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Abstract: The paper considers materials science aspects of the applications of the reversible hydrogen getters in vacuum-plasma devices. The selection of hydrogen getter material, which is located in the vacuum chamber of the installation, is based on a convenience of switching of its functions from the “internal” source of hydrogen supply to the mode of control over the hydrogen pressure by chemically “pumping” hydrogen from the volume into the getter. The energy of plasma particles bombarding the surface of the material allows controlling the supply of the plasma-forming gas (hydrogen). The arc-melted ZrV alloy modified by small amounts of oxygen was used as getter material. Hydrogen sorption characteristics of the alloy were studied in the Sieverts-type setup. The hydrides were characterised by vacuum Thermal Desorption Spectroscopy. X-ray diffraction was employed to study phase-structural composition of the getter and its hydride. A technology of the production of the MH elements for vacuum-plasma installations has been developed. The MH elements on the basis of the H-saturated ZrV(O) alloy have shown a resistance against sputtering during their bombardment by high-energy particles in vacuum. [Copyright &y& Elsevier]

Abstract: This work was focused on the studies of vanadium-based “low-temperature” bcc alloys as H storage materials. Both as cast and annealed at 1100  C quaternary alloys V92.5−x−y Zr7.5Ti7.5+x−y M y (M = Cr, Mn, Fe, Co, Ni; , 10; , 7.5) were studied. They were characterised by XRD, PCT hydrogen absorption–desorption measurements ( –120  C) and thermal desorption spectroscopy studies of H desorption from the saturated hydrides ( C). The thermodynamics of the VH∼2↔ VH∼1 transition and hydrogen sorption capacities ( H/M) were found to be significantly influenced by the substituting M-element. The reversible hydrogen storage capacity ( C,  bar) reaches 50–60% of its overall value. Complete hydrogen desorption proceeds in vacuum at C. The major future challenge of the work is in increasing of the easy-reversible part of the H storage capacity corresponding to transformation VH∼2↔ VH∼1 by reducing the content of H in the monohydride. [Copyright &y& Elsevier]

We have used neutron diffraction and magnetic measurements to investigate the changes in magnetic properties of the Kondo semimetal compound CeNiSn after charging with deuterium gas under moderate conditions. Charging with deuterium led to the formation of the monodeuteride CeNiSnD with filled TiNiSi structure. This compound gives rise to long-range antiferromagnetic ordering below TN=5.1 K. The ordered magnetic moment value equals 1.37(3) μB per Ce atom, the moments pointing along the [001] direction. No significant ordered magnetic moment on the Ni atoms has been observed by powder neutron diffraction. [Copyright &y& Elsevier]

The present work describes a structural characterization of the yttrium–carbon compounds, Y2C and YCoC, and their corresponding deuterides using temperature desorption spectroscopy (TDS) and high-resolution powder X-ray and neutron diffraction. Carbon atoms orderly occupy 1/3 (YCoC) or 1/2 (Y2C) of the available octahedra, Y4Co2 and Y6, respectively. Strong Y–C interactions lead to the ‘shrinking’ of these C-filled sites, with the Y–C bond distances between 2.49 and 2.51 A˚ for the compounds studied. Deuterium atoms in YCoCD0.5 and in Y2CD2.55 occupy two different types of octahedra, similar to those filled by C. The occupancy of D sites is related to the radii of the occupied interstices. Both the too small Y4Co2 and the too large Y6 octahedra have reduced filling. In Y2CD2.0–2.55 deuterium also nearly completely occupies Y4 tetrahedra. From TDS it is evident that D bonding weakens in the sequence Y4–Y6–Y4Co2. [Copyright &y& Elsevier]

Neutron diffraction performed on deuterated powder samples of Pr6Fe13Au shows that the crystal structure of the parent compound is retained upon charging with deuterium. The refined composition of the deuteride is Pr6Fe13AuD13. The deuterium atoms occupy various types of interstitial sites bounded by Pr and Fe atoms. Each of these sites is surrounded by at least two Pr atoms. A collinear antiferromagnetic ordering of the four Fe and the two Pr sublattices was reported previously for the uncharged Pr6Fe13Au compound. By contrast, a collinear ferromagnetic structure has been derived from the present neutron data of the deuteride. The easy moment direction is the same in Pr6Fe13AuD13 and Pr6Fe13Au, being perpendicular to the c-axis. For the deuteride this result was derived from a complementary synchrotron radiation X-ray study made on magnetically aligned particles of the ferromagnetic deuteride. [Copyright &y& Elsevier]

