Showing papers in "Journal of The Less Common Metals in 1982"
TL;DR: In this article, a detailed model for hysteresis is presented for metal hydride systems based on the requirement for dislocation production during both the formation and decomposition of hydrides.
Abstract: A detailed model for hysteresis is presented for metal hydride systems based on the requirement for dislocation production during both hydride formation and hydride decomposition. A quantitative illustration of the model is presented using the regular interstitial solution approximation. The relationship between the solvus hysteresis and pressure hysteresis is given. The model predicts that calorimetrically measured enthalpies for hydride formation and decomposition will not exhibit any differences arising from hysteresis but that the enthalpies determined from the temperature variations of the plateau pressures for hydride formation and decomposition will show differences due to hysteresis.
192 citations
TL;DR: In this article, the occurrence and structural features of these five structure types together with the tetragonal PbFCl type, an Fe2As-type derivative found earlier for RFeSi and RCoSi compounds were discussed.
Abstract: Over 100 new equiatomic ternary rare earth (R)-transition metal (T) silicides, germanides and gallides were synthesized and structurally analysed either by evaluating powder diffraction photographs or in the case of ScRhSi, ScPtSi, YNiSi, ScRuGe and PrPtGe by refining single-crystal diffraction data. The hexagonal ZrNiAl type, an Fe2P-type derivative, was found for ScRuSi and ScTGe (T ≡ Ru, Rh, Pd, Os). The orthorhombic TiNiSi type, a PbCl2-type derivative, was assigned to RRhGa (R ≡ Er, Y), RPdGa (R ≡ La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Lu, Y, Sc), RIrGa (R ≡ Er, Y), RPtGa (R ≡ La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y, Sc), YNiSi, RRhSi (R ≡ Er, Y, Sc), ScPdSi, RIrSi (R ≡ Gd, Er, Y, Sc), RPtSi (R ≡ Tb, Dy, Ho, Er, Tm, Lu, Y, Sc), RRhGe (R ≡ Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Y, Sc), RIrGe (R ≡ Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Y, Sc) and RPtGe (R ≡ Sm, Gd, Tb, Dy, Ho, Er, Tm, Y, Sc). The CeCu2 type, which is related to TiNiSi, was found for R(Pd0.5Ge0.5)2 (R ≡ La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Y) and R(Pt0.5Ge0.5)2 (R ≡ Ce, Pr, Nd) where the palladium or platinum and germanium atoms are arranged at random on the copper sites. The tetragonal LaPtSi type, a ThSi2-type derivative, was found for RPtSi (R ≡ La, Ce, Pr, Nd, Sm, Gd), LaIrGe and LaPtGe. Finally the cubic LaIrSi type, an SrSi2-type derivative, was found for LaIrSi. The occurrence and structural features of these five structure types together with the tetragonal PbFCl type, an Fe2As-type derivative found earlier for RFeSi and RCoSi compounds, are discussed.
186 citations
TL;DR: In this paper, the dielectric constants and loss tangents of mixed Li-Ni ferrites of various compositions were measured at room temperature using a capacitance bridge in the frequency range 10 2 -10 5 Hz.
Abstract: The dielectric constants and dielectric loss tangents of mixed Li-Ni ferrites of various compositions were measured at room temperature using a capacitance bridge in the frequency range 10 2 –10 5 Hz. A qualitative explanation for the composition and frequency dependence of the dielectric constant is given. The dielectric constant for these mixed ferrites is roughly inversely proportional to the square root of the resistivity.
126 citations
TL;DR: The results of an experimental investigation of the phase diagrams of 14 BaF 2 -(Y, Ln)F 3 systems at temperatures ranging from 800 °C to the melting points are reported in this paper.
