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Zirconium cobalt alloy (ZrCo) is a promising candidate for tritium storage in fusion reactor, but the surface poisoning caused by trace impurities greatly limits its application. In this work, the interaction mechanisms between nitrogen and ZrCo surface are theoretically explored at the atomic level for the first time. Specifically, the surface exhibits a strong affinity for N atoms with an adsorption energy around −2.0 eV, indicating N can block hydrogenation active sites on ZrCo surface. Seven distinct molecularly adsorbed states have been identified, with their adsorption energies varying from −0.15 to −1.37 eV, depending on both the adsorption site and molecular orientation. The electronic structures and charge distributions indicate that the electrons transfer from ZrCo surface to the anti-bonding orbitals of N 2 , which becomes readily activated with an elongation bond length. Meanwhile, the good mobility of N 2 adsorbate facilitates its dissociation occurring on the specific sites with the energy barriers below 0.3 eV and highly exothermic reaction energies around −3.0 eV, making its dissociative adsorption both kinetically and thermodynamically favorable. Moreover, the high coverage of nitrogen on ZrCo surface significantly restricts hydrogen adsorption and dissociation. Therefore, our results can provide insight into understanding nitrogen poisoning effect on ZrCo surface. • The ZrCo surface exhibits a more affinity for N atoms than H atoms. • The adsorption energy of N 2 is dependent on surface site and molecular orientation. • The good mobility of N 2 adsorbate facilitates its dissociation on the specific sites. • The high coverage of nitrogen significantly restricts hydrogen adsorption and dissociation. [ABSTRACT FROM AUTHOR]

When zirconium alloy undergoes water corrosion reaction during the service process, it absorbs hydrogen to form brittle hydrides, which is one of the main reasons for the deterioration of the mechanical properties of zirconium alloy. There is an urgent need to find an effective method to regulate brittle hydrides to restore the properties of hydrogen-containing zirconium alloys. This study conducted electropulsing treatment on the hydrogen-charged nuclear grade Zr-4 alloy, and the results showed that the electropulsing process caused the hydrides to transform from large-sized brittle stripe-shaped δ-phase to the small-sized ζ-phase. The hydrogen content in the alloy is significantly reduced, which basically restores the mechanical properties of the alloy. However, in the comparative experiment of isothermal heat treatment at 400 °C, brittle hydrides did not dissolve and their mechanical properties did not recover. A mathematical model was established for the characteristics and morphological changes of strip hydrides, and the current density distribution and introduced free energy during the microstructure evolution process were calculated and analyzed. The calculation results indicate that the pulsed current promotes the decomposition of hydrides through the introduction of free energy, reduces the activation energy of hydrogen atom diffusion, accelerates the diffusion and desorption of hydrogen atoms, and realizes the repair of mechanical properties of hydrogen-charged zirconium alloy. • The regulation of brittle hydride of Zr alloy by pulsed current was studied. • Pulsed current promotes the phase transition of brittle hydrides at lower temperatures. • Pulsed current restores the properties of hydrogen-charged zirconium alloy. • The dissolution temperature and activation energy of hydrides are reduced. [ABSTRACT FROM AUTHOR]

Reactor pressure vessels and fuel cladding tubes have repeatedly failed due to zirconium hydrides. Zirconium hydride precipitation and growth are directly affected by hydrogen atom transport properties, which would make nuclear fuel storage less safe over long periods of time. Herein, we employ first-principles calculations to investigate the hydrogen diffusion mechanism in zirconium hydrides, utilizing on-the-fly machine learning force field molecular dynamics. It is verified that the machine learning force field can accurately describe the hydrogen atomic diffusion properties in zirconium hydrides at several temperatures and compositions. The atomic migration paths of hydrogen in zirconium hydrides as well as their barriers and pre-factors are also calculated. According to our results, the temperature and composition of zirconium hydrides affect the microscopic dynamical behavior of hydrogen. [Display omitted] • H diffusion in a range of ZrH 2-x and temperatures studied by on-the-fly MD and kMC. • H diffusion vary with H/Zr ratio above 1.75 more/less at lower/higher temperature. • On-the-fly MD found diffusion coefficients and phases agree well with experiments. [ABSTRACT FROM AUTHOR]

Using the WIEN2k code, first-principles simulations of ZrXH 3 (X = Zn, Cd) hydride perovskites are performed to determine their hydrogen storage properties. The purpose of this study is to investigate their structural, optoelectronic, hydrogen storage, mechanical and thermoelectric properties. The structural analysis demonstrates their stability through the heat of formation along with desorption temperature and shows that these compositions belong to the orthorhombic space group Cmcm (no.63). The band structure and density of states are estimated for electronic characteristics, indicating the metallic nature of both compositions. Analysis of elastic properties such as elastic constants, Pugh's ratio, bulk modulus, Poisson's ratio, and anisotropy factor are explored to determine the mechanical stability of these compositions and demonstrate their suitability as a transport medium in hydrogen storage systems even at higher pressure. To study the optical behavior of the perovskites under consideration for hydrogen storage applications, the dielectric parameters, dielectric constants, refractive index, optical conductivity, absorptivity, and energy loss function are studied. The present paper represents the initial theoretical effort toward future exploration of these materials for hydrogen storage applications. [Display omitted] Using the WIEN2k code, first-principles simulations of ZrXH 3 (X = Zn, Cd) hydride perovskites are performed to determine their hydrogen storage properties. The purpose of this study is to investigate their structural, optoelectronic, hydrogen storage, mechanical and thermoelectric properties. The structural analysis demonstrates their stability through the heat of formation along with desorption temperature and shows that these compositions belong to the orthorhombic space group Cmcm (no.63). The band structure and density of states are estimated for electronic characteristics, indicating the metallic nature of both compositions. Analysis of elastic properties such as elastic constants, Pugh's ratio, bulk modulus, Poisson's ratio, and anisotropy factor are explored to determine the mechanical stability of these compositions and demonstrate their suitability as a transport medium in hydrogen storage systems even at higher pressure. To study the optical behavior of the perovskites under consideration for hydrogen storage applications, the dielectric parameters, dielectric constants, refractive index, optical conductivity, absorptivity, and energy loss function are studied. The present paper represents the initial theoretical effort toward future exploration of these materials for hydrogen storage applications. • Stability of ZrXH 3 (X = Zn, Cd) hydride perovskites is confirmed by Enthalpy of formation. • ZrXH 3 (X = Zn, Cd) hydride perovskites have high value of decomposition temperature. • The gravimetric hydrogen storage capacities comes out to be 1.89 % and 1.46 % respectively. • Metallic behavior is reveled by electronic structure of these hydrides. [ABSTRACT FROM AUTHOR]

The hydrogen storage potential of a 2D analogue of graphyne, holey graphyne (HGY) monolayer decorated with the zirconium adatom is explored by the first-principles study. The Zr adatom exhibits a strong binding affinity on the HGY monolayer with −4.44 eV binding energy through an electronic charge transfer mechanism. Consequently, a localized spatial electrostatic field emerges around the Zr adatom and tends to result in the H 2 molecules being adsorbed via the Kubas interaction. This interaction is due to back-and-forth charge transfer between the H-1s orbital and the Zr-4d orbital, resulting in a net charge gain by the H-1s orbital and leading to H H bond elongation. Furthermore, the high energy barrier for Zr diffusion over the HGY monolayer effectively averts the metal clustering concern. The thermal response of Zr-decorated HGY near room temperature and at elevated temperatures is examined via ab-initio molecular dynamics simulations. Each Zr adatom has the capacity to accommodate five hydrogen molecules, exhibiting adsorption energies spanning from −0.24 to −0.45 eV, leading to a notably high hydrogen weight percentage of 7.5, above the DOE's criterion of 5.5 wt%. This study validates the effectiveness of utilizing thermodynamically and energetically stable Zr-decorated HGY as an outstanding medium for hydrogen storage. [Display omitted] • H 2 storage in Zr decorated holey graphyne is analyzed using DFT. • MD simulations confirm the thermal stability of the complexes. • Each Zr adsorbs 5 H 2 leading to 7.5 wt%. • H 2 adsorption occurs via Kubas interaction. [ABSTRACT FROM AUTHOR]

