Influence of crystallinity on the structural and hydrogenation properties of Mg2X phases (X=Ni, Si, Ge, Sn)

Janot, Raphaël; Cuevas, Fermín; Latroche, M.; Percheron-Guégan, A.

doi:10.1016/j.intermet.2005.05.003

Cited by 74 publications

(69 citation statements)

References 29 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…No hydrogen uptake could be observed, but the formation of the rhombohedral phase occurred in a shorter time (3 h) than milling under argon (12 h). The decomposition of Mg 2 Sn was not observed, even for long milling times, but the rapid formation of the rhombohedral phase under hydrogen can be understood by the formation of small quantities of MgH 2 leading to the Mg-deficient Mg 9 Sn 5 rhombohedral compound [14].…”

Section: Tinmentioning

confidence: 98%

“…When MgH 2 mixed with Si is heated until the hydrogen is released, it forms the intermetallic Mg 2 Si [13]. While the reaction is reversible in a ball-mill environment with hydrogen [14][15][16], application of pressures of hydrogen to Mg 2 Si up to 185 MPa and 350°C has not yielded a hydride phase [13,17] except when the Mg 2 Si particle size was reduced to 10 nm. Even then, the yield was low and the kinetics very poor [18].…”

Section: Siliconmentioning

confidence: 99%

See 1 more Smart Citation

Mg-based compounds for hydrogen and energy storage

Crivello

Denys

Dornheim³

et al. 2016

Appl. Phys. A

Self Cite

155

View full text Add to dashboard Cite

Magnesium-based alloys attract significant interest as cost-efficient hydrogen storage materials allowing the combination of high gravimetric storage capacity of hydrogen with fast rates of hydrogen uptake and release and pronounced destabilization of the metalhydrogen bonding in comparison with binary Mg-H systems. In this review, various groups of magnesium compounds are considered, including (1) RE-Mg-Ni hydrides (RE = La, Pr, Nd); (2) Mg alloys with p-elements (X = Si, Ge, Sn, and Al); and (3) magnesium alloys with d-elements (Ti, Fe, Co, Ni, Cu, Zn, Pd). The hydrogenation-disproportionation-desorption-recombination process in the Mg-based alloys (LaMg 12 , LaMg 11 Ni) and unusually high-pressure hydrides synthesized at pressures exceeding 100 MPa (MgNi 2 H 3 ) and stabilized by Ni-H bonding are also discussed. The paper reviews interrelations between the properties of the Mg-based hydrides and p-T conditions of the metal-hydrogen interactions, chemical composition of the initial alloys, their crystal structures, and microstructural state.

show abstract

Section: Tinmentioning

confidence: 98%

Section: Siliconmentioning

confidence: 99%

Mg-based compounds for hydrogen and energy storage

Crivello

Denys

Dornheim³

et al. 2016

Appl. Phys. A

Self Cite

155

View full text Add to dashboard Cite

show abstract

“…3), and hence MgH 2 /Si phase segregation, meaning they release the least amount of hydrogen. Milled materials contain a lot of grain boundaries that act as fast diffusion paths for hydrogen atoms [56] hence the faster reaction rates.…”

Section: Desorption Reaction Kineticsmentioning

confidence: 99%

Reaction kinetic behaviour with relation to crystallite/grain size dependency in the Mg–Si–H system

et al. 2015

View full text Add to dashboard Cite

a b s t r a c tAn empirical understanding of the relationship between crystallite size and reaction kinetics for the dehydrogenation of MgH 2 in the presence of Si was determined. MgH 2 was combined with Si under different conditions to obtain varying crystallite sizes of both reactants. Thermal analysis and isothermal desorption were undertaken to obtain reaction kinetic information and therefore determine activation energies as well as the rate limiting step for each of the different crystallite sizes. It was found that there is a strong correlation between crystallite size and activation energy for the growth of the Mg 2 Si phase, however, any correlation between the nucleation (of Mg 2 Si) activation energy was less evident. Direct measurements of kinetic behaviour from a manometric Sieverts apparatus showed that initial reaction kinetics were fastest when MgH 2 was mixed with Si nanoparticles, however, this sample was not able to fully desorb. Data from the Sieverts measurements were then used with well-known theoretical models to determine the rate limiting step of the reaction. The three dimensional Carter-Valensi (or contracting volume) diffusion model could be used to describe the rate limiting step for most of the reactions. These results have led to a proposed mechanism for the formation of Mg 2 Si during the decomposition reaction.

