Showing papers in "Journal of The Less Common Metals in 1987"
TL;DR: In this article, a brief historical survey is given of how the study of coercitivity mechanisms in SmCo5 permanent-magnet materials eventually led to the discovery of the favorable hydrogen sorption properties of the compound LaNi5.
Abstract: A brief historical survey is given of how the study of coercitivity mechanisms in SmCo5 permanent-magnet materials eventually led to the discovery of the favourable hydrogen sorption properties of the compound LaNi5. It is shown how continued research by many investigators dealing with a variety of different physical and chemical properties has resulted in an advanced understanding of some of the principles that govern hydrogen absorption and which are responsible for the changes in physical properties that accompany it. The problems associated with various applications of LaNi5-based hydrogen-storage materials are also briefly discussed. A large part of this paper is devoted to the applicability of LaNi5-type materials in batteries. Research in this area has resulted in the development of a new type of rechargeable battery: the nickel-hydride cell. This battery can be charged and discharged at high rates and is relatively insensitive to overcharging and overdischarging. Special attention is given to the nature of the electrode degradation process and the effect of composition variations in LaNi5-related materials on the lifetime of the corresponding hydride electrodes when subjected to severe electrochemical charge-discharge cycles.
409 citations
TL;DR: In this paper, a numerical model for transient heat and mass transfer within metal hydride reaction beds is presented, and theoretical predictions based on this model are compared with experimentally determined reaction rates and pressure-temperature distributions within the reaction beds.
Abstract: A numerical model for transient heat and mass transfer within metal hydride reaction beds is presented. Theoretical predictions based on this model are compared with experimentally determined reaction rates and pressure-temperature distributions within the reaction beds. In addition, a mathematical treatment of the behaviour of coupled reaction beds is shown and as an example calculated hydrogen pressures are compared with experimental results.
199 citations
TL;DR: In this article, the magnetic properties of a series of ternary compounds of the composition RFe 10 V 2 (R ≡ Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Lu and Y) X-ray diffraction showed that these materials crystallize in the tetragonal ThMn 12 structure.
Abstract: We have studied the magnetic properties of a series of novel ternary compounds of the composition RFe 10 V 2 (R ≡ Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Lu and Y) X-ray diffraction showed that these materials crystallize in the tetragonal ThMn 12 structure The Curie temperature falls into the range 483 to 616 K From high-field magnetic measurements made at 42 K on aligned powders it was derived that the iron sublattice anisotropy is about 4 T, while the rare earth sublattice anisotropy is comparatively low in most of the compounds studied
163 citations
TL;DR: In this paper, an extremely simple picture of the hydrogen-metal interaction is developed capable of describing in a quantitative way a vast number of experimentally observed phenomena such as the molecular adsorption and dissociation process, the properties of chemisorbed hydrogen, surface and bulk diffusion, interstitial hydrogen and the trapping of hydrogen at defects.
Abstract: The present understanding of hydrogen interacting with metals as provided by the effective medium theory and self-consistent model calculations is reviewed. An extremely simple picture of the hydrogen-metal interaction is developed capable of describing in a quantitative way a vast number of experimentally observed phenomena such as the molecular adsorption and dissociation process, the properties of chemisorbed hydrogen, surface and bulk diffusion, interstitial hydrogen and the trapping of hydrogen at defects.
142 citations
TL;DR: In this article, the authors used two groups of catalytic additives, i.e., hydrogen pumps and catalytic reaction catalysts, to fabricate hydrogen storage materials consisting of unusual pairs of metals.
Abstract: Mechanical alloying is a promising new way to fabricate hydrogen storage materials consisting of unusual pairs of metals. Mechanical alloying can be used more easily for fabricating Mg2Ni, other MgNi and intermetallic systems than melting and sintering techniques. Systems such as MgFe, MgCo, MgNb and MgTi, that cannot be prepared by conventional techniques, can be fabricated by mechanical alloying, in addition to any other pairs or more complex mixtures of metals and non-metals.
