AB5 Alloys Research Articles

AB5-based metal hydride embedded in polyethylene and polymethylmethacrylate for hydrogen storage

Loose powder in metal hydride reactors poses challenges, such as poor thermal conductivity and tube deformation. To address these issues, the metal powder can be encapsulated in a polymer-based matrix to form pellets. This encapsulation helps make the pellets oxygen-impermeable, capable of accommodating the volumetric expansion of metal hydrides, and increases system processability. This study investigates the use of polymer-based pellets containing AB5-based compounds for ambient hydrogen storage. Polymers were selected using ANSYS Granta software, and polyethylene and polymethylmethacrylate were chosen. The AB5 alloy activation in the pellet occurs efficiently after 3 min at 20 °C and 30 bar of hydrogen, facilitated by ball milling-induced reactive surfaces and increased grain boundaries. The optimized pellet, comprising 90 wt% AB5 powder in a PE matrix, exhibits stable hydrogen storage properties, with good mechanical resistance and minimal powder loss (below 3%) over 20 hydrogen sorption cycles in an in-house fabricated single-tube metal hydride reactor.

A cluster-based computational thermodynamics framework with intrinsic chemical short-range order: Part I. Configurational contribution

Exploiting Chemical Short-Range Order (CSRO) is a promising avenue for manipulating the properties of alloys. However, existing modeling frameworks are not sufficient to predict CSRO in multicomponent alloys (>3 components) in an efficient and reliable manner. In this work, we developed a hybrid computational thermodynamics framework by combining unique advantages from Cluster Variation Method (CVM) and CALculation of PHAse Diagram (CALPHAD) method. The key is to decompose the cumbersome cluster variables in CVM into fewer site variables of the basic cluster using the Fowler-Yang-Li (FYL) transform, which considerably reduces the number of variables that must be minimized for multicomponent systems. CSRO is incorporated into CALPHAD with a novel cluster-based solution model called FYL-CVM. This new framework brings more physics into CALPHAD while maintaining its practicality and achieves a good balance between accuracy and computational cost. It leverages statistical mechanics to yield a more physical description of configurational entropy and opens the door to cluster-based CALPHAD database development. The application of the FYL-CVM model in a prototype fcc AB alloy demonstrates its capability to calculate the phase diagram and thermodynamic properties with remarkable accuracy comparable to CVM. The hybrid CVM-CALPHAD framework represents a new methodology for thermodynamic modeling that enables atomic-scale order to be exploited for materials design.

"Impact of hydride composite materials on thermochemical hydrogen compression"

The formation of a hydride from a metal or intermetallic alloy is an exothermic reversible chemical reaction. The thermodynamic properties governing hydride formation facilitate their thermochemical applications, such as hydrogen compression. Thermal transport inside the materials is of highest importance for system dynamics and its productivity. In this contribution, we demonstrate a two-stage thermochemical hydrogen compressor using the AB5 alloy LaNi5 in the first stage and an AB2 alloy TiMn2 (Hydralloy®) in the second stage. To evaluate the impact of the thermal conductivity of the materials, the productivity of the compressor was compared for pure metal hydride compacts (MH) and metal hydride composite materials (MHC). Compared to pure MH pellets, the MHC used in this study contain expanded natural graphite (ENG), a secondary phase with highest thermal conductivity. As the radial thermal conductivity of the MHC increased, the time required for the loading, temperature change and unloading steps was successfully reduced by 400%. Productivity was increased by over 320 % from 14 NlH2/(kgMaterial*h) to 44 NlH2/(kgMaterial*h). Overall, MHC have the potential to simplify handling, reactor design and reduce investment costs for thermochemical compression systems. Thus, MHC have highest impact and potential for thermochemical applications.

The influence of trihaloacetic acids on the hydrogen sorption properties of palladium nanoparticles-modified AB5 alloy in aprotic ionic liquid: Towards ionic liquid-based electrolytes for hydride batteries

Binary mixtures of acetic acid/trihaloacetic acids with aprotic ionic liquid – 1-ethyl-3-methylimidazolium methanesulfonate ([EMIM][MS]) are used as electrolytes for hydrogen electrosorption measurements. Preliminary studies are performed with palladium limited volume electrode to determine optimum concentration of the acid additives for hydrogen capacity and physicochemical properties of the electrolytes. The results obtained for trichloro- and tribromoacetic acid indicate that their decarboxylation occurs after mixing with [EMIM][MS] and dissolution of palladium is observed in contact with the decomposed electrolyte. Research on hydrogen capacity of palladium nanoparticles-modified AB5-type alloy is performed in mixtures of acetic acid and trifluoroacetic acid of optimum concentration. The best electrochemical performance is demonstrated by 2 M acetic acid/[EMIM][MS] mixture. The determined value of specific capacity of the investigated hydrogen absorbing material reaches 230 mAh g−1 and is close to that previously obtained from aqueous solutions of acids or bases.

