Reactive ball milling in hydrogen was applied to synthesize nanocrystalline Mg- and Mg8Mm20Ni-based hydrides with crystallite size below 10
nm. These hydrides were studied by
in situ synchrotron ...X-ray diffraction performed at the Swiss–Norwegian Beam Lines of the European Synchrotron Radiation Facility, Grenoble. Characterization of the phase-structural and microstructural state of the constituents during the reversible processes of synthesis and decomposition of the hydrides upon application of hydrogen pressure or vacuum at temperatures 20–350
°C and kinetics of hydrogen uptake was performed. Details of the mechanism of the phase-structural transformations were provided by high time resolution of the synchrotron X-ray diffraction data, high sensitivity in determining formation of the phase constituents, excellent accuracy in yielding the crystallographic characteristics and in probing the microstructural evolution of the constituents formed.
Display omitted
•New ternary YMgCo4 and YMgCu4 and quaternary YMgCo2Ni2 compounds were synthesized.•YMgNi4, YMgCo2Ni2 and YMgCo4 form hydrides with 4, 4.9 and 6.8H/f.u. capacity.•PCT desorption ...isotherms were studied for YMgNi4, YMgCo2Ni2 and YMgCo4−H2 systems.•The YMgCu4 compound does not interact with hydrogen under normal conditions.
New two ternary YMgCo4 and YMgCu4 and one quaternary YMgCo2Ni2 compounds have been synthesized by mechanical alloying with further annealing. The hydrogenation capacity of YMgCo4 reaches 6.8at.H/f.u. The Pressure-Composition-Temperature studies of YMgCo4–H2 and YMgNi4–H2 systems revealed that introduction of magnesium, accompanied by shrinking of the unit cell, decreases the stability of hydrides comparing to binary YCo2 and YNi2 compounds. The values of heat and entropy of the YMgCo4H6.8 hydride formation were calculated: ΔH=−27.9±0.8kJmol–1H2 and ΔS=−93.4±2.6Jmol−1H2K−1. The YMgCo2Ni2–H2 system shows intermediate thermodynamic properties compared to the ternary hydrides (ΔH=−28.8±0.2kJmol–1H2 and ΔS=−117.6±2.4Jmol–1H2K−1). The YMgCo4H6.8 and YMgCo2Ni2H4.9 hydrides keep the cubic structure of the parent compounds with a cell volume expansion of 23 and 14.4% respectively. It is shown that the YMgCu4 compound does not interact with hydrogen under normal conditions.
Two new ternary intermetallic compounds, CeMgCo4 (C15b pseudo-Laves phase, MgCu4Sn type) and Ce2MgCo9 (substitution derivative of PuNi3 type) were synthesized by mechanical alloying method. The ...structural and hydrogenation properties of these compounds were studied by X-ray diffraction and Pressure–Composition–Temperature measurements. Both compounds absorb hydrogen at room temperature and pressures below 10MPa forming hydrides with maximum compositions CeMgCo4H6 and Ce2MgCo9H12. Single plateau behavior was observed in P–C isotherm during hydrogen absorption/desorption by Ce2MgCo9 alloy. The CeMgCo4–H2 system is characterized by the presence of two absorption/desorption plateaus corresponding to formation of β-CeMgCo4H4 and γ-CeMgCo4H6 hydride phases. The structure of β-hydride CeMgCo4H(D)4 was determined from X-ray and neutron powder diffraction data. In this structure initial cubic symmetry of CeMgCo4 is preserved and hydrogen atoms fill only one type of interstitial sites, triangular MgCo2 faces. These positions are occupied by 70% and form octahedron around Mg atom with Mg–D bond distances 1.84Å.
Crystal structure of the β-CeMgCo4D4.2 deuteride. Octahedra of D-sites around Mg atoms are shown. Display omitted
► Two new ternary compounds have been synthesized in the Ce–Mg–Co system. ► Below 100bar H2 CeMgCo4 and Ce2MgCo9 reversibly absorb hydrogen at room temperature. ► Crystal structure of cubic CeMgCo4D4.2 deuteride has been determined.
A variant of the proton beam delivery system with an energy of 60 MeV for the future oncological ophthalmological center for proton radiation therapy at the isochronous cyclotron C-80 at PNPI was ...designed. The requirements to the beam characteristics were defined. On the basis of a series of calculations, the optimal parameters and composition of the beam line elements were determined. It is shown that such a beam line allows one to alternately and efficiently switch from the isotope production mode on the cyclotron to the mode of operation of the center for proton radiation therapy without fundamental overhaul of the accelerator systems.
Novel intermetallic hydrides Yartys, V.A.; Riabov, A.B.; Denys, R.V. ...
