Intermetallic Hydrides Research Articles

Arrhenius Jump Rate of Muons in Metals and Metallic Compounds

In our earlier papers [1-5] diffusion of muons in metals and non-stoichiometric metallic and intermetallic hydrides has been studied in a newly developed model which formulates the jump rate for muon diffusion in an Arrhenius form. The model considers the muons, upon being incident on the target, can diffuse through an electron gas of the target. While diffusing through the electron gas the muons find electrons to collide and result in an annihilation process in which energy is liberated from the target due to neutrino-antineutrino emission. This energy loss rate is made related to the jump rate for muon diffusion in all these targets. This study of muon diffusion is readily extended to the case of some metallic compounds which are used as good targets. Therefore this article becomes an extension of our previous works and presents some more results for the jump rate of muons in metals like platinum and lead and some good metallic compounds like ZrV2, Hf2 Co and V3Si.

Three Decades of Intermetallic Hydrides — What happened to the Applications?*

Three Decades of Intermetallic Hydrides — What happened to the Applications?*

The electronic properties of intermetallic hydrides with the K2PtCl6 structure

The authors present results from electronic structure calculations of the intermetallic hydrides M2M'H6 (M=Mg, Ca, Sr, M'= Fe, Ru, Os). Most of these hydrides have been recently synthesized and characterized, all showing the K2PtCl6 cubic structure. They have determined their energy bands and densities of electronic states by means of the non self-consistent augmented-plane-wave method. The results show that the nine hydrides are semiconductors with relatively large energy gaps. These isostructural and isoelectronic families of hydrides have been studied in order to establish correlations between the ordering of the electronic states and the energy gaps in terms of differences in metal-hydrogen distances and atomic energy level. They observe that the splitting between the bonding and antibonding M' d(eg) orbitals is responsible for the increase of the energy gap as the atomic number of M'increases. Nevertheless, the presence of d states from the divalent metals Ca and Sr modifies the nature of the unoccupied conduction states above the energy gaps. In general, a reduction of the energy gap is obtained in the Ca- and Sr-derived hydrides.

Role of active surface in processes of hydrogen sorption-desorption by intermetallic compounds

Abstract The influence of surface composition on hydrogen activation in the process of liquid-phase hydrogenation of organic compounds was determined by the investigation of intermetallic hydrides LaNi 5-x Cu x H n ( x = 1–4) and La 1-x Ce x Ni 5 H n ( x = 0.15–0.35). The complex of physicochemical methods showed that the formation dynamics and the nature of the active surface layer are determined by both the preliminary processing conditions and the reaction medium impact. It is shown that by varying the reaction medium composition it is possible to give a useful rise in the preferential segregation of one of the alloy components and to create active centers with definite composition on the surface. The investigation of the dependence of hydride catalytic activity on intermetallic nature, hydride forming pressure, sorption capacity and hydride surface composition allows us to draw the conclusion that surface center composition has a decisive influence on both hydrogen sorption-desorption kinetics and organic compound hydrogenation.

Interaction of intermetallic compounds with hydrogen at pressures up to 250 MPa: the LaCo 5− xMn x-H 2 and CeNi 5−H 2 systems

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.

Trends in the Electronic Structure of Intermetallic Hydrides: M2M'H6 (M = Mg, Ca, Sr, M' = Fe, Ru, Os)*

Article Trends in the Electronic Structure of Intermetallic Hydrides: M2M'H6 (M = Mg, Ca, Sr, M' = Fe, Ru, Os)* was published on January 1, 1993 in the journal Zeitschrift für Physikalische Chemie (volume 181, issue 1-2).

Phase transformations in hydrogen sorption-desorption by hydrides of intermetallic compounds of the CrB structural type

The authors consider phase transformations in intermetallic-H{sub 2} systems, occurring during sorption-desorption of hydrogen. As the objects of investigation, the authors used intermetallic hydrides of the CrB structural type: ZrNiH{sub 3.0}, HfNiH{sub 3.0}, ZrCoH{sub 3.0}, HfCoH{sub 3.0}. The phase transitions have been studied for the first time by in situ X-ray phase analysis. The authors have identified the following phases: ZrNiH{sub 1.0}, HfNiH{sub 1.0}, HfNiH{sub 3.0}, ZrCoH{sub 3.0}. The authors have shown the effect of the composition of the intermetallic compounds on the phase transitions for sorption-desorption processes.

Intermetallic hydrides as components of hydrogenation catalysts

Intermetallic hydrides as components of hydrogenation catalysts

Investigation on synthesis, characterization and hydrogenation behaviour of the La 2Mg 17 intermetallic

Synthesis, structural characterization and hydrogenation behaviour of the La 2Mg 17 system have been investigated. One of the interesting results obtained is the hydrogen desorption at room temperature. For the first hydrogenation cycle, the as-synthesised intermetallic. La 2Mg 17, is activated up to 150 ± 10°C under hydrogen pressure, but no activation through heat treatment is needed for absorption—desorption for the second and subsequent cycles. The hydrogen desorption capacity of La 2Mg 17 is calculated by weight percentage and hydrogen capacity per mole of La 2Mg 17. The maximum value corresponds to 6.63% which represents one of the highest hydrogen capacities exhibited by a reversible intermetallic hydride system.