Pd-H as an irreplaceable model system for the study of hydrogen electrosorption in aqueous and non-aqueous electrolytes

Even though Pd-H system has been known since the nineteenth century, it is still of interest to scientists. Pd thin film electrode (called as a Limited Volume Electrode – LVE) is able to electrosorb hydrogen form aqueous (acid, base) and non-aqueous electrolytes (e.g. ionic liquids). Therefore Pd-H is an irreplaceable model system for the study of hydrogen electrosorption in different media. The paper presents: (1) short overview of the study of hydrogen sorption in Pd, (2) the detailed description of the electrochemical measurement methods and (3) the equations for the determination of hydrogen electrosorption charges needed to hydrogen electrosorption isotherms creation. The presented approach can be applied for laboratory work. The results show that Pd-LVE can be effectively used as a model system before the studies of multicomponent hydrogen storage alloys (e.g. AB5 alloys).Graphical abstract

Connectionist technique estimates of hydrogen storage capacity on metal hydrides using hybrid GAPSO-LSSVM approach

The AB2 metal hydrides are one of the preferred choices for hydrogen storage. Meanwhile, the estimation of hydrogen storage capacity will accelerate their development procedure. Machine learning algorithms can predict the correlation between the metal hydride chemical composition and its hydrogen storage capacity. With this purpose, a total number of 244 pairs of AB2 alloys including the elements and their respective hydrogen storage capacity were collected from the literature. In the present study, three machine learning algorithms including GA-LSSVM, PSO-LSSVM, and HGAPSO-LSSVM were employed. These models were able to appropriately predict the hydrogen storage capacity in the AB2 metal hydrides. So the HGAPSO-LSSVM model had the highest accuracy. In this model, the statistical factors of R2, STD, MSE, RMSE, and MRE were 0.980, 0.043, 0.0020, 0.045, and 0.972%, respectively. The sensitivity analysis of the input variables also illustrated that the Sn, Co, and Ni elements had the highest effect on the amount of hydrogen storage capacity in AB2 metal hydrides.

Stoichiometry and annealing condition on hydrogen capacity of TiCr2-x AB2 alloys

This study presents the effect of stoichiometry and annealing condition on Ti–Cr AB2-type hydrogen storage alloys. Prior to annealing the majority phase of the as-cast alloys was the C14 Laves phase, with separate Ti and Cr phases. Annealing treatment (1273 K/14 d) led to a transition from C14 to C15 Laves phase structure. Both C14 (as-cast) and C15 (annealed) cell size increased with Ti content, up to a ratio (Cr/Ti) of 1.6, due to B-site Ti substitution in the lattice up to a limit. Pressure composition isotherm (PCI) measurements demonstrated alloys containing a greater Ti content had a better maximum hydrogen storage capacity (1.5 vs. 1.03 wt%) and lower plateau pressure (9.4 vs. 15.8 bar) at 253 K. Annealing resulted in a lower storage capacity (1.05 vs. 1.49 wt%), greater plateau pressure (ca. 30 bar) and flatter plateau slope (25 % reduction in plateau slope). Reduction in hydrogen storage capacity of annealed alloys could be due to diffusion of residual Cr in the alloy into the C15 Laves phase during the annealing process, thereby changing the local composition as confirmed through X-ray diffraction (XRD).

ИССЛЕДОВАНИЕ ТРИБОТЕХНИЧЕСКИХ СВОЙСТВ КОМПОЗИЦИОННОГО МАТЕРИАЛА НА ОСНОВЕ АЛЮМИНИЕВОЙ МАТРИЦЫ АРМИРОВАННЫЙ СТАЛЬЮ ИЛИ БАЗАЛЬТОМ

