Hydrogen absorption and desorption by quasicrystalline and related approximant powders produced by mechanical alloying in the Mg-Al-Zn system

Icosahedral quasicrystalline (i-phase) Mg₄₄Al₁₅Zn₄₁ and related Frank-Kasper (cubic approximant) phase powders, which were produced by mechanical alloying from the elemental powder mixture and subsequent heat treatment, respectively, have been hydrogenated with hydrogen gas at a temperature of 573 K and a hydrogen pressure of 4.2 MPa. The hydrogen solubility limit for both powders is almost the same and was estimated to be about 16 at%, and no crystallographic structural dependence was found for the hydrogen solubility. The approximant phase powder was structurally stable after hydrogenation but the i-phase powder decomposed into the approximant and MgZn₂ intermetallic phases. Hydrogen desorption occurred at temperatures above about 600 K for both powders and was accompanied by the evaporation of zinc. The kinetics of the hydrogen desorption as well as the zinc evaporation were slightly different in each powder because of the formation of the MgZn₂ phase in the i-phase powder after hydrogenation.