Hydride Formation Research Articles

Isothermal stress reorientation of hydrides in Zr-2.5Nb pressure tube alloy

• For the first time, in-situ hydride reorientation phenomenon in Zr-2.5Nb alloy has been investigated. • Threshold stress for reorientation of hydrides was determined under isothermal condition using a specially designed setup. • Threshold stress values determined using in-situ and ex-situ methods were comparable. The precipitation of hydrides normal to the transverse direction in Zr-2.5%Nb pressure tube alloy when cooled under stress above a threshold value, is known as stress reorientation of hydrides. The ex-situ threshold stress values reported in the literature were determined using pre-charged samples heated to a peak temperature to dissolve all the hydrides, cooled to reorientation temperature followed by cooling under stress from reorientation temperature. Leger and Donner performed in-situ reorientation experiments using samples having hydride deposited on its surface. In both cases, hydride reorientation occurred during cooling. In the present investigation, for the first time, experiments were done to study the reorientation phenomenon using in-situ gaseous charging of samples under stress at a constant temperature using a specially designed set up. It is expected that the threshold stress determined by in-situ method used in the present investigation will more closely resemble the formation of radial hydrides under reactor operating conditions. In this work, the threshold stress values for reorientation of hydrides in Zr-2.5%Nb pressure tube material were determined using both in-situ and ex-situ methods. The precipitation of hydrides normal to the transverse direction in Zr-2.5%Nb pressure tube alloy when cooled under stress above a threshold value is known as stress reorientation of hydrides. In the present investigation, for the first time the threshold stress (σ th ) for reorientation of hydrides in Cold worked and stress relieved (CWSR) Zr-2.5Nb alloy pressure tube material was determined by using a specially designed fixture shown below consisting of load train comprising sample, pull rod and load cell connected in a series, mounted between two rods welded to a flange. A flexible bellow is welded to flange and pull rod to accommodate the displacement of pull rod and to ensure vacuum leak tightness. Ports are provided in the flange to measure the temperature of sample and to connect the system to vacuum pump. The entire setup after sample loading is inserted into the glass tube and loaded into a resistance heated furnace samples were charged with hydrogen under stress at constant temperature. It is expected that the threshold stress determined by in-situ method will more closely resemble the formation of radial hydrides under reactor operating conditions.

Energetic characteristics of hydrogenated amorphous silicon nanoparticles

• Plasma-synthesized amorphous Si NPs ( a -nSi) incorporate abundant hydrogen. • The reactivity of a -nSi/KClO 4 increases by a factor of six compared with nAl. • The energetic performance of nSi is correlated with its hydrogen content. • In situ release of hydrogen from hydrides enhances the reactivity. In this work, we utilize a low-temperature non-equilibrium plasma to nucleate and grow sub-10 nm Si particles with varying degrees of crystallinity by tuning the level of power coupled into plasma discharge. Temperature-programmed desorption spectroscopy shows that as-prepared amorphous Si nanoparticles ( a -nSi) incorporate more hydrogen than crystalline Si nanoparticles ( c -nSi). Further, hydrogen is incorporated in the material in the form of higher silicon hydrides with a lower desorption temperature. Combustion cell measurements show that when formulated with KClO 4 , a -nSi outperforms its crystalline counterpart with respect to pressure output. The pressurization rate of a -nSi/KClO 4 composite increases by a factor of six compared with nAl to 0.66 MPa·μs −1 . Evidence of hydrogen release (∼730 K) from Temperature-jump time-of-flight mass spectrometry (T-Jump TOFMS) of a -nSi/KClO 4 suggests the creation of Si dangling bonds prior to ignition (∼820 K), which then react exothermically with oxygen liberated from KClO 4 , leading to ignition. Explosive reaction of H 2 /O 2 mixture likely contributes to the rapid pressure rise. The enhanced energetic performance of hydrogenated a -nSi compared to its crystalline counterpart suggests that incorporation of hydrogen is a promising strategy for improving the performance of nanoenergetic materials.

