Hydride Alloys Research Articles

Advance in and prospect of moderator materials for space nuclear reactors

Since 1960s, many countries led by the United States and Russia have done a lot of research on space nuclear reactor power. Moderator is an important functional component in a nuclear reactor operating with a thermal neutron spectrum. This paper reviews the moderation principle, main existing problems, research status as well as main challenges ahead and possible solutions of moderator materials in space nuclear reactor. Aiming at the problems of hydrogen cracking, the low utilization rate of nuclear fuel and hydrogen loss of moderator materials, the assumption of using high entropy alloy hydride as a moderator material is put forward. Moreover, this paper also points out the metal elements suitable for nuclear reactor, while discussing the advantages and disadvantages of several typical elements, hoping to provide a reference for the selection and fabrication of moderator materials. Highlights Sketch the moderating mechanism and the moderator selection principle. Summarize the problems and solutions in the preparation of metal hydride. Summarize the application status of zirconium hydride and yttrium hydride moderator materials. Predict the future development trend and feasible methods of moderator materials.

Modeling of the microstructural behavior of hydrided zirconium alloys

A multiphase microstructural system of two types of hydrides; f.c.c. δ and b.c.c.. e hydride precipitates within a parent h.c.p. zircaloy-4 parent matrix were modelled by a crystalline dislocation-density and a finite-element (FE) method that is specialized for large inelastic strains and nonlinear behavior. The different crystalline structure of the hydrides, the parent matrix, and the orientation relationships between the different crystalline phases have been accounted for and modeled with a validated FE approach. The effects of radial hydride factors, hydride volume fraction, hydride morphology, and hydride orientation and distribution on overall behavior were investigated. The predictions provide an understanding of why a distribution of circumferential hydrides have higher strength and ductility than a distribution of radial hydrides. Furthermore, zircaloy δ (f.c.c.) hydride systems have less ductility and strength than the zircaloy e (b.c.c.) systems.

Hydrogen storage and electrochemical properties of annealed low-Co AB5 type intermetallic compounds

The structure, hydrogen storage and electrochemical properties of annealed low-Co AB5-type intermetallic compounds have been investigated. La-alloy, Nd-alloy and Cr-alloy are used to represent La0.8Ce0.2Ni4Co0.4Mn0.3Al0.3, La0.6Ce0.2Nd0.2Ni4Co0.4Mn0.3Al0.3 and La0.6Ce0.2Nd0.2Ni3.8Co0.4Mn0.3Al0.3Cr0.2, respectively. The XRD results indicated that annealed samples are all single-phase alloys with CaCu5 type structure. The maximum of both hydrogen content and discharge capacity is obtained for La-alloy 1.23 wt%H2 and 321.1 mA h/g, respectively. All the investigated alloys are quiet stable with ΔH of hydrogen desorption about 36–38 kJ/mol H2. Cycle life of alloy electrode has been improved by partial substitution of La for Nd and Ni for Cr. The highest capacity retention of 92.2% after 100 charge/discharge cycles at 1C has been observed for Nd-alloy. The hydrogen diffusion coefficient measured by PITT is higher at the start of charging process and dramatically reduces by 2–3 order of magnitude with saturation of β-hydride. The highest value 6.9 × 10−13 cm2/s is observed for La alloy at 100% SOC. Partial substitution La for Nd and Cr for Ni in low-Co AB5 metal hydride alloys slightly reduces maximum discharge capacity, HRD performance and hydrogen diffusion kinetics. Low-Co alloys show good overall electrochemical properties compared to high-Co alloys and might be perspective materials for various electrochemical applications.

