ИСТИНА

Mg is the metal useful for storage hydrogen because able to absorb reversibly a large amount of hydrogen and is environmentally harmless. However, high temperature of the dissociation (high stability) of MgH2 and slow kinetic of hydrogenation reaction both are not favourable for wide using of MgH2 for different practical applications. [1, 2]. At present work stability of the MgH2 samples was studied using of the X-ray diffraction method. Two sets of the samples were prepared by thermodesorption (vacuuming at temperature about 4000C) of the MgH2 powder. All obtained samples have two phases (Mg and MgH2) in the different proportion. The first set of the samples in air and at room temperature demonstrate a high stability and not decomposed for several months, containing both Mg and MgH2 phases unchanged. The second set of the samples was cooled down in liquid nitrogen (fast quenched) and heated back until to the room temperature. After several days it was revealed that second set of the samples decomposed and the samples contained practically only Mg phase. This behaviour indicates that at low temperature followed by heating may be occurred phase transition from MgH2 to Mg, coexisting in the samples. These phases have ordered and disordered hydrogen and due to the different diffusion of the hydrogen atoms the proportion of these phases starts to change at diverse temperature. This leads to decreasing of the stability of the second set samples.