The Crystal Structures in Hydrogen Absorption Reactions of REMgNi4-Based Alloys (RE: Rare-Earth Metals)

REMgNi4-based alloys, RE(2−x)MgxNi4 (RE: rare-earth metals; 0 < x < 2), with a AuBe5-type crystal structure, exhibit reversible hydrogen absorption and desorption reactions, which are known as hydrogen storage properties. These reactions involve formation of three hydride phases. The hydride formation pressures and hydrogen storage capacities are related to the radii of the RE(2−x)MgxNi4, which in turn are dependent on the radii and compositional ratios of the RE and Mg atoms. The crystal structures formed during hydrogen absorption reactions are the key to understanding the hydrogen storage properties of RE(2−x)MgxNi4. Therefore, in this review, we provide an overview of the crystal structures in the hydrogen absorption reactions focusing on RE(2−x)MgxNi4.

RESEARCH OF THE KINETICS OF THE FIRST HYDRATION OF MATERIAL TIFE + TI2FE, OBTAINED BY EXPLOSIVE LOADING OF MIXTURES OF TITANIUM AND IRON POWDERS

The kinetics of the processes of primary hydrogenation of material based on TiFe obtained by explosive pressing of titanium and iron powders with subsequent heat treatment has been investigated. Using the results obtained and mathematical processing of the curves using the Avraami-Erofeev equation, it was revealed that the mechanism of their saturation with hydrogen corresponds to the classical concepts of reaction diffusion. The process begins with the formation of a layer of solid solutions of hydrogen on the surface of the material in the initial phases of the material and after the latent period continues with the formation of a layer of hydride phases. t is shown that the hydrogen storage material TiFe + TiFe has a significantly higher hydrogen capacity than single-phase TiFe.

Study of the hydrogenation effect on the structure and flattening of tubular samples of PT-7M titanium alloy

In this work, we analyze the effect of hydrogen embrittlement on the performance of PT-7M titanium alloy products. The above examples show that PT-7M titanium alloy products with a high hydrogen content are prone to cracking, the probability of their destruction increases. In the initial state, the samples were annealed in vacuum at 680 о. Hydrogenation of the samples was carried out by the diffusion method at room temperatures to concentrations of 0.002, 0.005 and 0.01 % (by mass) in a Siverts laboratory setup. The hydrogen content in the samples was determined on a highly sensitive G8 Galileo gas analyzer. To assess the effect of hydrogen embrittlement on the plastic properties and tendency to crack formation, the samples were tested for flattening. The structural state of the alloy was analyzed, which showed that hydride phases were observed to increase with increasing hydrogen concentration. The effect of structural changes in the alloy on the microhardness was studied. The X-ray diffraction analysis also showed the presence of hydride precipitates in the PT-7M alloy. Using the CAE ANSYS engineering complex, a numerical simulation of the stress-strain state of samples was carried out during a flattening test. The simulation results showed that the maximum stresses during flattening exceed the tensile strength. One of the reasons for the hydride phase precipitation is high stresses, which is also confirmed by the results of flattening tests and metallographic analysis: in local zones with an increased level of stresses in the material structure, a higher concentration of the TiHx hydride phase. Flattening tests also showed that the cause of cracking during flattening testing is the presence of brittle hydrides in the structure of the material: cracks are formed by the destruction of hydride phases. In the initial state and with a low hydrogen content (up to 0.002 mass %) no cracks were found in the samples. Thr research was conducted within the framework of the grant RNF No. 19-19-00332 "Development of scientifically substantiated approaches, hardware and software facilities for monitoring of damage of construction materials, based on the artificial intellect approaches to provide safe operation of technical objects in the Arctic conditions".

Dynamics of cavitation zone development during sonication of suspensions of magnesium particles

The cavitation activity during ultrasonic treatment of magnesium particles has been investigated. The cavitation activity recorded in a continuous mode of ultrasonic treatment altered in a wide range at constant output parameters of the generator. The rate and nature of cavitation activity variation depended on the mass fraction of particles in the suspension. It has been demonstrated that during the ultrasonic treatment of magnesium aqueous suspensions it is possible to determine the following stages: growth of cavitation activity, reaching a maximum followed by a decrease and reaching a plateau (or repeated cycles of increasing or decreasing cavitation activity). The complex nature of the cavitation activity dynamics is associated with the participation of hydrogen released as a result of the chemical interaction of magnesium particles with water in the formation of the cavitation zone. The magnesium particles modified with ultrasound were characterised with the use of scanning electron microscopy, X-ray phase analysis and thermal analysis. It has been found that ultrasonic treatment of magnesium particles resulted in the formation of magnesium hydroxide and magnesium hydride phases.

Magnetization and XRD Studies of Laser Heat Treated SmCo5 Powders

The microstructure and magnetization of SmCo5 micro-particles may be used as feedstock for 3D printing to make miniature strong magnets. Thus, the magnetic response and microstructures of commercially available SmCo5 micro-particles were studied under various heat treatments using a high wattage laser. The magnetization of laser heat treated powders at 50-watt showed an increase in magnetization, while the 75-watt melt showed a little to no change. Unfortunately, the coercivity of both laser heat treated samples decreased significantly. Oxidation during the heat treatment is suspected to result in low coercivity. Purging with argon-gas prior to laser heating showed improved coercivity. To further minimize the oxidation problem a set of SmCo5 powder was reduced prior to laser heat treatment using a constant flow of hydrogen gas while being heated at various temperatures from 100 oC to 400 oC for a period of ~4 hours. The results show that the magnetization generally increases with the temperature, while the coercivity decreases significantly. Another set of SmCo5 was annealed in a vacuum furnace for one hour at temperatures between 200 oC and 400 oC in order to confirm that no hydride phases were formed during reduction. The magnetization and coercivity showed similar variations with annealing temperature to those for the reduced powders confirming that these variations may be due to change in crystal structure rather than formation of hydrides. X-ray Diffraction (XRD) studies were performed to identify the changes in crystal phases.

In Situ Time-Resolved Decomposition of β-Hydride Phase in Palladium Nanoparticles Coated with Metal-Organic Framework

The formation of palladium hydrides is a well-known phenomenon, observed for both bulk and nanosized samples. The kinetics of hydrogen adsorption/desorption strongly depends on the particle size and shape, as well as the type of support and/or coating of the particles. In addition, the structural properties of hydride phases and their distribution also depend on the particle size. In this work, we report on the in situ characterization of palladium nanocubes coated with HKUST-1 metal-organic framework (Pd@HKUST-1) during desorption of hydrogen by means of synchrotron-based time-resolved X-ray powder diffraction. A slower hydrogen desorption, compared to smaller sized Pd nanoparticles was observed. Rietveld refinement of the time-resolved data revealed the remarkable stability of the lattice parameters of α- and β-hydride phases of palladium during the α- to β- phase transition, denoting the behavior more similar to the bulk materials than nanoparticles. The stability in the crystal sizes for both α- and β-hydride phases during the phase transition indicates that no sub-domains are formed within a single particle during the phase transition.