The study objective is to evaluate the tribo-engineering properties of composite materials based on an aluminum matrix reinforced with steel or basalt in comparison with a material without reinforcement, and to develop a technology for obtaining such composite materials. Frames consisting of multidirectional fibers were used as reinforcing components: basalt wool (175-200 kg/m3 density); steel wool (4# class); melting temperatures of steel and basalt, which make up steel and basalt wool, are above 10000C, which makes it possible to pour aluminum without changing the aggregate state of reinforcing frames. The percentage of reinforcing components by weight is 4-5%. Deformable AB aluminum alloy was used as a matrix, which differs from the alloys of Al-Mg-Si system because of its higher level of tensile and yield strength. The composite materials under study were obtained by the liquid–phase method - casting according to melting models. Tribo-engineering properties were tested on a friction machine in the medium of Lukoil standard 10W40 SF/CC engine oil. To determine the anti-wear properties, tests were carried out for 1 hour, and to determine the antisize properties and the seizure load, tests were carried out with a constant increase in the load on the friction unit. The assessment of anti-wear and antisize properties was carried out by comparing the values of wear spots and seizure loads. It is found that the anti-wear properties increase by 76-85% when reinforcing samples with basalt wool and by 46-76% when reinforcing with steel wool in relation to an unreinforced sample. Antisize properties increase with basalt reinforcement by 23%, and decrease by 7% with steel reinforcement. Studies on assessing tribo-engineering properties of samples obtained by casting from AB aluminum alloy reinforced with basalt and steel have shown an improvement in anti-wear and antisize properties in relation to samples from AB alloy without reinforcement.

Optimization of LaNi5 hydrogen storage properties by the combination of mechanical alloying and element substitution

LaNi5 is a commercial hydrogen storage alloy with great potential. But its performance still needs to be optimized to meet the standard proposed by the US Department of Energy. Element substitution is a very important method to optimize the performance of hydrogen storage alloys, especially suitable for AB5 alloys. As a novel method to produce nanocrystalline hydrogen storage alloys, mechanical alloying is also often applied to optimize the properties of hydrogen storage alloys.In this work, first of all, the simulation method based on first principles is applied to predict the performance of 8 elements substituting Ni respectively, and select the most suitable element to substitute Ni. Then the phase composition characterization, hydrogen storage performance tests and electrochemical performance tests were carried out. It was found that mechanical alloying can greatly improve the hydrogen storage performance of LaNi5, and different ball milling times can bring about different performance changes. After adding Cr to the ball-milled LaNi5, the properties of the formed LaNi4Cr were further improved.

Development and optimization of a two-stage metal hydride hydrogen compressor with AB2-type alloys

This study reports the development of a two-stage metal hydride hydrogen compressor (MHHC) capable of compressing hydrogen from 1 to 30 MPa through a temperature change between 20 and 150 °C. AB2-type hydrogen storage alloys in the C14 Laves phase are employed, where A = Ti and Zr and B = Cr, Mn, and V. The pressure transfer conditions between the two stages are investigated, and the composition of the AB2 alloys is optimized accordingly: the Mn content x in Ti0.8Zr0.2Cr1.9−xMnxV0.1 and the Zr content y in Ti1−yZryCr1.2Mn0.8, for the 1st and the 2nd stage materials, respectively. A laboratory-scale two-stage compressor is fabricated and operated using the selected alloys, whereby hydrogen is successfully compressed to 30 MPa. The compression capacity is analyzed to estimate the useable capacity of the materials. The results of this study can serve as a guide for the design and evaluation of multistage MHHCs.

Solubility of hydrogen in Ab alloy

In this work, the solubility of hydrogen is studied using the method of average energies, quasi-chemical approximation, as well as by introducing the consideration of the crystal molecular field of interstitial hydrogen atoms. By using the configuration method, the solubility of the H interstitial impurity in a binary alloy AB of the impurities which has a hexagonal symmetry structure of type B81 was investigated. It was shown that the effect of order on the solubility of interstitial impurities in an alloy is stronger in the case of filling octahedral interstices which is important, because can make it possible to choose the desired system with the hydrogen yield required for practical purposes.

Improved hydrogen storage properties of low-cost Ti–Cr–V alloys by minor alloying of Mn

V-based BCC solid-solution alloys have been considered as promising hydrogen storage materials due to their high hydrogen storage capacity; however, the low effective hydrogen desorption capacity and high cost of pure V have limited their practical application in fuel cell vehicles or devices. Herein, a low-V TiCr1.2(V–Fe0.203)0.6 hydrogen storage alloy with a hydrogen storage capacity of 3.35 wt% has been developed by using a low-cost FeV80 as raw material. To further increase the effective hydrogen desorption capacity, cheap Mn is first used to partially substitute for Cr in FeV80-based alloy. The Mn substitution alloy achieves an effective hydrogen desorption capacity of 2.07 wt% cutting-off at 0.1 MPa with good activation performance. It is ascribed that the minor alloying of Mn increases the dehydrogenation plateau pressure and reduces the hysteresis and the enthalpy change value. The dehydrogenation enthalpy decreases from 34.84 kJ/mol to 31.51 kJ/mol. The synergistic effect of Mn and Fe increases the abundance of the C14 Laves phase, which plays a catalytic role in hydrogen absorption and desorption. The cost of TiCr1.1Mn0.1(V–Fe0.203)0.6 alloy is much lower than that of using pure V, and even lower than some AB2 alloys based on cost estimation. The results of this study would provide a reference for the application of low-cost Ti–Cr-(FeV80) alloys for hydrogen storage.