ChemInform Abstract: The Positive Muon in the Intermetallic Hydride ZrV2Hx: A Muon Tracer Study Supplemented by Differential Thermoanalysis, Neutron Vibrational Spectroscopy, and Quasielastic Neutron Scattering

ChemInform Abstract: The Positive Muon in the Intermetallic Hydride ZrV2Hx: A Muon Tracer Study Supplemented by Differential Thermoanalysis, Neutron Vibrational Spectroscopy, and Quasielastic Neutron Scattering

Application of Mössbauer spectroscopy to physical metallurgy: The role of light interstitial elements

Light elements like hydrogen, nitrogen, and carbon, residing on interstitial sites of the host lattice, are capable of inducing noticeable changes in the physical properties of the material affected by their presence. Hydrogen uptake by different intermetallic compounds can lead to completely different results, depending on the chemical affinity between hydrogen and the constituent elements of the compounds. In the cases of considerable hydrogen concentrations, several distinct hydride phases can usually be found and identified by Mossbauer spectroscopy. Alterations of the magnetic behaviour of the intermetallic hydride are frequently observed. Nitrogen and carbon serve as agents for solid solution and precipitation hardening in commercial steels. Among the various methods for alloying with these elements and for controlling their distribution, implantation and surface treatment by use of a laser beam are of particular interest.

The positive muon in the intermetallic hydride ZrV2Hx: A muon tracer study supplemented by differential thermoanalysis, neutron vibrational spectroscopy, and quasielastic neutron scattering

ZrV2 is an intermetallic compound with energetically different interstitial sites, which upon hydrogenation are successively filled with hydrogen (thermodynamic distribution). When a positive muon is added as a microscopic probe, it is thermalized at random and thus at low temperatures statistically distributed over the available (unblocked) interstices. By varying the preloading we scan the accessible hydrogen sites and find that at high hydrogen content three kinds of interstices are occupied, in contradiction to literature diffraction data. This surprising result is confirmed by a detailed neutron vibrational spectroscopy study on ZrV2Hx which is presented as well. The temperature dependence of the μ+ relaxation rate is textbook-like in empty ZrV2: static muon at T<50 K, complete motional narrowing at T>200 K. In ZrV2Hx, however, the relaxation rate exhibits an intermediate plateau which we attribute to a relocation of the muon. The motion of the muon above 150 K is interpreted as being directly related to the hydrogen diffusion which we have separately measured by means of quasielastic neutron scattering. In addition, we investigated the ZrV2/H phase diagram by differential thermoanalysis.

Review of Recent Theoretical Investigations of the Electronic Structure of Intermetallic Hydrides*

Article Review of Recent Theoretical Investigations of the Electronic Structure of Intermetallic Hydrides* was published on February 1, 1989 in the journal Zeitschrift für Physikalische Chemie (volume 163, issue 2).

Coal liquefaction using an intermetallic hydride to distribute hydrogen and catalyze the reaction

Iron-titanium alloy forms a reversible metal hydride which stores hydrogen as atomic hydrogen within its metal matrix at a density exceeding liquid hydrogen. The alloy has also been shown to have substantial catalytic properties towards hydrogenation reactions. In this paper we examine the alloy as a vehicle to both transport and distribute hydrogen to slurried coal and catalyze the liquefaction process. Batch liquefaction experiments produced conversions of approximately 50% for industrially handled Utah (SUFCO) and Alabama Blue Creek coals slurried in either tetralin or 1-methylnaphthalene in less than 30 min at a temperature of 260°C and a pressure of 4.14 MPa. Comparison of the liquefaction results in tetralin and 1-methylnaphthalene suggested that tetralin was involved as a shuttling agent rather than a donor solvent for this approach. This catalytic process reduced the nitrogen, sulfur, and oxygen contents of the Utah coal by 25%, 50%, and 89.5% respectively, while the sulfur content of the Alabama coal was reduced by 34%. Both a simple first order mechanism and a more complex second order mechanism closely modeled the liquefaction data. Calculation, based on a run using non-hydrided FeTi, produced a catalytic turnover number of 3·10 −2 molecules of hydrogen per site per s. This approach overcomes problems encountered in other liquefaction processes, while converting coal to liquid products at reduced operating conditions. A hydrogen adsorption study of the spent alloy showed a 4% deactivation of the catalyst.