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) A˚) 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 P6¯2m (No. 189); a=7.24197(10); c=3.93514(7) A˚) proceeds with a formal ‘negative’ volume expansion effect and leads to the formation of strong Ho–H bonds. [Copyright &y& Elsevier]

Two hydrogenated intermetallics with the highest Al/Zr ratio among the hydrogen-absorbing Zr–Al compounds, Zr4Al3 and Zr3Al2, have been studied by synchrotron X-ray, powder neutron diffraction and thermal desorption spectroscopy. Initial intermetallic compounds are quite different with respect to Al–Al interactions and contain plain Kagome Al nets (Zr4Al3) or Al–Al pairs (Zr3Al2). In hexagonal Zr4Al3D2.68 (space group (s.g.) P6322; a=11.0017(4); c=11.1694(5) A˚) a 2a×2a×2c superstructure is formed as a result of deuterium ordering in half of the available Zr4 tetrahedra. These tetrahedra share common corners and edges and form layers separated by 6363 Al-nets. In tetragonal Zr3Al2D2.26 (s.g. P42/mnm; a=7.5970(3); c=7.2613(3) A˚) in addition to the completely filled Zr4 tetrahedra hydrogen partially occupies Zr3 triangular sites. Thermal stability of the studied deuterides and Zr–D bonding characteristics can be related to the size of the occupied Zr4 tetrahedra. Higher thermal stability of Zr3Al2D2.26 agrees well with the existence of large Zr4 sites and contrasts to the behavior of Zr4Al3D2.68 containing ‘contracted’ Zr4 tetrahedra and having weaker Zr–D bonds. [Copyright &y& Elsevier]

Abstract: ‘Hybrid’ RNi3 (R=rare earth metal) crystal structures are built of the slabs of simpler types, CaCu5 and MgZn2. Different affinities of these slabs to hydrogen result in unusual “anisotropic” expansion of the RNi3 and R2Ni7 (R=La, Ce) structures upon hydrogenation. This work focuses on studies of the hydrogenation behaviour of LaNi3 and on the properties of the hydrides of the modified by Mg and Mn La–Ni alloys. The crystal structure of LaNi3D2.8 and the crystal structure and hydrogen storage behaviours of the La1.5Mg0.5Ni7 and La(Ni1−x Mn x )3 (x =0; 0.067; 0.133; 0.2; 0.267; 0.3; 0.333; 0.4) alloys were in focus. The deuteration of LaNi3 with PuNi3 type of structure leads to the formation of LaNi3D2.8 and is accompanied by a deformation of the metal matrix causing a change of the initial rhombohedral symmetry (space group ) to a monoclinic one (space group C2/m; a =8.6408(7)Å, b =4.9281(4)Å, c =32.774(3)Å; β =90.850(8)°; V =1395.5(2)Å3). Similar to the earlier studied CeNi3D2.8, preferential occupation by deuterium atoms of the AB2 layers takes place, leading to the “anisotropic” expansion of the unit cell along [001] (Δc/c =30.6%). 14 occupied D crystallographic sites have 4 chemically different types of metal-atom surroundings, including Ni4 (2), La2Ni2 (2), La3Ni (6), and La3Ni3 (4). Modification of the La–Ni alloys by magnesium and manganese leads to the formation of intermetallic compounds crystallising with the PuNi3, CeNi3, and Ce2Ni7-type structures. An ordered substitution of La by Mg in the MgZn2-type slabs was observed, causing a complete alteration of the hydrogenation behaviour of the original LaNi3 alloy. La1.5Mg0.5Ni7D 9 isotropically expands upon its formation and leads to a substantial increase of the stability against hydrogenation-induced amorphisation. On the other hand, replacement of Ni by Mn leads to the change in crystal-structure type from PuNi3 to CeNi3 in the LaNi3−x Mn x alloys (x >0.1). An ordered substitution of Ni by Mn proceeds inside the RNi5 slabs only. This decreases the stability of the initial alloy against amorphisation on hydrogenation. [Copyright &y& Elsevier]

Metal hydrides can store hydrogen at low pressures and with high volumetric capacity. For the possible application as storage medium in hydrogen stand-alone power systems, large metal hydride hydrogen storage units are usually required. A reliable and verified kinetic correlation is an important tool in the designing process of a larger storage unit. This paper describes kinetic investigation of a AB5-type alloy and its corresponding hydride, with the purpose of finding a semi-empirical correlation suitable for use in heat and mass transfer modelling and engineering design of metal hydride storage units. [Copyright &y& Elsevier]

