Synthesis and decomposition mechanisms of ternary Mg2CoH5 studied using in situ synchrotron X-ray diffraction |
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Authors: | M NorekTK Nielsen M Polanski I KunceT P?ociński LR JaroszewiczY Cerenius TR JensenJ Bystrzycki |
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Affiliation: | a Faculty of Advanced Technology and Chemistry, Military University of Technology, 2 Kaliskiego Str., 00-908 Warsaw, Poland b Center for Energy Materials, iNANO and Department of Chemistry, University of Aarhus, DK-8000 Aarhus C, Denmark c Faculty of Materials Science and Engineering, Warsaw University of Technology, 141 Wo?oska Str., 02-507 Warsaw, Poland d MAX-lab, Lund University, S-22100 Lund, Sweden |
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Abstract: | A ternary Mg2CoH5 hydride was synthesized using a novel method that relies on a relatively short mechanical milling time (1 h) of a 2:1 MgH2-Co powder mixture followed by sintering at a sufficiently high hydrogen pressure (>85 bar) and heating from RT to 500 °C. The ternary hydride forms in less than 2.5 h (including the milling time) with a yield of ∼90% at ∼300 °C. The mechanisms of formation and decomposition of ternary Mg2CoH5 were studied in detail using an in situ synchrotron radiation powder X-ray diffraction (SR-PXD). The obtained experimental results are supported by morphological and microstructural investigations performed using SEM and high-resolution STEM. Additionally, thermal effects occurring during the desorption reaction were studied using DSC. The morphology of as-prepared ternary Mg2CoH5 is characterized by the presence of porous particles with various shapes and sizes, which, in fact, are a type of nanocomposite consisting mainly of nanocrystallites with a size of ∼5 nm. Mg2CoH5 decomposes at approximately 300 °C to elemental Mg and Co. Additionally, at approximately 400 °C, MgCo is formed as precipitates inserted into the Mg-Co matrix. During the rehydrogenation of the decomposed residues, prior to the formation of Mg2CoH5, MgH2 appears, which confirms its key role in the synthesis of the ternary Mg2CoH5. |
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Keywords: | Magnesium-cobalt hydride Synthesis Mechanical milling In situ SR-PXD Microstructure |
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