Quantitative predictions of thermodynamic hysteresis: Temperature-dependent character of the phase transition in Pd–H

The thermodynamics of phase transitions between phases that are size-mismatched but coherent differs from conventional stress-free thermodynamics. Most notably, in open systems such phase transitions are always associated with hysteresis. In spite of experimental evidence for the relevance of these effects in technologically important materials such as Pd hydride, a recipe for first-principles-based atomic-scale modeling of coherent, open systems has been lacking. Here, we develop a methodology for quantifying phase boundaries, hysteresis, and coherent interface free energies using density-functional theory, alloy cluster expansions, and Monte Carlo simulations in a constrained ensemble. We apply this approach to Pd–H and show that the phase transition changes character above approximately 400 K, occurring with an at all times spatially homogeneous hydrogen concentration, i.e., without coexistence between the two phases. Our results are consistent with experimental observations but reveal aspects of hydride formation in Pd nanoparticles that have not yet been accessible in experiment.

Synthesis and biological evaluation of some hybrid 2-quinolinone derivatives containing cinnamic acid as anti-breast cancer drugs

ABSTRACT. A new series of hybrid 2-quinolinone derivatives were synthesized by using 7-hydroxy-4-methyl-1-amino-quinolin-2-one (2) and cinnamic acid. Hybrid halogenated 2-quinolinone derivatives (3-(7-hydroxy-4-methyl-3,6,8-tribromo-2-oxo-2H-quinolin-1-ylamino)-3-phenyl acrylic acid (4) and 3-(7-acetoxy-4-methyl-3,6,8-tribromo-2-oxo-1H-quinolin-1-ylamino)-3-phenyl acrylic acid (7)) were prepared via the halogenation of 3-(7-hydroxy-4-methyl-2-oxo-2H-quinolin-1-ylamino)-3-phenyl acrylic acid (3) with bromine to give compound 4 with acetic anhydride led to the formation of hydride halogenated 2-quinolinone derivative (7). All the synthesized hybrid 2-quinolinone and hybrid halogenated 2-quinolinone derivatives were tested for their cytotoxicity against MCF-7 cell line. DNA flow cytometric analysis of compounds 3 showed cell cycle arrest at G2/M phase with concomitant increase of cells in apoptotic phase. Dual annexin-V/propidium iodide staining assay of compound 3 revealed that, the selected molecule increases the apoptosis of MCF-7 cells more than control.
 
 KEY WORDS: Quinolinone, Hybrid, Cinnamic acid, Apoptosis, MCF-7 cells
 
 Bull. Chem. Soc. Ethiop. 2021, 35(3), 551-564.
 DOI: https://dx.doi.org/10.4314/bcse.v35i3.7

The role of H-H interactions and impurities on the structure and energetics of H/Pd(111).

Understanding hydrogen incorporation into palladium requires detailed knowledge of surface and subsurface structure and atomic interactions as surface hydrogen is being embedded. Using density functional theory (DFT), we examine the energies of hydrogen layers of varying coverage adsorbed on Pd(111). We find that H-H and H-Pd interactions promote the formation of the well-known 3×3 phases but also favor an unreported (3 × 3) phase at high H coverages for which we present experimental evidence. We relate the stability of isolated H vacancies of the (3 × 3) phase to the need of H2 molecules to access bare Pd before they can dissociate. Following higher hydrogen dosage, we observe initial steps of hydride formation, starting with small clusters of subsurface hydrogen. The interaction between H and Pd is complicated by the persistent presence of carbon at the surface. X-ray photoelectron spectroscopy experiments show that trace amounts of carbon, emerging from the Pd bulk despite many surface cleaning cycles, become mobile enough to repopulate the C-depleted surface at temperatures above 200K. When exposed to hydrogen, these surface carbon atoms react to form benzene, as evidenced by scanning tunneling microscopy observations interpreted with DFT.