The commercial ZK60 (Mg-5.7 wt%Zn-0.6 wt%Zr) magnesium alloy was used to investigate the effects of organic solvents along with CNTs and graphene on hydrogen absorption characteristics. The ZK60 alloy was plastically deformed via equal channel angular pressing using route B A at 300 °C and processed for 12 passes. The mechanically removed chips of deformed ZK60 alloy were milled with 5 wt% graphene or 5 wt% CNTs along with organic solvents (toluene and cyclohexane) in a high energy ball mill at 1725 rpm for 20 h. The kinetics and hydrogen storage were measured using Sievert's apparatus for five cycles at different absorption/desorption temperatures. At 320 °C/320 °C absorption/desorption temperature, the maximum hydrogen absorption with 5 wt% CNTs and 5 wt% graphene was 7.13 wt% and 7.28 wt%, respectively, reaching more than 98% within 10 min. The additions of CNTs and graphene could significantly reduce the hydrogenation temperature because the hydrogen storage and kinetics at 280 °C/280 °C were very close to 320 °C/320 °C. At 320 °C/320 °C absorption/desorption temperature, the maximum hydrogen absorption of 5 wt% CNTs or 5 wt% graphene with the addition of 1 ml toluene was about 6.5 wt%, and the hydrogen absorption with the addition of 2 ml toluene was reduced to 5.5 wt%. The addition of 2 ml cyclohexane along with CNTs and graphene had maximum hydrogen absorption of 6.3 wt% and 6.9 wt%, respectively, after five cycles of hydrogen absorption/desorption at 320 °C/320 °C. At the same absorption/desorption temperature, the number of cycles had no obvious effect on hydrogen storage and kinetics, indicating the absorbed hydrogen was completely released during the desorption process. • ZK60 alloy was ball milled with CNTs and graphene along with different concentrations of organic additives. • Additions of CNTs and graphene along with toluene & cyclohexane can significantly reduce the hydrogenation temperature. • Toluene and cyclohexane addition with CNTs and graphene has enhanced hydrogenation efficiency. • Maximum hydrogen capacities with CNTs and graphene are higher than 7 wt% at 320 °C/320 °C de/hydrogenation temperature. [ABSTRACT FROM AUTHOR]

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. AB 2 -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 AB 2 alloys is optimized accordingly: the Mn content x in Ti 0.8 Zr 0.2 Cr 1.9 − x Mn x V 0.1 and the Zr content y in Ti 1 − y Zr y Cr 1.2 Mn 0.8 , 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. • A two-stage MHHC, compressing H 2 from 1 to 30 MPa in the 20–150 °C range, is reported. • AB 2 -type hydrogen storage alloys, (Ti, Zr)(Cr, Mn, V) 2 , are employed for the MHHC. • The transfer pressure from the 1st to 2nd stage is examined and optimized. • Linear coefficients to estimate the plateau pressures are derived. • The estimated useable capacities are compared with the compression capacities. [ABSTRACT FROM AUTHOR]

The effects of Fe substitution by Zr on the microstructure, hydrogen storage properties and oxidation resistance of the TiFe 0.85-x Cr 0.15 Zr x (x = 0, 0.05, 0.10, 0.15) alloys are studied in this work. It is shown that all the alloys are consisted of TiFe phase, MgZn 2 -type phase and minor Ti phase. The introduction of Zr causes no change for the TiFe main phase. All the alloys absorb hydrogen directly under mild conditions without any activation process. As Zr content increases, the maximum hydrogen storage capacity of the first hydrogenation increases while the reversible hydrogen storage capacity decreases. The marked change of the first hydrogenation properties may be due to the formation of the bright phase (MgZn 2 -type phase). The decrease of the reversible hydrogen storage capacity is due to the formation of the stable hydrides Cr 2 ZrH 3 and TiH 2 , which start to decompose at around 700 °C. During the air exposure test, the alloys with higher Zr content show good oxidation resistance. For the PCT measurement, the alloys with higher Zr show lower hydrogen absorption and desorption platform pressure, which means more stable hydrides are formed during the first hydrogenation. Moreover, the rate limiting step model of the first and fifth hydrogenation processes of all the alloys has also been investigated in detail. • TiFe 0.85- x Cr 0.15 Zr x (x = 0, 0.05, 0.10 and 0.15) alloys were prepared. • Regulating Zr content changed effectively the first hydrogenation properties. • MgZn 2 -type phase could act as a pathway to assist hydrogen diffusion. • Oxidation resistance increased with the introduction of Zr content. • Two kinds of irreversible hydrides were formed in the hydrogenation process of the alloys with Zr. [ABSTRACT FROM AUTHOR]

We have explored the hydrogen storage capacity of zirconium doped psi-graphene employing Density Functional Theory. The Zr atom binds strongly on psi-graphene with a binding energy of −3.54 eV due to charge transfer from Zr 4d orbital to C 2p orbital. Zr atom adsorbs 9H 2 molecules with an average binding energy of −0.38eV/H 2 and an average desorption temperature 484.21 K. The gravimetric weight percent is 11.3 which meets the benchmark set by DoE. Zr and H 2 molecules bond by Kuba's interactions involving electron flow between metal d orbital and H 1s orbital. We have investigated the structural stability of the system at room temperature and at 400 K using ab-initio Molecular Dynamics (MD) simulations. Thus, we can attribute that our system is stable, recyclable and can be used as an excellent hydrogen storage medium. This work may inspire the experimentalist to synthesize psi-graphene based material for hydrogen storage. [Display omitted] • Using DFT, hydrogen storage is reported and analysed in Zr doped psi-graphene. • The Zr atom attached on the psi graphene system has a binding energy of −3.54eV. • The Zr atom could hold 9H 2 molecules with an average binding energy of −0.38eV. • Ab-initio MD simulations showed the system is stable till 400 K. • Metal-metal clustering is hindered by the diffusion energy barrier of 1.372eV. [ABSTRACT FROM AUTHOR]

With hydrogen contents 6.69 and 7.49 wt%, Sn(AlH 4) 4 and Zr(AlH 4) 4 were experimentally synthesized, but their structures, bonding natures and hydrogen storage properties were not further investigated. This paper determines the low energy structures of Sn(AlH 4) 4 and Zr(AlH 4) 4 crystals by using global optimization algorithm combined with density functional theories, and analyze their electronic structures and bonding properties. The most stable structures of Sn(AlH 4) 4 and Zr(AlH 4) 4 contain isolated H 2 molecules. The formation enthalpies of Zr(AlH 4) 4 reaches 1.0 eV and the value of Sn(AlH 4) 4 is a little smaller. In Zr(AlH 4) 4 , the AlH 5 , AlH 6 and Al 2 H 6 units are connected tightly by Zr atoms through H bridges. In Sn(AlH 4) 4 , the AlH 6 units form a net structure, and the Sn atom exists in SnH 3 with one shared H atom. The bonding characteristics are analyzed by calculating charge populations and crystal orbital hamilton population (COHP). The metal components (Al, Sn, Zr) and H atoms form polarized covalent bonds. The covalent contributions are close for Sn–H and Al–H bonds but the charge values on the Sn atoms are much smaller. For the Zr–H bonds, both the charges on the Zr atoms and the covalent contributions are smaller than the values of the Al–H bonds. Combining the bonding natures and the structure features, it suggests that proper electronegativity of the metal atoms (Sn and Zr here) is the key factor for the stabilities and reversible hydrogen storage properties of metal aluminum hydrides. • The crystal phases of Sn(AlH 4) 4 and Zr(AlH 4) 4 are predicted. • The metal components (Al, Sn, Zr) and H atoms form polarized covalent bonds. • In Zr(AlH 4) 4 , Polarized covalent Zr–H bond is weaker than Al–H bond. • Hydrogen storage capacity in Sn(AlH 4) 4 and Zr(AlH 4) 4 reaches 6.69 and 7.49 wt%,respectively. • The electronegativity of metal atoms in aluminum hydrides is related to structural stability and reversible hydrogen storage. [ABSTRACT FROM AUTHOR]

