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The features of phase transformations during interaction of BCC-type Ti 0.25 Zr 0.25 V 0.15 Nb 0.15 Ta 0.2 high-entropy alloy (HEA) with hydrogen and the accompanying thermal effects have been examined using the Tian-Calvet calorimetric technique. The alloy was produced by the pendent drop melt extraction method in the form of microfibers and then coated with a thin layer of palladium to eliminate the preliminary high-temperature activation and enable first hydrogenation at room temperature. Two reaction stages were distinguished on the measured heat emission curves. Using XRD data, these stages were attributed to the formation of a BCC-type hydrogen solid solution and a phase transition to FCC-type dihydride phase. Recorded values of the reaction enthalpy decrease in absolute terms from 145 kJ/mol H 2 (dilute solid solution) to 73–77 kJ/mol H 2 (BCC→FCC) and to 20 kJ/mol H 2 (H solution in FCC dihydride). The overall heat emission of the entire process as a whole is 110 kJ/ mol H 2. The course of the dehydrogenation process depends strongly on the applied temperature and at 493 K results in the formation of a BCT-type monohydride, which was not detected during hydrogenation. The detailed calorimetric data obtained here significantly change the previously existing ideas about thermal effects during this type HEAs hydrogenation, based on calculations using the Van't-Hoff equation. The reported findings are of special importance for various hydrogen related applications of HEAs [Display omitted] • Hydride formation in Ti 0.25 Zr 0.25 V 0.15 Nb 0.15 Ta 0.2 high-entropy alloy has been studied. • Pd coating was used to enable room-temperature first hydrogenation. • Calorimetric technique was applied to distinguish phase transformations. • Heat effects for different phase transformations have been evaluated. • Structure transformations during hydrogen absorption have been characterized by XRD. [ABSTRACT FROM AUTHOR]

The effect of short-term mechanical activation in a ball mill on the thermodynamics of interaction with hydrogen and the structure of intermetallic and hydride phases was studied for a series of AB 5 type alloys from the standpoint of their use as filler in metal-polymer membranes. It was found that the activation processing leads, as expected, to a decrease in the size of coherent scattering domains and an increase in the lattice strain, while the phase composition and unit cell parameters remain unaffected. Despite this, there is a significant change in the pressure-composition isotherms, a reduction of the total capacity ad the plateau region. XRD study of the hydride phases evidences smaller volume expansion of the intermetallic crystal lattice at hydrogen absorption for the alloys subjected to mechanical activation. Analysis of the obtained thermodynamic and structural data allows us to consider the mechanically activated LaNi 4.8 Al 0.2 as the most appropriate for low-pressure and low-temperature application in the hydrogen separation composite membranes. La 0.7 Ce 0.3 Ni 4.5 Cu 0.5 and LaNi 5 with maximum activation treatment of 3 min are more promising for use at elevated pressures. • Effect of short mechanical activation on AB 5 -type alloys was studied. • Unit cell remains unaffected after MA. • Absorption capacity, isotherm plateau length and lattice volume expansion decrease. • The most appropriate compositions for metal-polymer membranes are suggested. [ABSTRACT FROM AUTHOR]

Single phase ternary (TiFe) 100-x Ni x alloys were synthesized through high-energy ball milling. Ni solubility in equiatomic TiFe reaches 10 at. %, exceeding the values known from the equilibrium diagram of state and those obtainable by conventional arc melting. The reactivity of mechanically alloyed (TiFe) 95 Ni 5 with hydrogen was investigated in detail by a combination of volumetric and calorimetric methods. The influence of Ni addition on the pressure-composition isotherms and the reaction enthalpies was evaluated. Finally, the hydrogenation behavior was compared with Ni-free mechanically alloyed TiFe and with literature data on different TiFe-Ni alloys. • The (TiFe) 100-x Ni x alloys, with non-equilibrium Ni content, were obtained by MA. • The (TiFe) 95 Ni 5 demonstrates a simplified activation and reversible hydrogen capacity. • The (TiFe) 95 Ni 5 & TiFe alloys, obtained by MA, revealed similar hydrogen concentration. • The MA (TiFe) 95 Ni 5 has a good thermal stability of the hydride phase. [ABSTRACT FROM AUTHOR]

Mesoporous chromium( iii) terephthalate MIL-101 was treated with aqueous solutions of sodium fluoride, chloride, and bromide. The properties of the resulting compounds to sorb nitrogen, hydrogen, and methane were studied. The methane sorption was shown to depend on the nature of the inserted halide ion. The treatment with a sodium chloride solution leads to an increase in the methane uptake by MIL-101. [ABSTRACT FROM AUTHOR]

