Mechanochemical synthesis of nanostructured chemical hydrides in hydrogen alloying mills

Mechanical alloying of magnesium metal powders with hydrogen in specialized hydrogen ball mills can be used as a direct route for mechanochemical synthesis of emerging chemical hydrides and hydride mixtures for advanced solid-state hydrogen storage. In the 2Mg-Fe system, we have successfully synthesized the ternary complex hydride Mg2FeH6 in a mixture with nanometric Fe particles. The mixture of complex magnesium-iron hydride and nano-iron released 3-4 wt.%H-2 in a thermally programmed desorption experiment at the range 285-295 degrees C. Milling of the Mg-2Al powder mixture revealed a strong competition between formation of the Al(Mg) solid solution and the beta-MgH2 hydride. The former decomposes upon longer milling as the Mg atoms react with hydrogen to form the hydride phase, and drive the Al out of the solid solution. The mixture of magnesium dihydride and nano-aluminum released 2.1 wt.%H-2 in the temperature range 329-340 degrees C in the differential scanning calorimetry experiment. The formation of MgH2 was suppressed in the Mg-B system; instead, a hydrogenated amorphous phase (Mg,B)H-x was formed in a mixture with nanometric MgB2. Annealing of the hydrogen- stabilized amorphous mixture produced crystalline MgB2. (C) 2006 Elsevier B.V. All rights reserved.