Deflagration characteristics of freely propagating flames in magnesium hydride dust clouds

The flame propagation processes of MgH_(2)dust clouds with four different particle sizes were recorded by a high-speed camera.The dynamic flame temperature distributions of MgH_(2)dust clouds were reconstructed by the two-color pyrometer technique,and the chemical composition of solid combustion residues were analyzed.The experimental results showed that the average flame propagation velocities of 23μm,40μm,60μm and 103μm MgH_(2)dust clouds in the stable propagation stage were 3.7 m/s,2.8 m/s,2.1 m/s and 0.9 m/s,respectively.The dust clouds with smaller particle sizes had faster flame propagation velocity and stronger oscillation intensity,and their flame temperature distributions were more even and the temperature gradients were smaller.The flame structures of MgH_(2)dust clouds were significantly affected by the particle sinking velocity,and the combustion processes were accompanied by micro-explosion of particles.The falling velocities of 23μm and 40μm MgH_(2)particles were 2.24 cm/s and 6.71 cm/s,respectively.While the falling velocities of 60μm and 103μm MgH_(2)particles were as high as 15.07 cm/s and 44.42 cm/s,respectively,leading to a more rapid downward development and irregular shape of the flame.Furthermore,the dehydrogenation reaction had a significant effect on the combustion performance of MgH_(2)dust.The combustion of H_(2)enhanced the ignition and combustion characteristics of MgH_(2)dust,resulting in a much higher explosion power than the pure Mg dust.The micro-structure characteristics and combustion residues composition analysis of MgH_(2)dust indicated that the combustion control mechanism of MgH_(2)dust flame was mainly the heterogeneous reaction,which was affected by the dehydrogenation reaction.

Recent progress in thermodynamic and kinetics modification of magnesium hydride hydrogen storage materials

Hydrogen energy has emerged as a pivotal solution to address the global energy crisis and pave the way for a cleaner,low-carbon,secure,and efficient modern energy system.A key imperative in the utilization of hydrogen energy lies in the development of high-performance hydrogen storage materials.Magnesium-based hydrogen storage materials exhibit remarkable advantages,including high hydrogen storage density,cost-effectiveness,and abundant magnesium resources,making them highly promising for the hydrogen energy sector.Nonetheless,practical applications of magnesium hydride for hydrogen storage face significant challenges,primarily due to their slow kinetics and stable thermodynamic properties.Herein,we briefly summarize the thermodynamic and kinetic properties of MgH2,encompassing strategies such as alloying,nanoscaling,catalyst doping,and composite system construction to enhance its hydrogen storage performance.Notably,nanoscaling and catalyst doping have emerged as more effective modification strategies.The discussion focuses on the thermodynamic changes induced by nanoscaling and the kinetic enhancements resulting from catalyst doping.Particular emphasis lies in the synergistic improvement strategy of incorporating nanocatalysts with confinement materials,and we revisit typical works on the multi-strategy optimization of MgH2.In conclusion,we conduct an analysis of outstanding challenges and issues,followed by presenting future research and development prospects for MgH2 as hydrogen storage materials.

Unveiling a novel metal-to-metal transition in LuH_(2):Critically challenging superconductivity claims in lutetium hydrides

Following the recent report by Dasenbrock-Gammon et al.[Nature 615,244–250(2023)]of near-ambient superconductivity in nitrogendoped lutetium trihydride(LuH_(3-δ)N_(ε)),significant debate has emerged surrounding the composition and interpretation of the observed sharp resistance drop.Here,we meticulously revisit these claims through comprehensive characterization and investigations.We definitively identify the reported material as lutetium dihydride(LuH_(2)),resolving the ambiguity surrounding its composition.Under similar conditions(270–295 K and 1–2 GPa),we replicate the reported sharp decrease in electrical resistance with a 30%success rate,aligning with the observations by Dasenbrock-Gammon et al.However,our extensive investigations reveal this phenomenon to be a novel pressure-induced metal-to-metal transition intrinsic to LuH_(2),distinct from superconductivity.Intriguingly,nitrogen doping exerts minimal impact on this transition.Our work not only elucidates the fundamental properties of LuH_(2)andLuH_(3),but also critically challenges the notion of superconductivity in these lutetium hydride systems.These findings pave the way for future research on lutetium hydride systems,while emphasizing the crucial importance of rigorous verification in claims of ambient-temperature superconductivity.