Due to the large difference in atomic size between Zr and Nb, TiVNbZr high entropy alloy possesses greater lattice distortion. The change of Zr content can affect the stability of hydrides, which can have an important impact on the hydrogen storage performance. In order to explore the effect of Zr/Nb on hydrogen storage properties, Ti 32.5 V 27.5 Nb 40- x Zr x (x = 7.5, 10, 12.5, 15) high entropy alloys composed of BCC phase are designed. It is found that with the increase of Zr/Nb, the dendritic microstructures first disappear and then gradually become coarse. The Zr-rich BCC phase and the Nb-rich BCC phase appear in the interdendritic and dendritic regions, respectively. Ti 32.5 V 27.5 Nb 25 Zr 15 shows excellent activation performance, which is related to the Zr-rich BCC phase with the most catalytic phase on the surface. The hydrogen storage performance of low Zr/Nb composition is better at low temperature, and that of high Zr/Nb composition becomes better after rising to high temperature. This is because with the change of Zr/Nb, low temperature can promote the hydrogen absorption reaction and high temperature can increase the diffusion rate of hydrogen atoms in the interstitial positions of the alloy. Ti 32.5 V 27.5 Nb 32.5 Zr 7.5 achieves the best hydrogen absorption capacity of 1.71 wt % at 150 °C. All components undergo a transition from the BCC phase to the FCC phase during the hydrogen absorption process, and then change to a single-phase BCC structure after dehydrogenation. With the increase of Zr content, the first step desorption temperature raises in turn, owing to the stronger thermal stability of hydride. • The formation of Zr-rich BCC phase is beneficial to the improvement of hydrogen storage performance. • With the increase of Zr/Nb ratio, TiVNbZr high-entropy alloy can obtain greater lattice distortion. • The Zr-rich BCC phase has better sensitivity at high temperatures, but it is less sensitive to low temperatures. [ABSTRACT FROM AUTHOR]

The surface structures and relative stabilities of low miller-index surfaces of ε-ZrH 2 and γ-ZrH have been investigated as a direct function of environmental conditions (hydrogen partial pressure p H 2 and temperature T) from the first-principles thermodynamic calculations. The results were used to construct their surface phase diagrams for a wide p H 2 range at T = 300 and 900K. The γ-ZrH surfaces tend to be dominated by the Zr-rich (101) with the 101-ns-2Zr1H termination. The surface energy would depend on T and p H 2 , with a value of 1.2–1.3 J/m2. For p H 2 > e−53 at 300K (or p H 2 > e−5.3 at 900K), γ-ZrH can no longer be stable but have the tendency to transform into ε-ZrH 2 , by consistently absorbing H from the gaseous environment. The ε-ZrH 2 surfaces tend to be dominated by the stoichiometric (111) facet with the 111-stoi-2H termination and the surface energy of 1.29 J/m2. • Surface stabilities of stable ZrH x phases are evaluated over >20 model structures. • Surface phase diagrams are constructed based on calculated formation energies. • Dominant surface structures under any given T and p H 2 can be thus predicted. [ABSTRACT FROM AUTHOR]

It is well known that element substitution is vital to an improvement of hydrogen storage capacity degraded by hydrogen-induced disproportionation of zirconium-cobalt (ZrCo) alloy. Contrary to other studies, this work is devoted to investigating the hydrogen desorption behavior of Zr 1- x Nb x Co 1- y Cr y H 3 (x = 0–0.25 and y = 0–0.125) systems formed by Nb substitution and Nb/Cr co-substitution in the ZrCoH 3 crystal using the first-principles calculations based on the density functional theory. Firstly, the preferred positions of Nb and Nb/Cr substitutions are determined through the minimum total energy. Lattice constants and the density of states are employed to characterize the bonding behavior between atoms. The thermodynamic properties of Zr 1- x Nb x Co 1- y Cr y H 3 are also assessed by the enthalpy of formation and equilibrium hydrogen pressure. It is shown that both the thermodynamic stability and dehydrogenation temperature of ZrCoH 3 decrease by increasing the Nb content, which is attributed to the fact that the Zr–H and Co–H binding capabilities are weakened by the presence of Nb. In addition, there are weaker thermal stability, lower dehydrogenation temperature, smaller volume of 8e site, and comparable volume of the hydride after ZrCoH 3 is co-substituted by Nb and Cr, thereby promoting the hydrogen release and enhancing the anti-disproportionation performance. Clearly, both Nb doping and Nb/Cr co-doping possess a positive effect on the hydrogen desorption ability of ZrCoH 3. More importantly, it is discoverable that compared to other substitution systems, the dehydrogenation temperature is the least for the Zr 0.75 Nb 0.25 Co 0.875 Cr 0.125 hydride, highlighting that Nb and Cr co-substitution is more beneficial to improving the dehydrogenation performance of ZrCo-based alloy. [Display omitted] • Effects of Nb doping and Nb/Cr co-doping on dehydrogenation properties of ZrCo–H systems are examined. • The dehydrogenation temperature is found to decrease by the Nb/Cr substitution. • The Zr–H and Co–H binding capabilities are weakened by the presence of Nb. • Co-substitution plays a more positive role on the thermodynamic performance. [ABSTRACT FROM AUTHOR]

The main crisis that impedes the way to successful hydrogen generation for energy purposes is the paucity of efficient hydrogen storage materials. Using First Principles calculations, we predict that zirconium atom adorned on the surface of an advanced carbon allotrope; penta graphene can attach 11 molecular hydrogens as a maximum, having average adsorption energy of −0.42 eV. This gives gravimetric hydrogen uptake of 14.8 wt%, far more than the Department of Energy's requirement of 5.5 wt%. Due to electron transfer from the 3d orbitals of zirconium to 2p orbital of carbon atom of pentagraphene, Zr is tightly linked to it, with a strong adsorption energy of −3.41 eV. The adsorption of hydrogen molecules on Zr is because of Kubas type of interactions involving electron transfer from Zr 3d orbital to hydrogen 1s orbital and subsequently, back donation from H 1s to Zr 3d orbital providing suitable adsorption energy for fuel cell applications which is higher than physisorption but lower than chemisorption energy. The stability of the structure (Zr-decorated pentagraphene) has been verified through Molecular Dynamics Simulations at 300 K and metal-metal clustering is prevented by the substantial energy barrier for the movement of Zr atom on pentagraphene. As the system is stable, adsorption energy of H 2 molecules is in the desired range (0.2–0.7 certified by DoE), wt% of H 2 is more than DoE's prescription, we infer from our DFT results that Zr-decorated pentagraphene may be a promising reversible high-capacity hydrogen storage material. • Zr atom binds strongly on penta graphene with binding energy −3.41 eV. • Maximum of 11H 2 adsorbed on single Zr atom with wt % of hydrogen as 14.8. • Average binding energy of H 2 is −0.42 eV/H 2 , suitable for fuel cell applications. • Zr doped penta graphene stable at upto 500 K verified by MD simulations. • Adsorption of H2 by Kubas interactions with charge transfer between Zr 4d and H 1s. [ABSTRACT FROM AUTHOR]

