Hydrogen-absorbing magnesium composites prepared by mechanical grinding with graphite: effects of additives on composite structures and hydriding properties

Novel Mg/G composites were prepared by mechanical grinding of magnesium (Mg) and graphite (G) with benzene as an additive. The addition of benzene was very important in determining the composite structures and hydriding properties. The composites prepared without benzene (designated hereafter as (Mg/G)(none)) showed negligible activity for hydriding, whereas the use of benzene during grinding led to drastic changes in composite structures, leading to much improved hydriding. Transmission electron microscopy (TEM), X-ray diffraction (XRD) and Raman spectroscopy were used to characterize the structures of the Mg/G composites, especially for the mode of degradation of graphite structure during grinding. In the course of the composite formation in the presence of benzene (referred to as (Mg/G)(BN)), the graphite structure was predominantly degraded by cleavages along graphite layers, while the graphite for (Mg/G)(none) was broken irregularly and disorderly, leading to rapid amorphization. Moreover, the additive for the composite formation plays an important role in promoting synergetic actions induced during the mechanical grinding of magnesium and graphite, in which the flaked graphite formed by fracture along graphite layers interacts with divided magnesium with charge-transfer. X-ray photoelectron spectroscopy (XPS) of (Mg/G)(BN) proved the charge-transfer from magnesium to graphite carbons. (C) 1999 Elsevier Science S.A. All rights reserved.