Synergistic effect for improving the hydrogen storage capability and electrochemical performance of AB2 Laves phase alloys

The structure of a series AB2 Laves-type metal hydride alloys, in which Ce was doped into Ti0.24Zr0.76Ni1.15Mn0.7V0.15 and annealed the alloys, was studied and correlated to hydrogen storage properties and electrochemical performances. X-ray diffraction, scanning electron microscope, and energy-dispersive spectroscopy results revealed that Ce formed a CeNi3 secondary phase instead of entering the Laves phases. The synergistic effect of the CeNi3 and (Ti,Zr)Ni phase improved the hydrogen storage and electrochemical discharge properties of the Ce-doped (Ce0.02) alloy. Especially, the secondary phases could decrease the hydrogen absorption plateau, reduce the hysteresis phenomenon, and increase the hydrogen storage capacity (from 0.9 wt% to 1.4 wt% at 25 ℃). The formation of CeNi3Hx hydride on the surfaces of alloy electrodes led to a higher discharge capacity (∼500 mAh/g) and a faster activation rate. The Ce0.02 alloy also showed a good cyclic stability ∼82.08%, after 500 charge-discharge cycling, which could be ascribed to the good corrosion resistance of the CeNi3 phase on the surface of alloy. In addition, annealing treatment promoted the depletion of (Ti,Zr)Ni secondary phase and the transformation from the C14 to C15 phase. The Ce-doped AB2 alloy can be used as a hydrogen storage and hydride battery electrode material.

Influence of Fe on the Hydrogen Storage Properties of LaCeNi Alloys.

LaNi5 intermetallic compounds with a hexagonal CaCu5 type structure can react reversibly with hydrogen. The element substitutions in LaNi5 can significantly change the hydrogenation properties, allowing to tune them to a large extent. It could be very advantageous to partially replace Ni or La with other elements to reduce the cost of this alloy as well as the equilibrium pressure of absorption and desorption. The hydrogen storage properties of ball-milled AB5 alloys containing the elements La, Ce (A-rare elements) and Ni, Fe (B-transition metals) were studied in this paper. Although the substitution of Ni (atomic radius 1.49 Å) with Fe atom (atomic radius 1.56 Å) increased the unit cell volume from 86.4149 to 87.947 5 Å3 of the LaNi5 phase, its hydrogen storage capacity was still close to the value 1.4 wt %. The enthalpy (ΔH) of hydride formation for hydrogen absorption and desorption of the experimental alloys was in the range of 29-32.6 kJ/mol. A very favorable effect of Fe on the sorption properties was found in the significant reduction of the equilibrium pressure of absorption and desorption. These studied experimental Fe-containing alloys were able to store hydrogen at 300 K and with pressure under 0.1 MPa. The fastest sorption kinetics of hydrogen was found in alloys with FeNi phase particles located on the surface of the powder. However, if the FeNi phase was segregated at the grain boundaries, it acted as a barrier limiting the growth of the hydride phase. This led to a decrease of the hydride sorption kinetics.

Enhancement of hydrogen storage performance in shell and tube metal hydride tank for fuel cell electric forklift

Novel metal hydride (MH) hydrogen storage tanks for fuel cell electric forklifts have been presented in this paper. The tanks comprise a shell side equipped with 6 baffles and a tube side filled with 120 kg AB5 alloy and 10 copper fins. The alloy manufactured by vacuum induction melting has good hydrogen storage performance, with high storage capacity of 1.6 wt% and low equilibrium pressure of 4 MPa at ambient temperature. Two types of copper fins, including disk fins and corrugated fins, and three kinds of baffles, including segmental baffles, diagonal baffles and hole baffles, were applied to enhance the heat transfer in metal hydride tanks. We used the finite element method to simulate the hydrogen refueling process in MH tanks. It was found that the optimized tank with corrugated fins only took 630 s to reach 1.5 wt% saturation level. The intensification on the tube side of tanks is an effective method to improve hydrogen storage performance. Moreover, the shell side flow field and hydrogen refueling time in MH tanks with different baffles were compared, and the simulated refueling time is in good agreement with the experimental data. The metal hydride tank with diagonal baffles shows the shortest hydrogen refueling time because of the highest velocity of cooling water. Finally, correlations regarding the effect of cooling water flow rate on the refueling time in metal hydride tanks were proposed for future industrial design.