To better understand the hydrogen diffusion mechanisms in monoclinic zirconia that take place in fuel rod cladding during reactor operation, we calculate the diffusion paths of different defects involving hydrogen and oxygen vacancies using Density Functional Theory with hybrid functionals, and use them to obtain the hydrogen and oxygen diffusion coefficients. We find a hydrogen diffusion coefficient varying between 10−10 to 10−20 cm2⋅s−1 at 600 K, strongly depending on the hydrogen to oxygen vacancy ratio. We find that the interstitial hydrogen atoms are the main diffusing species even though they are not the dominant configuration of hydrogen atoms. We confirm the existence of different huge trapping effects, which slow the hydrogen diffusion. The main mechanism is either the trapping of hydrogen atoms in oxygen vacancies or the formation of interstitial dihydrogen molecules depending on the hydrogen to oxygen vacancy ratio. [Display omitted] • Interstitial hydrogen molecules are stable in zirconia, but do not diffuse. • Interstitial hydrogen atoms are the diffusing species but not the most concentrated. • Oxygen vacancies have a huge trapping effect on hydrogen atoms. • The hydrogen to oxygen vacancy concentration ratio controls the diffusion coefficient. [ABSTRACT FROM AUTHOR]

In this work, the anti-impurity gas poisoning ability and hydrogen storage properties of Ti–Cr alloy by introducing zirconium as additive have been investigated. The results showed that all alloys had C14-type main phase and Ti minor phase. The lattice parameter a, c and cell volume of the C14-type phase rose as Zr content increased. Furthermore, after introducing Zr, all alloys could absorb hydrogen immediately without any prior heat treatment or hydrogen exposure with/without prolonged air exposure. The maximum hydrogen storage capacity and the average effective hydrogen storage capacity of TiCr 2 alloy also increased with Zr content. The cycle properties of all alloys with/without prolonged air exposure were also discussed. The results showed that all alloys had good cycle stability even if the alloys were exposed to the air for 2 days. The above results suggested that the addition of Zr had a positive effect on improving the hydrogen storage properties and anti-impurity gas poisoning properties of TiCr 2 alloy. Finally, the mechanisms of first hydrogenation kinetic of all alloys with/without prolonged air exposure were also investigated by using the rate limiting step. • Zr was introduced to Ti–Cr hydrogen storage alloys for the first time. • Adding Zr can improve first hydrogenation properties of TiCr 2 alloy. • The lattice parameters a and c of C14-type phase rise as Zr content increases. • Adding Zr can enhance anti-impurity gas poisoning properties of TiCr 2 alloy. • Alloys after adding Zr have good cycle stability with/without prolonged air exposure. [ABSTRACT FROM AUTHOR]

This study aims at identifying the rate-limiting step and quantifying the kinetic constants of diffusion and deuterium desorption from a Zircaloy-4 alloy oxidized in light primary water. Secondary Ion Mass Spectrometry deuterium concentration profiles in ZrO 2, combined with finite elements simulations, reveal that the deuterium desorption from an oxidized Zircaloy-4 alloy is kinetically controlled by a mixed regime of surface recombination and diffusion in the oxide in the 600 K–1000 K temperature range. At lower temperatures, desorption is controlled by the deuterium diffusion in the oxide layer whereas at higher temperatures the surface recombination reaction dominates. [Display omitted] • During heat treatment a deuterium concentration gradient in the oxide layer appeared. • The deuterium did not desorb after 7 days at 773 K and 19 days at 723 K under vacuum. • The desorption rate constant equals to 2 x 10 − 8. e x p (− 34500 R T ) m4 mol−1 s−1. • The deuterium diffusion coefficient in zirconia equals to 2 x 10 − 8. e x p (− 156100 R T ) m2 s−1. • Deuterium desorption is rate-limited by surface recombination and diffusion in ZrO 2. [ABSTRACT FROM AUTHOR]

Under normal operating conditions in nuclear pressurized water reactors, tritium produced by ternary fission occurring within the uranium fuel may cross the whole cladding in zirconium alloy before being released in primary water during operation, or in containers during transportation and storage. The study aims at identifying and quantifying the rate-limiting steps of this permeation process by using deuterium as isotopic tracer for tritium. A dedicated permeation device revealed that, at 773 K, deuterium permeation kinetics from the metal was limited by the surface recombination reaction. In association with gaseous deuterium charging and Thermal Desorption Spectrometry, the apparent activation energy of the deuterium desorption showed that the permeation device induced stress and strain in the specimens. A stress-free Zircaloy-4 exhibited an apparent activation energy around 240 kJ mol−1 it dropped down to around 140 ± 10 kJ mol−1 when under stress, in the 623 K–773 K temperature range. • The deuterium permeation kinetics is controlled by the surface recombination step. • The native oxide does not seem to limit the desorption rate between 623 K and 773 K. • The apparent energy activation of the deuterium desorption is impacted under stress. • A stress-free Zircaloy-4 exhibited an apparent activation energy around 240 kJ mol−1. • A Zircaloy-4 under stress exhibited an apparent activation energy around 140 kJ mol−1. [ABSTRACT FROM AUTHOR]

In the research, we firstly reported the morphology and microstructure evolution of surface hydride in Zircaloy-4-500 ppmH during hydrogen desorption process. The morphological evolution of surface hydride in hydrogen desorption process was investigated with BSE-TOPO and AFM, revealing that the spot-like or string convex features along surface hydride were present at 573 K and disappeared at 1073 K. The microstructure observation with TEM (prepared with cryo-FIB) indicates that the surface region of convex feature actually consists of two layers of fine α-Zr grains, which were the hydrogen-depletion region created by hydrogen release. The formation mechanism of surface hydride convex was the diffusion of hydrogen from the internal to the surface, leading to the generation of multiple δ-hydrides in sub-surface. Therefore, the hydrogen desorption mechanism was also proposed. As the channeling of hydrogen release, surface hydride actually plays a crucial part in hydrogen desorption process. [Display omitted] • The formation of string convex feature along surface hydride was firstly reported. • The surface region of convex feature consists of two layers of fine α-Zr grains. • The diffusion of hydrogen leads to the phase transformation of α-Zr to δ-hydrides. • Surface hydrides act as the channeling of hydrogen release in desorption process. [ABSTRACT FROM AUTHOR]

This paper proposes a mathematical model for the oxidation process of zirconium under the theory of oxygen diffusion in Zircaloy. The model considers ZrO 2 , α -Zr(O), and β- Zr phases at high temperatures (1273 K–1800 K) in an equivalent fuel rod. The model also considers the heat transfer phenomenon, the decay heat after shutdown, the heat released by the oxidation reaction, the loss of coolant water in the core and the heat transported by the steam produced. A computer program was coded in the C++ environment. The accident scenario of a BWR short term station blackout was simulated with this model. The results are compared with the ones obtained using MELCOR and RELAP/SCDAP codes. The comparison yielded an approximate result for total hydrogen production at the end of the simulation, with a difference of −2.7% compared with RELAP/SCDAP, and a difference of −1.11% with MELCOR. With the present model it is possible to calculate the growth of ZrO 2 , α -Zr(O), and β -Zr phases through the cladding. • A nuclear fuel rod cladding oxidation and hydrogen production model. • The diffusion theory in a multiphase environment is considered. • Results are compared with specialized codes, RELAP/SCDAP and MELCOR. • The oxygen concentration distribution within the cladding thickness is explicitly determined. • Model predicts the pre and post transition process in the growth of the ZrO 2 and α -Zr layers. [ABSTRACT FROM AUTHOR]