Phase-field simulations of the effect of temperature and interface for zirconiumδ-hydrides

Hydride precipitation in zirconium cladding materials can damage their integrity and durability.Service temperature and material defects have a significant effect on the dynamic growth of hydrides.In this study,we have developed a phasefield model based on the assumption of elastic behaviour within a specific temperature range(613 K-653 K).This model allows us to study the influence of temperature and interfacial effects on the morphology,stress,and average growth rate of zirconium hydride.The results suggest that changes in temperature and interfacial energy influence the length-to-thickness ratio and average growth rate of the hydride morphology.The ultimate determinant of hydride orientation is the loss of interfacial coherency,primarily induced by interfacial dislocation defects and quantifiable by the mismatch degree q.An escalation in interfacial coherency loss leads to a transition of hydride growth from horizontal to vertical,accompanied by the onset of redirection behaviour.Interestingly,redirection occurs at a critical mismatch level,denoted as qc,and remains unaffected by variations in temperature and interfacial energy.However,this redirection leads to an increase in the maximum stress,which may influence the direction of hydride crack propagation.This research highlights the importance of interfacial coherency and provides valuable insights into the morphology and growth kinetics of hydrides in zirconium alloys.

Understanding the catalysis of chromium trioxide added magnesium hydride for hydrogen storage and Li ion battery applications

This study explores how the chemical interaction between magnesium hydride(MgH_(2))and the additive CrO_(3) influences the hydrogen/lithium storage characteristics of MgH_(2).We have observed that a 5 wt.%CrO_(3) additive reduces the dehydrogenation activation energy of MgH_(2) by 68 kJ/mol and lowers the required dehydrogenation temperature by 80℃.CrO_(3) added MgH_(2) was also tested as an anode in an Li ion battery,and it is possible to deliver over 90%of the total theoretical capacity(2038 mAh/g).Evidence for improved reversibility in the battery reaction is found only after the incorporation of additives with MgH_(2).In depth characterization study by X-ray diffraction(XRD)technique provides convincing evidence that the CrO_(3) additive interacts with MgH_(2) and produces Cr/MgO byproducts.Gibbs free energy analyses confirm the thermodynamic feasibility of conversion from MgH_(2)/CrO_(3) to MgO/Cr,which is well supported by the identification of Cr(0)in the powder by X ray photoelectron spectroscopy(XPS)technique.Through high resolution transmission electron microscopy(HRTEM)and energy dispersive spectroscopy(EDS)we found evidence for the presence of 5 nm size Cr nanocrystals on the surface of MgO rock salt nanoparticles.There is also convincing ground to consider that MgO rock salt accommodates Cr in the lattice.These observations support the argument that creation of active metal–metal dissolved rock salt oxide interface may be vital for improving the reactivity of MgH_(2),both for the improved storage of hydrogen and lithium.

Properties of radiation defects and threshold energy of displacement in zirconium hydride obtained by new deep-learning potential

Zirconium hydride(ZrH_(2)) is an ideal neutron moderator material. However, radiation effect significantly changes its properties, which affect its behavior and the lifespan of the reactor. The threshold energy of displacement is an important quantity of the number of radiation defects produced, which helps us to predict the evolution of radiation defects in ZrH_(2).Molecular dynamics(MD) and ab initio molecular dynamics(AIMD) are two main methods of calculating the threshold energy of displacement. The MD simulations with empirical potentials often cannot accurately depict the transitional states that lattice atoms must surpass to reach an interstitial state. Additionally, the AIMD method is unable to perform largescale calculation, which poses a computational challenge beyond the simulation range of density functional theory. Machine learning potentials are renowned for their high accuracy and efficiency, making them an increasingly preferred choice for molecular dynamics simulations. In this work, we develop an accurate potential energy model for the ZrH_(2) system by using the deep-potential(DP) method. The DP model has a high degree of agreement with first-principles calculations for the typical defect energy and mechanical properties of the ZrH_(2) system, including the basic bulk properties, formation energy of point defects, as well as diffusion behavior of hydrogen and zirconium. By integrating the DP model with Ziegler–Biersack–Littmark(ZBL) potential, we can predict the threshold energy of displacement of zirconium and hydrogen in ε-ZrH_(2).