The effect of hydrogenation on the fracture of Ti2AlNb-based alloy during ball milling

In this work we have studied the effect of phase composition and microstructure of a rapidly solidified Ti2AlNb-based alloy containing hydrogen on deformation of the alloy during ball milling and production of a fine-dispersed powder. Hydrogen is introduced into the alloy up to a concentration of 2.0 wt%. The X-Ray diffraction (XRD) analysis and Scanning Electron Microscopy (SEM) show that the alloy has the following phase compositions depending on hydrogen content: β + O, β/β-hydride, β/β-hydride + intermetallic hydride (Ti2AlNbHx) or a single-phase intermetallic hydride. It is found that in the hydrogenated β + O alloy containing a small amount of hydrogen a strong decrease in ductility occurs, but this does not affect the ball milling and synthesis of the fine-dispersed powder. Efficient milling of the rapidly solidified alloy has been achieved when hydrogen content was 1.2 wt% and exceeding this value when a transformation from the H-saturated solid solution into a hydride phase is observed in the alloy or the formation of a single phase hydride occurs.

Cluster dynamics simulation of Zr hydrides formation on grain boundaries in Zr

The delta hydrides formation in zirconium cladding under irradiation and thermal aging is studied by the rate theory modeling. The precipitates may lead to cracking of the clad and are investigated both experimentally and theoretically. The rate theory studies published so far are based on the well-established classical nucleation theory, but use several assumptions, e.g. of homogeneous hydride nucleation mode and spherical shape of precipitates, which contradict observations. In this work we continue the development of the hydride precipitation model by taking into consideration the observed preferential nucleation of the platelet-shaped hydrides on grain boundaries, and analyze the importance of such modifications by comparing calculations performed with different approaches. We also extract information from the literature on the hydrogen solution energy and alpha Zr / delta hydride interface energy, which define the hydrogen-hydride binding energy as a function of precipitate size, and show that the observed hydride size and density are well described with the use of the capillary approximation. The difference in precipitation kinetics during thermal annealing of samples with pre-existing level of hydrogen and under irradiation to the same final hydrogen concentration is elucidated. This improves our understanding of the factors affecting hydride formation in the clad.

Hydrogen absorption/desorption reactions of the (TiVNb)85Cr15 multicomponent alloy

Ti-V-Nb-Cr alloys have been reported as potential candidates for hydrogen storage applications. Investigating the processes of absorption and desorption is paramount to understand the hydrogen storage properties of these novel alloys and to develop more efficient hydrogen storage materials. In this work, we investigated the hydrogen absorption/desorption reactions of the (TiVNb)85Cr15 BCC multicomponent alloy by laboratory and synchrotron X-ray diffraction, Pair Distribution Function (PDF) analyses, Transmission Electron Microscopy (TEM) and thermo-desorption analyses (TDS). Hydrogen absorption behavior was studied by pressure-composition-isotherm (PCI) at room temperature, which demonstrated levels of absorption around 2 H/M (H/M = hydrogen-to-metal ratio) with low equilibrium pressure. The results showed a multi-step hydrogenation process: alloy ↔ BCC solid solution ↔ BCC intermediate hydride ↔ FCC dihydride. PDF analyses showed that the partially hydrogenated alloy at different levels of H/M and the fully hydrogenated alloy can be reasonably described by models with phases presenting random atomic distribution in the metal crystallographic sites. Moreover, the partially hydrogenated sample prior to the complete formation of the intermediate hydride showed evidence of two co-existing BCC phases.