In order to determine the threshold stress intensity factor and critical hydride length for delayed hydride cracking in Zr-2.5Nb pressure tube alloy, the distribution of normal stress in the plastic zone of crack tip by the developed method that combines theory calculation with extended finite element method (XFEM) was improved. The fracture process of two-phase composites containing Zr-2.5Nb and hydride precipitate was simulated by XFEM. Based on that, critical hydride length L C corresponding to the theoretical model for K 1H was estimated. Meanwhile, to illustrate the validity of theoretical and numerical methods, recent theoretical models and experimental measurements were utilized to verify the results of this paper. The theoretical model of DHC was improved to estimate the critical hydride length corresponding to threshold stress intensity factor. The predicted value of critical hydride length is close to the experimental values. • Distribution of the normal stress in plastic zone is improved by valid estimation of σ 0. • The theoretical model combining XFEM is used to calculate the K 1H and L C. • The influence of hydride size on the instability fracture point is revealed by XFEM. [ABSTRACT FROM AUTHOR]

Under Pressurized Water Reactor normal operating conditions, the external surface of zirconium alloys cladding absorbs a fraction of the hydrogen produced by water reduction. During spent fuel transport, hydrogen may desorb from the cladding. The study aims to identify and quantify the rate-limiting step in the hydrogen desorption process initially present in the alloy. To better understand this process, the Thermal Desorption Spectrometry (TDS) was used in association with X-ray Photoelectron Spectroscopy analysis. TDS results were analysed with finite elements simulations using the Cast3M code. The optimization of the kinetic constants of hydrogen desorption was performed with CEA (Alternative Energies and Atomic Energy Commission)-tool URANIE. Results showed that hydrogen desorption kinetics from the metal is limited by the surface molecular recombination. Arrhenius-type temperature dependence of kinetic constants allowed to simulate experimental data with a good agreement. The optimized activation energy and the pre-exponential factor for desorption processes were in the range of 290 ± 10 kJ mol−1 and 3 × 107 m4 mol−1 s−1 respectively. • Thermal desorption analysis identified the rate-limiting step of hydrogen desorption. • The hydrogen desorption rate is controlled by the surface recombination step. • By coupling Cast3M with URANIE, the surface recombination constant was quantified. • The desorption rate constant equals: k d e s ' = 3 x 10 7. exp (− 2.90 x 10 5 R T ) m4 mol−1 s−1. [ABSTRACT FROM AUTHOR]

In this work, the results of the irradiation of untreated, preliminarily Ar+-bombarded and Cr-coated samples of zirconium alloy E110 (Zr-1%Nb) with deuterium atoms and ions of deuterium plasma were compared with the results of their exposure to superheated water steam (673 K, 11 MPa; 673 K, 0.1 MPa; 633 K, 0.1 MPa). It was concluded that, despite of the difference in the rates of the oxide layer formation, the features of hydrogenation are similar under the two kinds of impact. However, the hydrogen uptake under irradiation occurs hundreds of times faster than during the steam test. The most effective hydrogenation was achieved under irradiation of the E110 sample with 300–500 eV/at ions of deuterium plasma without oxygen. These circumstances allow suggesting the irradiation with ions of hydrogen plasma as an accelerated hydrogenation test of zirconium alloys and protective coatings under conditions simulating the environment of light-water reactor's core. The proposed method could be realized using a simple plasma device and it does not require high power consumption or special qualification of staff. • Features of zirconium hydrogenation in steam and in hydrogen plasma are similar. • Zirconium hydrogenation in plasma occurs hundreds of times faster than in steam. • Plasma irradiation can be used as accelerated out-of-core test of zirconium alloys. • Accelerated and steam tests of protective layers on zirconium give the same results. [ABSTRACT FROM AUTHOR]

Abstract In this paper we report the effect of air exposure on TiFe + 4% Zr alloy and how the hydrogen capacity could be recovered by processing the alloy by cold rolling and ball milling. It has been noted that the alloy could not absorb hydrogen after 7 days of air exposure. To restore the hydrogenation capability of the alloy, it was mechanically treated using cold rolling and ball milling. It was found that the air exposed alloy could be hydrogenated after 30 min of ball milling under argon or after cold rolling. Effect of cold rolling and ball milling on first hydrogenation for pure TiFe alloy was also investigated. Highlights • TiFe with 4 wt% Zr alloy was synthesized. • Effect of air exposure on first hydrogenation kinetics were studied. • The alloy became inactive towards first hydrogenation after air exposure. • Ball milling and cold rolling were effective to re-activate the alloy. • Effect of cold rolling and ball milling on pure TiFe alloy was also investigated. [ABSTRACT FROM AUTHOR]

Element doping is an effective way to improve the performance of hydrogen storage. The influences of Ti- and Hf-substituted dopants on the hydrogen storage and mechanical properties in a Zirconium-Cobalt alloy have been investigated by the first principle method. The results show that the Ti and Hf atoms preferentially occupy the Zr atoms to form new Zr 7 Co 8 Ti and Zr 7 Co 8 Hf compounds. The cohesive energy of Zr 7 Co 8 Ti and Zr 7 Co 8 Hf are −7.518 eV/atom and −7.531 eV/atom, thus Zr 7 Co 8 Hf shows a better structural stability than Zr 7 Co 8 Ti. The B/G ratio of Zr 7 Co 8 Ti and Zr 7 Co 8 Hf are 3.42 and 3.89, respectively, which indicates that Ti doping could increase the ductility of the alloy, thus improving the recycling performance of the alloy. The calculation for the electronic structure, mechanical property and structural stability may provide an effective way and theoretical evidence for the better design and optimization of hydrogen storage materials. [ABSTRACT FROM AUTHOR]

The effects of addition of Zr, Ni and Zr 7 Ni 10 on the crystal structure, microstructure and hydrogen absorption of Body Centred Cubic (BCC) 52Ti-12V-36Cr were investigated. We found that addition of Zr and/or Ni led to the formation of a Ni/Zr rich secondary phase. This secondary phase is responsible for the much faster first hydrogenation of the alloys with additives compared to the bare BCC alloy. Zirconium addition had positive influence on incubation time and intrinsic hydrogenation kinetics while nickel addition improved the hydrogen capacity. Among the additives tested, Zr 7 Ni 10 is the best for optimized hydrogenation kinetics and capacity. [ABSTRACT FROM AUTHOR]

This paper describes the hydrogenation behavior of Zr-1Nb alloy Ti-implanted by plasma immersion ion implantation (PIII). Hydrogen sorption kinetics of the Ti-modified alloy was investigated under gas-phase hydrogenation at 400 °C for 1 h. The influence of implantation time on the protective properties of the modified layer was shown. The lowest hydrogen absorption as well as the highest hydrogen trapping efficiency was achieved after PIII for 30 min. The main contribution to the reduction of hydrogen permeation is the formation of an oxide layer consisting of mixed TiO 2 and ZrO 2 on the modified surface of the alloy. X-ray photoelectron spectroscopy (XPS) revealed that PIII titanium oxide exists on the surface in the form of TiO 2 , which transforms to mixed Ti 2 O 3 and TiO 2 after hydrogenation. The thickness of the modified layer increases with implantation time that improves the efficiency of hydrogen trapping. All the absorbed hydrogen is gradually distributed in the modified layer and no hydrides are formed after hydrogenation in Ti-modified Zr-1Nb for 15 and 30 min. [ABSTRACT FROM AUTHOR]

In the present study, Zr 0.8 Ti 0.2 Co 1− x Fe x ( x = 0, 0.1, 0.2 and 0.3) alloys were prepared by arc melting method. The effect of Fe substitution on microstructure and hydrogen storage properties was studied systematically. The phase structure and hydrogen storage properties were characterized by X-ray diffraction (XRD), Electron Probe Micro-analysis (EMPA) and Sievert's type volumetric apparatus. XRD and EPMA analysis show that Zr 0.8 Ti 0.2 Co alloy forms cubic phase ZrCo and traces of ZrCo 2 , while the alloys of composition with x = 0.1, 0.2 and 0.3 form cubic phase ZrCo with the secondary Laves phases Zr(Co,Fe) 2 and Zr 2 Co. The cell volumes and content of the secondary phase increase gradually as the content of Fe substitution increases. The hydrogen storage experiment shows that Fe substitution for Co ameliorates initial hydriding kinetic property and shortens the incubation duration of the Zr 0.8 Ti 0.2 Co 1− x Fe x ( x = 0.1, 0.2 and 0.3) alloys, compared with Zr 0.8 Ti 0.2 Co alloy. The improved kinetic property is due to the catalyst effect of the secondary phase, which makes it favorable for the application in International Thermonuclear Experimental Reactor (ITER). [ABSTRACT FROM AUTHOR]

