Hydrogen In Solid Solution Research Articles

Hydrogen states and contents in superelastic TiNi alloy after cathodic polarization

The superelastic TiNi alloy sometimes undergo failure under wet environments owing to hydrogen absorption and/or hydride formation; however, the effects of electrochemical conditions such as potential and pH and the hydrogen state and content on the susceptibility of the material to such degradation processes remain unveiled. In this study, the hydrogen content in the solid-solution state and hydride state in superelastic TiNi alloy were determined upon applying a constant cathodic potential in sulfate solution, and the dependence of the contents on the potential and solution pH was investigated. The formation of hydride was detected via X-ray diffraction (XRD), and the hydrogen content in each state was determined by means of thermal gas desorption spectroscopy (TDS). The specimen receiving a smaller cathodic charge density showed no hydride in the XRD pattern and one obvious peak in hydrogen desorption rate at higher temperature in the TDS profile. In contrast, larger charge density induced hydride formation and two peaks in the hydrogen desorption rate at two different temperatures. The peaks at higher and lower temperatures in the TDS profile can be attributed to hydrogen in solid-solution and hydride states, respectively. The logarithmic content of hydrogen in each state increased almost linearly with increasing logarithmic charge density. Linear relationships were obtained irrespective of potential and pH, with slopes of 0.57 and 0.99 for the solid-solution and hydride states, respectively. The susceptibility to environment-assisted cracking suddenly increased at a charge density of 0.025 MC·m−2, at which the hydrogen contents in the solid-solution state and hydride states were determined to be 30 and 5 mass ppm, respectively.

Evaluation of hydrogen storage performance of Ti0.25Zr0.25V0.15Nb0.15Ta0.2 high-entropy alloy using calorimetric technique

The features of phase transformations during interaction of BCC-type Ti0.25Zr0.25V0.15Nb0.15Ta0.2 high-entropy alloy (HEA) with hydrogen and the accompanying thermal effects have been examined using the Tian-Calvet calorimetric technique. The alloy was produced by the pendent drop melt extraction method in the form of microfibers and then coated with a thin layer of palladium to eliminate the preliminary high-temperature activation and enable first hydrogenation at room temperature. Two reaction stages were distinguished on the measured heat emission curves. Using XRD data, these stages were attributed to the formation of a BCC-type hydrogen solid solution and a phase transition to FCC-type dihydride phase. Recorded values of the reaction enthalpy decrease in absolute terms from 145 kJ/mol H2 (dilute solid solution) to 73–77 kJ/mol H2 (BCC→FCC) and to 20 kJ/mol H2 (H solution in FCC dihydride). The overall heat emission of the entire process as a whole is 110 kJ/ mol H2. The course of the dehydrogenation process depends strongly on the applied temperature and at 493 K results in the formation of a BCT-type monohydride, which was not detected during hydrogenation. The detailed calorimetric data obtained here significantly change the previously existing ideas about thermal effects during this type HEAs hydrogenation, based on calculations using the Van't-Hoff equation. The reported findings are of special importance for various hydrogen related applications of HEAs

Optimization of V-Ti-Fe hydrogen storage alloy based on orthogonal experiments

Vanadium-based solid solution hydrogen storage alloys have attracted much attention because of their high hydrogen capacity, mild hydrogen absorption- desorption conditions, and high safety. However, the V-Ti-Fe alloys, developed at low cost, have a relatively low effective capacity and is unsuitable for practical production. In this work, (VxFe100-x)100-yTiy-z%Ce (x=0.83,0.85,0.87; y=16,18,20; z=1,2,3) alloys are designed by orthogonal method to investigate the effect of compositions on the microstructure and hydrogen storage properties. It is shown that the effective hydrogen capacity and desorption plateau pressure of the (VxFe100-x)100-yTiy-z%Ce alloy are related to multiple factors, such as lattice constants, tetrahedral interstitials of the BCC and BCT phases, electron concentration and Vickers hardness. The optimized alloy (V87Fe13)82Ti18-1 %Ce based on the orthogonal experiments shows a reversible hydrogen storage capacity of 2.17 wt% and a desorption plateau pressure of 0.373 MPa at 70°C. The reversible hydrogen capacity of (V87Fe13)82Ti18-1 %Ce is superior to most V-Ti-Fe alloys.