Abstract: The results of an experimental investigation of the phase diagrams of 14 BaF 2 -(Y, Ln)F 3 systems (Ln ≡ La, Ce, Pr, Nd, Sm — Lu) at temperatures ranging from 800 °C to the melting points are reported. Non-stoichiometric phases of Ba 1− x R x F 2 + x with defective fluorite structures were formed in all the systems. Maxima were observed on the fusibility curves of the fluorite solid solutions with R ≡ La — Tb. The limiting solubilities of lanthanide trifluorides in BaF 2 and the dependence of the unit cell parameters of the solid solutions on the composition were determined. Phases of composition Ba 4∓ x R 3± x F 17± x with maximum homogeneity in the region 39–49 mol.% were formed in the systems with R ≡ Sm — Lu. These phases melt incongruently (R ≡ Tb — Lu, Y) or decompose in the solid state (R ≡ Sm — Gd) and have a distorted fluorite structure (trigonal distortion). In the systems with R ≡ Sm — Tb a transition from the trigonal to the tetragonal phase which also has a deformed fluorite structure was observed on increasing the temperature. Non-stoichiometric Ln 1− y Ba y F 3− y phases with a defective tysonite (LaF 3 ) structure were formed in systems with R ≡ La — Ho. The thermal stability of these phases decreased rapidly with increasing difference in the sizes of the Ba 2+ and Ln 3+ ions. The statistical distribution of heterovalent cations with a large difference in ionic radii results in the formation of double compounds BaR 2 F 8 (R ≡ Dy — Lu, Y) crystallizing in the monoclinic BaTm 2 F 8 -type structure. These compounds melt congruently. In systems with R ≡ Yb, Lu a new phase of approximately the same composition is formed which crystallizes in the orthorhombic system (α-BaLu 2 F 8 type). These phases are probably high temperature modifications of BaR 2 F 3 . The coordinates of the invariant liquid ⇄ solid equilibria and the X-ray characteristics of the phases are reported.
114 citations
TL;DR: The lattice parameters of the fcc phases coexisting in the palladiumsolute-hydrogen (solute Ag, Au, Cu, Ni, Fe, Y, Ce and V) and nickel-solute -hydrogen systems prepared by electrolytic charging with hydrogen were measured at room temperature as a function of solute concentration using X-ray diffraction.
Abstract: The lattice parameters of the fcc phases coexisting in the palladiumsolute-hydrogen (solute Ag, Au, Cu, Ni, Fe, Y, Ce and V) and nickel-solute-hydrogen (solute Cu, Fe, Al and Si) systems prepared by electrolytic charging with hydrogen were measured at room temperature as a function of solute concentration using X-ray diffraction
110 citations
TL;DR: In this paper, the diffusion constants of hydrogen in Mg-Mg 2 Ni were investigated using a quasi-elastic neutron scattering technique with a high resolution backscattering spectrometer.
Abstract: Mg 2 Ni and the mixed system Mg-Mg 2 Ni are used as hydrogen storage media for industrial applications. The mechanism of hydrogen charge and discharge in Mg-Mg 2 Ni is not yet completely understood particularly because the kinetics of hydrogen exchange in magnesium are strongly influenced by the Mg 2 Ni phase. In order to investigate hydrogen exchange in Mg-Mg 2 Ni the diffusion constants of hydrogen in both systems have been investigated separately using a quasi-elastic neutron scattering technique with a high resolution backscattering spectrometer. The results show that the diffusion of hydrogen in the α phase of Mg 2 Ni occurs more slowly than in the α phase of magnesium, so that the fast kinetics of hydrogen exchange in the combined system Mg-Mg 2 Ni are probably influenced by surface effects. The diffusion rate in the β phase of magnesium is smaller by three orders of magnitude than that in the α phase.
94 citations
TL;DR: In situ X-ray diffraction measurements during stepwise hydrogenation of the intermetallic compound ZrNi confirmed the existence of a stable compound Z rNiH as mentioned in this paper, which is tetrahedrally coordinated by four zirconium atoms.
Abstract: In situ X-ray diffraction measurements during stepwise hydrogenation of the intermetallic compound ZrNi confirmed the existence of a stable compound ZrNiH. Neutron diffraction measurements on ZrNiD allowed a determination of the site occupied by deuterium. This site is tetrahedrally coordinated by four zirconium atoms as predicted earlier from a model based solely on geometric considerations. Occupation of this site causes the lattice to distort from an orthorhombic to a triclinic structure. The trihydride is formed when two completely different types of sites are filled, to the exclusion of the sites occupied originally, causing reversion of the lattice to an orthorhombic structure. Other confirmed predictions of the geometric model are discussed.
78 citations
TL;DR: In this paper, konstitutionelle, strukturelle und kristallchemische Daten uber the Phasen Ni 2 Al 3, NiAl 3, Pt 2 Al3, PtAl 3, PtAl 2, Pt 8 Al 21, Pt al 4 and AuAl 2 mitgeteilt.