Magnesium nickel hydride monocrystalline nanoparticles for reversible hydrogen storage

Although Mg-based hydrides are extensively considered as a prospective material for solid-state hydrogen storage and clean energy carriers,their high operating temperature and slow kinetics are the main challenges for practical application.Here,a Mg-Ni based hydride,Mg_(2)NiH_(4) nanoparticles(~100 nm),with dual modification strategies of nanosizing and alloying is successfully prepared via a gas-solid preparation process.It is demonstrated that Mg_(2)NiH_(4) nanoparticles form a unique chain-like structure by oriented stacking and exhibit impressive hydrogen storage performance:it starts to release H2 at~170℃ and completes below 230℃ with a saturated capacity of 3.32 wt%and desorbs 3.14 wt% H_(2) within 1800 s at 200℃.The systematic characterizations of Mg_(2)NiH_(4) nanoparticles at different states reveal the dehydrogenation behavior and demonstrate the excellent structural and hydrogen storage stabilities during the de/hydrogenated process.This research is believed to provide new insights for optimizing the kinetic performance of metal hydrides and novel perspectives for designing highly active and stable hydrogen storage alloys.

Hydrogen desorption kinetics mechanism of Mg-Ni hydride under isothermal and non-isothermal conditions

The Mg-Ni hydride was prepared by hydriding combustion synthesis under a high magnetic field. The dehydriding kinetics of the hydrides was measured under the isothermal and non-isothermal conditions. A model was applied to analyzing the kinetics behavior of Mg-Ni hydride. The calculation results show that the theoretical value and the experimental data can reach a good agreement, especially in the case of non-isothermal dehydriding. The rate-controlling step is the diffusion of hydrogen atoms in the solid solution. The sample prepared under magnetic field of 6 T under the isothermal condition can reach the best performance. The similar tendency was observed under the non-isothermal condition and the reason was discussed.

Properties of hydrogen permeation barrier on the surface of zirconium hydride

A hydrogen permeation barrier was manufactured by the in situ reaction of zirconium hydride with oxygen. A reduction in the hydrogen permeation of the oxide films was detected by measuring the mass difference of the zirconium hydride samples after the dehydrogenation experiment. The reaction of zirconium hydride with oxygen occurs only under the condition that the temperature is higher than 673 K in the oxygen partial pressure of 0.1 MPa. The oxide film is composed of two layers, a permeable oxide layer and a dense oxide layer, and the main phase of the oxide film is ZrO2 with baddeleyite structure. The XPS analysis shows that O-H bonds exist in the oxide film, which are helpful for resisting hydrogen diffusion through the oxide film.

Degradation Behavior of Electrochemical Performance of Sealed-Type Nickel/Metal Hydride Batteries

The degradation mechanism of electrochemical performance of sealed type nickel/metal hydride batteries was investigated. The results indicate that the degradation behavior of Ni/MH battery is not only owing to the lack of electrolyte, but also the deterioration of the active materials on the positive and negative electrodes of Ni/MH batteries. Scanning electron micrographs (SEM), X ray diffraction (XRD) and laser granularity analyses are presented. The particle pulverization and oxidation during charge/discharge are identified as the main causes for deterioration of the negative and positive electrode in nickel/metal hydride batteries, as well as the cross section cracking of both anode and cathode.