The influence of solid solution hydrogen and precipitated hydride on the creep behavior of Zircaloy-4

The effect of hydrogen on the creep rates of Zircaloy-4 claddings especially in the low hydrogen concentration remains largely unexplored while creep is considered a main mechanism for spent nuclear fuel failure along with hydride-induced mechanisms. Here, we study the influence of hydrogen on the creep behavior of low burnup Zircaloy-4 cladding from a microstructural perspective. The creep tests at 450 °C and 120 MPa reveal that specimens with hydrogen contents below the terminal solid solubility for dissolution (TSSD) at the test temperature exhibited decreased creep resistance as hydrogen concentration increased, while those with hydrogen contents above the TSSD demonstrated increased creep resistance with higher hydrogen concentration. The lowest creep resistance occurs at the hydrogen concentration corresponding to the TSSD. Additional microstructural analyses using electron backscattered diffraction (EBSD) show the increasing intra-granular/inter-granular hydride ratio in the post-crept specimens as the hydrogen concentration decreases, suggesting that hydrogen atoms in solid solution aid creep progression. Also, an increased amount of twin boundaries is observed in post-crept specimens with hydrogen concentration above TSSD. These results suggest that creep assessment in spent nuclear fuels may require caution especially in low-burnup regime.

Thermal creep in a pre-hydrided Zr1 % Nb nuclear fuel cladding tube

The effect of hydrogen on the thermal creep behaviour of Zr1 %Nb alloy fuel cladding tubes for use in light water-cooled nuclear reactors was investigated. The tubes were hydrogen charged using an alternative method with a hydrogen content in the range 371–656 wppm H. Comparative constant-stress creep tests were carried out at 350 °C, under stress ranging from 150 to 225 MPa, on both non-hydrided and hydrided tubes. These creep tests were followed by a microstructural analysis of the specimens exposed to creep using SEM and TEM. It was found that these creep tests were conducted in the transition zone between the power-law and power-law breakdown creep regions. Hydrogen, either in solid solution (atomic hydrogen) or as precipitated zirconium hydrides, altered the creep behaviour of the hydrided tubes, and the impact of hydrogen depended on the hydrogen content CH. It was observed that under the creep loading conditions considered here with a hydrogen content CH < 450 wppm H, the presence of hydrogen resulted in an increase in the creep rate; however, a higher concentration of hydrogen caused a decrease in the creep rate. The difference in the effects of hydrogen on the creep rate was explained by the different roles of hydrogen in solid solution and in the form of zirconium hydride precipitates.

Hydrogen enhanced localised plasticity of single grain α titanium verified by in-situ hydrogen microcantilever bending

The effect of hydrogen on the micromechanical characteristics of pure grade 2 titanium was investigated by comparing prenotched microcantilever bending in air versus in-situ electrochemical hydrogen charging. The nanoscale interaction between hydrogen and the metal's defects was analysed in three different grain orientations, i.e. the top surface parallel to {101‾2}, {0001}, and {202‾1}. The subsequent high resolution post-mortem characterisation enabled to characterise the interplay between hydrogen in solid solution and the dislocations in the local deformation process. The results showed that hydrogen facilitated a localised plasticity mechanism, causing hydrogen assisted degradation at the applied low hydrogen concentration below the hydride formation threshold. Meanwhile, hydrogen provoked a reduction in defect formation energy, following the defactant concept, which was responsible for a softening effect on the yield stress and flow stress. Furthermore, due to the anisotropic characteristics of the α titanium hexagonal close packed crystal lattice, the susceptibility to hydrogen effects also depended on the grain orientation. This single grain in-situ micromechanical testing is complementing the existing macroscaled identification of hydrogen effects in α titanium.