Journal of alloys and compounds,
02/2006, Letnik:
408
Journal Article
Recenzirano
The paper focuses on structural chemistry of novel intermetallic hydrides with unusual structural properties. In such “anisotropic” hydrides, a huge expansion proceeds in a sole crystallographic ...direction and leads to a dramatic differentiation of the properties of the hydrides along the direction of the expansion and normal to it. The behaviour of the “anisotropic” hydrides is dominated by the metal–hydrogen and hydrogen–hydrogen interactions in contrast to the “conventional” intermetallic hydrides where the metal–metal interactions are the most important ones. In sharp contrast to the known crystal structures of intermetallic hydrides, in “anisotropic” hydrides deuterium atoms do not fill
initially existing interstices but, instead, attract rare earth atoms into their surrounding and form
new D-
occupied sites. This paper will summarise our recent research on the “anisotropic” hydrides with a particular focus on two groups of materials: (a) RENiIn-based deuterides (RE
=
rare earth metal) containing the shortest known separation of hydrogen atoms in the structures of metal hydrides and (b) RENi
3–(CeNi
3) and RE
2Ni
7–(La
2Ni
7)-based deuterides which develop unusually large (59–63%) expansion of the constituent RENi
2 layers.
A new intermetallic deuteride Ce2Ni7D4.7 with an anomalous volume expansion has been studied. Its structure was solved on the basis of in situ neutron diffraction data. Expansion proceeds along the ...c-axis and within the CeNi2 slabs only. All D atoms are located inside these slabs and on the border between CeNi2 and CeNi5. Ordering of D atoms in the bulk of CeNi2 is accompanied by substantial deformation of these slabs thus lowering the hexagonal symmetry to orthorhombic space group Pmcn (No. 62); a = 4.9251(3) angstrom b = 8.4933(4) angstrom, c = 29.773(1) angstrom. Inside the CeNi2 layer the hydrogen sublattice is completely ordered; all D-D distances exceed 2.0 angstrom Local coordination of Ni by D inside the CeNi, blocks is of "open", saddle-like type. Hydrogen ordering is mainly determined by Ce-H and H-H interactions. The press ure-composition-temperature measurements yielded the following thermodynamic parameters of the formation of the hydride: Delta H = -22.4 kJ/MOl(H), Delta S = -59.9 J/(K mol(H)).
The present paper considers two unique volume effects associated with the formation of intermetallic hydrides, anomalously high linear and volume expansion (CeNi3→CeNi3D2.8) and unusual volume ...contraction (HoNiSn→HoNiSnD0.67). The crystal structures of both deuterides were solved on the basis of powder neutron diffraction data. The hexagonal CeNi3 anisotropically expands on hydrogenation along 00z (30.7%). In orthorhombic CeNi3D2.8 (space group Pmcn (No. 62); a=4.8748(3); b=8.5590(5); c=21.590(2) Å) this expansion proceeds within the CeNi2 slabs only (63.1%), with a ‘shrinking’ of the CeNi5 parts (−2.8%). All D atoms are located inside the CeNi2 part and on the border of CeNi2 and CeNi5. In sharp contrast to the known crystal structures of intermetallic hydrides, in CeNi3D2.8 deuterium atoms do not fill initially existing interstices but, instead, attract cerium atoms into their surrounding and form new D-occupied sites, Ce3Ni and Ce3Ni3. The hydrogenation of HoNiSn causes a transition from TiNiSi to the ZrNiAl type of structure. Transformation of the metallic sublattice into the ZrNiAl type results in a ‘shrinking’ of the Ho3Ni tetrahedra filled by D. Their occupation in HoNiSnD0.67 (space group P6̄2m (No. 189); a=7.24197(10); c=3.93514(7) Å) proceeds with a formal ‘negative’ volume expansion effect and leads to the formation of strong Ho–H bonds.
New ternary Mg–Mn–Ni alloys synthesised by high energy ball milling have been studied as hydrogen storage materials. A new Mg
3MnNi
2 ternary intermetallic compound of the Ti
2Ni type has been ...identified, its structure was studied by neutron diffraction. It has been shown that in the Mg–Mn–Ni system this intermetallic coexists with Mg, forming two-phase Mg–Mg
3MnNi
2 alloys. The Mg
3MnNi
2 compound reversibly absorbs about 1 wt.% of hydrogen already at room temperature and forms interstitial type Mg
3MnNi
2H
∼3 hydride. Substantially higher hydrogenation capacity has been observed in Mg–Mg
3MnNi
2 alloys with high Mg content, e.g. 5.4 wt.% for the Mg
88Mn
4Ni
8 alloy at 250–350 °C. Hydrogen absorption–desorption kinetics of these alloys are drastically improved compared to undoped magnesium due to catalytic effect of the Mg
3MnNi
2 phase.
