Influence of hydrogen loading conditions on the blocking effect of nanocrystalline Mg films

Uchida, Helmut Takahiro; Kirchheim, R.; Pundt, Astrid

doi:10.1016/j.scriptamat.2011.01.036

Cited by 25 publications

(18 citation statements)

References 29 publications

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“…Consequently, precipitation of hydrides such as coherent hydride clusters37 may have occurred. As the hydrides habit on basal planes with small thickness along <c>, they block H diffusion along <c>, reducing D c without affecting D a much, similar to the situation for H in hcp Mg36.…”

Section: Resultsmentioning

confidence: 80%

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Anisotropic hydrogen diffusion in α-Zr and Zircaloy predicted by accelerated kinetic Monte Carlo simulations

Zhang

Jiang

Bai

2017

Sci Rep

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This report presents an accelerated kinetic Monte Carlo (KMC) method to compute the diffusivity of hydrogen in hcp metals and alloys, considering both thermally activated hopping and quantum tunneling. The acceleration is achieved by replacing regular KMC jumps in trapping energy basins formed by neighboring tetrahedral interstitial sites, with analytical solutions for basin exiting time and probability. Parameterized by density functional theory (DFT) calculations, the accelerated KMC method is shown to be capable of efficiently calculating hydrogen diffusivity in α-Zr and Zircaloy, without altering the kinetics of long-range diffusion. Above room temperature, hydrogen diffusion in α-Zr and Zircaloy is dominated by thermal hopping, with negligible contribution from quantum tunneling. The diffusivity predicted by this DFT + KMC approach agrees well with that from previous independent experiments and theories, without using any data fitting. The diffusivity along is found to be slightly higher than that along , with the anisotropy saturated at about 1.20 at high temperatures, resolving contradictory results in previous experiments. Demonstrated using hydrogen diffusion in α-Zr, the same method can be extended for on-lattice diffusion in hcp metals, or systems with similar trapping basins.The diffusion of hydrogen in hcp metals has attracted extensive research interests for both its scientific merit and technological importance. It is the rate-limiting step for solid hydrogen storage in Mg based alloys 1 and for mechanical property degradation in Ti 2 and Zr alloys 3 . For instance, Zr-based alloys such as Zircaloy2 and Zircaloy4 (denoted as Zircaloy) are widely used as the cladding of fuel rods in nuclear reactors for their excellent corrosion resistance and very low absorption cross-section of thermal neutrons. During their service time, these alloys operate in extremely harsh environments, combining high temperatures and corrosive coolants such as water. In light water reactors, Zircaloy claddings directly contact coolant water, with a local temperature at the interface of about 400 °C. Consequently, Zircaloy react with water, producing an oxide layer at the interface and hydrogen (H), of which a substantial fraction infiltrates into the cladding interior 3 . Due to the low solubility of H in α -Zr, which is the main component of claddings, hydrides precipitate in the cladding matrix 4-6 . Hydride formation can detrimentally affect the cladding integrity primarily in two ways. First, the formation of hydrides reduces the fracture toughness of the cladding matrix 7,8 , increasing the probability of fuel failure when fuel-cladding mechanical interaction (PCMI) occurs during fuel operation. Second, upon cyclic thermal and mechanical loadings, hydrides can dissolve and reorient. During used-fuel storage, fracture may propagate via the so-called delayed-hydride-cracking (DHC) mechanism, which is induced by the dissolving of matrix hydrides and their subsequent re-formation at crack tips 3,9 . To mitigate thes...

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Section: Resultsmentioning

confidence: 80%

“…may be explained by the so-called blocking layer effect observed in experiments on H in hcp Mg36. In Zhang et al ., H diffusivity was measured using the surface segregation approach15.…”

Section: Resultsmentioning

confidence: 94%

Anisotropic hydrogen diffusion in α-Zr and Zircaloy predicted by accelerated kinetic Monte Carlo simulations

Zhang

Jiang

Bai

2017

Sci Rep

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“…In thin films, due to a larger amount of grain boundaries [10] the α-and the β-phase solubility limits are usually affected by the high defect concentration, changing the actual plateau width. Indeed, recent electrochemical studies observe a substantial-2 orders of magnitude-increase of the α-phase solubility in Mg films as compared to bulk [27]. The same authors observed a decrease in the β-phase solubility down to 1.8 H/M for 165 nm thick Mg film.…”