Multiscale evaluation of hydrogen-assisted mechanical degradation in grade 2 titanium

The mechanism of hydrogen embrittlement in grade 2 titanium was studied by a combined micro and nanoscale approach. Insights into the hydrogen related deformation and degradation mechanisms were acquired via a unique characterisation procedure, correlating the topological observations on the fracture surface after tensile testing to the dislocation arrangement underneath. Focused ion beam lift-out was employed to extract a subsurface slice perpendicular to the fracture surface. High resolution characterisation provided information about the dislocation configuration and active hydrogen-assisted degradation mechanism. A high hydrogen content forms a brittle titanium hydride phase, failing via hydride cleavage. At a moderate hydrogen quantity, hydrogen in solid solution is responsible for a ductility decrease via the hydrogen-enhanced localised plasticity mechanism.

Large-scale production of BCC solid solution hydrogen storage alloy

In this work, 52Ti–12V–36Cr + 4 wt% Zr alloy was synthesized at laboratory and large scales for comparative analysis of the hydrogen storage performance. A 5 g and 2 kg BCC solid solution alloy is synthesized by arc melting and induction melting, respectively. Crystal structure investigation revealed that both samples crystallized into a primary BCC phase and a secondary laves phase with no significant difference in the overall XRD pattern. First hydrogenation studies showed the maximum hydrogen storage capacity of arc melted alloy (AM) and induction melted alloys (IM) alloy are 3.5 wt% and 2.9 wt%, respectively, at room temperature under a hydrogen pressure of 20 bar. No visible incubation period was observed in AM alloy, whereas IM alloy showed an incubation period of 32 min with slower kinetics. The appearance of the incubation period and sluggish kinetics can be due to the formation of a passive layer during induction melting that changes the hydrogen sorption properties. The microstructural analysis confirmed the carbon contamination from the induction melting crucible and formation of the TiC phase in the matrix, which was absent in the AM alloy, significantly affecting hydrogen storage capacity. The enthalpy and entropy of 2 kg alloy are −65.84 kJ/mol and 188.92 J/mol-K.

Hydrogen enhanced localized plasticity in zirconium as observed by digital image correlation

Hydrogen embrittlement in zirconium alloys is a highly relevant research topic, important for ensuring the integrity of nuclear fuel clads. While the presence of hydrides in zirconium-based clad is a well-known risk factor due to their brittleness, the effect of the presence of hydrogen in solid solution is unclear.According to the Hydrogen Enhanced Localized Plasticity (HELP) model, hydrogen in solid solution may affect the mechanical performance of a metal by increasing dislocation mobility due to the shielding effect that hydrogen has on the interaction of dislocations with other types of defects. In the presented work, the presence of HELP has been assessed in Zircaloy-4 samples, under conditions relevant to the storage of spent nuclear fuel.Elevated temperature tensile tests were performed on samples containing localized areas of higher hydrogen concentration, as quantified by neutron radiography. Digital Image Correlation (DIC) analysis was performed on the specimen surfaces for quantitative characterization of strain heterogeneity during deformation to identify the regions where the plastic strain localization occurs.These regions could be correlated to elevated amounts of hydrogen in solid solution, that is, in the location immediately adjacent to dissolving hydrides, or in the areas of the samples with local hydrogen concentration close to the expected terminal solid solubility limit (TSS) in the test conditions.The results confirm the presence of localized softening caused by solid solution hydrogen, indicating that the HELP mechanism needs to be taken into account when modeling the mechanical response of zirconium-based nuclear fuel clads at elevated temperatures.

The First Application of Palladium–Phosphorus Catalysts in the Direct Synthesis of Hydrogen Peroxide: Reasons for the Promoting Action of Phosphorus

The main reasons for the promoting effect of phosphorus on the properties of Pd–P/ZSM-5 palladium catalysts in the direct synthesis of H2O2 from H2 and O2 under mild conditions are considered based on data from X-ray photoelectron spectroscopy (XPS), X-ray powder diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), and inductively coupled plasma mass spectrometry (ICP MS). It is shown that the introduction of phosphorus into the composition of the catalyst affects the dispersity, the electronic state of palladium in the surface layer, and the surface concentration of phosphate and phosphite ions. An increase in the H2O2 yield is favored by an increase in the dispersion of Pd–P-catalysts, inhibition of the side process of H2O2 decomposition by surface phosphate and phosphite ions, and a decrease in the solubility of hydrogen in solid solutions of phosphorus in palladium.