Abstract: Zusammenfassung Es werden konstitutionelle, strukturelle und kristallchemische Daten uber die Phasen Ni 2 Al 3 , NiAl 3 , Pt 2 Al 3 , PtAl 2 , Pt 8 Al 21 , PtAl 4 und AuAl 2 mitgeteilt Berechnete Atomabstande aluminiumreicher Phasen mit Metallen der VI–VIII Nebengruppe werden mit Bildungsenthalpien korreliert Schliesslich werden die strukturellen Gesetzmassigkeiten einiger Phasen vom Ni 2 Al 3 -Typ und die Abhangigkeit des mittleren Atomvolumens von der Zusammensetzung fur die Systeme Ni-Al und Pt-Al diskutiert
67 citations
TL;DR: In this paper, the electrical resistivities of RB2C2-type layer compounds are reported, including the pycnometric densities and Seebeck coefficients of RB 2C2 type layer compounds.
Abstract: The electrical resistivities ρ, the pycnometric densities and the Seebeck coefficients of RB2C2-type layer compounds are reported. Superconducting transitions were observed for YB2C2 and LuB2C2 at 3.6 K and 2.4 K respectively, but the compound LaB2C2 remained in the normal state down to 1.8 K. The ρ-T curves for the borocarbides CeB2C2 and PrB2C2 have a knee at 110 K and 20 K respectively which can be ascribed to crystal field effects on the ground states of Ce3+ and Pr3+. The ρ-T curves of RB2C2 (R ≡ Ce, Nd, Gd, Tb, Dy, Ho, Er and Tm) show a sharp change in slope at low temperatures, verifying the magnetic ordering found from earlier magnetic susceptibility measurements. TmB2C2 exhibited unusual behaviour in that the resistivities increased rapidly below the Neel temperature.
66 citations
TL;DR: In this paper, a kinetic model of the hydriding of LaNi 5 is suggested and rate equations of each step of the model are evaluated and compared with empirical results, where the rate-controlling step changes with time from the chemical adsorption of hydrogen molecules on the nickel surface to diffusion of hydrogen through hydride phase or to chemical reaction.
Abstract: A kinetic model of the hydriding of LaNi 5 is suggested and rate equations of each step of the model are evaluated and compared with empirical results. The rate-controlling step changes with time from the chemical adsorption of hydrogen molecules on the nickel surface to diffusion of hydrogen through the hydride phase or to chemical reaction, followed by diffusion control, at the interface of the hydride and the unreacted core of LaNi 5 . In all cases the final rate-controlling step is chemical reaction. These changes are due to the change in hydrogen flux with diffusion distance and interface area.
64 citations
TL;DR: In this article, the volume expansions of magnesium to MgH 2, Mg 2 Ni to high temperature Mg2 NiH 4 and high temperature MG 2 NiH4 to low temperature MG2NiH 4 were calculated from these data as 30.4% (0.2%) at 340 °C, 27.8% at 320°C and 0.3% at 234 °C respectively.
Abstract: The thermal expansion of the Mg-5.6 wt.% NiH 2 and Mg-55wt.% NiH 2 systems was examined by in situ X-ray powder diffraction using a specially designed apparatus for measurements at 500 °C and a hydrogen pressure of 5 MPa. The temperature dependence of the unit cell parameters of each alloy and hydride phase and the volume change associated with each phase transformation were determined. The thermal expansion data are summarized. The volume expansions of magnesium to MgH 2 , Mg 2 Ni to high temperature Mg 2 NiH 4 and high temperature Mg 2 NiH 4 to low temperature Mg 2 NiH 4 were calculated from these data as 30.4% (0.2%) at 340 °C, 27.8% (0.2%) at 320°C and 0.3% (0.1%) at 234 °C respectively (the standard deviations are given in parentheses).
TL;DR: In this paper, the formation of titanium hydride was studied as a function of current density and time, and X-ray diffraction patterns showed that a specific hydrides is formed at each current density, independent of the duration of the formation process.
Abstract: The electrochemical formation of titanium hydride was studied as a function of current density and time. X-ray diffraction patterns showed that a specific hydride is formed at each current density, independent of the duration of the formation process.
TL;DR: In this article, the authors present the results of new high resolution quasi-elastic neutron scattering measurements of the hydrogen diffusion coefficient in LaNi5H6 between 280 and 400 K. The diffusion coefficient follows the equation D = (2.1 ± 0.7) × 10−3 exp {−(275 ± 15) meV/kT} cm2 s−1 and decreases with decreasing hydrogen concentration.