Predicting Heat of Hydride Formation by the Graph Neural Network – Exploring Structure-Property Relation for Metal Hydrides

Predicting Heat of Hydride Formation by the Graph Neural Network – Exploring Structure-Property Relation for Metal Hydrides

Predicting Heat of Hydride Formation by the Graph Neural Network – Exploring Structure-Property Relation for Metal Hydrides

Predicting Heat of Hydride Formation by the Graph Neural Network – Exploring Structure-Property Relation for Metal Hydrides

Magnesium-based complex hydride mixtures synthesized from stainless steel and magnesium hydride with subambient temperature hydrogen absorption capability

Here, we present the results of the synthesis of a complex hydride previously described as Mg2(Fe, Cr, Ni)Hx formed during the reactive ball milling process of AISI 316 L stainless steel (316 L SS) and magnesium hydride under hydrogen pressure. The evolution of powder morphology and phase composition with milling time is presented. The reaction of magnesium hydride with 316 L steel was found to proceed faster than in case of the reaction of reference mixture containing pure iron. Obtained material was found to possess cubic K2PtCl6-structure with slightly different lattice parameter as compared to Mg2FeH6. The hydrogen content of the obtained samples was found to be around 4 wt%. The mixture that resulted from the decomposition of this synthesized sample was able to absorb around 1% of hydrogen even at − 50 ℃ via the formation of magnesium hydride.

Mechanical behavior of electrochemically hydrogenated electron beam melting (EBM) and wrought Ti–6Al–4V using small punch test

The influence of electrochemical charging of hydrogen at j = −5 mA/cm2 for 6, 12, 48 and 96 h on the structural and the mechanical behavior of wrought and electron beam melting (EBM) Ti–6Al–4V alloys containing 6 wt% β and similar impurities level was investigated. The length of the α/β interphase boundaries in the EBM alloy was larger by 34% compared to that in the wrought alloy. The small punch test (SPT) technique was used to characterize the mechanical behavior of the non-hydrogenated and hydrogenated specimens. It was found that the maximum load and the displacement at maximum load of the wrought alloy remained nearly stable after 6 h of charging, showing a maximum decrease of ∼32% and 11%, respectively. Similarly, hydrogenation of the EBM alloy resulted in a gradual degradation in mechanical properties with charging time, up to ∼81% and 86% in pop-in load and displacement at the “pop-in” load, respectively. The mode of fracture of the wrought alloy changed from ductile to semi-brittle with mud-cracking in all hydrogenated specimens. In contrast, the mode of fracture of the EBM alloy changed from a mixed mode ductile-brittle fracture to brittle fracture with star-like morphology. The degraded mechanical properties of the EBM alloy are attributed to its α/β lamellar microstructure which acted as a short-circuit path and enhanced hydrogen diffusion into the bulk as well as δa and δb hydride formation on the surface. In contrast, a surface layer with higher concentration of δa and δb hydrides in the wrought alloy served as a barrier to hydrogen uptake into the bulk and increased the alloy resistivity to hydrogen embrittlement (HE). This study shows that EBM Ti–6Al–4V alloy is more susceptible to mechanical degradation due to HE than wrought Ti–6Al–4V alloy.

Role of Low-Coordinated Ce in Hydride Formation and Selective Hydrogenation Reactions on CeO2 Surfaces

Role of Low-Coordinated Ce in Hydride Formation and Selective Hydrogenation Reactions on CeO₂ Surfaces

Importance of thermal conductivity and stress level during a phase (hydride) transformation in magnesium

There are many different systems of an autonomous energy storage including accumulators and storage devices for renewable energy. Systems based on reversible metal hydrogenation have recently been introduced. The selection of metals is based on considerations of temperature and pressure conditions of the hydrogenation/dehydrogenation cycle, as well as the desired storage hydrogen capacity. Magnesium is one of the main challenging metals with respect to these main conditions since having a hydrogen capacity up to 7.6 w.%. For Mg forming MgH2, it was soon established that the size of particles plays a critical role since the kinetics (rate) of hydride formation accelerates when the size of the particles decreases. The present study shows that the overall diameter of the particles is the main characteristic controlling the kinetics of hydride formation because of distinct issues. A distribution of the size entails a strong dispersion transferring the heat of reaction, which characterizes Mg to MgH2 phase transition. Moreover, the formation of MgH2, is accompanied by a great increase of the unit-cell volume, developing noticeable internal stresses within the surface layers of the particles, thus turning to a systematic flaking and a systematic decrease of sizes of the powder particles. The results of the numerical modeling comply with the experimental data. This makes it possible to predict the best size of the initial Mg powder able to achieve fast kinetics during hydrogenation. Furthermore, the present analysis demonstrates the best hydrogenation kinetics, not only when using fine powders, but also when the deviation from the average particle size is minimized.

