Discovering a new MgH2 metastable phase

Formation of a new metastable fcc-MgH2 nanocrystalline phase upon mechanically-induced plastic deformation of MgH2 powders is reported. Our results have shown that cold rolling of mechanically reacted MgH2 powders for 200 passes introduced severe plastic deformation of the powders and led to formati...

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Bibliographic Details
Published in:RSC advances 2018-01, Vol.8 (56), p.32003-32008
Main Authors: El-Eskandarany, Mohamed Sherif, Banyan, Mohammad, Al-Ajmi, Fahad
Format: Article
Language:English
Subjects:
Ball milling
Chemistry
Cold rolling
Cubic lattice
Diffraction
Dislocations
Hydrogen storage
Lathes
Metal hydrides
Metastable phases
Phase transitions
Plastic deformation
Reaction kinetics
Stacking faults
Storage capacity
Turning (machining)
Twinning
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Summary:Formation of a new metastable fcc-MgH2 nanocrystalline phase upon mechanically-induced plastic deformation of MgH2 powders is reported. Our results have shown that cold rolling of mechanically reacted MgH2 powders for 200 passes introduced severe plastic deformation of the powders and led to formation of micro-lathes consisting of γ- and β-MgH2 phases. The cold rolled powders were subjected to different types of defects, exemplified by dislocations, stacking faults, and twinning upon high-energy ball milling. Long term ball milling (50 hours) destabilized β-MgH2 (the most stable phase) and γ-MgH2 (the metastable phase), leading to the formation of a new phase of face centered cubic structure (fcc). The lattice parameter of fcc-MgH2 phase was calculated and found to be 0.4436 nm. This discovered phase possessed high hydrogen storage capacity (6.6 wt%) and revealed excellent desorption kinetics (7 min) at 275 °C. We also demonstrated a cyclic-phase-transformation conducted between these three phases upon changing the ball milling time to 200 hours.
ISSN:2046-2069
DOI:10.1039/c8ra07068g