We have pointed out that intimate contact of metals can be achieved in high energetic ball mills. This contact plays an important role in hydriding and dehydriding processes. In this study we have used two groups of catalytic additives. The first group are “hydrogen pumps” such as CeHx. In the second group the added metal does not form any hydride in the conditions under study, but is known as an H2 → HH reaction catalyst, e.g., cobalt, nickel and probably iron.
129 citations
TL;DR: In this paper, the Rietveld profile analysis method has been extended using a Fourier analysis of line profiles on the basis of the Warren-Averbach method for separating size and strain effects.
Abstract: The Rietveld profile analysis method has been extended using a Fourier analysis of line profiles on the basis of the Warren-Averbach method for separating size and strain effects. Assuming a given size distribution (Cauchy) and an adjustable strain variation in space, this method allows the simultaneous determination of the structural parameters and the size and strain parameters of the sample. It has been used for analysing the neutron diffraction pattern of β-LaNi 5 deuteride which exhibits a strongly anisotropic broadening. The mean coherency domain was chosen as an ellipsoid of revolution along the c axis. The structure is described in the space group P 6 3 mc as well as the P 31 c space group with five types of interstitial sites (three in the hypothetical fully ordered LaNi 5 D 7 phase). The strain parameter, i.e. the distribution of atomic positions around their equilibrium positions, varies by a factor of 2.5 while the mean particle size changes from 80 A to more than 2500 A in [ hk 0] and [00 l ] directions respectively.
105 citations
TL;DR: In this article, the question of whether in the two-phase region of a metal-hydrogen system the desorption branch of the hysteresis loop of an isotherm is nearer to equilibrium than the absorption branch is still an open question.
Abstract: The question of whether in the two-phase region of a metal-hydrogen system the desorption branch of the hysteresis loop of an isotherm is nearer to equilibrium than the absorption branch (concept I) or the absorption and the desorption branches both deviate to a similar extent from equilibrium (concept II) is still an open question. After a review of the literature on this problem we try to solve it for the systems Pd-D2 and Pd-H2 as examples by applying a new method based on isothermal measurements of p(n) and χ(n) (p is the pressure of D2 or H2, n is the atomic ratio D:Pd or H:Pd and χ is the magnetic susceptibility) in the field about the critical point. The evaluation of the p(n) isotherms measured in the homogeneous solution phase above the critical temperature Tc yielded a value of the critical concentration nc = 0.257 ± 0.004, equal for Pd-D2 and Pd-H2. On the basis of this nc value the other critical data were redetermined; the values Tc = 556 ± 1 K and pc = 39 ± 0.5 bar obtained for Pd-D2 deviate markedly from those accepted so far. By means of the absorption and the desorption branches of the p(n) and the χ(n) isotherms measured across the two-phase region below Tc the boundaries of this region, i.e. the coexistence curve, could be determined. Different boundary lines for absorption and desorption were obtained in the Tvs. n diagram resulting in nc(abs) = 0.295 ± 0.005 and nc(des) = 0.255 ± 0.005, which were also equal for both isotopes. The coincidence of nc(des) with the nc value from the homogeneous region decides the question in favour of concept I. The shift of the coexistence curve obtained from the absorption measurements relative to that from desorption is interpreted as being a consequence of the constraining pressure on the more voluminous β phase. By means of this shift the hysteretic behaviour of the χ(n) isotherms also becomes understandable.
97 citations
TL;DR: In this paper, a comparative study of Mg2Ni and a mechanically alloyed mixture Mg-55wt.%Ni has been carried out in the laboratory and it was shown that the amount of nickel has an important effect on the hydriding-dehydriding kinetics.