In the present study, the hydrogen storage performance of multi-principal-component ZrTiVNiCrFe alloy produced through rapid solidification has been examined by electrochemical methods and gas-solid reactions. XRD and EBSD analyses reveal the hexagonal Laves phase structure (type C14) with average grain size of 300 nm and root-mean-square microstrain of 0.19%. Cyclic voltammetry and electrochemical impedance spectroscopy analyses in the hydrogen sorption/desorption region give insight to the sorption/desorption kinetics and the change in the desorption charge in terms of the applied potential. The pressure-composition isotherms measured in course of gas-solid reaction confirm the hydrogen storage capacity reaching 1.6 wt% at the first hydrogenation at room temperature, then reducing to 1.3–1.4% during subsequent cycling. According to the calorimetric titration study, there is a significant hysteresis primarily caused by the non-equilibrium character of the hydrogenation process. • Single phase ZrTiVNiCrFe has been synthesized by melt spinning. • Reversible hydrogenation was confirmed by gas-solid and electrochemical methods. • Maximum hydrogen capacity at room temperature reaches 1.6 wt%. • Hydrogen desorption enthalpy of 38 kJ/mol H 2 was evaluated from calorimetric measurements. [ABSTRACT FROM AUTHOR]

In order to examine the influence of the production technique on the performance of hydride-forming multi-principal-component alloys, a series of alloys in the Ti–Zr–V–Nb–Ta-Hf system has been obtained by arc-melting and electron beam melting combined with pendant-drop melt extraction (EBM-PDME). Structure analysis shows that EBM-PDME method ensures the synthesis of single-phase alloys with BCC structure for all studied compositions. During hydrogenation, the complete and reversible BCC to FCC phase transformation with maximum hydrogen capacity up to 2.0 wt% occurs. Mechanical and thermophysical investigations demonstrate high values of tensile strength, plasticity and thermal conductivity, which allow the alloys to be used as materials for membrane hydrogen separation. • EBM-PDME method ensures the synthesis of single-phase alloys with BCC structure. • Complete and reversible BCC to FCC phase transformation occurs upon hydrogenation. • Maximum hydrogen capacity reaches 2.0 wt%. • Promising thermal and mechanical properties were found. • Alloys have prospects for use as membrane materials for hydrogen separation. [ABSTRACT FROM AUTHOR]

• Thermodynamic model of single-phase high entropy alloys formation was developed. • Single-phase TiVZrNbTa equiatomic alloy was synthesized by various techniques. • Effect of synthesis method on alloy hydrogenation behavior was examined. • Alloy synthesis from melt results in improved stability upon hydrogenation. A thermodynamic model was proposed to assess the feasibility of the synthesis of single-phase multi-principal-component alloy. Based on this model, single-phase TiVZrNbTa equiatomic alloys with body centered cubic (BCC) structure were obtained by arc melting (AM), electron beam melting with pendant drop melt extraction (EBM-PDME) and mechanical alloying (MA). The alloys were characterized by powder X-ray diffraction, scanning and transmission electron microscopy, thermal analysis and mechanical testing. The hydrogenation behavior of the synthesized materials was studied by a volumetric method. It was found that for AM and EBM-PDME alloys a complete BCC-to-FCC structure transformation occurs upon hydrogenation, and hydrogen concentration in the hydrides formed reaches 1.5 H/M (1.6 wt%). MA alloy undergoes partial amorphization with maximum hydrogen absorption capacity of 0.9 wt%. [ABSTRACT FROM AUTHOR]

The interaction of mesoporous chromium( iii) terephthalate [Cr3O(C8H4O4)3F(H2O)2] (MIL-101) with an aqueous solution of the anionic cluster [Re4S4F12]4− ({Re4}) afforded a novel hybrid material {Re4}@MIL-101. According to the elemental analysis data, one cavity of the nanoporous framework contains up to two-three tetranuclear rhenium clusters. The hybrid sorbent obtained reversibly absorbs up to 3.7 wt.% hydrogen at 77 K and 30 atm. [ABSTRACT FROM AUTHOR]

• Metal-polymer composite membranes have been prepared via MA. • Composite membranes consist of LaNi 5 -type alloy and polyethylene. • Addition of metal filler leads to a drop of the phase transition activation energy. • Hydrogen processing results in a shift of the internal friction peak. In the present work, mechanical properties of metal-polymer composite membranes for hydrogen separation have been investigated by tensile test and mechanical spectroscopy methods. The membranes were prepared by high-energy ball milling and subsequent thermal pressing of a powder mixture of polyethylene with 10 wt% hydride-forming intermetallic compound LaNi 2.5 Co 2.4 Mn 0.1. The membranes were then subjected to activation by long exposure in a hydrogen atmosphere. The static tensile test showed a slight decrease in membrane tensile strength after hydrogen activation that may be explained by intermetallic particle embrittlement. Mechanical spectroscopy study reveals a shift of the internal friction peak of the activated membrane by 22 K towards lower temperatures and a small decrease of the activation energy of polyethylene viscoelastic transformation from 144 kJ/mol to 138 kJ/mol. [ABSTRACT FROM AUTHOR]