Metallographic and numerical characterization of MgH 2 -Mg system
- PDF / 1,967,384 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 40 Downloads / 206 Views
1127-T07-07
Metallographic and numerical characterization of MgH2-Mg system Annalisa Aurora1, Massimo Celino1, Fabrizio Cleri2, Daniele Mirabile Gattia1, Simone Giusepponi1, Amelia Montone1, Marco Vittori Antisari1 1
ENEA – C.R. Casaccia, Via Anguillarese 301, 00123 S. Maria di Galeria (Rome), Italy
2
IEMN – CNRS (UMR-8520), Université des Sciences et Technologies de Lille, F-59652 Villeneuve d’Ascq cedex, France
ABSTRACT The remarkable ability of magnesium to store significant quantities of hydrogen has fostered intense research efforts in the last years in view of its future applications where light and safe hydrogen-storage media are needed. Magnesium material, characterized by light weight and low cost of production, can reversibly store about 7.7 wt% hydrogen. However, further research is needed since Mg has a high operation temperature and slow absorption kinetics that prevent the use in practical applications. For these reasons a detailed study of the interface between Mg and MgH2 is needed. Further insights are gained by characterizing the Mg-MgH2 system from both the experimental and the numerical point of view. The study of the MgH2-Mg phase transformation in powder samples has been performed to gain detailed metallographic information. A method for studying this phase transformation by cross sectional samples scanning electron microscopy observation of partially transformed material has been developed. This method exploits the peculiar features of this system where the MgH2 phase is insulating and the Mg is a metallic conducting phase. This difference can induce a contrast between the two phases owing to the different secondary emission yield. Further insights are gained by characterizing Mg-MgH2 interfaces by means of accurate first-principle molecular dynamics simulations based on the density-functional theory. Extensive electronic structure calculations are used to characterize the equilibrium properties and the behavior of the surfaces in terms of total energy considerations and atomic diffusion.
INTRODUCTION Magnesium hydride is one of the most promising candidates as hydrogen storage media in the automotive industry due to its very high capacity and low cost. However further research efforts are needed to employ this technology in practical applications. This is due primarily to the slow kinetics and high operating temperature. Improvements can be obtained by mechanically milling MgH2 that is able to introduce a high density of crystal defects and a fine dispersion of second phase particles with catalytic effects [1,2]. Moreover the addition to Mg hydride of small amounts of catalytic metals has been indicated as a promoting factor in the surface dissociation
of the H2 molecule [3]. For these reasons a detailed experimental and theoretical study is needed to fully characterize the desorption mechanism at the interface Mg-MgH2 [4]. Experimentally, a protocol for the metallographic study of the phase transformation in the MgH2-Mg system is developed. Partially desorbed MgH2 powders are examine
Data Loading...