Abstract: The kinetic characteristics of magnesium have been improved either by adding a catalyst or by using magnesium-based alloys. A comparative study of Mg2Ni and a mechanically alloyed mixture Mg-55wt.%Ni has been recently carried out in the laboratory. The mixture presents some interesting properties and the preparation of this material is easier and less energy consuming owing to the absence of heating. However, while the hydrogen capacity (3.2 wt.%) is close to that of Mg2Ni, it is significantly smaller than that of magnesium (7.6 wt.%). Therefore, to improve this characteristic, several compositions of mechanically alloyed mixtures Mg-xwt.%Ni with a lower nickel weight content have been studied (x = 5, 10 and 25). It was shown that the amount of nickel has an important effect on the hydriding-dehydriding kinetics. The decrease of the particle size and the augmentation of the density of defects are because of hydriding-dehydriding cycling. These effects are enhanced by an increase in the nickel content and increase the rate of the hydriding and dehydriding reactions. In contrast, the hydrogen storage capacity diminishes as the amount of nickel increases. For these reasons, Mg-10wt.%Ni and Mg-25wt.%Ni are the most favourable compositions.
95 citations
TL;DR: In this article, a method of mechanical alloying was used to produce an Mg-25%Fe composite hydrogen storage material and the activation of the mechanical alloy was completed by the third cycle of hydriding.
Abstract: A method of mechanical alloying was used to produce an Mg-25%Fe composite hydrogen storage material. The presence of a pure metallic iron surface in contact with the magnesium leads to the promotion of the dissociative adsorption of hydrogen and the hydrogenation of Mg-25%Fe begins at the maximum rate even in the first cycle of hydriding. The activation of the mechanical alloy is completed by the third cycle of hydriding. The process of formation of Mg2FeHx is also studied.
92 citations
TL;DR: In this paper, it was shown that the nucleation is rate determining in the initial hydriding only and that the growth takes place entirely by interface migration of hydrogen from the particle surface.
Abstract: Experiments on a large number of magnesium powders varying in particle size, morphology, purity and surface oxidation have shown that most of these parameters influence the kinetics of the hydride formation. Although no single step in the reaction will in general be rate determining we have in a previous investigation been able to assign a nucleation and growth model to the initial hydriding of an atomized powder. This powder of nearly spherical particles (d ≈ 90 μm) with a thin oxide coating has also been used in this investigation of the nucleation and growth mechanisms. It is found that the nucleation is rate determining in the initial hydriding only and that the growth takes place entirely by interface migration of hydrogen from the particle surface. The pressure-nucleation relation and impurity effects on the ultimate degree of reaction are discussed.
87 citations
TL;DR: In this paper, the application of the hydrogen decrepitation (HD) process to the production of rare earth containing permanent magnets is discussed and the characteristics of the HD powder of all three alloy types are compared with those of the normal milled material.
Abstract: In this article, the application of the hydrogen decrepitation (HD) process to the production of rare earth containing permanent magnets is discussed. It is shown that the HD process can be applied successfully to the production of SmCo 5 − , Sm 2 (Co, Fe, Cu, Zr) 17 − and Nd 2 Fe 14 B-type magnets. The particular HD conditions for each category of permanent magnet are described. The characteristics of the HD powder of all three alloy types are compared with those of the normal milled material and it is seen that significant advantages accrue from the use of the HD powder.
TL;DR: In this paper, the electrochemical capacities and the durabilities for charge and discharge cycling of Ti1−YZrYNiX alloy hydride electrodes were examined. And a coefficient was introduced to evaluate quantitatively the durability.
Abstract: The electrochemical capacities and the durabilities for charge and discharge cycling of Ti1−YZrYNiX alloy hydride electrodes were examined. It was found that the zirconium-rich alloys such as Ti0.5Zr0.5Ni1.0, Ti0.2Zr0.8Ni1.35 and Ti0.2Zr0.8Ni1.25 have considerably large capacities and good durabilities. Nickel or copper plating on hydride powder was very effective in improving the durability. In addition, a coefficient was introduced to evaluate quantitatively the durability.
TL;DR: The use of NH 4 Br in the conversion of rare earth oxides (M 2 O 3 ), hydrated bromides (H 2 O) or the metals scandium, yttrium and lanthanum to lutetium, to anhydrous tribromide (MBr 3 ) provides a plethora of chemistry as discussed by the authors.
