V.N. Verbetsky

Interaction of intermetallic compounds with hydrogen at pressures up to 250 MPa: the LaCo5−xMnx-H2 and CeNi5−H2 systems

Abstract A new method has been proposed for the synthesis and thermodynamic study of intermetallic hydrides at pressures of gaseous hydrogen up to 250 MPa. From preliminary experiments on hydrogen compressibility and consideration of available p - V - T data for hydrogen at high pressures we have chosen a modified van der Waals equation giving a calculation error of 0.1%–0.5% or less. Absorption and desorption isotherms for the LaCo 5− x Mn x -H 2 ( x −0.05) and CeNi 5 −H 2 systems were measured at temperatures from 195 K up to room temperature. The highest hydrogen content obtained in a hydride composition of LaCo 5− x Mn x does not exceed 8 at. H per formula unit, and for the high pressure plateau ΔH abs = ΔH des =14.4 kJ (mol H 2 ) −1 and ΔS abs = ΔS des =110.2 J K −1 (mol H 2 ) −1 . In the CeNi 5 -H 2 system the existence of a single plateau and considerable hysteresis were observed.

Transformations of magnetic phase diagram as a result of insertion of hydrogen and nitrogen atoms in the crystalline lattice of R2Fe17 compounds

Abstract The effect of hydrogen and nitrogen insertions on the magnetic properties (Curie temperatures, saturation magnetization, magnetocrystalline anisotropy) of R 2 Fe 17 compounds have been studied. Structural and magnetic investigations have been performed by means of X-ray diffraction, torque and pendulum magnetometer techniques and high-field magnetization measurements on R 2 Fe 17 H x single crystals and on magnetically aligned powder samples of R 2 Fe 17 N y . The hydrides and nitrides still retain the structure of their parent compounds, but the unit cell volumes are expanded. The Curie temperatures are increased by both hydrogenation and nitrogenation. Magnetic phase diagrams of the investigated compounds have been obtained. The effects of the nitrogen and the hydrogen atoms on the rare-earth sublattice anisotropy have been found to be opposite and this is determined by the orientation of the quadrupole moment q of the asymmetric 4f shell with respect to the direction of the resulting magnetic moment of 4f electrons.

Structure and hydrogen sorption properties of (Ti,Zr)-Mn-V alloys

The present investigation is a part of the series of works on the development of new materials as highly efficient hydrogen accumulating media. Earlier we reported on the investigation of Ti–Mn–V alloys of Laves phase type. This work is the continuation of these studies. The work was aimed on the determination of concentration boundaries of Laves phase and investigation of hydrogen sorption properties of alloys. Using X-ray, EDXA and electron microscopy methods the phase compositions of over 50 alloys were studied. The Laves phase concentration boundaries were determined to extend up to 26 at.% of vanadium. Compared to ternary Ti–Mn–V system the region of λ1-phase is about 2 at.% wider for Ti–Mn side of concentration triangle. Depending on metal concentrations lattice parameters were determined to increase proportionally with increasing titanium or vanadium concentration according to Vegard rule. The interaction of alloys with hydrogen was studied by PC-isotherm method. The isotherms were measured at three different temperatures and thermodynamic parameters of reaction were calculated using the vant Hoff equation. The hydrogen sorption properties were analysed in view of overall alloy composition. The enthalpy of desorption was found to depend proportionally on unit cell volume of alloy.

Thermodynamic particularities of some CeNi5-based metal hydride systems with high dissociation pressure

Abstract The thermodynamic behaviour of the CeNi 5 H 2 , Ce 0.8 La 0.2 Ni 5 H 2 and Ce 0.8 La 0.2 Ni 4.7 Cu 0.3 -H 2 systems during a few activation absorption-desorption cycles was studied by means of high gaseous pressure technique. P-C isotherms in the temperature range from 273 to 353 K were measured and thermodynamic parameters for hydride formation and decomposition reactions were calculated. For all studied systems the same hydrogen capacity (6.5–6.8 H atoms per AB 5 unit at 1000 atm and 296 K) and the same isotherm shape with a long nearly horizontal plateau and very large hysteresis were obtained. The change in alloy composition in the range CeNi 5 →Ce 0.8 La 0.2 Ni 5 →Ce 0.8 La 0.2 Ni 4.7 Cu 0.3 led to an increase in plateau length and a decrease in hysteresis factor P abs /P des . The hysteresis factor also decreased considerably after two or three activation cycles, by 4–8 times as compared with the first cycle. This phenomenon was connected not only with an absorption pressure decrease but also with a significant increase in desorption pressure. The relative change P 1 /P act in equilibrium pressure during the activation did not depend on alloy composition for the absorption reaction, but in the case of desorption it decreased with partial substitution of Ce and Ni by La and Cu correspondingly.