ВЛИЯНИЕ ФАЗОВОГО СОСТАВА МАТЕРИАЛОВ СИСТЕМЫ ТИТАН-ЖЕЛЕЗО НА ВОДОРОДНУЮ ЕМКОСТЬ

The hydrogen adsorption properties of the phases in the materials of the Ti-Fe system have been considered. It has been shown that an increase in the content of β-Ti and Ti2Fe in their structure is accompanied by a significant increase in hydrogen absorption during primary hydrogenation. The methods of mathematical data processing based on the classical Avraham-Yerofeev equation allowed us to reveal that hydrogen saturation of the materials under consideration starts from formation of hydrogen solid solutions in the initial material phases and continues with formation of the hydride phases after the latent period.

Experimental investigations with neutron radiography of hydrogen effects by elastic stresses on cladding tubes under conditions similar to interim dry storage

Abstract. During operation in light-water reactors, Zircaloy cladding tubes take up hydrogen that precipitates under specific temperature–pressure conditions after operation in the form of zirconium hydrides. These zirconium hydrides have a detrimental effect on the mechanical stability of the cladding tubes. The conditions for their formation and their orientation need to be forecasted in order to determine that the spent nuclear fuel remains shielded during interim dry storage. Internal and external stresses that affect the cladding tubes throughout their slow cooling process during interim dry storage may worsen and accelerate the cladding tubes' embrittlement with regard to possible reorientation processes of zirconium hydrides. Generally, hydrogen in solid solution follows gradients in temperature, concentration, and stress. Consequently, hydrogen moves from higher to lower temperatures and from lower to higher stresses due to the thermodynamically more favourable conditions. In order to investigate elastic stress conditions similar to those during interim dry storage of hydrogenated cladding tubes, a modified mobile tensile testing machine was designed to elongate zirconium samples under defined temperatures of up to 500 ∘C. During the experiments, hydrogen movements within the samples are monitored by in situ neutron radiography. Because of the very low neutron cross section of zirconium, the metal is nearly invisible for neutrons, and the contrarily behaving hydrogen that scatters neutrons strongly appears as dark contrast in neutron images. Due to the sample's different cross section profile, the tensile stress created by the tensile testing machine is amplified and thus should lead to visible hydrogen movements. This paper describes neutron radiography experiments under different temperature–time conditions with hydrogenated tensile zirconium samples that simulate stress conditions of cladding tubes during interim dry storage.

Thermochemical Analysis of Hydrogenation of Pd-Containing Composite Based on TiZrVNbTa High-Entropy Alloy

The microcalorimetric hydrogen titration technique combined with conventional volumetric measurements has been used to reveal peculiarities of the hydrogenation of the single-phase TiZrVNbTa equiatomic high-entropy alloy. The alloy has been produced in the form of microfibers by the pendent drop melt extraction technique. Palladium coating of the fibers has been applied to enable first hydrogenation at room temperature without additional activation. An analysis of the obtained data allows us to evaluate the dependence of hydrogenation enthalpy on the hydrogen concentration in the alloy. Three concentration ranges, presumably related to the formation of the hydrogen solid solution, monohydride and dihydride phases, have been identified, and the corresponding ΔH values of about −100, −80 and −60 kJ/mol H2, respectively, have been determined.

АНАЛИЗ ВЛИЯНИЯ ФАЗОВОГО СОСТАВА МАТЕРИАЛОВ СИСТЕМЫ "ТИТАН-ЖЕЛЕЗО" НА ВОДОРОДНУЮ ЕМКОСТЬ ПРИ ПЕРВИЧНОМ ГИДРИРОВАНИИ

The hydrogen adsorption properties of the phases in the materials of the Ti-Fe system have been considered. It has been shown that an increase in the content of β-Ti and Ti2Fe in their structure is accompanied by a significant increase in hydrogen absorption during primary hydrogenation. The methods of mathematical data processing based on the classical Avraham-Yerofeev equation allowed us to reveal that hydrogen saturation of the materials under consideration starts from formation of hydrogen solid solutions in the initial material phases and continues with formation of the hydride phases after the latent period.

