Hydriding–dehydriding behavior of magnesium composites obtained by mechanical grinding with graphite carbon

Novel Mg/G composites were prepared by mechanical grinding of magnesium (Mg) and graphite carbon (G) with cyclohexadiene, cyclohexene, cyclohexane, benzene or tetrahydrofuran as an additive. The presence of organic additives during the grinding was very important in determining the composite structures and hydriding–dehydriding properties. The composites prepared without additives [designated hereafter as (Mg/G)none] showed negligible activity for hydriding, whereas the use of additives led to drastic changes in composite structures, leading to much improved hydriding and dehydriding behavior. The effectiveness of organic additives in the initial hydriding was in the order: cyclohexadiene≈tetrahydrofuran≈cyclohexene>benzene>cyclohexane. In the course of the composite formation in the presence of organic additives, the graphite was predominantly degraded by cleavages along graphite layers, resulting in the occurrence of synergetic interactions with magnesium. The graphite for (Mg/G)none was broken irregularly and disorderly to rapid amorphization with negligible interactions with magnesium. Various metal-doped Mg/G composites obtained by grinding of magnesium and graphite with organometallic solutions (Al(C2H5)3, Ti(OC3H7)4, Fe(C5H5)2, Ni(C5H5)2 or Zn(C2H5)2) in benzene have been further examined. Ti-doped Mg/G composites using Ti(OC3H7)4 among others showed an excellent activity; the initial hydriding activity increased above 10-fold relative to that for the metal-free composites.