Abstract: We present the results of new high resolution quasi-elastic neutron scattering measurements of the hydrogen diffusion coefficient in LaNi5H6 between 280 and 400 K. The crucial importance of multiple-scattering corrections in the evaluation of data at small momentum transfers is demonstrated. The diffusion coefficient follows the equation D = (2.1 ± 0.7) × 10−3 exp {−(275 ± 15) meV/kT} cm2 s−1 and decreases with decreasing hydrogen concentration. The anomalous concentration dependence and the existence of composite spectra at large momentum transfers is explained by hydrogen diffusion in the presence of structural traps.
TL;DR: In this paper, electrical resistivity measurements of LaNi 5 and MmNi 4.5 (Mm misch metal) films which were obtained by vacuum vapour deposition were carried out in an atmosphere of hydrogen.
Abstract: Electrical resistivity measurements of LaNi 5 and MmNi 4.5 Mn 0.5 (Mm misch metal) films which were obtained by vacuum vapour deposition were carried out in an atmosphere of hydrogen. Resistivities of the films initially increased immediately and then decreased during the absorption process of hydrogen. The reverse is true for the desorption process. The intermetallic compound films did not pulverize even after 150 cycles of absorption-desorption of hydrogen if the thickness of the film was less than 10 × 10 4 nm.
TL;DR: In this article, the temperature dependences of the diffusion coefficient and the solubility of hydrogen in Pd-Ag and PdAu alloys with silver and gold contents in the range 0-50 at.
Abstract: The temperature dependences of the diffusion coefficient and the solubility of hydrogen in Pd-Ag and Pd-Au alloys with silver and gold contents in the range 0–50 at.% were investigated using the electrochemical method.
TL;DR: In this article, the Zr 1− x Ti x MnFe-H 2 systems with x = 0.2 and 0.3 were studied as a function of composition, temperature, and hydrogen dissociation pressure (0.01-50 atm).
Abstract: The Zr 1− x Ti x MnFe-H 2 systems with x = 0.2 and 0.3 were studied as a function of composition, temperature (23–200 °C) and hydrogen dissociation pressure (0.01–50 atm). The hydrogen vapor pressure of the ZrMn 2 -H 2 system is raised approximately 400-fold by the replacement of zirconium by titanium and of manganese by iron without significantly impairing its hydrogen capacity. The hydrides of Zr 1− x Ti x MnFe alloys have dissociation pressures in the range 1–2 atm at room temperature (23 °C). The hydrogen densities of the alloys compared with that of liquid hydrogen range from about 1.0 to 1.4. The enthalpies and entropies of dehydrogenation are exceptionally low (10–11 kJ (mol H 2 ) −1 and 46–50 J (mol H 2 ) −1 K −1 respectively). The kinetics of hydrogen absorption and desorption are extremely fast. Desorption of hydrogen in the two-phase field α + β follows first-order kinetics with activation energies of 34–38 kJ mol −1 . The energetics of hydrogen charging and discharging for the Zr 0.8 Ti 0.2 MnFe alloy are smaller than those for LaNi 5 or other accepted hydrogen storage materials. Similarly, a hydride compressor using Zr 0.8 Ti 0.2 MnFe alloy appears to be significantly more efficient than the LaNi 5 hydride compressor.
TL;DR: The low temperature Nb-H phase diagram was evaluated by measuring the static magnetic susceptibility χ ( T, x ) in the temperature range 4.2 K and 270 K.
Abstract: The low temperature Nb-H phase diagram was evaluated by measuring the static magnetic susceptibility χ ( T , x ) in the temperature range 4.2 K ⩽ T ⩽ 270 K and the hydrogen concentration range 0 x = [ H ]/[ Nb ] χ ( T , x ) depends weakly on the temperature T but decreases rapidly with the hydrogen concentration x . Phase transitions manifest themselves as susceptibility anomalies, determined either at constant concentration or at constant temperature, and appear as discontinuities, peaks or kinks. These features aid in the construction of the phase boundaries in the x - T plane. The low temperature phase diagram determined by the susceptibility method is divided into two parts: for x x > 0.7 they are vertical. Low temperature phase transitions, which manifest themselves in the χ ( T = 0 K , x ) dependence, have been established for x values of 0.46, 0.73, 0.78, 0.83, 0.85, about 0.9 and about 1.0. Intermediate temperature phases occur in the range 0.15 x x = 0.80 and x = 0.82. Examination of the Ta-H phase diagram suggested that the susceptibility measurements made previously in this system should be reevaluated. This led to a modification of the phase boundaries of the ζ phases at x ≈ 0.59 and x = 0.72. The revised diagram was confirmed by a new set of measurements.