Laves phase hydrogen storage alloys for super-high-pressure metal hydride hydrogen compressors

Ti-Cr- and Ti-Mn-based alloys were prepared to be low- and high-pressure stage metals for a double-stage super-high-pressure metal hydride hydrogen compressor. Their crystallographic characteristics and hydrogen storage properties were investigated. The alloy pair Ti0.9Zr0.1Mn1.4- Cr0.35V0.2Fe0.05/TiCr1.55Mn0.2Fe0.2 was optimized based on the comprehensive performance of the studied alloys. The product hydrogen with a pressure of 100 MPa could be produced from 4 MPa feed gas when hot oil was used as a heat reservoir.

Hydride vapor phase epitaxy for gallium nitride substrate

Due to the remarkable growth rate compared to another growth methods for gallium nitride(GaN)growth,hydride vapor phase epitaxy(HVPE)is now the only method for mass product GaN substrates.In this review,commercial HVPE systems and the GaN crystals grown by them are demonstrated.This article also illustrates some innovative attempts to develop homebuilt HVPE systems.Finally,the prospects for the further development of HVPE for GaN crystal growth in the future are also discussed.

Preparation and Properties of Zirconium Hydrideon the surface of MCM-41 Mesoporous Molecular Sieves

Zirconium monohydride bonded to the framework oxygen of MCM-41 surface was prepared by the reaction of tetraneopentyl zirconium with MCM-41 surface hydroxyl groups, followed by the hydrogenolysis of the resulted product. The surface hydride was characterized by using infrared spectroscopy, solid-state NMR, elemental analysis, gas-phase chromatography and chemical probing reaction. It was shown that this surface species is stable below 150 ’C and can catalytically crack alkanes into methane and ethane at 100 .

Enhanced dehydrogenation performances and mechanism of LiBH_4/Mg_(17)Al_(12)-hydride composite

Mg17Al12-hydride （abbreviated as MAH） was selected as a destabilization agent to improve de/rehydrogenation properties of LiBH4. 58LiBH4＋Mg17Al12-hydride composite was prepared by ball-milling. It is found that the dehydrogenation of ball-milled LiBH4/MAH composite presents a two-step reaction for hydrogen release. The composite starts desorbing hydrogen at about 300 ℃ and yields 9.8%of hydrogen （mass fraction） below 500 ℃. By adding MAH, the dehydrogenation kinetics of LiBH4 is improved and the dehydrogenation temperature of LiBH4 is also lowered by 20 ℃. High rehydriding capacity of 8.3% was obtained for the dehydrogenated composite in the first cycle at 450 ℃. The XRD analysis shows the formation of MgB2 and AlB2 in the dehydrogenation process, which reduces the thermodynamics stability of LiBH4 system and is beneficial to the reversible hydrogen storage behaviors of LiBH4/MAH composite.

Growth and doping of bulk GaN by hydride vapor phase epitaxy

Doping is essential in the growth of bulk GaN substrates,which could help control the electrical properties to meet the requirements of various types of GaN-based devices.The progresses in the growth of undoped,Si-doped,Ge-doped,Fedoped,and highly pure GaN by hydride vapor phase epitaxy(HVPE) are reviewed in this article.The growth technology and precursors of each type of doping are introduced.Besides,the influence of doping on the optical and electrical properties of GaN are presented in detail.Furthermore,the problems caused by doping,as well as the methods to solve them are also discussed.At last,highly pure GaN is briefly introduced,which points out a new way to realize high-purity semi-insulating(HPSI) GaN.

Kinetics and mechanism of titanium hydride powder and aluminum melt reaction

Based on the measurement of the released hydrogen gas pressure （PH2）, the reaction kinetics between TiH2 powder and pure aluminum melt was studied at various temperatures. After cooling the samples, the interface of TiH2 powder and aluminum melt was studied. The results show that the-time curves have three regions; in the first and second regions, the rate of reaction conforms zero and one order, respectively; in the third region, the hydrogen gas pressure remains constant and the rate of reaction reaches zero. The main factors that control the rate of reaction in the first and second regions are the penetration of hydrogen atoms in the titanium lattice and the chemical reaction between molten aluminum and titanium, respectively. According to the main factors that control the rate of reaction, three temperature ranges are considered for the reaction mechanism： （a） 700-750°C, （b） 750-800°C, and （c） 800-1000°C. In the first temperature range, the reaction is mostly under the control of chemical reaction; at the temperature range of 750 to 800°C, the reaction is controlled by the diffusion and chemical reaction; at the third temperature range （800-1000°C）, the dominant controlling mechanism is diffusion.