The recent powder neutron diffraction study of the crystal structure of LaNiInD1.22 [J. Alloys Comp. 330–322 (2002) 132] concluded on the formation of a D…D pair with an unusually short interatomic distance of 1.63 A˚. Hydrogen atoms in LaNiInD1.22 occupy a single crystallographic site and are coordinated by face-sharing La3Ni tetrahedra (92% occupancy). PCT measurements show that hydrogen storage capacity of LaNiIn, 1.63 at.H/formula unit, exceeds the limit of 1.33 at.H/LaNiIn when the La3Ni sites are completely occupied. In the present work, in situ powder neutron diffraction data were collected under D2 pressure of 4.6 bar in order to study the deuteride with a maximum D content in the metal matrix. In the hexagonal structure of LaNiInD1.63 (space group P6¯2m; a=7.3874(4); c=4.6816(2) A˚) Rietveld refinements showed that deuterium atoms occupy 36% of the available distorted La3NiIn2 octahedra, in addition to the 96% filled La3Ni sites. The structure of LaNiInD1.63 represents the first example of a deuteride containing direct In–D bonds (2.346(2) A˚). H bonding to the La3NiIn2 sites is rather weak and a desorption from these sites takes place at room temperature and hydrogen pressures below 1 bar. [Copyright &y& Elsevier]

Abstract: This paper summarises collaborative activities of South African and Norwegian groups in the development and characterisation of the advanced hydride-forming materials obtained by surface modification of AB5-type substrate by fluorination and/or electroless deposition of single- or mixed-metal coatings on the basis of palladium. The surface modification was shown to significantly improve activation performance and poisoning tolerance of the hydride-forming materials. In particular, hydrogen absorption rate, after long-term pre-exposure to air, was shown to be increased by ∼100 times for the surface-modified materials, as compared to the unmodified alloy. It was shown that the surface modification route significantly influenced surface morphology and rate of hydrogenation. Finally, feasibility of application of the surface-modified hydride-forming materials for efficient hydrogen separation from gas mixtures containing CO2 and CO has been demonstrated. The approach undertaken has the potential in tailoring of new classes of highly efficient and robust composite H storage materials for hydrogen separation and purification. [Copyright &y& Elsevier]

Abstract: Kinetics of H uptake/release in Mg can be improved by alloying with Ni and RE, as well as by reducing the grain size of the Mg alloy. Both these approaches were applied in the present work for the alloy 72wt.% Mg–20wt.% Ni–8wt.% Mm (ternary eutectic Mg–Mg2Ni–MmMg12). The alloy was processed by the equal channel angular pressing (ECAP) technique. In ECAP the sample is subjected to heavy plastic strain by pressing it through a die with an angle of 90°. ECAP treatment resulted in a fine microstructure compared to the rather heterogeneous as-cast material. Hydrogenated and non-hydrogenated samples were investigated using SEM and XRD. Hydrogenation properties were studied by TDS and PCT. Hydrogenated samples consist of MgH2, Mg2NiH4 and MmH2+x and exhibit a maximum H-storage capacity of ∼5.5wt.%. To initiate the first hydrogenation, the alloy needs to be activated at ∼300°C. However, already after one hydrogenation cycle its H-absorption becomes quite fast: 4.5wt.% H is absorbed in just 15min. Vacuum TDS (heating rate 0.5°C/min) shows that desorption starts at low temperature, ∼135°C, with a peak at ∼210°C. The alloy was also subjected to high energy ball milling (HEBM) in Ar or H2 to yield further refinement of the microstructure. ∼1wt.% Nb2O5 was added to facilitate H exchange. The H sorption characteristics of the alloy treated by ECAP and HEBM have been compared with the ones for the as-cast material. [Copyright &y& Elsevier]

Abstract: Desorption of hydrogen from the powders of metal hydrides (MH) is affected by several interplaying processes including hydrogen desorption from and recombination on the metal surface, diffusion within the bulk metal and different hydride phases, and decomposition of the hydride phase. In present work, possible mechanisms of hydrogen release from the MH are proposed and discussed. Analytical models are developed which cover common distributed and confluent cases. The models adequately fit the experimental data of the thermal desorption spectroscopy and barometric thermocycling studies. Rate constants of the reactions of hydrogen release from the MH are evaluated on the basis of the fitting of the experimental data by the proposed models. These data are of significant importance in the assessments of suitability of the MH in particular applications. [Copyright &y& Elsevier]

