Nanostructured rapidly solidified LaMg₁₁Ni alloy. II. In situ synchrotron X-ray diffraction studies of hydrogen absorption-desorption behaviours

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• 作者：Roman V. Denys^a ; ^b ; Andrey A. Poletaev^a ; ^c ; ¹ ; Jan Petter Maehlen^a ; Jan Ketil Solberg^c ; Boris P. Tarasov^d ; Volodymyr A. Yartys^a ; ^c ; ^{volodymyr.yartys@ife.no}
• 关键词：Hydrogen storage materials ; Rapid solidification ; Magnesium alloys ; Synchrotron X-ray diffraction ; Scanning electron microscopy
• 刊名：International Journal of Hydrogen Energy
• 出版年：2012
• 期刊代码：42_03603199
• 类别：ch
• 出版时间：April, 2012
• 卷：37
• 期：7
• 页码：5710-5722
• 文件大小：1471 K

摘要

Recently, the present authors have reported dramatic improvements in the hydrogenation behaviours of nanostructured LaMg₁₁Ni prepared by Rapid Solidification, caused by modifications of the microstructure and crystal structure. The aim of the present work was to study the mechanism and kinetics of the hydrogen interaction with rapidly solidified LaMg₁₁Ni by employing in situ synchrotron X-Ray diffraction studies of hydrogen absorption-desorption processes in hydrogen gas or in vacuum.

These studies uncovered a number of temperature-dependent phase structural transformations contributing to reversible hydrogen absorption and desorption, including (a) formation of metastable (in hydrogen) solid solutions of Ni in La₂Mg₁₇ with Ni substitution on both La and Mg sites; (b) amorphisation and nanostructuring of the alloys depending on the solidification rate; nanocrystallisation of the amorphous alloys proceeding at rather low glass transition temperatures and yielding nanocrystallites of Mg₂Ni/Mg_1.9La_0.1Ni and La_1.8Mg₁₇Ni_1.0; (c) the mechanism of the Hydrogenation-Disproportionation-Desorption-Recombination processes resulting in a two-step cooperative Mg-assisted phase transformation where a low temperature decomposition of LaH₂ led to the recombination of the intermetallics LaMg₁₂ and La_2鈭?em>xMg₁₇Ni_x. The metastable solid solutions of Ni in the La₂Mg₁₇-based intermetallic show high hydrogenation rates and, despite they decompose during the cycling of hydrogen absorption and desorption, the formed on cycling nanocrystallites of Mg₂Ni further maintain high catalytic activity of the materials towards the hydrogen absorption.