Hydrogen interaction with RNi3 type intermetallic compounds at high gaseous pressure

Pressure-composition isotherms for CeNi 3 -H 2 , CeNi 2.2 Mn 0.8 -H 2 and ErNi 3 -H 2 systems were measured at pressures up to 2000 atm and at temperatures from - 78°C to 23°C. New hydride phases RNi 3 Hs 5.5-5.6 were synthesized and characterized by X-ray diffraction. Thermodynamic parameters of formation-decomposition reactions at low temperature for intermediate ErNi 3 H 4 phase were calculated as ΔH = 23.8 kJ mol -1 and ΔS = 103 J K -1 mol -1 . The phenomenon of irreversible hydrogen absorption at high pressure was found for all studied systems. Thermal desorption peculiarities for CeNi 3 H x and ErNi 3 H x hydrides were determined.

Structural and magnetic properties of Lu2Fe17Hx (x=0; 3) single crystals

Abstract The structural and magnetic characterization of Lu2Fe17Hx (x=0; 3) single crystals is presented. The host alloy crystallizes with a disordered variant of hexagonal (Th2Ni17-type P63/mmc) structure. It is observed that the host alloy symmetry is retained upon hydrogenation. Hydrogen is found to be accommodated in the rare earth-rich octahedral position. The Neel temperature of the hydride Lu2Fe17H3 is increased by 35 K per hydrogen atom. The magnetization and magnetic anisotropy constant remains practically unaffected in the hydride Lu2Fe17Hx at x=3.

Metal hydrides: properties and practical applications. review of the works in cis-countries

Abstract A short review of RandD in the field of hydrogen hydride technologies in Russia and CIS countries is presented. As a result of basic research of physical and chemical features of intermetallic alloys and their hydrides, their structural peculiarities, absorption kinetics, thermal processes, etc., methods have been developed for creation high efficient alloys for different applications in metal hydride technology. Original devices such as hydrogen accumulators, thermal compressors, heat transformation systems and other experimental devices with unique characteristics have been created. The results of reviewed RandD demonstrate high efficiency of metal hydride technologies. These investigations and developments give reliable scientific and technical background for the development of the new research projects in the framework of the new Russian program of RandD in hydrogen energy and technology and for international cooperation.

Effect of substitution on F.C.C. and B.C.C. hydridephase formation in the TiCr2–H2 system

Abstract Phase transformations of TiCr 1.8 , ZrCr 2 , Ti 0.9 Zr 0.1 Cr 1.8 , Ti 0.7 Zr 0.3 Cr 1.8 and TiCr 1.7 Fe 0.1 intermetallic compounds during their interaction with hydrogen at pressuresfrom 1 to 200 MPa and temperatures of 195 and 295 K are studied. Formation of three types ofhydride phases are stated by X-ray diffraction method: (I) hexagonal Laves phase preserving theMgZn 2 structure of the initial intermetallic, (II) F.C.C. phase of CaF 2 structure type which can be considered as a solid solution in the pseudobinary TiH 2 -CrH 2 system and (III) B.C.C. phase with W-structure type—high temperature β solution in the metallic Ti–Cr system stabilized by hydrogen. It was shown that partialsubstitution of titanium by zirconium up to 30% did not change the general scheme of phasetransformations, while the addition of iron suppressed the formation of phases (II) and (III) in allexperimental pressure and temperature ranges. The conditions of formation, X-ray parameters andthermal stability have been determined for synthesized hydride phases in the TiCr 2 -H 2 and substituted systems.

Magnetocrystalline anisotropy of R2Fe17Hx (x=0, 3) single crystals

Abstract The magnetocrystalline anisotropy of R 2 Fe 17 (R=Y, Gd, Tb, Ho and Er) and their hydrides are studied by analyzing the magnetization curves of single crystal samples in the temperature range 4.2–300 K in magnetic fields up to 140 kOe. There is no noticeable influence of hydrogenation on the magnetic anisotropy in the Y 2 Fe 17 and Gd 2 Fe 17 compounds. An easy-plane to easy-cone transition is detected for a Tb 2 Fe 17 H 3 single crystal after hydrogenation. A significant change of the magnetization process has been observed in the hydrides Ho 2 Fe 17 H 3 and Er 2 Fe 17 H 3 . Hydrogenation induces a FOMP-type transition in the Ho 2 Fe 17 H 3 compound and, on the contrary, leads to the disappearance of the FOMP type transition in the Er 2 Fe 17 H 3 compound. The obtained results are discussed on the basis of a model based on the interaction of the quadrupolar moment and the magnetic moment of the 4f electron shell of the rare earth ion with the interstitial hydrogen. It is established that the orientation of the quadrupolar moment of the asymmetric 4f shell with respect to the direction of the resulting magnetic moment of 4f electrons plays an important role.

Calorimetric investigation of the hydrogen interaction with Ti0.9Zr0.1Mn1.1V0.1

Abstract The interaction of hydrogen with Ti 0.9 Zr 0.1 Mn 1.1 V 0.1 compound was studied by means of calorimetric and P – C isotherm methods. The obtained results allow to propose the existence of two hydride phases in the Ti 0.9 Zr 0.1 Mn 1.1 V 0.1 –H 2 system in the temperature range 72–116°C.