The Electrochemical Behavior of Unmodified and Pd-NPs Modified AB5 Hydrogen Storage Alloy in Selected Protic and Aprotic Ionic Liquids (ILs): Towards ILs-Based Electrolytes for Ni-MH Batteries

The objective of this work was to study the electrochemical behavior of AB5 alloy and its composite with Pd nanoparticles in selected ionic liquids. The protic ionic liquid (diethylmethylammonium triflate) and the mixture of aprotic ionic liquid (1-ethyl-3-methylimidazolium methanesulfonate) with parent superacid were used as electrolytes in the process of hydrogen electrosorption in AB5 alloy electrodes. The impact of the surface modification of AB5 electrode with Pd nanoparticles has been checked. The studies revealed that the highest hydrogen absorption capacity can be obtained in Pd-NPs-AB5 electrode in DEMA-TFO. It was found that the surface modification with Pd-NPs facilitates the activation of the electrode and results in stabilization of the plateau potential of discharging. The studies show that more effort should be put into the synthesis of less corrosive tailored ionic liquids suitable to be used as electrolytes in hydride batteries.

RADIAL EXTRUSION OF A PIPE BILLET WITH INTERNAL LEDGE. EXPERIMENTAL VERIFICATION OF THEORETICAL FORMULAS DURING EXTRUSION WITH HARDENING OF ALUMINUM ALLOY AB

A continuation of the experimental verification of theoretical results, begun in previous articles, is outlined. Various studies of extrusion of a hardening material – aluminum alloy AB – have been carried out. The method of accounting for hardening in technological calculations is shown in detail. The high accuracy of the obtained calculation formulas is confirmed.

Equilibrium vacancy concentration and thermodynamic quantities of BCC defective alloys FeCrSi and VWSi under pressure

In this paper, we present the analytic expressions of the cohesive energy, the alloy parameters, the equation of state, the mean nearest neighbor distance, the Helmholtz free energy, equilibrium vacancy concentration and thermodynamic quantities such as the isothermal compressibility, the thermal expansion coefficient, the heat capacities at constant volume and at constant pressure for BCC defective ternary substitutional and interstitial alloy ABC derived by the statistical moment method. The obtained thermodynamic quantities depend on temperature, pressure, concentration of substitutional atoms, concentration of interstitial atoms and equilibrium vacancy concentration. Thermodynamic quantities of BCC defective metal A, BCC defective substitutional alloy AB, BCC defective interstitial alloy AC and BCC defective metal A are specific cases for thermodynamic quantities of BCC defective ternary substitutional and interstitial alloy ABC. The theoretical results are calculated numerically to alloys FeCrSi and VWSi. Our calculated results of thermal expansion coefficient and heat capacities at constant pressure for main metals Fe, V are in good agreement with experimental data. Our other calculated results for thermodynamic quantities of alloys FeCrSi and VWSi at different temperature, pressure, concentration of substitutional atoms and concentration of interstitial atoms orient and predict new experimental data in the future

Production of AB5 materials from spent Ni-MH batteries with further tests of hydrogen storage suitability

A novel approach for the reuse of rare earth (REE) elements generated during hydrometallurgical processing of Ni-MH batteries as alternative sources is provided to valorize Ni-MH batteries wastes. The production of AB5-based alloys from spent Ni-MH waste was thoroughly investigated. The REE elements were recovered as a mixture in oxalate form and annealed at 900 °C to obtain a single-phase REEs oxide REE2O3. Citrate gel and glycine nitrate processes followed by the Ca reduction process under H2 atmosphere were used to produce the AB5 alloys. The alloys were successfully produced, and their crystal structure and morphology have been studied using X-ray diffraction (XRD), scanning electron microscopy (SEM) with supporting energy-dispersive X-ray (EDS) analysis. Nanoparticles with a size of 173±3 nm and 150±8 nm were observed using transmission electron microscopy (TEM) for CG and GNP alloys. Studied samples were subjected to hydrogenation, and the structural changes were depicted.

Study on thermodynamic and elastic properties of B2-FeSi by statistical moment method

The thermodynamic and elastic theory of B2 substitutional alloy AB and B2 interstitial alloy AB under temperature and pressure are derived by the statistical moment method. In the case of zero concentration of substitutional atoms B and interstitial atoms B, we obtain the thermodynamic and elastic theory of main metal A with simple cubic structure. Our numerical calculations according to the model of interstitial alloy for B2-Fe99Si1 and the model of substitutional alloy for B2-Fe50Si50 in the temperature interval from zero to 1500 K and the pressure interval from zero to 160 GPa are in relatively good with experiments and other calculations.