EVOLUTION OF PROPERTIES OF THE Mg-H2 SYSTEM WITH GRAPHITE DURING MILLING TIME

V. FUSTER; F. CASTRO; G. URRETAVIZCAYA

Islandia

Simposio; International Symposium on Metal-Hydrogen Systems: Fundamentals and Applications; 2008

Magnesium-based systems for hydrogen storage are intensively investigated due to magnesium’s high theoretical storage capacity (7.6 wt.%). However, its low kinetics and high operation temperatures do not meet the industry requirements for practical applications. To overcome these drawbacks, many efforts have been made, one of them is to try differents additives: transition metals, transition metal oxides and carbon allotropes, such as graphite and carbon nanotubes. We synthesized magnesium hydride via reactive mechanical milling in a low energy device under 5 bar hydrogen and room temperature from a mixture of magnesium powder with 10 wt.% graphite flakes, and also from elementary magnesium subjected to identical conditions as the reference. In this work, we report phase analysis by X-ray diffraction, thermal dehydriding properties by differential scanning calorimetry and microstructural characteristics by microscopy, at different stages during the milling process. When graphite is present in the starting powder, the time required to achieve full completion of the hydriding reaction is 50 hs, half the time necessary when no additive is employed. Furthermore, the magnesium hydride exhibits better thermal behaviour because of its lower decomposition temperatures at every milling time considered.