Roles of Anthracite Coal in Preparation of Magnesium-Based Hydrogen Storage Materials

摘要

The functions of anthracite coal in the preparation of MgH2 for hydrogen storage frommagnesium by means of reactive milling under hydrogen atmosphere were investigated. The anthracitecoal plays three roles in the milling process. The first role is dispersive agent to prevent Mg particles fromcold welding during milling, where the powders show moderate and very slight aggregation after 3 h ofmilling when the coal additives are 20 wt.% and 30 wt.%, respectively, but seriously weld into bulk andadhere to the surface of milling balls and the inner walls of milling vials when they are less than 10 wt.%.The second one is milling media to reduce the size of Mg particles efficiently by its sharp and hard edges.TEM observation shows the particle size of MgH_2 is around 20-60 nm in the presence of 30 wt.% ofanthracite coal after 3 h of milling and, meanwhile, the crystal grain size is approximately 29.7 nm fromXRD analysis. The third role is lubricant to prevent the particle shape from becoming irregular. TEMobservation shows MgH2 particles are oblique hexagonal prism. In addition, morphology observationindicates that the coal can separate Mg particles to prevent them from melting together, and FT-IRanalysis shows that hydrogen can chemically absorb on the surface of coal with abundant surfacedangling bonds induced by milling. The hydrogen capacity of coal is over 1.39 wt.% on hydrogenatedcarbon basis determined by volumetric method.