Capacity degradation mechanism of ternary La–Y–Ni-based hydrogen storage alloys

La–Y–Ni-based alloys are suitable candidates for hydrogen storage materials. However, their applications are limited by their rapid capacity degradation. In this study, the capacity degradation mechanism of ternary La–Y–Ni-based alloys and the effect of the La/Y ratio on their cyclic stability are investigated from the perspective of electrochemistry and solid/H2 reactions. During hydrogen absorption/desorption on LaY2Ni9, La2Y4Ni21 and La5Y10Ni57 alloys, the discrete expansion/contraction properties of the [AB5] and [A2B4] subunits in the hydrogen solid solution and hydrides leads to the lattice strain, which results in pulverization. Severe pulverization aggravates the oxidation/corrosion of the alloys caused by active La and Y. The amorphization/pulverization and oxidation/corrosion of the alloys can be reduced by adjusting their [AB5]/[A2B4] subunit ratio to decrease the lattice strain; this can enhance their cyclic stability. The cyclic stability of the La–Y–Ni-based alloys in the electrolyte decreases with the lower La/Y ratio. This trend is opposite to that observed in the solid/H2 system. Y-poor and Y-rich alloys are suitable for electrochemical and solid-state hydrogen storage applications, respectively. This work provides insights on improving the cycle life of La–Y–Ni-based hydrogen alloys.

Simulation of hydrogen diffusion along the axial direction in zirconium cladding tube during dry storage

This study presents an updated mHNGD (modified hydrogen nucleation-growth-dissolution) model by improving atomic fraction of solid solution hydrogen with the use of instantaneous solid solution concentration and carefully selecting hydrogen solubility curves specific to reactor cladding materials. An explicit finite difference method was applied to simultaneously solve diffusion and phase change kinetics and ensure stable solution. The code validation with past experiments demonstrate improved accuracy. A prototypic hottest fuel pin in assembly average discharge burnup of 50 MWd/kgU of CASTOR® V/21 dry storage cask was simulated. The result of the reference case shows that the increase in the hydrogen amount at the upper end of the cladding due to hydrogen migration after ∼20 years of dry storage was limited to ∼50 wt.ppm with the initial Peak Cladding Temperature (PCT) of 394 ℃. The aspirational increase in discharge burnup to 70 MWd/kgU results in the upper end hydrogen increase to ∼80 wt.ppm with the same initial PCT. This study demonstrates that hydrogen migration along the axial direction during dry storage practically poses no safety challenge as its amount is limited and can be further alleviated by extending the wet storage period.

Determination of hydrogen diffusibility and embrittlement susceptibility of high-strength steel evaluated at different temperatures based on the local equilibrium theory

The effects of diffusible or non-diffusible hydrogen on hydrogen trapping states and hydrogen embrittlement susceptibility of cold-drawn pearlitic steel have been quantitatively evaluated at temperatures of 30 °C and 240 °C based on Oriani's local equilibrium theory. Hydrogen absorbed in cold-drawn pearlitic steel had two trapping states; Peak 1 H desorbed below 200 °C and Peak 2 H desorbed above 200 °C as determined by thermal desorption analysis. Peak 1 H with a binding energy between hydrogen and a trapping site (Eb) of 56 kJ·mol−1 was diffusible and harmful to hydrogen embrittlement at 30 °C. That was because the Eb of Peak 1 H was lower than that of Oriani's local equilibrium condition of 69 kJ·mol−1 at 30 °C. In contrast, Peak 2 H with an Eb of 76 kJ·mol−1 was non-diffusible and innocuous. That was because the Eb of Peak 2 H was higher than 69 kJ·mol−1 at 30 °C. However, Peak 2 H was diffusible and harmful to hydrogen embrittlement at 240 °C. That was because the Eb of Peak 2 H was lower than that of the local equilibrium condition of 117 kJ·mol−1 at 240 °C. These findings indicate that hydrogen diffusibility and embrittlement at a certain temperature can be determined by the local equilibrium condition. Hydrogen embrittlement at 240 °C was presumably caused by solid-solution hydrogen because hydrogen was not trapped at dislocations and grain boundaries, and vacancy-type defects formed by plastic strain were annihilated at 240 °C.

