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Abstract: The effect of Al additive on microstructures and hydrogen storage characteristics of Ti26.5Cr20(V0.45Fe0.085)100−x Al x Ce0.5 (x =0, 0.5, 1.0 and 1.5at.%) alloys have been studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and P–C-isotherm measurements. All of Al-added alloys consist of major BCC and secondary Al–Ce–O phases. The EDS analysis results show that aluminum is poor in the BCC phase but enriches in the secondary Al–Ce–O phase. As Al additive content increased, both the lattice parameters of the BCC phase and the hydrogen desorption equilibrium pressures increase, but the hydrogen storage capacities decrease. It is revealed that the substitution solid solution with BCC structure is formed by the substitution of Al for V atoms. It decreases the hydride stability of the BCC phase and degrades the hydrogen storage performance of the Al-added Ti26.5Cr20(V0.45Fe0.085)100−x Al x Ce0.5 alloys. [Copyright &y& Elsevier]

Abstract: The thermodynamics of hydrogenation for the Ti1−x Zr x MnCr (x =0, 0.1, 0.2, 0.32, 0.5, 0.7, 0.9, 1.0) alloys, which are characterized by the XRD Rietveld analysis as C14-type Laves phase, are evaluated by P–C isotherms measurements at different temperatures. Along with the increase of Zr content in the alloys, the pressure of the absorption/desorption plateau decreases monotonously; the average value of ǀΔHǀ increases linearly, and the average value of ǀΔSǀ decreases slightly; on the other hand, the hysteresis of hydrogenation reduces to a minimum at x =0.32, and then rises again; the slope of the plateau increases first, then decreases, forming a maximum at x =0.5. For the hydride formation of the Ti1−x Zr x MnCr alloys, the values of ǀΔHǀ and ǀΔSǀ increase with the hydrogen concentration, except for that of the Ti0.8Zr0.2MnCr, where an opposite trend occurs, but all the ǀΔHǀ values in the Ti1−x Zr x MnCr–H2 system are considerably lower than those in most Laves phase hydride systems. As combined effects of these trends, the Ti0.5Zr0.5MnCr alloy with the highest microstrain induced from the greatest mismatch of different atoms in the lattice, possesses the greatest plateau slope and the smallest variation width of ǀΔHǀ for the hydride formation; on the other hand, the Ti0.68Zr0.32MnCr alloy exhibits the best hydrogen storage properties, with a reversible hydrogen capacity of 216ml/g, and good plateau characteristics. [Copyright &y& Elsevier]

Abstract: The structural relationship between the hydride phases in Ti–Mo–H solid solution system (Mo content up to 15at% in the alloy) during dehydrogenation process under annealing has been studied by conventional and in situ X-ray powder diffraction and transmission electron microscopy (TEM) analysis. During dehydrogenation, the saturated hydrides of the Ti–Mo alloys with fcc δ-phase structure transfer into bcc β-phase at higher temperatures. An associated hydrogen concentration reduction for the δ-phase hydride is observed in the process. However, as the hydrogen concentrations decrease to certain values (H/M∼1.1–1.7), the unsaturated δ-phase formed at high temperature would become unstable at lower temperature, and transfer into a tetragonal phase (denoted the ɛ-phase here). Unlike that of the ɛ-phase in Ti–H system, the phase transition does not occur for the saturated δ-phase with hydrogen concentration close to the stoichiometric limit. The hydrogen concentration of this ɛ-phase hydride is in between that of the tetragonal γ and ɛ-phase in Ti–H system, but more close to the γ-phase. The occurrence region of this ɛ-phase expands along with the increase of the Mo content in the alloys. The phase has a lattice similar to that of the ɛ-phase in Ti–H system with corresponding fct unit-cell c/a <1. [Copyright &y& Elsevier]