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Storing hydrogen in solid metal hydrides provides a safe and efficient storage approach. However, the large volume expansion of metal hydrides during hydrogen absorption imposes substantial stresses on the wall of a hydrogen storage tank. In this study, volume expansion behavior of a V-based hydrogen storage alloy, V61Cr24Ti12Ce3, with body-centered-cubic, was investigated using a self-developed in situ expansion testing device. The lattice expansion of the V61Cr24Ti12Ce3 alloy after full hydrogenation was determined to be 37.85% using X-ray diffraction(XRD). The powder bed, composed of alloy powder with an average size of 3.35 mm in diameter, displays a large volume expansion ratio of 131% at the first hydrogen absorption cycle and 40–45% in the following four cycles. The stable compact bed, made of alloy powders, organic silicone gel, and graphite flakes, shows significantly smaller volume expansion ratio, which is 97% at the first cycle and 21% at the second cycle, and stabilizes at 13% in the following cycles. Also, the compact bed shows similar hydrogen absorption capacity, but faster absorption kinetics compared to the powder bed. [ABSTRACT FROM AUTHOR]

The V 72 Ti 18 Cr 10 alloy was prepared by a co-precipitation-reduction method in order to consume less energy during whole-life alloy manufacturing, and the phase evolution process in hydrogenation/dehydrogenation process was investigated. The structure refinement analysis of the alloy contented with 1 ​wt% hydrogen after hydrogenation shows that BCC phase, BCC-hydride phase and FCC phase coexisted, but little BCT phase was found. It indicates that the phase evolution process during hydrogenation was BCC→ BCC-hydride→ FCC, nevertheless the formation of BCT phase was restrained. The limited particle sizes of the alloy in the range of 0.1–5 ​μm and fewer defects than the normal alloy ingot contributed to the suppression of BCT formation. The annealed alloy, which had similar particle sizes with the unannealed alloy, has less unevenness of the compositions than the unannealed alloy, and the annealed alloy showed flatter plateau in the hydrogenation PCT (pressure-composition-temperature) curves. However, the BCT phase in the annealed alloy appeared in its dehydrogenation process owing to the produced defects during the following dehydrogenation and the hydrogenation process. The alloy with the limited particle sizes even in the range from 0.1 ​μm to 5 ​μm could not prevent the generation of BCT phase in the dehydrogenation process. • V 72 Ti 18 Cr 10 alloy with small particle sizes from 0.1 ​μm to 5 ​μm was synthesized by co-precipitation-reduction method and annealing method followed by. • The phase evolution process of the alloy in hydrogenation process is BCC.→ BCC-hydride→ FCC, where BCT is suppressed successfully. • The BCT phase appears in its dehydrogenation process, indicating the particle size is still too large. [ABSTRACT FROM AUTHOR]

We have developed an improved Finnis-Sinclair (IFS) potential for vanadium-rich V–Ti–Cr random alloys with body-centred cubic structure. An extra exponential term is added to the original FS potential to enhance the repulsive interaction. The IFS potential is fitted to experimental crystal structure, cohesive energy and elastic constants of pure metals (V, Ti and Cr) and theoretical data of binary alloys (V 15 Ti, V 15 Cr and Ti 8 Cr 8 ). The good agreement of the predicted formation energies of mono-vacancy and self-interstitial of octahedral interstitial site, tetrahedral interstitial site, <111>-dumbbell, <110>-dumbbell, and <100>-dumbbell with available experimental and theoretical data confirms the validity of our IFS potential in pure V. Furthermore, the agreement of elastic properties and defect properties of typical alloy (V–4Ti–4Cr) with experimental or DFT data also support the applicability of the IFS potential in V-rich ternary V–Ti–Cr alloys. Finally, this work also provides a reference to develop empirical potentials for other ternary alloys. [ABSTRACT FROM AUTHOR]

Synthesis of V-Ti-Cr solid solution alloy by co-reduction of V2O5, Cr2O3 and TiO2 with aluminium in an open bomb reactor was investigated. The reduction of V2O5 and Cr2O3 was highly exothermic while reduction of TiO2 was not sufficiently exothermic for self-sustaining reaction. A range of composition of V2O5, Cr2O3 and TiO2 mixture was chosen to make overall process sufficiently exothermic to sustain the reaction in a controlled manner. After the co-reduction, V-Ti-Cr-Al solid solution was obtained. As-obtained solid solution was refined by electron beam melting (EB) to remove the aluminium and residual oxygen. EB melted V-Ti-Cr thus obtained contains substantially less amount of aluminium (~0.081%.) Throughout the synthesis process the prepared products were analyzed using scanning electron microscope (SEM), energy dispersive X-ray fluorescence (EDAX), chemical analysis, gravimetric analysis and X-ray diffraction.

Properties of Laves phase compounds can be tailored by alloying and microstructural engineering. V-substituted cubic TiCr2Laves phase has been studied to understand the location of V atoms in the lattice, by structural imaging and first-principle computations. Even though Ti, V and Cr appear next to each other in the periodic table, V preferentially replaces the Ti lattice producing anti-site defects. The defect formation energy for V substitution in Ti and in Cr lattice is 0.29 and 0.40 eV, respectively. V replacement in the Ti lattice generates atomic scale strain. Atomic numbers of V, Ti and Cr being very close, this phase is not quite suitable for incoherent imaging for understanding the structure and the chemistry. Instead, difference in channelling behaviour of electron waves along the Ti columns and along the Cr columns could be exploited to preferentially image the individual atom columns. Nature of the exit phase wave, phase and amplitude has been used to understand the contrast qualitatively. The intensity distribution of any particular atom column that is disturbed by the presence of foreign atom has been used to detect the position of V atoms. This method could be extended to study other Laves phases and complex intermetallic structures to understand their structure, defects and interfaces. [ABSTRACT FROM PUBLISHER]

Abstract: Hydrogen storage is one of the most important issues to realize hydrogen society especially for on-board usage. Recently, high-pressure metal hydride (MH) tank attracts many attentions due to its high volumetric hydrogen storage density and relatively easy heat management. To emphasize its merits, further improvements of properties of MH, such as capacity, hydrogen desorption capability at low temperature and durability, are required. In this paper, V–Ti–Cr alloys of V-rich compositions were investigated with perspective of increasing of hydrogen desorption pressure and durability. In both of 60at%V–Ti–Cr and 80at%V–Ti–Cr alloys, good relationship between hydrogen desorption pressure and Ti content was observed. In comparing with 60at%V–Ti–Cr alloys, 80at%V–Ti–Cr alloys showed good durability. It is quite notable that relationship between limitation line (upper substitution limit of Ti by Cr without degradation of hydrogen capacity) and desorption pressure for V–Ti–Cr ternary system with V-rich composition is clarified. And also, it is revealed that in the case of V–Ti–Cr ternary system, not only Ti/Cr ratio but also V content is important factor to obtain alloys with high hydrogen desorption pressure. 75at%V–5at%Ti–Cr as-cast sample showed good durability, hydrogen desorption capability at low temperature and relatively high effective hydrogen capacity simultaneously. [ABSTRACT FROM AUTHOR]