Influence of hydride precipitated at the tip of the crack on crack propagation in zircaloy-4 is numerically investigated using the extended finite element method (XFEM). Numerical simulation is performed on compact tension specimen to understand the effects of crack and hydride lengths on crack propagation in terms of stress intensity factor and J-integral. The values of stress intensity factor and J-integral indicate that hydride induces the crack instability. The stress intensity factor decreases with the precipitation of brittle hydride phase at the crack tip, resulting in hydride-assisted crack propagation. A comparison of crack propagation behaviour with different hydride lengths is also presented. The crack remains stable in the absence of the hydride while it propagates when hydride is considered at its tip for the same applied load. The crack arrests only after reaching to the zircaloy metal matrix causing complete fracture of hydride. [ABSTRACT FROM AUTHOR]

We perform first-principles calculations to investigate the effects of alloying substitutions (i.e. Ti, Hf, Sc, Fe, Ni and Cu) on hydrogen-induced disproportionation of ZrCo alloy. H at the 8e site of ZrCoH 3 (H(8e)) plays the key role in the disproportionation process. It is found that H(8e) prefers to form strong covalent-like binding with the neighboring Co and its substitute elements, which is distinctly different from H at the 4c 2 and 8f 1 sites. Alloying substitutions can restrain or accelerate the disproportionation by influencing the Zr H(8e) bond length and the size of the 8e site. Judged from this, the anti-disproportionation ability of these alloying substitutions is identified. Our results of Ti, Hf, Sc, Fe and Ni are in good agreement with the previous experimental results. It is also predicated that Cu can accelerate hydrogen-induced disproportionation of ZrCo alloy. [ABSTRACT FROM AUTHOR]

The effects of Pd coating with different deposition concentration (PdCl 2 0.2 g L −1 , 0.6 g L −1 , 1.0 g L −1 ) on the surface morphology, microstructure and hydrogen storage performances of ZrCo alloy have been investigated. Results show that spherical Pd particles have been deposited on the surface of ZrCo alloy successfully, which transfer from sparse arrangement to continuous and compact film with increasing deposition concentration of PdCl 2 . The hydriding kinetic property of all Pd coated alloys is improved compared with the bare alloy, which is due to the catalyst effect of Pd coating. The hydriding rate of the samples firstly increases and then decreases with increasing deposition concentration, which is closely related to the surface morphology and thickness of Pd coating. The hydriding kinetic property of the samples is greatly improved after 5 cycles, although Pd particles on the alloy surface peel off to some extent. This phenomenon indicates that the accumulated fresh surface during cycling makes a greater contribution to the improved hydriding kinetic property and the catalyst effect of Pd coating is weakened during cycling. [ABSTRACT FROM AUTHOR]

In this study, an attempt has been made to improve the storage properties of ZrCo based alloy, which is being considered as an important material for storage of hydrogen isotopes in the proposed fusion reactors. Herein, we report the hydrogen isotope storage behaviour of titanium doped Zr 1−x Ti x Co (x = 0, 0.1, 0.2 and 0.3) ternary alloys. Alloys were prepared by arc melting method and characterised by XRD, SEM and EDS. XRD analysis indicates that all ternary alloys form cubic phase similar to ZrCo phase. Hydrogen/deuterium desorption pressure-composition isotherms were generated in the temperature range of 523–583 K, by employing Sieverts' apparatus. All isotherms show a single plateau which confirms the one step absorption–desorption of hydrogen isotopes by Zr 1−x Ti x Co alloys. Equilibrium plateau pressure of hydrogen/deuterium was found to increase with increase in Ti content of Zr 1−x Ti x Co alloys. Based on the trend in the equilibrium pressures of the dehydrogenation and de-deuteration reactions, it can be inferred that the partial pressure of tritium over the tritide will be higher than that of deuterium and hydrogen partial pressures. This makes Ti substituted alloys suitable for storage of hydrogen isotopes owing to lower desorption temperature as desired for ITER SDS. [ABSTRACT FROM AUTHOR]

In this paper, we report the microstructure and hydrogen storage properties of Ti 0.95 FeZr 0.05 , TiFe 0.95 Zr 0.05 and TiFeZr 0.05 alloys prepared by arc melting. We found that all these alloys are made of a TiFe phase with small amount of zirconium in solid solution and a secondary phase which is zirconium rich. This special microstructure is actually responsible for the enhanced activation (first hydrogenation) kinetics of these alloys. First hydrogenation of Ti 0.95 FeZr 0.05 alloy proceed faster than for the other two alloys. This is probably due to a finer distribution of the bright secondary phase. Pressure-composition isotherms of TiFeZr 0.05 and Ti 0.95 FeZr 0.05 alloys are similar while the alloy TiFe 0.95 Zr 0.05 shows the highest capacity. These results demonstrate that a very slight variation of composition could have an important effect of microstructure and hydrogen storage behaviours. [ABSTRACT FROM AUTHOR]

Zirconium is a kind of deuterium absorption materials and can be used as a candidate deuterium carrier in the nuclear fusion industry. However, it usually cracks after deuterium absorption and fails in its application. For the prevention of cracks, copper particles with good ductility were added into the zirconium by spark plasma sintering (SPS) synthesis method. The results showed that the addition of the Cu element affected the cracking behavior of Zr–xCu alloys significantly. With the addition of the 5%Cu no cracking was observed, and an addition of the 10%Cu lead to an observation of a few large cracks within the second phase, compared in size to the small cracks that appeared in Zr. Moreover, the addition of the Cu element decreased the deuterium absorption capacity of the Zr–xCu alloys and changed the deuterium absorption mechanism from three-dimension diffusion in the Zr alloy to chemical reaction in the Zr–10%Cu alloy. The pressure–composition–temperature (PCT) curves showed that all the Zr alloys had two plateau pressures at 900 °C, and the addition of Cu had an effect on the plateau pressure. After 10 cycles of deuterium absorption–desorption, Zr–5%Cu sample kept a integrity morphology with no cracking at low magnification, on the contrary Zr–10%Cu sample broken into pieces, though both of them kept a higher relative deuterium absorption capacity than that of Zr. [ABSTRACT FROM AUTHOR]

Zirconium based alloys have potential applications in automobile, energy and spacecraft industries. The structural, electronic, elastic, vibrational and thermodynamic properties of orthorhombic ZrNi and ZrNiH 3 are studied in detail using the projector augmented wave method and the generalized gradient approximation based on density functional theory. The optimized lattice parameters of both ZrNi and ZrNiH 3 agree well within ±1% from the experimental values. The electronic structure analysis shows significant contribution of 4 d and 3 d orbitals of Zr and Ni to the fermi energy level, respectively and along with signatures of two types of hydrogen atoms occupying the lattice of ZrNiH 3 . Elastic property calculation of these two compounds showed mechanical stability and anisotropy at ambient pressure. In addition, the phonon calculation of both the compounds showed that ZrNi is dynamically stable but ZrNiH 3 is dynamically unstable. The formation energies (Δ f H ) of ZrNi and ZrNiH 3 at 0 K, after zero point energy correction, have been estimated to be −41.87 kJ/mol and −78.25 kJ/mol H 2 , respectively. The temperature dependent thermodynamic functions of ZrNi and ZrNiH 3 have also been calculated from the Debye-Grüneisen quasi-harmonic approximation. [ABSTRACT FROM AUTHOR]