Obtention of Nb47Ti and Ti13Nb13Zr Alloys Powders by Hydride-Dehydride Process for Additive Manufacturing Applications

In this work, the hydride-dehydride process (HDH) parameters to obtain Nb47Ti and Ti13Nb13Zr alloys powders were investigated, aiming the production of orthopedic implants by additive manufacturing (AM). Nb47Ti and Ti13Nb13Zr alloys were previously obtained by electron beam melting furnace (EBMF). During the hydriding step, the alloys were heated at two activation temperatures, 800 and 1000 °C, under constant hydrogen pressure (1.8 bar), for 40 min followed by a controlled cooling rate step (2 °C/min). The hydride alloys were milled in a ring-type mill, for milling times ranging from 2 to 6 min, until to achieve the required particle size range (between 15 and 45 μm). The dehydriding step of the alloys was carried out under high vacuum at 700 °C for times up to 5 h. The alloys treated under distinct HDH steps were characterized by X-ray diffraction, scanning electron microscopy, dynamic image analysis, inert gas fusion and gravimetry. The alloys hydrides (δTiHx phase) were detected in both investigated activation temperatures, with hydrogen (H) contents up to 3.04 and 3.62 wt.% for the Nb47Ti and Ti13Nb13Zr alloys, respectively. During the hydriding step it was also observed a significant increase of nitrogen (N) and oxygen (O) contents regarding he as-cast alloys. The Nb47Ti alloy showed a lower embrittlement degree than the Ti13Nb13Zr alloy, resulting in higher milling times to reach the required particle size distribution. The higher oxygen pick up was observed during the milling step. After the dehydriding step, the HDH powders showed H contents lower than 0.01 wt.%, beside a significant N decreasing. Particles with irregular (or angular) shapes were obtained. However, the particle size was in the required range.

Optimized Tin Bismuth Alloy Modified with Silver Vanadate Nanorods Prepared via Powder Metallurgy: Search for Biomedical Application

In this study, a new bismuth tin eutectic alloy and other samples of the same composition doped with variable concentration of silver vanadate nanorods were prepared using new route powder metallurgy. X-ray diffraction of prepared silver vanadate approves the formation of  phase silver vanadate (-AgVO3). Transmission electron microscopy shows the formation of AgVO3 nanorods of radius ranging (20-40 nm). X-ray diffraction of alloys doped with silver vanadate and mechanical tests show that hardness and creep behavior data are composition-dependent parameters with silver vanadate content. Antimicrobial tests against pathogenic grams, fungi, and yeast showed that the addition of silver vanadate nanorods stimulates the action of hydride alloy and increases their activity against bacterial strains. In hospitals, biomedical devices may contaminate infection; doping devices with nanoparticles may make it auto clean besides conserving its mechanical properties.

Effects of yttrium doping on helium behavior in zirconium hydride films

The zirconium hydride alloy films with different yttrium concentration were prepared by magnetron sputtering and studied using ion beam analysis (IBA), X-ray diffraction (XRD), thermal desorption spectrometry (TDS), positron annihilation spectroscopy (PAS) and nanoindentation. It was found that the yttrium atom, which is originally insoluble in zirconium metal, can largely dissolve in the zirconium hydride matrix through the introduction of hydrogen. The helium thermal desorption experiment shows that as the doped amount of yttrium atoms increases, a large number of helium atoms will be released in the form of helium bubbles at the grain boundaries in the matrix at ca. 900K. Combined with XRD results, it is concluded that as the yttrium atoms are introduced, more grain boundaries will form in the zirconium hydride matrix. These grain boundaries act as crystal defects, which have a strong trapping effect on helium atoms, causing a large number of helium bubbles to aggregate at the grain boundaries in the matrix. In addition, it is noteworthy that yttrium doping can increase the hardness and elastic modulus of zirconium hydride.

Study of hydrogen storage properties of oxygen modified Ti- based AB2 type metal hydride alloy

A multi component AB2 type hydrogen storage intermetallic alloy (A = Ti0.85Zr0.15, B2 = Mn1.22Ni0.22Cr0.2V0.3Fe0.06; was investigated in this work. The intermetallic specified above was modified by oxygen to yield the composition AB2O0.05. The oxygen was introduced by adding TiO2 to the charge, with corresponding decrease of the Ti amount, followed by arc melting and annealing at the same conditions as for the oxygen free AB2-type alloy. The addition of oxygen to the alloy did not change much the PCT properties; the only difference was that the plateau pressure for the oxygen-modified alloy increased slightly. Both alloys have shown to be excellent candidates for H2 storage, particularly for utility vehicles, due to their relatively high reversible H2 storage capacity (1.6 wt%) and low plateau pressure at room temperature (<5 bar). The addition of oxygen improved hydrogen absorption kinetics in the AB2 alloy allowing it to immediately absorb H2 without activation while for the non-modified sample an incubation period (30 min) was observed at the same conditions.