Abstract: The crystal structure of NdNiInD1.2 contains D–D pairs with the shortest known separation of 1.56 Å. This work was aimed on studies of the factors influencing the formation and the length of such a pair. We have studied the NdNiIn-based alloys, in which Ni or In are partially substituted by the chemically related elements, Cu or Al, respectively. Three equiatomic intermetallics, NdNiIn, NdCuIn and NdNiAl, are isostructural and crystallise with the ZrNiAl type of structure. In the NdNi1−x Cu x In (; 0.02; 0.05; 0.25; 0.50; 0.75 and 1.00) quaternary system a complete solid solubility range has been found. In contrast, in the Al-containing NdNiIn1−x Al x alloys the range of a solid solution is limited to the region NdNiIn–NdNiIn0.75Al0.25. The substitutions result in regular changes in V, a, c and of the hexagonal unit cells. Small substitutions by Cu and Al () do not lead to significant changes in H content and types of the crystal structures formed (PND data). However, a decrease in the stability of the hydrides is observed. In NdNi1−x Cu x In, Cu has a strong preference for the occupation of the CuIn6 trigonal prisms. An increase of the Cu content is accompanied by a decrease of the D/Nd(Ni1−x Cu x )In ratio and a distinct growth of the distance between Ni(Cu) and D (from 1.51 to 1.84 Å). pairing is very sensitive to the content of both Al and Cu. When the level of substitution exceeds , H pairing becomes unstable and H atoms favour other types of ordering in the metal sublattice. [Copyright &y& Elsevier]

NdNiSnD and PrNiSnD monodeuterides have been studied by 119Sn Mo¨ssbauer spectroscopy at variable temperatures between 4.2 and 300 K. Deuterium insertion into the RE3Ni sites induces at low temperatures a magnetic splitting of the tin nuclear levels. Slightly different magnetic ordering temperatures, 25(1) and 20(1) K, were evidenced for the Nd- and Pr-containing deuterides, respectively. The Mo¨ssbauer spectra suggest a similar type of local structures for both compounds, with a mutual substitution of Sn and Ni atoms. The magnetic behaviour is discussed in relation to the different spin waves mechanisms. [Copyright &y& Elsevier]

This work focused on studies of the phase composition and crystal structure of LaxMm1−xNi4.7Sn0.3 (x=0, 0.5 and 1.0) alloys, where Mm denotes La-rich mischmetal produced by Norsk Hydro ASA. The alloys have been studied using conventional powder and synchrotron X-ray diffraction (XRD), powder neutron diffraction and scanning electron microscopy (SEM). After annealing at 950 °C the alloys were nearly single-phase materials with small precipitations of RENiSn equiatomic intermetallics formed at grain boundaries. Hydrogen absorption–desorption studies at 298, 323 and 348 K showed (a) a ‘flat’ structure of the pressure–composition isotherms; (b) a rather broad range of working H storage capacities; (c) an increase of the plateau pressures and decrease in both enthalpy and entropy changes following an increase of the Mm content in the alloy; and (d) fast formation–decomposition rate. Desorption isotherms were approximated by a recently developed model of phase equilibria in the metal–hydrogen systems. In situ powder neutron diffraction studies of the system MmNi4.7Sn0.3–D2 show that in the region of α-solid solution deuterium insertion leads to a gradual increase of the unit cell volume reaching 1.9%. In the hexagonal β-MmNi4.7Sn0.3 D4.51 deuteride D atoms occupy two of four available types of tetrahedral interstices including 6m RE2(Ni,Sn)2 and 12n RE(Ni,Sn)3. [Copyright &y& Elsevier]

Abstract: Hydrogen storage performance of the TiFe-based materials suffers from difficulties with hydrogenation and sensitivity towards impurities in hydrogen gas reducing hydrogen uptake rates and decreasing the cycle stability. In present work the surface modification of the sintered Ti1.1Fe0.9O x and arc-melted TiFe was performed using autocatalytic deposition of the Pd-based catalytic layers in order to achieve improvement of the H storage characteristics. Pd deposition proved to be efficient in significant facilitation of the hydrogenation ability of the materials at moderate H2 pressures and room temperature, even after their long exposure to air. Activation performance of the sintered Ti1.1Fe0.9O x is superior than that for the arc-melted TiFe. This effect was associated with the presence of the oxygen-containing suboxide Ti4Fe2O1−x in the sintered sample acting as a hydrogen transfer catalyst. γ-Aminopropyltriethoxysilane pre-functionalization and subsequent Pd–P autocatalytic deposition onto the sintered Ti1.1Fe0.9O x intermetallic substrate resulted in a better hydrogenation kinetics compared to the samples prepared by the conventional Pd deposition. [Copyright &y& Elsevier]