Study On The Effect Of Carbon In The Preparing Process Of Mg-based Hydrogen Storage Materials

There are three problems existing in the process of large-scale application of hydrogen storage materials, one is how to improve hydrogen storage density of the materials, another is how to make hydriding-dehydriding manipulation condition moderate, and the last is how to decrease the cost of hydrogen storage materials and save precious metals. The Mg-based hydrogen storage materials have been prepared with carbonized and pre-graphitized anthracite and metal Mg used as the main materials by ball milling, and the structures and properties of the materials have been characterized and tested by transmission electron microscope (TEM), powder X-ray diffraction (XRD), differential scanning calorimeter (DSC), etc. The results indicate that the hydriding-dehydriding properties have great improvement. By the research of structure and property differences of the materials prepared with different crystallite carbon contents, ball milling intensities, ball milling time and different kinds of carbon, the effect of crystallite carbon in aiding milling, hydrogen storage and catalysis in the preparing process of Mg-based hydrogen storage materials is proposed, and the mechanism of aiding milling, hydrogen storage and catalysis is discussed.After carbonization and pre-graphitization, there are plentiful microapertures forming and the specific surface area increases rapidly. Also, there are some graphite-like layer structures forming, which are different from graphite for their ordered two-dimension plane, ordered three-dimension structure in short range but disordered structure in long range, and the units of crystallite structure shape, that is why it is called crystallite carbon (CC in short).The properties of the materials have been tested and the structures of the materials have been characterized by the testing device of dehydriding capacity devised by ourselves, TEM, XRD, DSC, etc. And the results indicate that the materials have no conglutination and the size reaches nanograde in 2h as CC content more than 40wt%. But the hydrogen storage capacities are lowered with excessive CC content, and 70Mg30CC has the highest dehydriding capacity 4.35wt%, while 60Mg40CC has lower dehydriding temperature. Meanwhile, the increase of CC content makes for amorphous structures. The change of ball milling intensity leads to the change of deformation amount, deformation work and deformation times of the materials in the collision and extrusion process. The higher the ball milling intensity is, the higher energy the sample obtains, the more defects the crystal gets, and the higher probability the active carbon atoms appear in, so the more distinct the effect of CC on catalysis and hydrogen storage of Mg is. The size of 40Mg60CC reaches nanograde in 2h ball milling for CC's good effect of dispersion and aiding milling. But as the ball milling time prolonging, the more fine particles lead to the increase of surface energy which causes agglomeration of grains. The destruction degree of crystal structures is aggravated, and the material milled for 4h assumes amorphous phase homogeneously. Also, the dehydriding temperature of the material decreases as ball milling time prolonging. The hydrogen storage properties of the materials added active carbon and graphite are worse than that added CC, which is determined by the amorphous structure of active carbon and ordered layer structure of graphite.A preliminary discussion for the mechanism of aiding milling, hydrogen storage and catalysis of CC is given as the results of characterization and test, which provides theoretical support for further increase of hydrogen storage capacity and improvement of hydriding and dehydriding properties.