Direct reduction of upgraded titania slag by magnesium for making low-oxygen containing titanium alloy hydride powder

Upgraded titania slag (UGS) is a titanium-rich material with over 90 wt% titanium dioxide and some minor elements such as Fe, Al, Cr, and Si, which is mainly used for preparing TiO2 and TiCl4. In this study, UGS was directly reduced with magnesium powder in a hydrogen atmosphere. Titanium alloy hydride powder with the oxygen content of 0.032 wt% was obtained. The minor elements of Fe, Si, Al, and Cr from the UGS were kept in the final powder with the main phase of TiH1.924(δ), and minor intermetallic phases of HFe2Ti, Ti5Si3H0.9 and Cr1.8TiH5.3. EDS elemental mapping results indicated that HFe2Ti and Ti5Si3H0.9 intermetallics formed bright phase islands in the matrix. The reduction mechanism and the reaction sequence were discussed based on the thermodynamic modelling with the assistance of HSC chemistry software. The possibility of hydrogen reduction of titanium oxides was discussed as well.

High-capacity Zr-based AB2-type alloys as metal hydride battery anodes

This work focused on the structural and electrochemical properties of AB2-type Zr/Ti-based metal hydride anode alloys. The as-cast and annealed Ti0·24Zr0·76Ni1·1Mn0·7V0.2 alloys were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and electrochemical characterization (EC). X-ray diffraction (XRD) results indicated the presence of homogenous C14 Laves phase in the annealed alloy, and the major C15 and C14 phases coexisted with the TiNi and Zr9Ni11 secondary phases in the as-cast alloy. SEM images showed the phase compositions in these alloys and confirmed the significant decrease in the secondary phases of the annealed alloy. During EC, the as-cast alloy showed better activation performance than the annealed alloy. This result was related to the catalytic effect of the Ti-/Zr-related secondary phases during electrochemical reactions. Annealing increased the maximum discharge capacity from ∼350 mAh/g for the as-cast alloy to ∼400 mAh/g for the annealed alloy during activation. The annealed alloy also showed considerable cycling stability and a slightly high discharge rate. We developed a C14-Laves phase metal hydride alloy showing a discharge capacity ∼400 mAh/g at a 100 mA/g rate (C/4) suitable for electric vehicle (EV) application.

The impact of metal hydride material activation to storage percentage of hydrogen in this material

Currently, a lot of focus is dedicated to metal hydride alloy and options of their utilization. Mankind must solve energy problems due to constant population growth and use of non-renewable energy sources. The World resources of oil are limited and therefore the mankind must start utilizing the alternative energy sources for example hydrogen. Its known that the hydrogen can be stored by metal hydride alloys what it represents the safety way of storage with absence high pressure and temperature. The process by produce of the alloy with good absorption properties the research does not end. Some alloy absorbs the hydrogen after they produce immediately, however a lot of them need the activation for improvement or starting absorption process. Process of activation is very important for achieving the maximum capacity at moderate temperature.

A Review of Hydride Precipitates in Titanium and Zirconium Alloys: Precipitation, Dissolution and Crystallographic Orientation Relationships

This work proposes a review of recent results on the formation and dissolution of hydrides in HCP alloys (Ti and Zr alloys) correlated to the nature of crystallographic hydride phases and their ORs. The crystallographic coherence observed between the surface hydride layer and the substrate is very important for many applications as for biomaterials devices. Five particular orientation relationships (OR) were identified between titanium/zirconium hydride precipitates and the oc-Ti and a-Zr substrates. In addition, the nature of hydrides have a large implication on the ductility, the strain hardening, and the local plastic strain accommodation in the Ti alloys. Our studies using XDR, TEM and SEM-EBSD have been demonstrating that the nature of the hydride phase precipitates depends on the hydrogen content. DSC has been used to obtain the hydride dissolution and precipitation energy values at the bulk scale, whose difference can be associated to misfit dislocations. Local in-situ TEM dissolution observations show the depinning of part of misfit dislocations during dissolution process. Hydride reprecipitation is thus possible only if hydrogen is not driven away during heating by misfit dislocations depinning.