TL;DR: In this paper, the effect of surface and bulk properties of FeTix on its hydrogen storage characteristics was investigated by X-ray photoelectron spectroscopy, Mossbauer and metallographic observations, and it was shown that several problems encountered with FeTi can be reduced if alloys with a non-equilibrium structure are prepared by the addition of excess titanium.
Abstract: The effect of the surface and bulk properties of FeTix (1 =⩽ x ⩽ 2) on its hydrogen storage characteristics was investigated by X-ray photoelectron spectroscopy, Mossbauer spectroscopy and metallographic observations. It is shown that several problems encountered with FeTi, such as the necessity of employing activation treatment and the surface sensitivity resulting from poisoning by impurity gases, can be reduced if alloys with a non-equilibrium structure are prepared by the addition of excess titanium.
TL;DR: A cursory re-examination of the Ce-Sn system was carried out using metallographic and X-ray analyses as mentioned in this paper, and the lattice parameters of selected compounds were measured.
Abstract: A cursory re-examination of the Ce-Sn system was carried out using metallographic and X-ray analyses. The existence of the following phases was observed or confirmed: Ce3Sn, α-Ce5Sn3, β-Ce5Sn3, Ce5Sn4, Ce11Sn10 (approximate formula), Ce3Sn5 (approximate formula), Ce3Sn7, Ce2Sn5 and CeSn3. The lattice parameters of selected compounds were measured. The heats of formation of a number of Ce-Sn alloys were determined using a direct isoperibol calorimeter and the following values (kcal (g atom) −1) were found: Ce3Sn, −11.8 ± 0.5; Ce5Sn3, −17.5 ± 1.0; Ce5Sn4, −20.0 ± 1.0; Ce3Sn5, −18.0 ± 1.0; CeSn3, −14.0 ± 0.5. The results obtained are discussed briefly and are compared with those already known for other rare earth alloys with p-block elements.
TL;DR: In this paper, the phase diagram in the region 25% to 50% Co was clarified in conjunction with magnetic and superconductive studies, and the appearance of a metastable Y 3 Co 2 phase was found in as-cast alloys of 38% to 40% Co.
Abstract: In conjunction with magnetic and superconductive studies the phase diagram in the region 25%–50% Co was clarified. While Y 3 Co, Y 8 Co 5 and YCo form by peritectic reactions, the other phase in this range, formerly thought to be Y 4 Co 3 and now shown to be Y 9 Co 7 , forms by a peritectoid reaction at 725 °C. A complication in as-cast alloys of 38%–40% Co is the appearance of a metastable Y 3 Co 2 phase.
TL;DR: In this article, the heat of transformation was established by differential scanning calorimetry to be 2 kcal (mol Mg 2 NiH 4 ) −1, and the structure of the metal sublattice was determined using 54 lines.
Abstract: Mg 2 Ni hydride exhibits a phase transformation at about 230 °C. The high temperature form has the CaF 2 structure whereas X-ray diffraction indicates that the low temperature form has a distorted cubic structure. Analysis of the X-ray powder patterns of the low temperature form shows that it has a monoclinic structure with a = 13.201 2(22) A , b = 6.406 7(13) A , c = 6.491 3(11) A and β = 93.21(2)°. The extinctions indicate a body-centred lattice and a c glide plane. This structure can also be represented as a C -face-centredlattice with a = 15.033 5(23) A , b = 6.406 7(13) A , c = 6.491 3(11) A , β = 118.75(2)° and space group Cc . The structure of the metal sublattice was determined using 54 lines. The heat of transformation was established by differential scanning calorimetry to be 2 kcal (mol Mg 2 NiH 4 ) −1 .
TL;DR: In this article, the activation energy of amorphous Zr1−xCox ribbons was derived from the dependence of Tx on the heating rate and the difference in the concentration dependence of both series of activation energies was ascribed to a temperature-dependent configurational entropy associated with the presence of chemical short-range ordering in the amorphized Zr-Co alloys.
