High Pressure XRD Structural Study of Intermetallic Hydrogen Storage Material ZrFe2 (original) (raw)
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Crystal structure, hydrogen absorption and thermodynamics of Zr1-xCoxFe2 alloys
Journal of alloys and compounds, 2007
In this paper, the structural and hydrogen storage properties of Zr 1−x Co x Fe 2 (x = 0.2, 0.3, 0.4, 0.5) hydrogen storage alloys have been systematically investigated. XRD analysis of the alloys have revealed that all the alloys were formed as a single phase alloys having C14 laves phase hexagonal structure. With increasing Co addition, the unit cell volume decreases. P-C-T curves were measured in the pressure and temperature range of 0.5 ≤ P ≤ 60 bar and 303 ≤ T ≤ 373 K using a Sievert type apparatus. The results indicate that with increasing Co content in the samples, the plateau pressure increases whereas hydrogen storage capacity and stability decreases.
High pressure in situ diffraction studies of metal–hydrogen systems
a b s t r a c t "Hybrid" hydrogen storage, where hydrogen is stored in both the solid material and as a high pressure gas in the void volume of the tank can improve overall system efficiency by up to 50% compared to either compressed hydrogen or solid materials alone. Thermodynamically, high equilibrium hydrogen pressures in metal-hydrogen systems correspond to low enthalpies of hydrogen absorption-desorption. This decreases the calorimetric effects of the hydride formation-decomposition processes which can assist in achieving high rates of heat exchange during hydrogen loading-removing the bottleneck in achieving low charging times and improving overall hydrogen storage efficiency of large hydrogen stores. Two systems with hydrogenation enthalpies close to −20 kJ/mol H 2 were studied to investigate the hydrogenation mechanism and kinetics: CeNi 5 -D 2 and ZrFe 2−x Al x (x = 0.02; 0.04; 0.20)-D 2 . The structure of the intermetallics and their hydrides were studied by in situ neutron powder diffraction at pressures up to 1000 bar and complementary X-ray diffraction. The deuteration of the hexagonal CeNi 5 intermetallic resulted in CeNi 5 D 6.3 with a volume expansion of 30.1%. Deuterium absorption filled three different types of interstices, Ce 2 Ni 2 and Ni 4 tetrahedra, and Ce 2 Ni 3 half-octahedra and was accompanied by a valence change for Ce. Significant hysteresis was observed between deuterium absorption and desorption which profoundly decreased on a second absorption cycle.
Synthesis, characterization and hydrogenation of ZrFe2-xNix (x= 0.2, 0.4, 0.6, 0.8) alloys
International Journal of …, 2007
Hydrogen storage properties and structural properties in ZrFe 2−x Ni x (x = 0.2, 0.4, 0.6, 0.8) alloys, prepared by arc melting in argon atmosphere, have been investigated. Powder XRD study shows that the lattice constants and the unit cell volume of ZrFe 2−x Ni x (x = 0.2, 0.4, 0.6, 0.8) alloys having C15 Laves phase cubic structure decreases with increasing Ni content due to the smaller atomic radius of Ni compared to Fe. Surface morphology and elemental composition of the alloys were investigated by SEM and EDX. Hydrogen absorption pressure-composition (P .C) isotherms were investigated in the ranges 303 K T 373 K and 0.5 bar P 50 bar using a Sievert type apparatus. The P .C isotherms show the single plateau region in the temperature and pressure range studied. The plateau pressure increases with increasing Ni content for a given temperature. The entropy and enthalpy of dissolved hydrogen in ZrFe 2−x Ni x .H (x = 0.2, 0.4, 0.6, 0.8) have been calculated by means of the vant Hoff plot and the variation of these parameters with hydrogen content is discussed with respect to the existence of , + , and phase regions in the P .C isotherms. ᭧
Thermodynamics and Structural Aspects of Hydrogen Absorption In Zr1-XCrxFe2 Alloys
International Journal of Hydrogen …, 2007
The hydrogen storage properties of Zr 1−x Cr x Fe 2 (x = 0.2, 0.3, 0.4, 0.5) alloys have been obtained in the pressure and temperature range of 0.5 P 60 bar and 303 K T 373 K. The alloys have been characterized by XRD and SEM. The results show that all the alloys were having C14 laves phase hexagonal structure. The substitution of Cr in Zr site leads to the contraction of their lattice. The P -C-T isotherms of the alloys showed the existence of , + , and regions. The maximum hydrogen intake capacity is around 3.131 H/f.u. at 303 K and at 48 bar pressure for Zr 0.8 Cr 0.2 Fe 2 alloy. The average relative partial molar enthalpy and entropy of hydrogen at plateau region have been calculated for all the alloys. The presence of , + , and region as seen in P -C isotherm has been confirmed by the variation of thermodynamical parameters with hydrogen content. ᭧
Zeitschrift für Physikalische Chemie, 1989
Stoichiometric and "hyperstoichiometric" (Zr-Ti)(Mn-Fe)2+x alloys are known to exhibit large possibilities for hydrogen storage. Structural investigations performed on the alloys and their hydrides using X-ray, electron and neutron diffraction, thermogravimetric techniques, have permitted to evidence super structure effects due to metal ordering within or between the A and B sublattices of the initial C14 type of Laves phase. This will yield to develop structural models for the hydrogen localization in tetrahedral sites and the stability of the hydrides.
Crystallography of low Z material at ultrahigh pressure: Case study on solid hydrogen
Matter and Radiation at Extremes
Diamond anvil cell techniques have been improved to allow access to the multimegabar ultrahigh-pressure region for exploring novel phenomena in condensed matter. However, the only way to determine crystal structures of materials above 100 GPa, namely, X-ray diffraction (XRD), especially for low Z materials, remains nontrivial in the ultrahigh-pressure region, even with the availability of brilliant synchrotron X-ray sources. In this work, we perform a systematic study, choosing hydrogen (the lowest X-ray scatterer) as the subject, to understand how to better perform XRD measurements of low Z materials at multimegabar pressures. The techniques that we have developed have been proved to be effective in measuring the crystal structure of solid hydrogen up to 254 GPa at room temperature [C. Ji et al., Nature 573, 558-562 (2019)]. We present our discoveries and experiences with regard to several aspects of this work, namely, diamond anvil selection, sample configuration for ultrahigh-pressure XRD studies, XRD diagnostics for low Z materials, and related issues in data interpretation and pressure calibration. We believe that these methods can be readily extended to other low Z materials and can pave the way for studying the crystal structure of hydrogen at higher pressures, eventually testing structural models of metallic hydrogen.
Journal of physics. Condensed matter : an Institute of Physics journal, 2015
Structural, thermodynamic and elastic properties of the hydrogen-zirconium system including all major hydrides are studied from first principles. Interstitial hydrogen atoms occupy preferentially tetrahedral sites. The calculations show that a single vacancy in α-Zr can trap up to nine hydrogen atoms. Self-interstitial Zr atoms attract hydrogen to a lesser extent. Accumulation of hydrogen atoms near self-interstitials may become a nucleation site for hydrides. By including the temperature-dependent terms of the free energy based on ab initio calculations, hydrogen adsorption isotherms are computed and shown to be in good agreement with experimental data. The solubility of hydrogen decreases in Zr under compressive strain. The volume dependence on hydrogen concentration is similar for hydrogen in solution and in hydrides. The bulk modulus increases with hydrogen concentration from 96 to 132 GPa.