Surface Hydrides on Fe2P Electrocatalyst Reduce CO2 at Low Overpotential: Steering Selectivity to Ethylene Glycol.

Development of efficient electrocatalysts for the CO2 reduction reaction (CO2RR) to multicarbon products has been constrained by high overpotentials and poor selectivity. Here, we introduce iron phosphide (Fe2P) as an earth-abundant catalyst for the CO2RR to mainly C2-C4 products with a total CO2RR Faradaic efficiency of 53% at 0 V vs RHE. Carbon product selectivity is tuned in favor of ethylene glycol formation with increasing negative bias at the expense of C3-C4 products. Both Grand Canonical-DFT (GC-DFT) calculations and experiments reveal that *formate, not *CO, is the initial intermediate formed from surface phosphino-hydrides and that the latter form ionic hydrides at both surface phosphorus atoms (H@Ps) and P-reconstructed Fe3 hollow sites (H@P*). Binding of these surface hydrides weakens with negative bias (reactivity increases), which accounts for both the shift to C2 products over higher C-C coupling products and the increase in the H2 evolution reaction (HER) rate. GC-DFT predicts that phosphino-hydrides convert *formate to *formaldehyde, the key intermediate for C-C coupling, whereas hydrogen atoms on Fe generate tightly bound *CO via sequential PCET reactions to H2O. GC-DFT predicts the peak in CO2RR current density near -0.1 V is due to a local maximum in the binding affinity of *formate and *formaldehyde at this bias, which together with the more labile C2 product affinity, accounts for the shift to ethylene glycol and away from C3-C4 products. Consistent with these predictions, addition of exogenous CO is shown to block all carbon product formation and lower the HER rate. These results demonstrate that the formation of ionic hydrides and their binding affinity, as modulated by the applied potential, controls the carbon product distribution. This knowledge provides new insight into the influence of hydride speciation and applied bias on the chemical reaction mechanism of CO2RR that is relevant to all transition metal phosphides.

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.

Effect of varying Ni content on hydrogen absorption–desorption and electrochemical properties of Zr-Ti-Ni-Cr-Mn high-entropy alloys

The crystal structure, pressure composition isotherms, and electrochemical properties of Zr0.2Ti0.2Ni0.2+xCr0.2Mn0.2 (x = 0, 0.025, 0.05, 0.075, and 0.1) high-entropy alloys (HEAs) were investigated. The crystal structures of all the HEAs consisted of two phases: a primary phase with a C14-type (Zr0.5Ti0.5)Mn2 hexagonal structure and a secondary phase with a B2-type Ti0.6Zr0.4Ni cubic structure. Rietveld analysis revealed that the secondary phase increased with an increase in the x value. The hydrogen storage capacity of the HEAs was lower than that of the alloy with x = 0 because of an increase in the B2-type Ti0.6Zr0.4Ni phase, whereas the change in enthalpy of hydride formation (|ΔH|) decreased with increasing x, leading to the instability of hydrides. The alkaline treatment was performed by immersing HEA powders or electrode in a 6 M KOH aqueous solution at 378 K for 2 h. The Zr0.2Ti0.2Ni0.2Cr0.2Mn0.2 alloy surface changed to a porous and rough structure, and a ZrO2 passive thin layer on their surface, which is replaced by NiO or Ni(OH)2 after the alkaline treatment. The charge–discharge tests conducted using the HEA negative electrodes for Ni-MH batteries depict that the discharge capacity increased with an increase in x, and the highest discharge capacity was 368 mAh g‐1 at x = 0.075 after the alkaline treatment. On increasing the x value, the high-rate dischargeability and cycle performance were also enhanced.