Analysis of Heat Balance of MH Separator

The paper deals with the thermal balance of a metal hydride separator, primarily a tank containing a metal hydride alloy subjected to heating and cooling processes caused by absorption and desorption. As during the equipment operation it is necessary to ensure heating and cooling, the amount of the required heat to be supplied and removed must be identified. The article also deals with hydrogen separation from undesired components of synthetic gas which is formed in a plasma reactor during the waste gasification process.

Study of ion spectra of a vacuum Arc ion source with titanium-nickel alloy hydride cathode

An experimental study of the ion charge state distribution and mass-charge component of vacuum arc discharging with titanium-nickel alloy hydride by the time-of-flight method is carried out. The study shows that the charging states of titanium ion and nickel ion are 1+, 2+, and 3+. Besides, in the early stage of the discharging process (0–30 μs), the proportion of H+ gradually increases with time and reaches a maximum ratio of 57% at 30 μs, the proportion of Tin+ and Nin+ (n = 1,2,3) gradually decreases with time and reaches a minimum ratio of 43% at 30 μs; In the later stage of the discharging process (30 μs-270 μs), the proportion of H+ begins to decrease rapidly and remains unchanged at around 12% during the period spanning from 75 μs to 270 μs; the proportion of Tin+ and Nin+ (n = 1, 2, 3) gradually increases with time and remains around 88% from 75 μs to 270 μs.

Chemisorption-repulsion energies of H2 on surface (110) of Mg1-xMx alloys (M = Al, Ni, Zn; 0.0 ≤ x ≤ 0.20) as a function of temperature.

In recent years, the popularity of metal hydrides has increased considerably for hydrogen storage and their applications in hydrogen fuel cells. Their potential applications for clean energy are promissory. However, the temperatures required for adsorption and desorption are extremely high, which range between 500 and 700K, making their use impractical. To overcome these difficulties, the following work considers using three hydride alloys: magnesium-aluminum (MgAl), magnesium-nickel (MgNi), and magnesium-zinc (MgZn). The Mg concentrations were set to be between 80 and 100wt% in order to reduce the temperatures of adsorption and desorption in contrast with the temperatures of pure magnesium. The chemisorption and repulsion energies of the hydrogen molecule on the surface (110) of the different metallic alloys were studied at 0, 200, 400, 600, and 700K, respectively. The study was based on the density functional theory (DFT), with the module DMol3 of the molecular simulation program Materials Studio, which was used to obtain these energy values. The results confirm that adding aluminum, nickel, or zinc into magnesium matrix increases the chemisorption and decreases the energy repulsion values on surfaces of the metallic alloys, improving the effectiveness of the hydrogen storage.

Path integral study on C15-type Laves TiCr2 hydride

The path integral method has been applied for the C15-type Laves alloy hydride, TiCr2H1.3, to treat quantum mechanical effects on atomic nuclei. The atomic interaction is simulated by the machine learning potential which reproduces well the results of density functional calculations. The canonical ensemble is sampled using the hybrid Monte Carlo method at 300 K. The predicted heat of solution, −19 kJ/mol H2, agrees well with the available experimental data. Hydrogen atoms dominantly occupy the 96g sites which form the closed hexagonal rings (HRs). Two H diffusion paths, the intra- and inter-HR paths, are identified, for which the activation barriers are evaluated to be 63 and 155 meV, respectively. They most likely correspond to different two H hopping modes assigned in the nuclear magnetic resonance experiment.

Elaboration of Chemical Hydrogen Source Based on Hydrides of Magnesium Alloys

In the present work, Mg–Ni–Mm alloys (where Mm is a mixture of rare earth metals) are studied to elaborate a chemical hydrogen source for portable energy systems based on fuel cells characterized by high gravimetric energy density used for unmanned air vehicles and robot systems. Hydrogen generation on demand by hydrolysis of metal hydrides (MgH2, Mg2NiH4) is proposed for the fuel cell power supply because it is the most efficient method characterized by high hydrogen storage density, safety, and low costs of the stored energy. The influence of the composition of alloys on the hydrogen absorption properties and hydrogen generation during hydrolysis is studied.

