AB-INITIO INVESTIGATION OF HYDROGEN ABSORPTION BY MAGNESIUM NANOPARTICLES

Stability and binding energy of magnesium hydrides MgHx (x = 0.5... 2) is investigated by ab-initio calculations. Compare the binding energies of all known MgH2 crystalline phases it is shown that these MgHx partly saturated hydrides should split up to pure Mg and MgH2 phases due to spinodal decomposition. Also the hydrogen atom hop rates between nearest minima in the pure Mg and basic MeH2 alpha-phase are calculated. The finding explain the low rate of magnesium saturation by hydrogen. Moreover the hydrogen hop rate in Mg7Sc and Mg7Ti crystals are calculated. It is shown that the rate in Mg7Sc between nearest minima in the vicinity of Sc atom is similar with that for pure MgH2 alpha-phase whereas the analogous rate in Mg7Ti is at similar to 2.5 * 10(6) times greater. It means that hydrogen diffusion inside Mg-Ti alloys would be essentially facilitated. By calculation of the magnesium surface specific energy and using simple pressure estimation it is defined that for Mg nanoparticles of radius R > 5 nm the binding energy and geometry is practically coincide with these values for bulk material, so for such nanoparticle modeling it is possible to use results of the bulk material calculations what is far easier.