Stripping of carbon coatings in radio-frequency inductively coupled plasma of H2/Ar

This article describes the stripping of amorphous carbon (a-C) coatings in an H 2 /Ar atmosphere using a radio-frequency inductively coupled plasma (RF-ICP) source. The power of the RF-ICP source, atmosphere composition (H 2 /Ar) and bias potential strongly affect the stripping rate (0.7–9.3 μm/h), while the operating pressure has less influence (2.7–3.2 μm/h). The selectivity of stripping of a-C and titanium coatings can be varied from 1 up to ~90 by changing the atmosphere composition. Chemical sputtering plays a key role in the productivity and selectivity of carbon stripping, it should have a higher rate compared to physical sputtering to enable high selectivity of coating stripping. Raman spectroscopy reveals the increase in graphitization degree and decreasing less ordered carbon of a-C coatings under stripping in H 2 /Ar plasma. Phase transformations of sublayer or substrate materials could occur under coating stripping in a reactive atmosphere in the example of hydride formation (TiH 2-x ) in a Ti sublayer. • Stripping of carbon coatings in RF-ICP plasma of H 2 /Ar. • Stripping selectivity of carbon coatings is regulated by H 2 /Ar flow rates. • Graphitization of a-C coatings under stripping in H 2 /Ar plasma.

Production of Aluminium Hydride by Plasma Chemical Catalytic Reaction

In the plasma chemical reaction between aluminium chloride and hydrogen, it is on the reactor substrate that aluminium chloride compounds form, which, under the right conditions, can help obtain AlH3 in stoichiometric composition. A rising partial pressure of Н2 in the reaction zone serves as the main stimulant for the AlH3 formation. The rate of this plasma chemical reaction tends to rise in the presence of palladium catalyst. Highly dispersed particles of palladium on charcoal blend with aluminium chloride particles, and this mechanical mixture gets processed in a lowtemperature plasma reactor in a hydrogen flow at the temperature of up to 2·104 К. A higher dispersion degree of the catalyst particles is associated with a higher yield of aluminium hydride. The concentration of palladium on charcoal mixed with aluminium chloride aimed at enhancing the formation of aluminium hydride should not exceed 2%, as any further increase in the catalyst concentration does not benefit the AlH3 yield but rather affect it. This can be attributed to the fact that once a certain catalyst concentration has been reached, the slow stage of the heterogeneous catalytic reaction between hydrogen and aluminium chloride particles involves Н2 absorption on their surface, where the presence of catalyst has no effect on the reaction rate. The plasma chemical reaction between hydrogen and aluminium chloride particles in the presence of palladium catalyst results in the formation of aluminium hydrides with an orthorhombic structure. It was found that the rate of the catalytic reaction tends to rise as the aluminium hydride layer forms. This can be attributed to the fact that the AlH3 formed acts as a catalyst. The catalytic effect of aluminium hydride was proved by plasma chemical reduction of cobalt from its oxides in the presence of elemental sulphur. An aluminium-cobalt mixture gets formed as a result.

High-entropy alloys as anode materials of nickel - metal hydride batteries

High-entropy alloys are potential candidates for various applications including hydrogen storage in the hydride form and energy storage in batteries. This study employs HEAs as new anode materials for nickel - metal hydride (Ni-MH) batteries. The TixZr2-xCrMnFeNi alloys with different Ti/Zr ratios, having the C14 Laves structure, are used. These alloys are selected because they show room-temperature hydriding/dehydriding capability. The HEAs successfully act as negative electrode of Ni-MH batteries with good charge/discharge cyclability, while there are optimum Ti/Zr ratios for the highest storage capacity and the fastest activity. These findings introduce HEAs as potential anode materials for Ni-MH battery application.