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Analysis of deformation twins and the partially dehydrogenated microstructure in nanocrystalline magnesium hydride (MgH2) powder / M. Danaie in Acta materialia, Vol. 58 N° 8 (Mai 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 8 (Mai 2010) . - pp. 3162–3172 Titre : Analysis of deformation twins and the partially dehydrogenated microstructure in nanocrystalline magnesium hydride (MgH2) powder Type de document : texte imprimé Auteurs : M. Danaie, Auteur ; S.X. Tao, Auteur ; P. Kalisvaart, Auteur Année de publication : 2011 Article en page(s) : pp. 3162–3172 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Hydrogen  storage  TEM  Magnesium  hydride Résumé : Cryo-stage transmission electron microscopy (TEM), supported by Density Functional Theory (DFT), is employed to explore the microstructure of magnesium hydride (MgH2) powders. Mechanical milling results in deformation twinning of the hydride. The crystallography of the twins is established. DFT analysis shows that the twin unit cell is just as thermodynamically stable as the undeformed α-MgH2 matrix. It is hypothesized that the twins contribute significantly to the observed milling-induced kinetic enhancement by acting as high diffusivity paths for hydrogen. Energy-filtered TEM analysis on partially desorbed MgH2 demonstrates that nucleation and growth of metallic magnesium occurs non-uniformly. Larger powder particles are a composite of isolated magnesium grains heterogeneously nucleated on the remaining hydride. Smaller particles are either fully transformed to magnesium or remain entirely a hydride. There is little evidence for any “core–shell” structure. It is also shown that in situ hydrogen desorption in the TEM is not representative of the elevated-temperature ex situ sequence. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000856 [article] Analysis of deformation twins and the partially dehydrogenated microstructure in nanocrystalline magnesium hydride (MgH2) powder [texte imprimé] / M. Danaie, Auteur ; S.X. Tao, Auteur ; P. Kalisvaart, Auteur . - 2011 . - pp. 3162–3172. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 8 (Mai 2010) . - pp. 3162–3172 Mots-clés : Hydrogen  storage  TEM  Magnesium  hydride Résumé : Cryo-stage transmission electron microscopy (TEM), supported by Density Functional Theory (DFT), is employed to explore the microstructure of magnesium hydride (MgH2) powders. Mechanical milling results in deformation twinning of the hydride. The crystallography of the twins is established. DFT analysis shows that the twin unit cell is just as thermodynamically stable as the undeformed α-MgH2 matrix. It is hypothesized that the twins contribute significantly to the observed milling-induced kinetic enhancement by acting as high diffusivity paths for hydrogen. Energy-filtered TEM analysis on partially desorbed MgH2 demonstrates that nucleation and growth of metallic magnesium occurs non-uniformly. Larger powder particles are a composite of isolated magnesium grains heterogeneously nucleated on the remaining hydride. Smaller particles are either fully transformed to magnesium or remain entirely a hydride. There is little evidence for any “core–shell” structure. It is also shown that in situ hydrogen desorption in the TEM is not representative of the elevated-temperature ex situ sequence. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645410000856