Finite element modeling of hydrogen migration and hydride precipitation in Zr alloys

The Finite Element software, ABAQUS® together with subroutine codes written in FORTRAN is used to fully couple the mass diffusion – displacement analysis of hydrogen redistribution and hydride precipitation in a stress gradient. Since the redistribution of hydrogen in solid solution is driven by gradients in H concentration, stress, and temperature, two different precipitation models were investigated in specimens subjected to such gradients, and the results validated against available experimental data and analytical solutions where applicable. Simulation results obtained with the new Hydride Nucleation Growth and Dissolution (HNGD) model that considers growth in the hysteresis region show closer agreement with experimental observations, signifying that the previous hydride precipitation model may be underestimating the amount of hydride precipitation.

Determination of the hydrogen heat of transport in Zircaloy-4

During operation in a nuclear reactor, Zr-based nuclear fuel cladding is subject to waterside corrosion which can lead to hydrogen ingress. The hydrogen that enters the material will migrate to colder spots and precipitate as zirconium hydrides if the hydrogen content exceeds the hydrogen terminal solid solubility in the material. Since a temperature gradient is established in the radial direction of the cladding during operation, the hydrides can preferentially precipitate at the colder outer surface of the cladding. Other gradients can also occur in the longitudinal and azimuthal directions of the cladding tube. As a consequence, hydrogen redistributes itself in response to the concentration and temperature gradients present in the sample. The response of the hydrogen in solid solution to temperature gradients is governed by the heat of transport Q* as a function of temperature, so it can be used in the BISON code. A set of experiments was set up to determine the heat of transport (Q*), in which a uniformly hydrided Zircaloy-4 sample is annealed under a fixed temperature gradient at a range of temperatures, and the resulting hydrogen distribution is analyzed to determine Q*. The results are discussed in terms of existing literature.

Design of multicomponent alloys with C14 laves phase structure for hydrogen storage assisted by computational thermodynamic

Design methods with predictive properties modeling are paramount tools to explore the vast compositional field of multicomponent alloys. The applicability of an alloy as a hydrogen storage media is governed by its thermodynamic properties, which can be represented by pressure-composition-temperature (PCT) diagrams. Therefore, the prediction of PCT diagrams for multicomponent alloys is fundamental to design alloys with optimized properties for hydrogen storage applications. In this work, a strategy to design C14-type Laves phase multicomponent alloys for hydrogen storage assisted by computational thermodynamic is presented. Since electronic and geometrical factors play an important role in the formation and stability of multicomponent Laves phase, valence electron concentration (VEC), atomic radius ratio (rA/rB), and atomic size mismatch (δ) are initially considered to screen a high number of compositions and find alloy systems prone to form Laves phase structure. Then, CALPHAD method was employed to investigate the phase stability of alloys of the (Ti, Zr or Nb)(V, Cr, Mn, Fe, Co, Ni, Cu, or Zn)2 system, resulting in 440 alloys prone to solidify as C14 Laves phase structure. In addition, we present a thermodynamic model, which allowed calculating the PCT diagrams of the suggested C14 Laves phase alloys based solely on the alloy's composition. For these calculations, the entropy and enthalpy of hydrogen solution in the C14 Laves phase were modelled considering that hydrogen solid solution occurs only at the A2B2-type interstitial sites of the C14 Laves phase structure. Therefore, the room temperature PCI diagrams of 440 C14 Laves phase multicomponent alloys were calculated. Experimental pressure-composition-isotherm (PCI) diagrams of six C14 Laves phase alloys were compared against the calculated ones. Although the PCI curve shapes were not perfectly predicted for some alloys, the order of magnitude of the equilibrium pressure for all the tested alloys were well predicted. The results show that C14 Laves phase multicomponent alloys within a wide range of equilibrium pressure at room temperature can be obtained, being promising candidates for different hydrogen storage applications, such as room temperature tanks, hybrid tanks and Ni-metal hydrides batteries.