including (a) formation of metastable (in hydrogen) solid solutions of Ni in La 2Mg17 with Ni substitution on both La and Mg sites; (b) amorphisation and nanostructuring of the alloys depending on the solidification rate; nanocrystallisation of the amorphous alloys proceeding at rather low glass transition temperatures and yielding nanocrystallites of Mg2Ni/ Mg1.9La0.1Ni and La1.8Mg17Ni 1.0; (c) the mechanism of the Hydrogenation-Disproportionation- Desorption-Recombination processes resulting in a two-step cooperative Mg-assisted phase transformation where a low temperature decomposition of LaH2 led to the recombination of the intermetallics LaMg12 and La2-xMg17Nix. The metastable solid solutions of Ni in the La2Mg17-based intermetallic show high hydrogenation rates and, despite they decompose during the cycling of hydrogen absorption and desorption, the formed on cycling nanocrystallites of Mg2Ni further maintain high catalytic activity of the materials towards the hydrogen absorption. © 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights.


Poletaev A.A.,Institute for Energy Technology of Norway | Poletaev A.A.,Norwegian University of Science and Technology | Denys R.V.,Institute for Energy Technology of Norway | Denys R.V.,Physico Mechanical Institute of NAS of Ukraine | And 5 more authors.
International Journal of Hydrogen Energy | Year: 2012

In our earlier publication (Poletaev et al., J Alloys Compd., 509S (2011) S633) we reported a drastic variation of the structural and hydrogenation properties of LaMg∼12 intermetallic alloy caused by Rapid Solidification (RS). In present work we have probed the effect of nickel during the chemical modification of LaMg12, in combination with RS, on the structure, microstructure and hydrogen absorption-desorption properties of the alloys. RS was performed at three solidification rates, 300-2000 rpm. Ni was found to form a solid solution replacing both La and Mg to yield La 1.7Mg16.7Ni0.6 intermetallic. With increasing RS cooling rates, the very fine, almost amorphous microstructures were formed. The LaMg11Ni alloy solidified at the highest cooling rate exhibited the fastest hydrogenation kinetics, reaching maximum hydrogenation capacity of 5.02 wt. % H. Studies of the hydrogenated RS ribbons showed the formation of the nano-scale embryos of MgH2, growing to form polyhedral grains of magnesium dihydride. © 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.


Denys R.V.,Physico Mechanical Institute of NAS of Ukraine | Zavaliy I.Y.,Physico Mechanical Institute of NAS of Ukraine | Berezovets V.V.,Physico Mechanical Institute of NAS of Ukraine | Paul-Boncour V.,French National Center for Scientific Research | Pecharsky V.K.,Iowa State University
Intermetallics | Year: 2013

A number of ternary Mg-Ti-Ni alloys have been synthesized by high energy ball milling, followed by annealing heat treatment. On the basis of X-ray phase analysis of these alloys an isothermal section of the Mg-Ti-Ni phase diagram at 500 °C has been constructed. One ternary intermetallic compound with Mg 3TiNi 2 stoichiometry that adopts an ordered Ti 2Ni-type structure has been identified. Binary cubic TiNi compound dissolves considerable amount of Mg to form a ternary phase Mg xTi 1-2/3xNi 1-1/3x crystallizing in the CsCl-type structure and existing over the range of compositions 0 < x ≤ 0.5. Other binary phases do not show appreciable solubility of the third component. The hydrogenation behavior of Mg 3TiNi 2 compound and Mg 0.5Ti 0.67Ni 0.83 solid solution phase has been studied. © 2012 Elsevier Ltd. All rights reserved.

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