S. A. Lushnikov

Interaction of RT3 (R=Ce, T=Co, Ni, Fe) intermetallic compounds with hydrogen under high pressure

Abstract Interaction in CeCo 3 –H 2 , GdFe 3 –H 2 and CeNi 2 Co–H 2 systems with hydrogen under pressure to 2000 atm. has been investigated. Intermetallic compounds CeCo 3 , GdFe 3 and CeNi 2 Co have CeNi 3 or PuNi 3 structure type. The maximum compositions of the hydride phases under high pressure CeCo 3 H 6.1 , GdFe 3 H 6.1 and CeNi 2 CoH 5.4 have been calculated on the basis of analysis of absorption–desorption isotherms at room temperature. According to X-ray analyses, additional implantation of hydrogen into hydride phases based on CeCo 3 , GdFe 3 and CeNi 2 Co under high pressure is accompanied by insignificant increases in their lattice volumes.

Structure and bonding configuration of hydrided ErNi3 and CeCo3

The intermetallic compounds ErNi3 and CeCo3 has been hydrided at low (pH2 ≤ 0.01 GPa) and high (pH2 up to 0.2 GPa) hydrogen pressures. X-ray and neutron diffraction characterization has shown that the resultant hydrides have structures of the same type (PuNi3) as the parent intermetallics and have a larger unitcell volume. We have identified the positions occupied by the metal and hydrogen atoms and have determined their positional parameters. The lattice anisotropy has been shown to vary little at high hydrogen concentrations. Our results indicate that the metal-hydrogen bonds in the hydrides studied are predominantly ionic for the rare-earth metals (Er and Ce) and predominantly metallic for the transition metals (Ni and Co).

Structure of thermally desorbed CeNi3-based hydrides

CeNi3Hx (x = 0.7, 0.8, 1.0, 1.8, 3.4, 3.8) hydrides have been prepared through hydrogen desorption from CeNi3 hydrogenated at low (pH2 = 0.01 GPa) and high (pH2 = 0.2 GPa) hydrogen pressures. Using X-ray and neutron diffraction, the hydrides are shown to be isostructural with CeNi3 (sp. gr. P63/mmc, no. 194). The lattice parameters of the hydrides vary appreciably with hydrogen content. The sequence of hydrogen release from different interstices in the desorption process is shown to be opposite to that of hydrogen uptake in the hydrogenation process. The solid-solution range in the desorbed hydrides is much broader than that upon hydrogenation. The extent of the solid solution is influenced by the phase composition of the parent intermetallic compound.

CeNi3-based Intermetallic hydrides

A hydride phase containing 5.0 H atoms per formula unit has been synthesized in the CeNi3-H2 system at a hydrogen pressure of 5 MPa and a temperature of 273 K. The hydride is very stable during storage in air, with no hydrogen release. Its lattice parameters have been determined by X-ray diffraction for different synthesis conditions.

Synthesis and structure of CeNi3D x

We describe the synthesis of CeNi3Dx deuterides at normal and high deuterium pressures. X-ray and neutron diffraction techniques were used to identify the position and determine the positional parameters of the metal and deuterium atoms. The deuterides are isostructural with the parent compound CeNi3 but have a larger unit cell. Increasing the deuterium content to the composition CeNi3D5.2 leads to partial amorphization of the material. The variation in unit-cell volume observed at low and high deuterium contents indicates that the metal-deuterium bonds are partially ionic and partially metallic.

High-Pressure Reactions in the CeCo3–H2 and GdNi3–H2Systems

Reactions in the CeCo3–H2and GdNi3–H2systems were studied at hydrogen pressures of up to 0.2 GPa. Using hydrogen absorption–desorption isotherms, the compositions of the high-pressure hydrides were determined to be CeCo3H6.8(–70°C) and GdNi3H5.1(–50°C). According to x-ray diffraction studies, high-pressure hydrogen absorption to above the stoichiometry CeCo3H4is accompanied by insignificant volume changes. In the GdNi3–H2system, the hydride phase amorphizes at high hydrogen contents.

Hydride formation in Ce(La)-Ni-Si ternary compounds

Abstract Hydrogen interaction with R 2 Ni 0.8 Si 1.2 , R 2 NiSi, R 2 Ni 1.2 Si 0.8 and R 6 Ni 2 Si 3 (R=La, Ce) compounds were studied. The new hydride phases, namely, La 2 Ni 0.8 Si 1.2 H 3.75 , La 2 NiSiH 3.9 , La 2 Ni 1.2 Si 0.8 H 4.4 , Ce 2 Ni 0.8 Si 1.2 H 3.7 , Ce 2 NiSiH 4.4 , Ce 2 Ni 1.2 Si 0.8 H 4.9 , La 6 Ni 2 Si 3 H 12 and Ce 6 Ni 2 Si 3 H 10.9 have been synthesised and characterised by X-ray diffraction and thermodesorption methods. All hydrides retained the structure type of the starting compounds with pronounced anisotropic distortion of crystal lattice: the increase of the «a» parameter at decreasing «c». Variation of the Ni/Si ratio in R 2 Ni 1−x Si 1+x (x=0, 0.4 and −0.4) markedly affected the hydrogen capacity and crystal lattice extension. The Ce-containing hydrides possessed a higher hydrogen contents but significantly smaller specific unit cell volume expansion per one hydrogen atom in comparison with La-based compounds.

Hydriding of TiMo alloys at high hydrogen pressures

We studied the interaction of Ti0.40Mo0.60 and Ti0.34Mo0.66 alloys with hydrogen and obtained hydrogen desorption isotherms at pressures of up to 250 MPa. At high hydrogen pressures, we observed the formation of Ti0.40Mo0.60Н1.1 and Ti0.34Mo0.66Н0.8 hydride phases. According to X-ray diffraction data, the hydrides consisted of phases with a body-centered cubic and face-centered cubic (CaF2 structure) lattices. The structure of the deuteride based on the Ti0.40Mo0.60 alloy was studied by neutron diffraction. We identified the sites occupied by deuterium atoms and determined their occupancies.

Interaction of vanadium alloys with hydrogen at high pressures

The interaction of the V0.95Cu0.05, V0.94Co0.06, and V0.9W0.1 alloys with hydrogen has been studied at hydrogen pressures of up to 250 MPa. We have constructed hydrogen absorption/desorption isotherms at different temperatures and determined the thermodynamic parameters of the systems. According to X-ray diffraction data, the high-pressure hydride phases V0.94Co0.06H1.4 and V0.9W0.1H1.2 consist of a face-centered cubic phase similar in structure to the γ-phase of vanadium dihydride. In the case of the vanadium-copper alloy, the maximum composition of the hydride is V0.95Cu0.05H0.5.

LaNi5- and RT3-based (R = Ce, Nd, Gd, Er; T = Co, Ni, Fe) hydrides prepared at low temperatures and H2 pressures

Hydride phases based on the intermetallic compounds LaNi5, CeCo3, NdNi3, GdFe3, DyCo3, and ErNi3 have been synthesized at a hydrogen pressure of 10 MPa and a temperature of 273 K. The phase composition of the synthesized materials and the lattice parameters of the hydride phases have been determined by X-ray diffraction. During storage in air at room temperature, the hydrides decompose more slowly than do their analogs synthesized at low pressure. The hydrogen content of the hydrides is higher than or similar to that of hydride phases synthesized at high pressure. X-ray diffraction results for the low-temperature RT3-based intermetallic hydrides demonstrate that their lattice is expanded to a lesser extent than that of their high-pressure analogs.