Abstract: Several new metastable Zr-Co phases were observed in a study of the crystallization of amorphous Zr1−xCox ribbons using differential scanning calorimetry and X-ray diffraction. The cubic structure of Zr2Co (Ni2Ti type) transformed into the tetragonal CuAl2 type upon heating. The crystallization temperatures Tx were analysed in terms of a model proposed earlier where the activation energy for crystallization is approximated by the formation enthalpy of a hole the size of a cobalt atom. Experimental values for the activation energy were derived from the dependence of Tx on the heating rate. The difference in the concentration dependence of both series of activation energies was ascribed to a temperature-dependent configurational entropy associated with the presence of chemical short-range ordering in the amorphous Zr-Co alloys.
TL;DR: In this paper, the effect of the addition of hydrogen to the nitrogen plasma is discussed in the light of the results of plasma diagnostics, such as emission spectroscopy, mass spectrography and the electrical double-probe technique, and the surface analysis.
Abstract: The nitriding of titanium in a nitrogen or a nitrogen-hydrogen plasma prepared using an r.f. discharge was studied. The reaction kinetics obey a general relationship Δ 2 + AΔw = B ( t + τ ) The addition of hydrogen to the nitrogen plasma increased the weight gain. Electron spectroscopy for chemical analysis showed that N 1s based on the N—H bond and Si 2s electrons were present on the surface of the nitrided titanium. The effect of the addition of hydrogen to the nitrogen plasma is discussed in the light of the results of plasma diagnostics, such as emission spectroscopy, mass spectroscopy and the electrical double-probe technique, and the surface analysis.
TL;DR: The ternary sulphides Ba2Re6S11 and Sr2Re 6S11 were synthesized by the reaction of the alkaline earth carbonates with rhenium at 1350 and 1450 °C respectively in a stream of H2S as mentioned in this paper.
Abstract: The ternary sulphides Ba2Re6S11 and Sr2Re6S11 were synthesized by the reaction of the alkaline earth carbonates with rhenium at 1350 °C and 1450 °C respectively in a stream of H2S. X-ray investigations on single crystals gave the structure of Ba2Re6S11. The atomic arrangement consists of a framework in which [Re6S8] clusters are linked in three dimensions according to the formulation { Re 6 S 8 ]S 6 2 } 4− . The barium ions are inserted in holes of this framework. Powder diffraction investigations showed that Sr2Re6S11 has a structure analogous to that of Ba2Re6S11. Measurements of the magnetic susceptibilities between 3.7 and 295 K show that Ba2Re6S11 has a diamagnetic behaviour. The distortion of [M6X8] clusters is discussed with respect to electronic configuration.
TL;DR: In this article, the authors measured the change in the equilibrium pressure of hydrogen in the MmNi5H system depending on the presence of rare earth metals such as samarium and cerium.
Abstract: Pressure-composition isotherms for La1−xRexNi5-H systems (x = 0-≈ 1; Re Ce, Pr, Nd and Sm) were measured. These rare earth metals are constituents of misch metal (Mm), and the change in the equilibrium pressure of hydrogen in the MmNi5H system depends on the presence of these constituents. Samarium and cerium were found to be characteristic of elements which produce a marked increase in the equilibrium pressure of hydrogen.
TL;DR: In this paper, it was shown that the high concentration phase has a disordered fluorite structure with a 0 = 4.27 A and its hydrogen content corresponds to TiCr1.8H5.3.
Abstract: An orthorhombic structure was originally assigned to the non-stoichiometric hydride TiCr1.8H3.6. Recent neutron and X-ray diffraction data indicated, however, that an alternative interpretation was possible, i.e. the solid consists of two hydride phases, an α′ Laves phase having a composition TiCr1.8H2.8 and an f.c.c. phase with a much higher hydrogen content. This proved to be the case and it was determined that the high concentration phase has a disordered fluorite structure with a 0 = 4.27 A . Its hydrogen content, as estimated from diffraction peak intensities, corresponds to TiCr1.8H5.3. We were not able to produce single-phase f.c.c. material but we prepared a mixed phase sample with an overall composition of TiCr1.8H4.8. The high pressure reaction leading to the formation of the fluorite phase is very sluggish and irreversible. Pressure-composition-temperature properties of this system were determined and are discussed and a revised phase diagram is proposed.