show abstract

“…So far, however, it appeared difficult to reload the formed Mg 2 Si ͑magnesium silicide͒, except during in situ ball milling under a 2.0 MPa hydrogen pressure resulting in the formation of MgH 2 particles with dimensions below about 5 nm. 14 In order to better understand the interaction between Mg, MgH 2 , and Si, we investigated the evolution of Mg-Si and Si-Mg bilayers on glass substrates created by subsequent sputter deposition of the respective species. In particular, we compared these types of bilayer systems upon hydrogen loading at 480 K using a 0.8 MPa hydrogen pressure and after a heat treatment at the same temperature in an inert He gas atmosphere, using XRD, positron depth profiling and electron microscopy for the analysis of the films.…”

Section: Layer-resolved Mg 2 Si Formation In Mg-si Bilayer Systemsmentioning

confidence: 99%

Positron depth profiling of the structural and electronic structure transformations of hydrogenated Mg-based thin films

Eijt

Kind

Singh

et al. 2009

Journal of Applied Physics

View full text Add to dashboard Cite

We report positron depth-profiling studies on the hydrogen sorption behavior and phase evolution of Mg-based thin films. We show that the main changes in the depth profiles resulting from the hydrogenation to the respective metal hydrides are related to a clear broadening in the observed electron momentum densities in both Mg and Mg 2 Ni films. This shows that positron annihilation methods are capable of monitoring these metal-to-insulator transitions, which form the basis for important applications of these types of films in switchable mirror devices and hydrogen sensors in a depth-sensitive manner. Besides, some of the positrons trap at the boundaries of columnar grains in the otherwise nearly vacancy-free Mg films. The combination of positron annihilation and x-ray diffraction further shows that hydrogen loading at elevated temperatures, in the range of 480-600 K, leads to a clear Pd-Mg alloy formation of the Pd catalyst cap layer. At the highest temperatures, the hydrogenation induces a partial delamination of the ϳ5 nm thin capping layer, as sensitively monitored by positron depth profiling of the fraction of ortho-positronium formed at interface with the cap layer. The delamination effectively blocks the hydrogen cycling. In Mg-Si bilayers, we investigated the reactivity upon hydrogen loading and heat treatments near 480 K, which shows that Mg 2 Si formation is fast relative to MgH 2 . The combination of positron depth profiling and transmission electron microscopy shows that hydrogenation promotes a complete conversion to Mg 2 Si for this destabilized metal hydride system, while a partially unreacted, Mg-rich amorphous prelayer remains on top of Mg 2 Si after a single heat treatment in an inert gas environment. Thin film studies indicate that the difficulty of rehydrogenation of Mg 2 Si is not primarily the result from slow hydrogen dissociation at surfaces, but is likely hindered by the presence of a barrier for removal of Mg from the readily formed Mg 2 Si.

show abstract

Influence of crystallinity on the structural and hydrogenation properties of Mg2X phases (X=Ni, Si, Ge, Sn)

Cited by 74 publications

References 29 publications

Mg-based compounds for hydrogen and energy storage

Mg-based compounds for hydrogen and energy storage

Reaction kinetic behaviour with relation to crystallite/grain size dependency in the Mg–Si–H system

Positron depth profiling of the structural and electronic structure transformations of hydrogenated Mg-based thin films

Contact Info

Product

Resources

About