Effect of Hydrogen Absorption on the Magnetic Properties of Pseudobinary Intermetallics Y(Mn1-xTx)2(T=Al,Co and Ni)

Magnetization measurement, 55 Mn NMR and 1 H NMR measurements were performed in hydrides of pseudobinary intermetallics Y(Mn 1- x T x ) 2 (T=Al, Co and Ni); x =0∼0.15). The magnetization measurement indicates that Y(Mn 1- x T x ) 2 H y with y ≦3.5 exhibit ferromagnetism with Mn moments ranging from 0.07 to 0.32 µ B and more charged Y(Mn 1- x T x ) 2 H 4.0 exhibit paramagnetic behaviours. From the x dependence of the mean Mn moment In Y(Mn 1- x Al x ) 2 H 3.0 , It was found that an appearance of the Mn moment is considerably sensitive to the Mn concentration. 55 Mn NMR signals are discussed based on the transferred hyperfine field from the neighbouring Mn moments. 1 H NMR signals are discussed in terms of a dipole interaction between the 1 H nuclei and the neighbouring Mn moments on the assumption that hydrogen atoms almost occupy only the g-sites which composed by two Y and two Mn atoms.

ChemInform Abstract: Reduction of Organic Compounds with Rare‐Earth Intermetallics Containing Absorbed Hydrogen.

AbstractThe alkenes (I) and (III), the acetylenes (VI), and the carbonyl compounds (VIII) are hydrogenated with the intermetallic hydride LaNi5H6 to yield the saturated hydrocarbons (II) and (VII), the partly hydrogenated derivative (IV), or the alcohols (IX).

On the “imaginary binary hydrides” model

The “imaginary binary hydrides” (IBH) model has been elaborated to predict the relative hydrogen site occupation in intermetallic hydrides. Utilization of Miedema's first version for calculating heats of formation ΔH of binary hydrides for input into the IBH model has led to good quantitative agreement with some experimentally derived data. Application of later versions for calculating ΔH values of binary hydrides for input into the IBH model yield unsatisfactory quantitative predictions. In the present work an attempt is made to understand the reason for the significant difference in the results of the IBH model upon the application of the various schemes for calculating ΔH values of binary hydrides. Consequently, several available experimental results for the heats of formation of metal-hydrogen systems in their solubility regions are considered. At high hydrogen concentrations the later versions, mentioned above, yield improved estimations of ΔH values. At low hydrogen compositions, however, Miedema's original model better reflects the variational behaviour of ΔH, especially in view of the fact that a constant term in ΔH does not change the results of the IBH procedure.

Hydrogasification of carbonaceous materials in the presence of catalytic systems derived from intermetallic hydrides

The paper contains some experimental data obtained for hydrogasification of physically mixed carbonaceous materials (activated coal, carbon blacks, graphite) with intermetallic hydride catalysts (ZrNiH 28; ZrCoH 2.8) in the temperature range from 623 to 1023 K at atmospheric pressure. Methane is shown to be the only reaction product, the rate of its formation depending on the size of the catalyst particles and the nature of carbonaceous material. Oxidation-reduction pretreatment of the hydridecarbon mixture is found to be effective in increasing methane formation and leads to a system, the components of which exert a synergistic effect on the hydrogasification of carbonaceous materials.

Hydrides of rare earth metals and intermetallics and topics in solid state science

Though there is continuing interest in basic research on hydrogen in, and on, metals, applied research on metal hydrides has known many ups and downs. About ten years ago it was thought that hydrides of intermetallic compounds would become important in the mobile and stationary storage of hydrogen as a synthetic fuel. Subsequently it became evident that hydrogen would not be an economic fuel in the immediate future, unless the cost of removing pollution was added to the price of fuels. Today applied research on metal hydrides is more oriented towards the use of hydrogen in closed systems, e.g., thermal compressors or heat pumps [1]. The aim of the present contribution is to show that metal hydrides are exciting materials allowing the study of many topics of solid state science.

Physicochemistry and crystallochemistry of intermetallic hydrides containing rare earths and transition metals

Various aspects of the interaction of hydrogen with intermetallic compounds belonging to the homologous series RT5, RT3 and RT2 (R ≡ rare earth metal or Sc; T ≡ Fe, Co, Ni) are described. The reactions of 150 compounds were studied experimentally to demonstrate that the direction of the reaction depends on the initial structure and on the nature of the R and T atoms. The interactions were shown to result in so-called hydrides of the intermetallic compounds in which the initial metal matrix either remains intact or increases in volume without a significant atomic rearrangement. X-ray structure studies and complete structure determinations of the hydride phases using neutron diffraction methods were carried out to investigate the principal rules governing the variations in hydride structures and properties. The insertion of hydrogen atoms into interstitial sites of the matrix lattice occurs at sites in an environment in which the lengths of the M-M bonds exceed the sum of the corresponding metal radii. The hydrogenolysis reaction which results in the formation of a binary hydride and the elimination of a transition metal was shown to be favoured thermodynamically. The mechanism of hydrogenolysis was studied.