Microstructure, surface properties and hydrating behaviour of Mg–C composites prepared by ball milling with benzene

Mg–graphite composites, suitable for hydrogen storage, have been synthesized by ball milling metallic Mg with different amounts of graphite and benzene. The microstructure and the surface chemical composition have been characterized in order to explain the kinetics of reaction with hydrogen. The presence of benzene in the milled blends induces a finer powder particle size, helps to preserve the structural integrity of the graphite crystals and results to be necessary for a complete transformation of the milled powder to the hydride phase by thermal reaction with hydrogen gas. On the other hand, it induces a more pronounced reaction of the milled Mg–C composites with the air. The transport properties of the resulting surface contamination layer appear to control the kinetics of thermal decomposition of the MgH2 phase, so that the addition of benzene induces a higher reaction temperature owing to a larger thickness of the surface compound.