Some Rare Earth Metallic Organohydrides with Biindenyl as the Ligand

Introduction It is well known that organometallic hydrides of rare earth metals are the catalysts and reducing reagents for the catalysis polymerization of alkenes and the catalysis hydrogenation of alkenoalkynes. There are four methods for the syntheses of organometallic hydrides of rare earth metals:（1） the thermal atomization of metals, i.e., the interaction of a rare earth metal with alkenes with a terminal alkyne;（2） the Ln—Cσ bond is broken with H;;（3） metal-

Determination of total arsenic by photo-decomposition of organoarsenic compounds and hydride generation electrothermal atomic absorption spectrometry

A method was developed for the determination of total arsenic concentration in less than ng/ml level by decomposition of organoarsenicals using photo -oxidation combined with in situ trapping of arsenic hydride on a palladium coated graphite tube with subsequent atomization and detection by AAS. The organoarsenicals include monomethylarsenic, dimethylarsenic, arsenobetaine, arsenocholine, o -aminobenzenarsenate and p -aminobenzenarsenate. The method is simple and sensitive. Detection limit was obtained from different arsenic compounds over the range from 0. 058 to 0.063 ng/ml as As (based on three times of the standard deviation of 10 blank measurements) and the relative standard deviations for ten replicate measurements were from 2.0 to 3.8%. The calibration curves of arsenic compounds including inorganic and organic arsenicals were linear over the range from 0.1 to 3.0 ng/ml as As. The recommended method has been applied to the determination of total arsenic in tap and lake water samples at ng/ml levels.

Superconductivity of Lanthanum Superhydride Investigated Using the Standard Four-Probe Configuration under High Pressures

Recently,the theoretically predicted lanthanum superhydride,LaH 10±δ,with a clathrate-like structure was successfully synthesized and found to exhibit a record high superconducting transition temperature T c≈250 K at∼170 GPa,opening a new route for room-temperature superconductivity.However,since in situ experiments at megabar pressures are very challenging,few groups have reported the∼250 K superconducting transition in LaH 10±δ.Here,we establish a simpler sample-loading procedure that allows a relatively large sample size for synthesis and a standard four-probe configuration for resistance measurements.Following this procedure,we successfully synthesized LaH 10±δwith dimensions up to 10×20μm^2 by laser heating a thin La flake and ammonia borane at∼1700 K in a symmetric diamond anvil cell under the pressure of 165 GPa.The superconducting transition at T c≈250 K was confirmed through resistance measurements under various magnetic fields.Our method will facilitate explorations of near-room-temperature superconductors among metal superhydrides.

Desorption behaviour and microstructure change of nanostructured hydrided AZ31 Mg alloy powders

In order to optimize the dehydriding process for producing nanocrystalline Mg alloy powders by hydriding-dehydriding treatment,nano-structured as-hydrided Mg-3%Al-1%Zn(AZ31 Mg)(mass fraction)alloy powders were thermally dehydrided at various temperatures from 275 to 375℃.The kinetics of hydrogen desorption was examined by hydrogen discharge measurement during dehydriding.The microstructure of the as-hydrided and the subsequently fully dehydrided alloy powders was investigated by X-ray diffraction analysis(XRD)and transmission electron microscopy(TEM),respectively.Both the desorption kinetics and the grain size of the alloy after complete dehydriding were found to be strongly dependent on the processing temperature.The higher the temperature,the faster the desorption,and the more significant the grain growth.When the desorption temperature was raised from 300 to 375℃,the time to achieve complete dehydriding was shortened from 190 to 20 min,and the average grain size increased correspondingly from 20 to 58 nm.