Absorption kinetics and hydride formation in magnesium films: Effect of driving force revisited

Uchida, Helmut Takahiro; Wagner, A.; Hamm, Magnus; Kurschner, J.; Kirchheim, R.; Hjörvarsson, Bjørgvin; Pundt, Astrid

doi:10.1016/j.actamat.2014.11.031

Cited by 55 publications

(70 citation statements)

References 51 publications

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“…This is also observed at a different illumination frequency. Figure S10 shows that, in both cases, the unhydrogenated material is left, which is, on first sight, unexpected from literature for Mg (21), but has also been found in hydrogenated niobium films (58). However, we explain this behavior, on the one hand, again with the formation of the blocking layer, which halts the vertical hydrogen front progression (59), leaving areas at the surface in the pristine state (see fig.…”

Section: Resultssupporting

confidence: 80%

“…As mentioned above, we observe substantial amounts of pristine metallic Mg on the surface of our films, even after 60 min of hydrogenation. Comparing our results to literature findings, this behavior appears unexpected as the film is expected to have fully hydrogenated after saturation (21). This apparent contradiction can be explained when closely examining the changing film morphology and particularly the film expansion.…”

Section: Resultscontrasting

confidence: 62%

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Watching in situ the hydrogen diffusion dynamics in magnesium on the nanoscale

et al. 2020

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Active plasmonic and nanophotonic systems require switchable materials with extreme material contrast, short switching times, and negligible degradation. On the quest for these supreme properties, an in-depth understanding of the nanoscopic processes is essential. Here, we unravel the nanoscopic details of the phase transition dynamics of metallic magnesium (Mg) to dielectric magnesium hydride (MgH2) using free-standing films for in situ nanoimaging. A characteristic MgH2 phonon resonance is used to achieve unprecedented chemical specificity between the material states. Our results reveal that the hydride phase nucleates at grain boundaries, from where the hydrogenation progresses into the adjoining nanocrystallites. We measure a much faster nanoscopic hydride phase propagation in comparison to the macroscopic propagation dynamics. Our innovative method offers an engineering strategy to overcome the hitherto limited diffusion coefficients and has substantial impact on the further design, development, and analysis of switchable phase transition as well as hydrogen storage and generation materials.

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Section: Resultssupporting

confidence: 80%

Section: Resultscontrasting

confidence: 62%

Watching in situ the hydrogen diffusion dynamics in magnesium on the nanoscale

et al. 2020

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“…These growth rate change was same in MgH 2 (int). These results be attributed to extremely low diffusion rate of H in MgH 2 when compared to that in Mg [12,13]. When the whole surface was covered with MgH 2 (sur), the supply rate of H to unreacted internal metallic Mg or AZ significantly decreased, halting the growth of MgH 2 (sur) and MgH 2 (int).…”

Section: Relationships Between Particle Size Of Mgh 2 (Int) and Al Comentioning

confidence: 98%

“…Mg is a metal and when it reacts with H 2 , MgH 2 forms an ionic bond and a weak covalent bond between Mg-H and the valence number of the ion is indicated as Mg 1.91+ and H 0.26− [11]. The diffusion coefficient of H in MgH 2 is several order of magnitude lower when compared to that in Mg: D H Mg = 7 × 10 −11 m 2 s −1 (300 K) in Mg and D H MgH2 = 1.1 × 10 −20 m 2 s −1 (305 K) in MgH 2 [12,13]. Based on these characteristics, powder Mg forms core-shell-type structure hydride, MgH 2 as a shell and unreacted Mg remains in the core [14,15] making progress of completely hydrogenation difficult.…”

Section: Introductionmentioning

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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“…The anisotropy causes a switchover of the energies of tetrahedral and octahedral interstitial sites. Magnesium−hydrogen thin films have been studied targeting the elastic destabilization of the thermodynamically very stable Mg−hydride phase as well as its nucleation and growth dynamics . For yttrium−hydrogen thin films the metal‐to‐semi‐conductor transition upon H absorption was investigated .…”

Section: Introductionmentioning

confidence: 99%

Structural Phase Transitions in Niobium Hydrogen Thin Films: Mechanical Stress, Phase Equilibria and Critical Temperatures

et al. 2019

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Metal−hydrogen (M−H) systems offer grand opportunities for studies on fundamental aspects of thermodynamics and kinetics. When the system size is reduced to the nanoscale, microstructural defects as well as mechanical stress affect the systems’ properties. This is contemplated for the model system of epitaxial niobium−hydrogen (Nb−H) thin films. Hydrogen absorption in metals commonly leads to lattice expansion which is hindered when the metal adheres to a flat rigid substrate. Consequently, high mechanical stress of about −10 GPa for 1 H/Nb are predicted, in theory. However, metals cannot yield such high stresses and respond with plastic deformation, commonly limiting measured stresses to −2 to −3 GPa for 100 nm Nb−H films. It will be shown that the coherency state changes with film thickness reduction, shifting the onset of plastic deformation to larger hydrogen concentrations. Below critical film thicknesses, plastic deformation is fully absent. The system then behaves purely elastic and ultra‐high stress of about −10 (±2) GPa can be obtained. Arising stress controls the phase stability of M−H systems, and the coherency state strongly affects the nucleation and growth dynamics of the phase transition. In case of Nb−H thin films of less than 8 nm thickness the common phase transformation from the α‐phase solid solution to the hydride phase is completely suppressed at 300 K. Related effects can be utilised to optimise metal−hydrides used in applications.

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Absorption kinetics and hydride formation in magnesium films: Effect of driving force revisited

Cited by 55 publications

References 51 publications

Watching in situ the hydrogen diffusion dynamics in magnesium on the nanoscale

Watching in situ the hydrogen diffusion dynamics in magnesium on the nanoscale

Magnesium-Based Materials for Hydrogen Storage: Microstructural Properties

Structural Phase Transitions in Niobium Hydrogen Thin Films: Mechanical Stress, Phase Equilibria and Critical Temperatures

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