Abstract: The use of NH 4 Br in the conversion of rare earth oxides (M 2 O 3 ), hydrated bromides (MBr 3 · x H 2 O) or the metals scandium, yttrium and lanthanum to lutetium, to anhydrous tribromides (MBr 3 ) provides a plethora of chemistry. In general, the two-step procedures start with the synthesis of a ternary bromide: (NH 4 ) 2 MBr 5 for M ≡ La to Nd and (NH 4 ) 3 MBr 6 for M ≡ Sm to Lu, Y, Sc. This is achieved at 200–250 °C from hydrated ternary bromides in an HBr gas stream, at 280 °C from NH 4 Br and M 2 O 3 (a 10:1 molar ratio for M ≡ La to Nd and a 12:1 molar ratio for M ≡ Sm to Lu, Y, Sc) or at 300 °C from NH 4 Br and M mixtures. The subsequent step is the decomposition of the ternary bromide to the binary tribromide MBr 3 in a vacuum at 350–400 °C. The actual decomposition pathways are dependent upon the size of the trivalent cation and may pass through the intermediate NH 4 M 2 Br 7 (M ≡ Nd to Dy).
TL;DR: In this article, the Heusler alloys Ni2MnSn and NiMn2Sn were investigated by means of neutron diffraction at 4.2 and 300 K, respectively.
Abstract: The Heusler alloys Ni2MnSn and NiMn2Sn were investigated by means of neutron diffraction at 4.2 and 300 K. In both compounds (L21 structure) the manganese atoms show a pronounced preference for occupying the octahedral site ( 1 4 1 4 1 4 ) while the nickel atoms tend to occupy the tetrahedral sites (000) and ( 1 2 1 2 1 2 ). The moment of the manganese atoms occupying some of the tetrahedral sites in NiMn2Sn (2.01 μB) is antiparallel to that of the manganese atoms at the octahedral sites (4.49 μb).
TL;DR: In this paper, the electronic structure of LaNi5H7 was investigated using recent crystallographic data, and information concerning the metal-H interactions were obtained from a comparison of the site and angular momentum analysis of the densities of states (DOS) of the pure intermetallic LNi5 and its hydride.
Abstract: Using recent crystallographic data, we have investigated the electronic structure of LaNi5H7. Information concerning the metal-H interactions are obtained from a comparison of the site and angular momentum analysis of the densities of states (DOS) of the pure intermetallic LaNi5 and its hydride. From our study of the total DOS of the intermetallic compound, available photoemission data and Fermi energy related properties such as electronic specific heat measurements are discussed.
TL;DR: In this article, the heats of intermetallic compounds of aluminium with cerium, erbium, and gadolinium were determined by solution calorimetry in liquid aluminium.
Abstract: The heats of formation of intermetallic compounds of aluminium with cerium, erbium and gadolinium were determined by solution calorimetry in liquid aluminium. The enthalpy of mixing of liquid aluminium-cerium alloys was obtained by measuring the enthalpy of melting of the compounds. The results are discussed on the basis of Miedema's model and in connection with the glass-forming ability of these alloys.
TL;DR: In this paper, a new hydride phase in the LaNi5-H2 system has been found by precise pressure-composition isotherm measurements at temperatures higher than 353 K.
Abstract: A new hydride phase in the LaNi5-H2 system has been found by precise pressure-composition isotherm measurements. Two plateaux on the isotherms have been clearly observed at temperatures higher than 353 K. The gap between the two plateaux that indicates the existence of the new phase appeared at the composition LaNi5H3. Results of in situ X-ray diffraction measurements show that the new phase LaNi5H3 has hexagonal structure which is the same as the solid solution phase (α phase) and the full hydride phase. The new phase is named β phase and the full hydride phase (LaNi5H6) which has been called β phase is named here γ phase. It was found that the β phase formed after reactions were carried out at temperatures higher than 343 K in desorption and 367 K in absorption. However, once the β phase appeared it formed even at room temperature. Change in lattice parameters has also been measured along the phase transformations. It was found that the lattice expansion accompanying hydride formation was anisotropic. The structure of the β-phase hydride is discussed.