Section: Hysteresis Behavior and Stress-strain Analysis Of Mg/ta/pd Tmentioning

confidence: 88%

“…A possible cause for the discrepancy between various techniques is connected, in our opinion, to the different hydrogen concentration in the films upon hydrogenation. Thus, due to relatively high current densities used in the electrochemical measurements, 300 nm thick Mg films were loaded only up to 1.2 H/M [27]. In order to prevent delamination of the films from the substrate in the gravimetric experiments, thick Mg films (380-800 nm) were allowed to absorb no more than 0.3 H/M [25].…”

Section: Hydrogenography Experiments On Mg/ta/pd Filmsmentioning

confidence: 99%

Thermodynamic Properties, Hysteresis Behavior and Stress-Strain Analysis of MgH2 Thin Films, Studied over a Wide Temperature Range

2012

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Using hydrogenography, we investigate the thermodynamic parameters and hysteresis behavior in Mg thin films capped by Ta/Pd, in a temperature range from 333 K to 545 K. The enthalpy and entropy of hydride decomposition, ∆H des = −78.3 kJ/molH 2 , ∆S des = −136.1 J/K molH 2 , estimated from the Van't Hoff analysis, are in good agreement with bulk results, while the absorption thermodynamics, ∆H abs = −61.6 kJ/molH 2 , ∆S abs = −110.9 J/K molH 2 , appear to be substantially affected by the clamping of the film to the substrate. The clamping is negligible at high temperatures, T > 523 K, while at lower temperatures, T < 393 K, it is considerable. The hysteresis at room temperature in Mg/Ta/Pd films increases by a factor of 16 as compared to MgH 2 bulk. The hysteresis increases even further in Mg/Pd films, most likely due to the formation of a Mg-Pd alloy at the Mg/Pd interface. The stress-strain analysis of the Mg/Ta/Pd films at 300-333 K proves that the increase of the hysteresis occurs due to additional mechanical work during the (de-)hydrogenation cycle. With a proper temperature correction, our stress-strain analysis quantitatively and qualitatively explains the hysteresis behavior in thin films, as compared to bulk, over the whole temperature range. OPEN ACCESSCrystals 2012, 2 711

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“…MgH 2 (int) formed only along Mg grain boundary, and did not form in Mg crystal grain. It is known that the diffusion of H atoms in Mg made the grain boundary a preferential route [20]. Therefore, the reason why MgH 2 (int) preferentially formed on grain boundary would be one factor of the fast diffusion of H atoms at Mg grain boundary.…”

Section: Formation Of Mgh 2 In Mg Corementioning

confidence: 99%

Magnesium-Based Materials for Hydrogen Storage: Microstructural Properties

Kondo¹,

Hiroyuki²

2020

Magnesium - The Wonder Element for Engineering/Biomedical Applications

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Magnesium (Mg) is hydrogenated as core-shell-type hydride. Therefore, increase of absorption capacity to the theoretical hydrogen capacity is still one of the most important issues for the hydrogen storage materials. In this study, the procedure of the core-shell structure as well as effect of Al concentration in Mg on the growth MgH2 in Mg were investigated. MgH2 was formed on the surface as well as inside of unreacted Mg core. The inside MgH2 was formed in a granular form on Mg grain boundary and its size increased by applying plastic deformation. Thickness of the surface MgH2 and size of the internal MgH2 increased with an increase in hydrogenation time until the hydride surface was completely covered with MgH2. However, the growth of the surface and internal MgH2 came to a halt after the surface was covered with MgH2. From these results, supplying H from metal side was dominantly contributed for growth of the surface and internal MgH2 because diffusion rate of H in Mg was much higher than that in MgH2. In addi tion, the growth of internal MgH2 as well as control of surface MgH2 can contribute to the promotion of the complete hydrogenation of Mg-based hydrogen storage materials.

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Influence of hydrogen loading conditions on the blocking effect of nanocrystalline Mg films

Cited by 25 publications

References 29 publications

Anisotropic hydrogen diffusion in α-Zr and Zircaloy predicted by accelerated kinetic Monte Carlo simulations

Anisotropic hydrogen diffusion in α-Zr and Zircaloy predicted by accelerated kinetic Monte Carlo simulations

Thermodynamic Properties, Hysteresis Behavior and Stress-Strain Analysis of MgH2 Thin Films, Studied over a Wide Temperature Range

Magnesium-Based Materials for Hydrogen Storage: Microstructural Properties

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