Electrochemical properties of the ZrNi alloy electrode with the boiling alkaline treatment were investigated. The boiling alkaline treatment was performed by immersing ZrNi powder or electrode in a boiling 6 M KOH aqueous solution for 4 h. During the boiling alkaline treatment, the bulk structure of the ZrNi powder, the B33 -type (CrB) structure, remained, whereas the outer ZrO 2 native surface was replaced by Ni(OH) 2 . The initial discharge capacity at 10 mA g −1 and 333 K for the ZrNi alloy electrode was increased from 18 to 320 mAh g −1 by the boiling alkaline treatment. However, cycle performance got worse, because the ZrNi alloy particles were pulverized for the charge–discharge cycles. [ABSTRACT FROM AUTHOR]

Zircaloys, rooted in their inherent passivity, are widely used as the cladding materials for light water reactors (LWRs) due to their desirable corrosion resistance against high temperature and high pressure water. The hydrogen permeation behavior on zircaloy with passive film, however, is rarely understood so far. In this work, the gaseous hydrogen permeation characteristic mainly on the defect evolution of nanoscale passive films of nanoscale passive films formed hydrothermally on different types of zirconium alloys (Zirconium, Zircaloy-4, N18 and M5) was explored and compared. Surface analytical techniques were implemented to evaluate the hydrogen permeation characteristic. The AES depth profiles showed that the as-prepared oxides were hundreds of nanometers in thickness and inward diffusion occurred upon hydrogen exposure. Electrochemical measurements suggested that the oxides formed on different types of zircaloys were of similar phase structures of monoclinic zirconia but with different oxygen vacancy concentrations. XPS results comparison confirmed that niobium enhances the hydrogen resistance of the oxides, yet tin causes degradation of the oxides in the reductive environment. In view of these analyses, the involving mechanism was first proposed and discussed on the basis of point defect reactions. [ABSTRACT FROM AUTHOR]

Four kinds of ZrVFe alloys with the C14 Laves phase structure had high hydrogen storage capacity under mild pressures, and those alloys would be promising for widespread application such as recovery of hydrogen derived from water splitting. Addition of titanium to ZrVFe lowered hydrogen desorption temperatures through increase of equilibrium pressures. Substitution of ferrovanadium for vanadium did not deteriorate hydrogen occlusion performance of ZrVFe, and provided with lower cost alloys. Another way to reduce the cost would be elimination of purifying step of vanadium prepared by the thermite process, but remaining aluminum proved to bring about lower hydrogen capacity, as evidenced by comparative experiments including a ZrVFe alloy with aluminum intendedly added. Every alloy had fairly good cycling durability except the one contaminated with aluminum. [ABSTRACT FROM AUTHOR]

The aim of this study is to understand the remarkable improvements achieved on the hydrogenation properties of TiFe alloy modified by Zr 7 Ni 10 alloy. For this purpose, comparative effect of 4 wt% Zr, Ni and Zr 7 Ni 10 alloy addition on hydrogenation, morphological and structural properties of TiFe alloy were investigated. Our results show that while zirconium addition has positive influence on hydrogen absorption capacity and kinetics of TiFe alloy, nickel addition has negative effect on these properties. Specific microstructure and Fe/Ti atomic ratio in intergranular phases are responsible for the obtained results. More specifically the present study shows that by zirconium addition, TiFe alloy could absorb hydrogen under moderate temperature-pressure conditions without any prior treatment. This modified system is also resistant to air exposure. [ABSTRACT FROM AUTHOR]

The addition of Al, Cu and Mn in Zr–Nb-based alloys was evaluated through corrosion and hydrogen absorption tests in cold rolled and annealed conditions. For the studied alloys, the heat treatment resulted in an α-Zr matrix with β-Nb precipitates and X-ray diffraction (XRD) confirmed the formation of hydrides after hydrogenation in all conditions evaluated. It was observed that the alloy with Al addition absorbed the largest amount of hydrogen and the alloy containing Cu took more time to begin the absorption. The alloy with Mn absorbed little hydrogen but the onset of absorption occurred in a short time. The results indicate that the alloy with Cu addition is the most promising and the alloy with Al addition is inadequate for nuclear application. [ABSTRACT FROM AUTHOR]

The kinetics of hydrogen absorption in Zr alloys containing Nb and Ta admixtures (10 wt%Nb, 12 wt%Ta and 10 wt%Nb&12 wt%Ta) is addressed. Hydrogen absorption is measured in the temperature range 400–700 °C at hydrogen pressure 1 bar using the volumetric method, and a kinetic analysis is performed to determine the mechanisms and rates of hydrogen absorption. To get further insight into hydrogen diffusivity in zirconium hydride, 1 H NMR spectroscopy is used to provide the activation energies for proton jumping in the studied samples. The tantalum is found to dominantly influence the surface reactivity, while niobium influences large decrease of the activation energy for hydrogen diffusion in the bulk of zirconium hydride. This behavior is linked to the information on the structure of the alloys obtained by XRD. [ABSTRACT FROM AUTHOR]

In the present study, the effect of Fe substitution for Co on the hydrogen isotope storage properties of ZrCo alloy has been investigated to ascertain the improvement in durability of ZrCo alloy against hydrogen induced disproportionation. The ZrCo 0.9 Fe 0.1 alloy was synthesized by arc melting and characterized by X-ray diffraction analysis, SEM and EDS. Hydrogen isotope storage behavior of this alloy was probed by generating the hydrogen/deuterium desorption pressure–composition isotherms (PCIs) for ZrCo 0.9 Fe 0.1 –H 2 /D 2 systems. Thermodynamic parameters like enthalpy and entropy change for desorption of hydrogen/deuterium in the ZrCo 0.9 Fe 0.1 –H 2 /D 2 systems were derived from the van't Hoff plots. This study reveals the normal hydrogen isotope effect for this alloy, depicting the higher equilibrium pressure of D 2 than that of H 2 at all experimental temperatures. In addition, the cyclic life studies were also performed on ZrCo 0.9 Fe 0.1 alloy at 583 K up to 50 cycles of hydrogen/deuterium absorption–desorption. Neutron diffraction studies were also carried out on ZrCo 0.9 Fe 0.1 deuteride to determine its crystal structure and interstitial sites occupied by deuterium atoms. The experimental results show that Fe substitution increases the durability against hydrogen induced disproportionation as compared to pure ZrCo alloy, which makes it favorable for storage of hydrogen isotopes. [ABSTRACT FROM AUTHOR]

In this study, the effects of partial substitution of Fe, in the ZrFe 2 -system alloys, by Cr or V are presented. The two studied alloys, ZrFe 1.8 V 0.2 and ZrFe 1.8 Cr 0.2 , have been synthesized by high frequency induction-levitation melting under inert Ar atmosphere. The induction furnace was equipped with a water-cooled copper crucible that permits the rapid solidification of the alloy after the melting. The crystal structures of the investigated alloys have been studied by the Rietveld analysis of the obtained X-ray diffraction (XRD) patterns. The microstructure has been observed by a scanning electron microscope (SEM) on polished samples of the alloys. Their hydriding properties have been studied with a high pressure Sievert's type apparatus, up to 200 bar. All pressure–composition–temperature (PCT) measurements have been obtained at 20, 60 and 90 °C. Two high temperature activation cycles have been conducted prior to PCT measurements. The results showed almost the same uptake for the alloys after identical activation and lowering of the plateau pressure in both cases. [ABSTRACT FROM AUTHOR]