TL;DR: In this paper, the nouveaux germaniures isotypes ont ete synthetises a 1173 K. (R w = 0,029) K. C'est un new type apparente au type Sc 5 Co 4 Si 10.
Abstract: Resume Les nouveaux germaniures isotypes ont ete synthetises a 1173 K. La structure de YIrGe 2 a ete determinee par diffraction X d'un monocristal: groupe spatial, Immm ; Z = 8; a = 4,2635(9) A , b = 15,9786(21) A , c = 8,8134(16) A , D x = 9,4 g cm −3 , μ ( Ag Kα ) = 42,9 mm −1 , F (000) = 1439, R = 0,028 pour 281 reflexions independantes. ( R w = 0,029). C'est un nouveau type apparente au type Sc 5 Co 4 Si 10 . YIrGe 2 , YPtGe 2 et CaPtGe 2 ne sont pas supraconducteurs au-dessus de 1,3 K.
TL;DR: In this article, the cubic phase LaNi2 (MgCu2 type) exists in a small homogeneity range (2.17 Extended X-ray absorption fine structure (EXAFS) studies at the Ni K edge for RNi2 and CeNi2 phases compounds has revealed a local disorder for both compounds which is more pronounced for LaNi 2 than for CeNi 2.
Abstract: It has been determined that the cubic phase LaNi2 (MgCu2 type) exists in a small homogeneity range (2.17 Extended X-ray absorption fine structure (EXAFS) studies at the Ni K edge for RNi2 (R ≡ La, Ce) Laves phases compounds has revealed a local disorder for both compounds which is more pronounced for LaNi2 than for CeNi2. X-ray powder diffraction measurements of the intermetallics on hydrogenation show an increase in the cell parameter for LaNi2 up to LaNi2H1 ( ΔV V = 1.4% ) and a decrease for CeNi2H1 ( ΔV V = − 0.5% ). Beyond 1 H atom mol−1 the cell parameter is almost constant. Above 3.5 H atom mol−1 the X-ray diffraction lines disappear completely. Transmission electron microscopy, magnetization and X-ray absorption spectroscopy (EXAFS and Ce LIIIedge) measurements allow us to conclude that these hydrides are amorphous (for XH⩾ 3.5). In addition, a change in the cerium valency occurs on hydrogenation.
TL;DR: In this article, the crystal structure data of the actinide elements and of binary compounds of actinides with non-metallic elements (X) with binary lattice parameters are presented.
Abstract: This paper covers crystal structure data of the actinide elements and of binary compounds of actinides (An) with non-metallic elements (X). A few ternary compounds closely related to binary ones are included. The compounds are classified according to X:An ratios and to structure types. Tables list the known compounds and their lattice parameters for each structure type.
TL;DR: In this article, the enthalpies of La(Ni(1−x)COx)5 compounds have been measured using a calorimetric method and the variation of these values as a function of composition is discussed using a tight-binding model to describe the electronic structure of these compounds.
Abstract: The enthalpies of formation of La(Ni(1−x)COx)5 compounds have been measured using a calorimetric method. The variation of these values as a function of composition is discussed using a tight-binding model to describe the electronic structure of these compounds. The enthalpy and entropy of formation of hydrides are deduced from the study of the change of their equilibrium pressures as a function of temperature. Correlations between structural and thermodynamic properties of the intermetallic compounds of the La(Ni1−x)Cox)5 series and their related hydrides are discussed.
TL;DR: In this article, the structural characteristics of the metal hydrides (hydrogen coordination, volume change and compressibility) are connected with electronic parameters (Fermi energy and density of states at the Fermi level).
Abstract: We suggest, as the result of a generalization of structural data on the hydrides of d transition metals, a simple model, within the framework of which the structural characteristics of the metal hydrides (hydrogen coordination, volume change and compressibility) are connected with electronic parameters (Fermi energy and density of states at the Fermi level). Volume effects have been considered by using a rigid d-band model. Phase transformations with changing hydrogen coordination have been predicted for a number of hydrides of d metals.