TL;DR: Magnetization measurements were carried out on ZrMn 2− x Fe x ( x = 0.4, 0.7 and 1.0) and their hydrides as mentioned in this paper.
Abstract: Magnetization measurements were carried out on ZrMn 2− x Fe x ( x = 0.4, 0.7 and 1.0) and their hydrides. All systems possess a hexagonal Laves phase structure (C14 structure). These compounds are found to absorb about 3.6 hydrogen atoms per formula unit. The hydrogen absorption is accompanied by a large expansion in volume ranging from 26% to 28% with no change in crystal structure. In this system, both the magnetic moments and the transition temperatures were found to be significantly larger in the hydride phases than in the corresponding host compounds. An increase in the magnetic moments on hydrogenation can be interpreted as a result of charge transfer from the transition metal atoms to hydrogen due to the difference of electronegativity. An increase in the magnetic ordering temperatures is attributed to a decrease in the electron concentration of 3d bands as well as to an increase in the lattice constants on hydrogenation. Spin glass behavior is exhibited by all the systems studied. The spin glass behavior is thought to originate from iron-rich clusters which occur as a consequence of statistical fluctuations in the manganese sublattice.
TL;DR: In this paper, a kinetic study of the hydriding reaction of TiFe and TiFe0.8Mn0.2 was performed by the pressure sweep method and a new method was developed by converting pressure versus time into the reacted fraction F versus time.
Abstract: A kinetic study of the hydriding reaction of TiFe and TiFe0.8Mn0.2 was performed by the pressure sweep method. A new method of analysing the pressure sweep data was developed by converting pressure versus time into the reacted fraction F versus time. At the initial stage of the reaction the rate-controlling step is chemisorption on the metal surface, and the rate equations for TiFe and TiFe0.8Mn0.2 at constant temperature T and constant pressure P0 are F = 3.5 × 10 −2 exp {− 800(cal mol −1 ) RT } P 0 −P eq T 1 2 t and F=5.0 × 10 −2 exp {− 1000(cal mol −1 ) RT } P 0 −P eq T 1 2 t respectively. At a later stage (0.35 (1-F ∗ 1 3 )=5.6 × 10 −3 exp {− 1000(cal(mol H) −1 ) RT } × (P 0 1 2 −P eq 1 2 )(t−t ∗ ) and (1-F ∗ ) 1 3 −(1-F 1 3 )=9.0 × 10 −3 exp{− 1500(cal(mol H) −1 ) RT } × (P 0 1 2 −P eq 1 2 (t−t ∗ ) respectively where t is time required to reach F and t ∗ is the time required to reach the initial stage. The rate increases with increasing pressure at constant temperature and with decreasing temperature at constant pressure. The addition of manganese to TiFe increases the hydryding rate as well as promoting activation (see Fig 13).As mangaanese is added the plateau pressure Peq is lowered resulting in a large driving force.
TL;DR: In this paper, the enthalpies of formation of LaNi 4 Mn, LaNi 3, LaNi 5, La Ni 4 Al and Th(Ni 1−x Al x ) 5 were measured by the calorimetric method.
Abstract: The enthalpies of formation of LaNi 4 Mn, LaNi 4 Cu and LaNi 4 Fe were measured by the calorimetric method. A relationship between these values and those of the enthalpies of hydrogenation is proposed. This model is applied to other systems such as LaNi 5 , LaNi 4 Al and Th(Ni 1− x Al x ) 5 .
TL;DR: The phase diagram of the Re-Si system was reinvestigated by means of high temperature methods of analysis as mentioned in this paper, and several modifications to the existing diagram were made to establish an extended rhenium solid solution (up to 10 at% Si) with a rapid quenching technique.
Abstract: The phase diagram of the Re-Si system was reinvestigated by means of high temperature methods of analysis We found several modifications to the existing diagram An extended rhenium solid solution (up to 10 at% Si) was established with a rapid quenching technique Within this terminal solid solution, the superconducting transition temperature increased from 17 to 52 K The phase corresponding to the “Re 5 Si 3 ” compound was homogeneous at 33 at% Si The peritectically formed equiatomic compound decomposed eutectoidally at 1650 °C and was superconducting at 15 K The compound ReSi 2 was found to be off stoichiometric, occurring at the composition ReSi 18