Catalytic enhanced hydrogen storage properties of Mg-based alloy by the addition of reduced graphene oxide supported V2O3 nanocomposite

A reduced graphene oxide (rGO)-supported V2O3 was synthesized via an impregnation method and then introduced (through mechanical milling) into the Mg85Al15 alloy. The results indicated that the combined effect of V2O3 and rGO played an important role in destabilizing the stability of Mg85Al15 alloy hydrides. When absorbed 1.0 wt% of H2, it was needed to heat the bare alloy to 220 °C at a rate of 2 °C·min−1. This temperature dropped to 181 °C and 192 °C, respectively, when V2O3 and rGO were used separately as catalysts. The temperature further decreased to 155 °C under the combined effect of V2O3 and rGO. At 250 °C, a complete reversible hydrogenation/dehydrogenation process occurred only in the Mg85Al15+V2O3 and Mg85Al15+V2O3@rGO samples. After the alloy was composited with V2O3@rGO, the apparent activation energy for hydrogen absorption/desorption decreased from 80.1 kJ mol−1/173.2 kJ mol−1 to 61.6 kJ mol−1/91.3 kJ mol−1, respectively.

Effects of lithium addition in AB2 metal hydride alloy by solid-state diffusion

In this study, microstructures and electrochemical properties of a Zr-based AB2-type metal hydride alloy (Ti12.1Zr21.3V10.5Cr7.5Mn8.1Co8.0Ni31.7Al0.8) doped with 6 wt% LiH by solid-state diffusion at different temperatures were investigated and compared with those of the base alloy sintered at the same conditions. Structural study by x-ray diffraction analysis exhibited a lattice expansion in the main C14 phase of the Li-doped alloys with a relatively low sintering temperature, indicating that Li incorporated into the C14 Laves phase but was evaporated at higher sintering temperatures. Addition of Li deteriorated both the electrochemical capacity and activation easiness; however, it improved the high-rate dischargeability (HRD). The benefit of Li addition on HRD can be associated with the increase in amount of metallic nickel clusters embedded in the surface oxide (estimated by the saturated magnetic susceptibility) and was a strong function of sintering temperature. As the sintering temperature increased, HRD increased due to the increase in amount of surface catalytic metallic nickel.

Capacity degradation of Laves phase-related body-centered-cubic solid solution metal hydride alloys in battery

The nickel/metal hydride (Ni/MH) is a good example of using metal hydride alloy which is cable of reversely storing the hydrogen energy in an electrochemical environment. The failure mode of two Laves phase-related body-centered-cubic metal hydride alloys doped with Y, and Ce separately in sealed Ni/MH batteries is studied by scanning electron microscopy with x-ray energy dispersive spectroscopy and x-ray diffraction analysis. These two alloys come from a series of studies targeting toward using Ni/MH battery as a low-cost and high-durability alternative to rival Li-ion battery in the electric vehicle application. This group of alloys demonstrates a discharge capacity up to 400 mAh g−1 under a C/4 discharge rate. The main failure mode of these two alloys is found to be selective dissolution of C14 phase which contributes to a fast increase in internal resistance. Due to the deprival of Cr from the first solidified BCC phase, the next solidified C14 phase does not have enough Cr to protect it from the KOH corrosion. Rapid quench fabrication method and addition of other corrosion-resistant non-BCC former, such as Cu, Pd, and Hf, in the alloy composition are suggested.

Design of a hydrogen compressor for hydrogen fueling stations

Hydrogen compressors dominate the hydrogen refueling station costs. Metal hydride based thermally driven hydrogen compressor (MHHC) is a promising technology for the compression of hydrogen. Selection of metal hydride alloys and reactor design have a great impact on the performance of the thermally driven MHHC. A thermal model is developed to study the performance characteristics of the two-stage MHHC at different operating conditions. The effects of heat source temperature and hydrogen supply pressure on the compression ratio and isentropic efficiency are investigated. Finite volume method is used for discretizing the reaction kinetics, continuity, momentum and energy equations. Metal hydrides selected for this analysis are Mm0.2La0.6Ca0.2Ni5 and Ti1.1Cr1.5Mn0.4V0.1. The thermal model was validated with the results extracted from an experimental study. Validation results demonstrated that the numerical results are in good agreement with the data reported in literature.