TL;DR: In this article, the authors investigated structure types in which each atomic position of the structure has the same near-neighbour environment and found that 2483 (99%) of these compounds crystallize in one of the five following general structure types: tetrahedron, octahedral, cubo-octahedron or rhombic dodecahedron.
Abstract: We have investigated structure types in which each atomic position of the structure has the same near-neighbour environment. We call these single-coordination types. 47 “classical” crystal structures of this single-coordination type exist which comprise 2511 binary, ternary and quaternary compounds. For 44 “classical” structure types we find that 2483 (99%) of these compounds crystallize in one of the five following general structure types: tetrahedron, octahedron, cubo-octahedron, rhombic dodecahedron or truncated hexagonal eclipsed bipyramid. Our three-dimensional structural-stability diagram separates these 2483 compounds into the five different general structure types with an accuracy of 97%.
TL;DR: There are 17 ScT2X intermetallic compounds, in which T is a member of the cobalt, nickel or copper group, and X is aluminium, gallium, indium or tin this article.
Abstract: There are 17 ScT2X intermetallic compounds, in which T is a member of the cobalt, nickel or copper group, and X is aluminium, gallium, indium or tin. Substitution of all or part of the lanthanoids (or yttrium) for scandium can be made in the series LnPd2In, LnNi2Sn, LnPd2Sn, LnCu2In, LnAg2In and LnAu2In. Unit cell constants are given and the role of atomic volume as a controlling factor is discussed.
TL;DR: In this paper, the effect of substitution of manganese for iron, titanium or both iron and titanium in an FeTi alloy (i.e., 0.1-0.3) was investigated.
Abstract: The effect of the substitution of manganese for iron, titanium or both iron and titanium in an FeTi alloy (i.e. Fe1−x TiMnx, FeTi1−xMnx and Fe 1−( x 2 ) Ti 1−( x 2 ) Mn x (x = 0.1–0.3)) on the hydriding during the initial hydriding process, the pressure-composition isotherms and the microstructure was investigated. The partial substitution of manganese for iron, titanium or both iron and titanium yielded FeTi activation at 303 K after an incubation period without any activation treatment (with the exception of the Fe0.9TiMn0.1 alloy). Fe 1−( x 2 ) )Ti 1−( x 2 ) Mn x and FeTi1−xMnx alloys were composed of an FeTi phase and a second phase, (Fe1−zMnz)1.5Ti. Fe1−xTiMnx alloys were predominantly composed of an FeTi phase with small amounts of second phases, (Fe1−zMnz)1.5Ti and Ti1.5Fe1−wMnw). However, after annealing, the second phases in the Fe1−xTiMnx alloys disappeared and an activation treatment at 673 K with a hydrogen pressure of 4 MPa was then required. The results obtained in this study showed that the presence of a second phase in the FeTi alloy played a crucial role in shortening the incubation time. The incubation time for the initial hydriding was dependent not only on the number of interfaces between the FeTi phase and the second phase, but also on the composition of the second phase, i.e. if the second phase readily reacts with hydrogen to form its hydride, even a small amount of second phase shortens the incubation period. Manganese substituted for iron in the FeTi phase and its composition was approximately represented by (Fe1−yMny)Ti. The plateau pressure decreased and the lattice parameter of the FeTi phase increased with increasing manganese content.
TL;DR: The structural and magnetic properties of RE 2 Fe 14 BH x hydrides with RE ≡ Y, Ce, Er have been studied as a function of x in this article, where both Curie temperature and magnetization are increased on hydriding the ternary bondes.
Abstract: The structural and magnetic characteristics of RE 2 Fe 14 BH x hydrides with RE ≡ Y, Ce, Er have been studied as a function of x . Both Curie temperature and magnetization are increased on hydriding the ternary bondes. Neutron diffraction experiments performed on deuterated samples have permitted the location of the host sites and the measurement of the magnetic moments of iron and RE. Different anomalies reported in the structural and magnetic behaviour of Ce 2 Fe 14 BH x are related to the change of electronic state on cerium.
TL;DR: In this paper, the desorption kinetics of magnesium hydride were studied by the thermal analysis technique, and a theoretical rate equation was derived, based on the continuous moving boundary model.
