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Electron microscopy studies of magnesium hydride
|Tomasz Płociński 1, Krzysztof J. Kurzydlowski 1, Jerzy Bystrzycki 2
1. Warsaw University of Technology, Faculty of Materials Science and Engineering (InMat), Wołoska 141, Warszawa 02-507, Poland
Hydrogen driven vehicles with fuel cells offer the most environmentally friendly automotive technology. Among the known metals and alloys with potential use in hydrogen storage, magnesium is generally regarded as the most promising because of its high capacity (7.6 wt.%) and low cost. Mechanical (ball) milling has proved to be simple and very effective technique for synthesizing Mg-related materials exhibited sufficiently fast hydriding/dehydriding kinetics for technical applications.
Microstructure and morphology of Mg/MgH2 powder (or compacts) are crucial material parameters for fast sorption kinetics. However, to our knowledge, there are only a few works in the literature about microstructure and morphology of MgH2 powder after processing and cycling hydrogen loading. One of that reasons is the behavior of this hydride under the electron beam. MgH2 starts to release hydrogen as soon as the electrons interact with thin sample and decomposed to Mg. The microstructural and structural investigations were performed using scanning electron microscope (FE SEM) equipped with duo-STEM detector and transmission electron microscope (TEM). This investigations were carried out on nanocrystalline MgH2 without and with Cr2O3 nanopowder as a catalyst.
Morphological investigations of mechanical (ball) milled MgH2 powders showed a MgH2 particle size of 0.5-10 μm. The bright field STEM images of milled MgH2 exhibited a homogeneous crystallite size distribution with average crystallite size smaller than 100 nm. The brittle nano-Cr2O3 particles are embedded by the MgH2 matrix, forming a nanocomposite structure. The particle size of Cr2O3 was found to be 10-300 nm. TEM investigations showed the presence of small fraction of MgO phase not only in the surface of MgH2 particles but also within the micrometric particles. These oxide regions are formed probably by aggregation of passivated MgH2 particles during the ball milling.
Presentation: Poster at E-MRS Fall Meeting 2007, Symposium J, by Tomasz Płociński
See On-line Journal of E-MRS Fall Meeting 2007
Submitted: 2007-05-17 11:51 Revised: 2009-06-07 00:44