The terminal solid solubility (TSS) of hydrogen in zirconium alloys has a hysteresis. The TSS of hydrogen in Zircaloy-4 during cooling and heating were studied using differential scanning calorimetry (DSC) with a hydrogen content of 40–731 wppm. A significant hysteresis gap was observed between the TSS for dissolution (TSSD) and precipitation (TSSP). It was confirmed that the hydrogen dissolution temperature was unaffected by the previous thermal history in comparison with the hydride precipitation temperature. The TSSP temperature increased with a decrease in the maximum temperature, but a significant temperature gap remained even when the maximum temperature was equal to the TSSD temperature. The terminal solid solubility of hydrogen in Zircaloy-4 can be represented by the following equations. TSSD: C = 2.255 × 10 5 exp (−39101/ RT ). TSSP: C = 4.722 × 10 4 exp (−26843/ RT ). TSSP2: C = 8.612 × 10 5 exp (−30583/ RT ). Based on the experimental results hydrogen solubility path depending on the previous thermal history was proposed. [ABSTRACT FROM AUTHOR]

In the present study, we have for the first time reported the occupancy of deuterium in a new interstitial site of ZrCoD 3 which explain the hydrogen induced disproportionation behavior of ZrCo alloy. We have also reported the effect of Ni substitution on interstitial site occupancy of deuterium in ZrCo 1− x Ni x D 3 , which in turn explains the improved durability of these Ni substituted deuterides against disproportionation. The crystal structure of the ZrCo 1− x Ni x ( x = 0.0, 0.1, 0.2, 0.3) deuterides was investigated by X-ray powder diffraction and neutron diffraction methods. The XRD data reveals a single phase formation for all deuterides with varying Ni content ( x ). The neutron diffraction study shows that deuterium occupies a new site 8 e in addition to 4 c 2 and 8 f 1 . Additionally, the Zr–D distance in 8 e site is shorter than that in ZrD 2 . Therefore, increase in 8 e site occupancy will in turn decreases the durability against disproportionation and vice-versa. Furthermore, the neutron diffraction reveals that occupancy of new 8 e site decreases and its Zr–D distance increases with increase in Ni content, which explicate the higher durability against disproportionation for Ni rich compound. [ABSTRACT FROM AUTHOR]

The deuterium desorption pressure-composition isotherms (PCIs) of ZrCo 1− x Ni x -D 2 ( x = 0, 0.1, 0.2 and 0.3) systems were generated in this study in the temperature range of 524–603 K using Sievert's type volumetric apparatus. Thermodynamic parameters like enthalpy and entropy change for deuterium desorption reactions involved in the ZrCo 1− x Ni x -D 2 systems were derived using the equilibrium pressure data of PCIs. In order to interpret the hydrogen isotope effect on the storage behaviour of ZrCo 1− x Ni x alloys, the results obtained in the present study were compared with the earlier reported data on the ZrCo 1− x Ni x -H 2 ( x = 0, 0.1, 0.2 and 0.3) systems. This comparison revealed that these alloys show normal hydrogen isotope effect where the equilibrium pressure of D 2 is higher than that of H 2 at all experimental temperatures. Based on these observation, it is expected that at the ITER SDS operating conditions the equilibrium pressure of tritium, deuterium and hydrogen will follow the order: p (T 2 ) > p (D 2 ) > p (H 2 ) for these alloys. [ABSTRACT FROM AUTHOR]

Abstract: The non-stoichiometric C15 Laves phase alloys namely Zr0.9Ti0.1V x (x = 1.7, 1.8, 1.9, 2.1, 2.2, 2.3) are designed and expected to investigate the role of defect and microstructure on hydrogenation kinetics of AB2 type Zr-based alloys. The alloys are prepared by non-consumable arc melting in argon atmosphere and annealed at 1273 K for 168 h to ensure the homogeneity. The microstructure and phase constitute of these alloys are examined by SEM, TEM and XRD. The results indicate the homogenizing can reduce the minor phases α-Zr and abundant V solid solution originating from the non-equilibrium solidification of as-cast alloys. Twin defects with {111}<011 > orientation relationship are observed, and the role of defects on hydrogenation kinetics is discussed. Hydrogen absorption PCT characteristics and hydrogenation kinetics of Zr0.9Ti0.1V x at 673–823 K are investigated by the pressure reduction method using a Sievert apparatus. The results show the hypo-stoichiometric alloys preserve faster hydrogenation kinetics than the hyper-stoichiometric ones due to the decrease of dendritic V. The excess content of Zr3V3O phase decreases the hydrogenation kinetics and the stability of hydrides. In addition, the different rate controlled mechanisms during hydrogen absorption are analyzed. The effects of non-stoichiometry on the crystal structure and hydrogen storage properties of Zr0.9Ti0.1V x Laves alloys are discussed. [Copyright &y& Elsevier]

In this work, the ZrTiVCrFeNi high entropy alloy was successfully synthesized from elemental powders near the equimolar ratio using Laser Engineered Net Shaping (LENS). The prepared alloy exhibited good chemical composition after laser deposition, compared to the nominal composition, which was further improved using high-temperature annealing at 1000 °C for 24 h. Better powder quality and the optimization of the LENS parameters are still necessary for obtaining the improved chemical homogeneity of the alloy after synthesis. The alloy exhibited a two-phase structure, i.e., the dominant C14 Laves phase matrix with a minor amount of the α-Ti solid solution, after synthesis and annealing. The PCT isotherms were measured up to 100 bar of hydrogen pressure at 50 °C after activation of the alloy by annealing at 500 °C for 2 h under vacuum. The obtained maximum hydrogen capacity was 1.81 wt.% after synthesis and 1.56 wt.% after additional annealing. The equilibrium pressure of hydrogen desorption was too low for a complete desorption reaction, resulting in the presence of a C14 hydride phase in the alloy after PCT tests. [ABSTRACT FROM AUTHOR]

Abstract: The hydrogen absorption cracking behavior of Zr-4 has been investigated based on the microstructure, hydrogen absorption amount as well as residual stress. The results show that the grain size has a pronounced effect on the hydrogen absorption cracking, with the increase of grain size from 30 μm to 500 μm, the cracks vary from small cracks of independence to large cracks that connect with each other along the radial direction. The unsaturated hydrogen absorption samples which consist of γ- and δ-hydrides present a crack-free surface while the saturated hydrogen absorption samples which consist of ɛ-hydride exhibit not only large cracks but also bulges on the surface. The hydride decomposition temperatures of ɛ → δ and δ → α during dehydriding are determined to be about 600 °C and 700 °C respectively. In the unsaturated hydrogen absorption samples, both the thickness expansion and radial residual stress present a positive liner correlation with the hydrogen absorption amount. Based on the experimental results a mechanism of hydrogen absorption cracking is proposed in zirconium alloys. [Copyright &y& Elsevier]

Abstract: ZrCo1−x Ni x (x = 0, 0.1, 0.2 and 0.3) alloys were prepared and their hydrogen storage behavior were studied. ZrCo1−x Ni x alloys of compositions with x = 0, 0.1, 0.2 and 0.3 prepared by arc-melting method and characterized by X-ray diffraction analysis. XRD analysis showed that the alloys of composition with x = 0, 0.1, 0.2 and 0.3 forms cubic phase similar to ZrCo with traces of ZrCo2 phase. A trace amount of an additional phase similar to ZrNi was found for the alloy with composition x = 0.3. Hydrogen desorption pressure–composition–temperature (PCT) measurements were carried out using Sievert''s type volumetric apparatus and the hydrogen desorption pressure–composition isotherms (PCIs) were generated for all the alloys in the temperature range of 523–603 K. A single sloping plateau was observed for each isotherm and the plateau pressure was found to increase with increasing Ni content in ZrCo1−x Ni x alloys at the same experimental temperature. A van''t Hoff plot was constructed using plateau pressure data of each pressure–composition isotherm and the thermodynamic parameters were calculated for desorption of hydrogen in the ZrCo1−x Ni x –H2 systems. The enthalpy and entropy change for desorption of hydrogen were calculated. In addition, the hydrogen absorption–desorption cyclic life studies were performed on ZrCo1−x Ni x alloys at 583 K up to 50 cycles. It was observed that with increasing Ni content the durability against disproportionation of alloys increases. [Copyright &y& Elsevier]