Abstract: To relate thermal desorption spectra to reaction kinetics and occupation site, the desorption kinetics of magnesium hydride were studied by the thermal analysis technique. The rate-controlling step for the desorption of magnesium hydride was assumed to be an interfacial chemical reaction and a theoretical rate equation was derived, based on the continuous moving boundary model. The apparent activation energy for the desorption of magnesium hydride is 142 kJ mol−1.
TL;DR: In this paper, a geometrical model applied to these compounds revealed that in the basal plane only the 12n site can be occupied, and the structural determination did not exclude the occupancy of a second site but gave a lower occupancy than the 12 n site.
Abstract: Powder neutron diffraction studies have been performed for the compounds α-LaNi 5 D x ( x = 0.1 and 0.4). In the P 6/ mmm space group of the intermetallic LaNi 5 , in the case of the “virgin” sample the deuterium atoms are found in the basal plane for the two compounds with strains localized in this plane but the deuterium atoms are displayed in all crystallographic directions for the “activated” sample. A geometrical model applied to these compounds revealed that in the basal plane only the 12n site can be occupied. Our structural determination did not exclude the occupancy of a second site but gave a lower occupancy than the 12n site.
TL;DR: In this article, the ternary chlorides (NH 4 ) 2 UCl 6 and (NH 3 ) 2 ThCl 6 were obtained via the ammonium chloride route from UH 3 and thorium metal respectively.
Abstract: Uranium and thorium tetrachloride (UCl 4 and ThCl 4 ) were obtained via the ammonium chloride route from UH 3 and thorium metal respectively, with the ternary chlorides (NH 4 ) 2 UCl 6 and (NH 4 ) 2 ThCl 6 acting as intermediates. The crystal structure of UCl 4 was refined ( R = 0.031, R w = 0.026). Cs 2 UCl 6 and Cs 2 ThCl 6 were synthesized, their lattice constants refined from powder data, and the crystal structure of Cs 2 UCl 6 refined from single-crystal data ( R = 0.066, R w = 0.052). Some indication for stacking disorder in the [00.1] direction was found. Metallothermic reductions of UCl 4 with lithium and sodium led to UCl 3 whose crystal structure was also refined ( R = 0.029, R w = 0.023). Potassium reduced UCl 4 to K 2 UCl 5 . No further reduction could be detected.
TL;DR: In this paper, the crystal structure of the hydrogen storage system γ-TiFeD 1.94(3) was re-investigated by neutron powder diffraction profile analysis at room temperature and 113 ± 17 bar D 2 pressure.
Abstract: The crystal structure of the hydrogen storage system γ-TiFeD 1.94(3) was re-investigated by neutron powder diffraction profile analysis at room temperature and 113 ± 17 bar D 2 pressure. In contrast with previous work which assumed a structure of monoclinic symmetry a structure of orthorhombic symmetry was assumed: space group Cmmm ; lattice parameters a = 7.029(4) A , b = 6.233(2) A , c = 2.835(1) A ; titanium in equipoint 4h ( x , 0, 1 2 ), x = 0.223(2); iron in 4i (0, y , 0), y = 0.2887(7); D1 in 4e ( 1 4 , 1 4 , 0); D2 in 2c ( 1 2 , 0, 1 2 ); D3 in 2a (0, 0, 0); agreement values after profile refinement R wp = 0.160, R I = 0.085, R F = 0.060; ( sin θ λ ) max = 0.59 A − 1 ; 85 inequivalent contributing reflections hkl ; 10 refined structural parameters. Refinements based on the less symmetric monoclinic model yield virtually the same fit and structure but require four more structural parameters. The structure is characterized by three types of octahedral metal atom interstices; two of type Ti 4 Fe 2 occupied by deuterium atoms D1 and D3 and one of type Ti 2 Fe 4 occupied by deuterium atom D2. The former are 100% occupied and the latter are 91% occupied. The shortest interatomic distances are Fe − D1 = 1.77 A , Ti − D2 = 1.95 A and D1 − D3 = 2.35 A .